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ABAC - BME - University of Connecticut

1. ut 29 Figure 23 Differential Amplifier Circuit 5 2 1 2 5 5 Filter Between the difference amplifier and the motor will be a large resistor This is to compensate for the fact that it will be difficult for the springs to center the potentiometer exactly This will cause there to be a slight difference in voltage between the terminals so there will be a small output voltage from the circuit This resistor serves to prevent these small voltages from influencing the motor by effectively removing them 2 1 2 6 Electric Motor The electric motor used to drive the bed back up and down will be a variable speed series wound DC motor In this motor the stator and rotor are connected in series across the voltage source see Figure 24 next page producing equal operating current in both By using a simple circuit see Figure 18 page 20 to control the applied voltage the DC voltage and speed of the motor can be controlled As it was explained previously the greater the voltage the faster the motor runs causing the actuator rise or lower faster and visa versa with less voltage Depending on the polarity of the voltage this will determine which way the rotor or armature rotates Positive voltage will cause the rotor to rotate such that it drives the actuator up and raise the bed Negative voltage will rotate the rotor in the opposite direction and cause the actuator to retract and lower the bed The major drawback of this motor type is t
2. beta coordinates defined by a back angle alpha and a knee angle beta a pattern that connects between a coordinate point 0 0 at which each of a back bottom and a knee bottom is horizontal and a coordinate point alpha sub 0 beta sub 0 which is a final reaching point for a back lift up operation and at which the back bottom is lifted up by a plurality of points is set an optimal pattern which provides less slipperiness and less oppressive feeling is acquired beforehand and a control section moves the back bottom and the knee bottom along the optimal pattern This reliably prevents a carereceiver from slipping regardless of subjective judgment by an operator or a carergiver at the time of performing a back lift up operation and back lift down operation of an electric bed It is therefore possible to prevent pressure from being applied onto the abdominal region and chest region of the carereceiver thus relieving the carereceiver and caregiver of the burden 13 4 Map for the rest of the report The rest of the report consists of the subunits of the previous designs the optimal design layout reason why the optimal design has been chosen realistic constraints safety issues impact of engineering solutions lifelong learning budget and timeline contributions of each team member and a short conclusion of this project 11 14 Project Design In this section there is a brief objective describing each design and its correspondi
3. 74 74 74 75 76 77 78 78 90 78 78 90 Figures and Tables Flow Chart 1 Optimal Flow Chart Figure 1 Invacare Adjustable Hospital Bed Figure 2 Full Electric Hand Pendant Figure 3 Air Powered Adjustable Bed Figure 4 Flex A Bed Base Figure 5 Basic Design of Handle Figure 6 Control Valves Figure 7 Calculation of Input Force on Springs Figure 8 Free Body Diagram of Lever Figure 9 PROCON Series 4 Pump Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 Figure 27 Figure 28 Figure 29 Figure 30 Figure 31 Figure 32 Figure 33 Figure 34 Figure 35 Figure 36 Figure 37 Figure 38 Figure 39 46 YZ Frame Motor Hose Connectors and Hydraulic Hosing Pressure Valoe Regulator Pressure Gage and Adapter Prince Double Acting Hydraulic Cylinder View of Intermediate Trunnion Mounting Style Clear Polycarbonate Sheets Overall Design Schematic Circuit Schematic Typical Rotary Potentiometer Internal Workings of Rotary Potentiometer Op Amp Inverting Amplifier Circuit Differential Amplifier Circuit Circuit for a Series Wound DC Motor Worm Gear Lead Screw Drive System Overall Schematic at 0 Degree Angle Design 2 Overall Back and Side View of Schematic at 70 Degrees Design 2 Free Body Diagram of Lifting System Linear Actuator Mounting Bracket Properties of A
4. 20 2 Team Member 2 Raymond Pennoyer Ray is concentrating in Bioinstrumentation which focuses on electronics Because of this he is developing the electric circuit The design testing and troubleshooting of the circuit are also his responsibility Another task assigned to him is the design of the PCB He also will have completed the machine shop training so he will help with machining parts as well 20 3 Team Member 3 Steven Frisk Steven is concentrating in bio solid mechanics Due to his experience with mechanical motion and structures the majority of his focus has been and will be with the motion of the bed and the motors actuators and controls used to move said bed So far he has designed the scissor jack system and calculated the required forces to lift the bed This includes calculating tilting motion of the jack as the bed is lifted along an arch as well as the rotational speed and torque required by the electric motor to provide the desired lifting speed and power 79 21 Conclusion The initial design is very similar to the optimal design which has been chosen However the one major component which has been changed continuously is the method with which the bed is lifted Initially the bed would be lifted by a hydraulic cylinder However this turned out to be overly noisy and had the potential to be unsanitary The hydraulic system was replaced by an electric motor driving a linear actuator This electric system would w
5. As with all engineering projects the safety of the hospital bed s user is paramount This project is designed for widespread use and if even one patient or caretaker is significantly injured then it is a failure The device will be employed in hospitals where children will be as well as those with reduced 68 coordination and muscle control so the exposed parts will be rounded off to prevent significant lacerations and contusions from collision Another basic safety feature is the absence of exposed joints that can cause pinching if someone s hand is in the wrong place at the wrong time Between January 1 1985 and January 1 2006 FDA received 691 incidents of patients caught trapped entangled or strangled in hospital beds The reports included 413 deaths 120 nonfatal injuries and 158 cases where staff needed to intervene to prevent injuries Most patients were frail elderly or confused 20 Also the Center for Disease Control and Prevention reports that in 1995 five out of every 100 admissions into a hospital in the United States resulted in a nosocomial infection 21 These hospital acquired infections resulted in 88 000 deaths in that year alone In order to control the spread of bacteria and viruses between bed users the exposed parts will all be made of easily sterilized aluminum More advanced safety issues have also been taken into account In the frenzied activity of the hospital it is certain that someone will accidentally b
6. Figure 30 page 31 is a picture of Al Be 80 20 and chart of its mechanical properties The design of this structure is seen in the overview of the frame in Figure 49 and 50 on pages 60 and 61 respectively This material will be ordered in the proper sizes and put together in the machine shop Once the frame is finished it will undergo a series of loading tests to test the strength of the structure If failure is to occur reinforcement will be added where necessary The overall schematic of the design as illustrated in the Microsoft VISIO drawings in Figures 23 and 24 demonstrates the pivoting of the actuator to allow for movement as the bed is operated and sustains a low profile when retracted Also the handle is positioned out of the way and designed for easy access All parts are secured with bolts to the frame of the bed or the Aluminum To demonstrate the final workings of this automatic back angle controller it will be fastened to a mock bed platform It can be made out of scrap Al Be 80 20 or welded with steel and have a metal platform attached to mimic the mattress This will allow the device to be tested under the weight of humans lying on the platform 14 2 3 Testing the Design Once the subunits are assembled to create the bed back angle controller the device needs to be tested for its functionality and reliability to ensure its safety The handle design will undergo testing in the springs and the safety switch The resistance sp
7. Ray EREECHEN Troubleshoot Circuit 5 days 8 00 17 00 Ray PRECOR NU NN Write Weekly Report 1 day 8 00 17 00 a reine a ee Update Website 1 day 8 00 17 00 e e a a NU NNNM Weekly Meeting 1 day 8 00 17 00 SCENE Test Motor 5 days 8 00 17 00 Ray pute sone NU PN Test Prototype Circuit with Motor 5 days 8 00 17 00 Ray pare os ZS ZZ aa Design PCB in ExpressPCB 5 days 8 00 17 00 Ray SECHS NN Order PCB 5 days 8 00 17 00 rae reee san Write Weekly Report 1 day 8 00 17 00 A Irene Is 8 Si Update Website 1 day 8 00 17 00 oo e a a NU NNNM Weekly Meeting 1 day 8 00 17 00 meseros Lem 18 NE NNNM Receive PCB 5 days 8 00 17 00 Lm jeseneers sep 3 la Solder Parts to PCB 5 days 8 00 17 00 Ray o ep Lem 9 in Test Soldered PCB 5 days 8 00 17 00 Ray aa rowers fsan ORR Raa Troubleshoot PCB 5 days 8 00 17 00 Ray Pavo o RO ES Test Completed PCB with Motor 5 days 8 00 17 00 Ray Fae Jensen Jo ae AS Construct Control Box 5 days 8 00 17 00 Ray 43 47 53 57 o innit ha 5 NU NN Write Weekly Report 1 day 8 00 17 00 oa rete e NN d Update Website 1 day 8 00 17 00 Spring Break 5 days 8 00 17 00 Cor leone sine Se 4 Implement Safety Lock Wiring 5 days 8 00 17 00 Ray d 3 2 2007 3 2 2007 D Weekly Meeting 1 day 8 00 17 00 pase NU NN Put Together Control Box with PCB 5 days 8 00 17 00 pure RPENU UU NN 63 Attach Handle to Control box and PCB 5 days 8 00 17 00 rong 3 12 2007 3 16 2
8. Stress psi F si DE F sin y Eq 5 A A Shear Due to Torsion psi d d zk O T e t Do d HN ud Ea 6 Tome F Ou A di i 64 Assuming that the force from the patient s weight is focused at about 1 3 of the length of the bed back 35 inches in length from the joint we assume that F is concentrated at D 15 inches Therefore the actuator will also be placed at this point so that the majority of the weight is directly supported The bed is also projected to lift from 0 degrees to 70 degrees of incline Therefore the actuator will be under the greatest tensile and shear stresses while at its maximum amount of incline To determine the proper material and diameter for the actuator shaft we assume the maximum load of 180 pounds is applied at the connection Knowing the force applied at the joints the proper mounting brackets must be used to compensate for movement of the actuator as its angled The clevis bracket Fig 29 will be pinned to both ends of the actuator to provide a sturdy attachment and allow for pivoting as the bed back angle changes Figure 29 Linear Actuator Mounting Bracket 10 36 2 1 2 6 Support Frame After understanding all the loads that this device needs to withstand a strong support frame for the actuator can be determined The most practical metal to use in this situation is Aluminum Beryllium Al Be 80 20 This is a light weight durable easy to assemble and cheaper way to structure this verse welding
9. an intermediate mounting bracket Applicable where interchangeability between actuators and positioners is desired e IEC 60601 1 Medical Electrical Equipment General Requirements for Safety Applies to the safety of medical electrical systems as defined as follows combination of items of equipment at least one of which must be medical electrical equipment and inter connected by functional connection or use of a multiple portable socket outlet Describes the safety requirements necessary to provide protection for the patient the operator and surroundings Cancels and replaces the first 67 edition published in 1992 and its amendment 1 1995 and constitutes a technical revision IEC 60601 1 2 Top Level standard for electromagnetic compatibility for electrical medical equipment IEC 60601 1 6 Medical electrical equipment Part 1 6 General requirements for safety Collateral standard Usability This Collateral Standard describes a usability engineering process and provides guidance on how to implement and execute the process to provide medical electrical equipment safety It addresses normal use and use errors but excludes abnormal use IEC 60601 2 38 Particular requirements for the safety of electrically operated Hospital beds Specifies requirements for safety of electrically operated hospital beds The object of this standard is to keep the safety hazards to patients operators and the environment as low as possible and to descri
10. angle of 0 Therefore we use this case to determine the maximum power required by 61 the motor In this case Fa W for which 200 lbs can be used for a patient weight of 180 lbs and compensating for the weight of the bed Also T 11 inches and H at 0 is 2 5 in By plugging these numbers into Equations 1 and 2 we find that the force required F is 852 74 Ibs The following equations are use to calculate the torque and power required to drive the scissor jack at the required rate F EIJITTESO Eq 4 14 F p n pull Eq 5 14 3 564 x10 Tou Where T The torque required by the motor F Force Applied by Lead Screw p Thread pitch in rev n Desired rotational speed rpm Since we know F only the thread pitch p and the rotational speed n needs to be determined To get a 70 degree raise in the bed angle we need the scissor jack to 16 inches This means that H will go from 2 5 inches to 10 5 inches Using these values we can find the change in 2L 2 AL for which the screw will travel This value comes out to be 15 inches At the maximum speed we would like the bed to travel from flat to a 70 degree raise in 3 seconds which means a velocity in the screw of 5 inches sec By trial and error and the use of Figure 47 on next page we found out the thread pitch should be 0 5 in rev and a 1 in diameter screw as shown in Figure 48 on next page Therefore to accomplish a 5 in sec travel the rotational speed would have
11. assume that F is concentrated at D 15 inches It was determined that the rod and frame will be placed at this point so that the majority of the weight is directly supported The bed is also projected to lift from 0 degrees to 70 degrees of incline To determine the proper material and diameter for the rod shaft it was assumed that the maximum load of 200 pounds is applied at the connection Calculations show that the rod will be under the greatest tensile and shear stresses while at its initial incline at zero degrees Table 2 next page has the calculated forces on the rod that the screw drive will have to apply to drive the cart and Figure 36 next page shows the forces graphically 46 Table S Calculations of Force on Rod as Angle of Bed Changes esa sasa 2000600116 e 200 2a 7531860 TD 60 211 6376 70 200 Force in Rod Vs Back Angle 800 700 600 900 400 300 200 100 Force in Rod Ibs 0 20 40 60 80 Back Angle degrees Figure 36 Graph of Force on Rod vs Back Angle Knowing the force applied at the joints the proper mounting brackets must be used to compensate for movement of the rod as its angled The clevis bracket Fig 29 page 30 will be pinned to both ends of the Al Be 80 20 rod to 47 provide a sturdy attachment and allow for pivoting as the bed back angle changes 2 1 3 8 Support Frame After understanding all the loads that this device nee
12. does exert with a constant force to stretch ratio or if the spring is defective as well as validating the spring constant 2 1 2 5 Electric Circuit 2 1 2 5 1 Overview The electric circuit in Figure 18 next page serves to translate the mechanical action on the control handle into action of the linear actuator Movement of the handle changes the relative voltages on either side of a potentiometer The voltages are passed through separate inverting amplifiers and are then compared by a differential amplifier This final voltage is then applied to the motor on the linear actuator The circuit will be designed and simulated in PSPICE After the parts come in the circuit will be constructed on a protoboard and tested using a digital multimeter Finally the parts will be 25 soldered into a circuit board designed for this purpose and once again tested with a multimeter before being integrated with the rest of the device DC Down Up Amp Amp X Vcc Vcc Vcc Differential Amp IVA Figure 18 Circuit Schematic 2 1 2 3 2 Potentiometer The potentiometer is directly attached to the handle A potentiometer is a variable resistor that acts as an electro mechanical transducer This means that it converts mechanical stimuli into electric effects The potentiometer will convert the displacement and direction of the handle into a variation of resistance within a circuit A potentiometer has three terminals that can be conn
13. estimated retail price of 313 combined with its smooth operation infinitely adjustable speed and ergonomic and intuitive control the functionality is well worth the price tag The costs of production are kept down by the use of existing parts but combined in a manner which allows for new and better operation of an existing product 18 Life long Learning Work on this project has expanded the knowledge of the engineering students Much research was required to understand the problems associated with this design New material and techniques were acquired such as the concept of extended physiological proprioception EPP This concept implies that devices should react to the user s input in an intuitive manner creating the sensation that it is an extension of the user s own body EPP was integrated into the device through the force sensitive handle that changes the pressure within the closed hydraulic system In order to design a handle that is used to detect the force placed upon it many different methods were considered There are many ways to detect the forces placed on an object but thus far there has not been a handle constructed for this purpose While exploring the options for this part the first idea used load cells to detect the force since they were used in Biomechanics lab to measure the tension force on various objects After looking into load cells by visiting various commercial and educational websites it became apparent that
14. iecwww p wwwlang E amp wwwprog sea227b p amp pro edb db1 amp x ics 11 gt Hospital Bed Safety Home Hospital Bed Safety U S Food and Drug Administration 14 Oct 2006 lt http www fda gov cdrh beds gt Weinstein Robert Nosocomial Infection Update Emerging Infectious Diseases Volume4 Issue 3 July Sept 1998 14 Oct 2006 http www cdc gov ncidod eid vol4no3 weinstein htm gt Manual Electric Hospital Beds A1 Adjustable Beds 15 Oct 2006 http www al adjustable beds com Manual Hospital Beds htm gt Adjustable Electric Hospital Beds A1 Adjustable Beds 15 Oct 2006 http www al adjustable beds com Full Electric Hospital Beds htm gt Strain Gages Omega Intoduction to Strain Gages Omega com 10 Oct 2006 http www omega com prodinfo StrainGages html gt 82 23 Acknowledgements We would like to express our gratitude to following individuals for their support and assistance in developing this device Dr John D Enderle Advisor Bill Prueshner Advisor David Kaputa Advisor Paul and Lisa DeStefano Engineering Consultants Ken Frisk Engineering Consultant Rehabilitation Engineering Research Center RERC Funding 24 Appendix 24 1 Updated Specification Electrical Parameters Voltage Input Voltage Operation Current Max Voltage Max Current Operation Fuse Environmental Parameters Operation Temperature Storage Temperature Execution Speed 120V AC 12V DC 49A 32V max 15A
15. in which the lead screw would sit The load would then be placed at one end of the lead screw As the nut is rotated by the motor the lead screw will be forced through it in one direction or the other via the threading on each This in turn would then drive the load upwards 3l Lead Screw Worm Gear Drive Load Motor Figure 25 Worm Gear Lead Screw Drive System 9 The rate of linear motion performed by an actuator such as this is a function of the revolution speed of the motor in revolutions per min rpm and the pitch of the thread in inches per revolution in rev as shown in Eq 2 V threadpitch angularspeed Eq 2 With each turn of the nut the lead screw will travel a distance equal to the pitch value of the thread Therefore the faster the motor spins the faster the load is moved In this design an actuator will be used to move a cart forward and backward along the length of the bed A solid rod will then be attached between the cart and the bed back via a pin at the bed upper pivot joint and then cart lower pivot joint as shown on the following pages in figures 26 amp 27 This pin will allow the rod to pivot at both ends as the cart traverses a track As the cart travels toward the foot of the bed the horizontal distance between the lower pivot joint and the upper pivot joint will be come shorter Since the rod remains a constant length this means that the vertical distance between the two joints mu
16. keep the majority of the control lever out of the way but allow both the patient and caretaker to comfortably work the device This should also help reduce the occurrences of the handle being bumped since only a fraction of it will be above the protection of the bed mattress Another feature is a safety lock which will be built into the handle In the occurrence of the lever being accidentally bumped this safety switch will prevent the bed from operating The safety switch similar in appearance to a hand brake on a bicycle will be a simple open loop switch When the safety switch is on the loop will be open Since the input is conveyed to the motor via an electric circuit any break in this will prevent the motor from being driven The safety switch will be placed on the under side of the lever so that accidental activation does not occur in the event of force being applied from the top of the handle such as the patient rolling over on the lever or a visitor sitting on it The safety switch will only require as little as one pound of force to unlock so that all users will be able to operate it easily 2 1 8 4 Resistance Spring The resistance springs are used in the control lever to bring the lever back to zero when the action is done and to correlate an input force with an output displacement into the valves To zero the lever two springs with identical spring constants k will be attached between the lever and opposite sides of the ret
17. of force to unlock it so that all users will be able to operate it 13 Inside of Box E c Safety Switch Top View Ji Side View Figure 5 Basic Design of Handle 2 1 1 4 Hydraulic Control Valves The hydraulic control valves are the physical control which the lever will be operating In this system two control valves are necessary in order to drive the bed both up and down at a controlled rate 14 MELTS Al INVE RISE EN PRESSURE EN RETURN Figure 6 Control Valves 2 1 Input from pump 2 Outlet back to pump 3 To top of cylinder 4 To Bottom of cylinder For use with a hydraulic cylinder the valves will serve two functions depending on the intended motion of the bed The cylinder will have two hoses running in to it one connected at either side of the driving piston positions 1 4 in Fig 6 When the lever is operated it will open up one of the valves to allow the pressure from the pump into one side of the driving piston At the same time the other valve will be opened to allow fluid out of the cylinder This open valve is connected to the end of the cylinder towards which the piston is traveling The valves therefore function to create a lower pressure in front of the piston while the pump creates a higher pressure behind it driving it in the opposite direction By controlling the flow out of the piston with the valv
18. out of a durable clear Polycarbonate Fig 16 so that all the parts will be visible and contained underneath the bed neatly together without exposing any of the components This should also make it easier to assemble the device since all the components are placed in the box The only assembly needed would be the connection of hoses and stabilizing the position of the hydraulic lift on top of the box It will hold the oil tank motor and pump hydraulic hosing connecting the components and have a place where the user can see the pressure gauge and easily access the pressure regulator valve so that it can be adjusted as needed Figure 16 Clear Polycarbonate Sheets 14 thick 5 The overall schematic of the design is shown next page in Figure 17 It demonstrates the pivoting of the hydraulic cylinder to allow for movement as the bed is operated and sustains a low profile when retracted Also the handle is positioned out of the way and designed for easy access All the remaining components are placed inside the polycarbonate box for protection and safety 22 See Bed Back pcc N itt Sek Control Handle Hydraulic Le Ns Lift Hydraulic Hosing Support Beam Polycarbonate box w pressure gauges motor and pump inside Figure 17 Overall design Schematic 14 1 2 Design 2 14 1 2 1 Objective The objective of this design was to implement an electric system in place of the hydraulic sys
19. steel parts together Below in Figure 30 is a picture of Al Be 80 20 and chart of its mechanical properties The design of this structure is seen in the overview of the frame in Figure 26 and 27 pages 27 28 This material will be ordered in the proper sizes and put together in the machine shop Once the frame is finished it will undergo a series of loading tests to test the strength of the structure If failure is to occur reinforcement will be added where necessary Nominal Density Ib in3 0 076 to 0 086 Yield KSI 23 to 40 Melting Point F 2010 to 2150 Chemical Family Metal matrix Ultimate KS 34 to 55 Elongation 17 to 7 Modulus MSI 19 to 28 Color Gray Figure 30 Properties of Aluminum Beryllium 80 20 11 12 The overall schematic of the design as illustrated in the Microsoft VISIO drawings in Figures 26 and 27 pages 27 28 demonstrates the pivoting of the actuator to allow for movement as the bed is operated and sustains a low profile when retracted Also the handle is positioned out of the way and designed for easy access All parts are secured with bolts to the frame of the bed or the Aluminum To demonstrate the final workings of this automatic back angle controller it will be fastened to a mock bed platform It can be made out of scrap Al Be 80 20 or welded with steel and have a metal platform attached to mimic the mattress This will allow the device to be tested under the weight of humans lying on the platform 3
20. they have a slow constant velocity and use open loop controls to set the back angle These controls require a certain level of dexterity that some users may not have This device needs to accommodate the user s handicap whether it is the patient or the care taker operating the device and allow for them to be easily adjusted 13 3 Previous Work Done By Others Current designs of adjustable beds with back angle controllers Most competitors offer an open loop switch which adjusts the bed at a constant rate Below are some similar products on the market 13 3 1 Products Package includes Mattress and Side Rails 859 00 free shipping Full Electric Figure 1 Invacare Adjustable Hospital Bed InvacareO This product is a fully electric adjustable bed which adjusts the legs and back in a similar manner to patent 7 058 999 Figure 2 Full electric Hand Pendent InvacareO This is the controller to the Invacare Adjustable Hospital Bed It uses a series of open loop switches to adjust the legs and back of the bed Figure 3 Air powered Adjustable bed ProBed 2 This is an adjustable bed which uses inflatable pillows to lift the legs and back independently Figure 4 Flex A Bed Base Flex A Bed 3 The Flex A Bed Base is the basic frame which supports any type of mattress and adjusts the bed electronically 13 3 2 Patent Search Results Patent Number 6 000 077 Single Motor Fully Adjustable Bed A d
21. to drive the bed back up and down will be a variable speed series wound DC motor In this motor the stator and rotor are connected in series across the voltage source see Figure 24 page 25 producing equal operating current in both This circuit see Figure 31 page 34 design uses pulse width modulation PWM to control the speed of the motor As it was explained previously the greater the voltage the faster the motor runs causing the actuator to rise or lower faster and visa versa with less voltage Depending on the polarity of the voltage this will determine which way the rotor or armature rotates Positive voltage will cause the rotor to rotate such that it drives the actuator up and raise the bed Negative voltage will rotate the rotor in the 57 opposite direction and cause the actuator to retract and lower the bed The major drawback of this motor type is that if a no load condition occurs zero torque speed the motor could accelerate beyond its mechanical design limit and fail 10 However this will never happen in this device because there will always be some load on the system due to the weight of the bed back In choosing a motor an appropriate revolution speed in rotations per minute RPM must be found and the motor must be able to handle the voltage outputted by the circuit This can be tested by supplying a range of DC power to the motor and measuring the RPMs by the use of a tachometer to verify its speed For prop
22. with Inside box containing circuit h l teh board sprines and output wires Poa io swe EE H inside handle for safe to power dc motor operation Figure 39 Basic Inside Design of Handle This shape is designed to keep the majority of the control lever out of the way but allow both the patient and caretaker to comfortably work the device This should also help reduce the occurrences of the handle being bumped since only a fraction of it will be above the protection of the bed mattress Another feature is a safety lock which will be built into the handle In the occurrence of the lever being accidentally bumped this safety switch will prevent the bed from operating The safety switch similar in appearance to a hand brake on a bicycle will be a simple open loop switch The easiest way to implement this switch is to use a push to make switch Fig 40 next page A push to make switch returns to its normally open off position when you release the button since the input is conveyed to the motor via an electric circuit any break in this will prevent the Da motor from being driven The safety switch will be placed on the under side of the lever so that accidental activation does not occur in the event of force being applied from the top of the handle such as the patient rolling over on the lever Or a visitor sitting on it The safety switch will only require as little as one pound of force to unlock so that all users will be able to op
23. 007 Attach Springs to Handle and Box 5 days 8 00 17 00 T 3 16 2007 3 16 2007 65 Write Weekly Report 1 day 8 00 17 00 PITE NU NN Update Website 1 day 8 00 17 00 Cor Inte 8 NU NN Weekly Meeting 1 day 8 00 17 00 os eneen mm ZS UC NN Test Handle with PCB 5 days 8 00 17 00 recono oos la S NN Attach Motor to Control Handle 5 days 8 00 17 00 ro recorta mm NS NN 70 Test Control Handle and Motor 5 days 8 00 17 00 mereces ls ae E 71 Machine Jack Connections 5 days 8 00 17 00 Ray Nr a NS NN 72 Write Weekly Report 1 day 8 00 17 00 re uw O a NN 73 Update Website 1 day 8 00 17 00 a ee lia 5 NS NN Weekly Meeting 1 day 8 00 17 00 punto cone sa INS PN Assemble Jack to Bed Frame 5 days 8 00 17 00 Steve r engen em IU e Attach Motor to Jack 5 days 8 00 17 00 Steve mr seais em ges SERR naea Attach Control Box to Bed 5 days 8 00 17 00 Alaena m umecasosonon oon SOSU CORN my 78 Wire Control Box to Motor 5 days 8 00 17 00 Ray E a M NN 79 Double Check Assembly of ABAC Parts 5 days 8 00 17 00 oo moneen nay Eg Write Weekly Report 1 day 8 00 17 00 Cor uate nay NU NN Update Website 1 day 8 00 17 00 e Inten a 3 NU NN Weekly Meeting 1 day 8 00 17 00 Pur a a 5 83 Test For Accessibility for Disabled Clients 5 days 8 00 17 00 Pure Asm mm 5 75 Test for Blind Person Accessibility 5 days 8 00 17 00 Pure ooon 5 5 Test for Arthritic Person Accessibility 5 days 8 00 17 00 e eenegen ooon 5 5 T
24. 20A 0 250 F 50 250 F max 0 5 sec Mechanical Input 1 20 Ibs Range of Motion 0 72 Compressed Scissor Jack Length lt 6 Extended Scissor Jack Length 20 24 2 Purchase Requisitions and FAX quotes Purchase Order Number Camping World Scissor Jack 1 Digi Key Corp Mosfets 2 Lee Spring Compression Springs 3 The Home Depot Bed Frame Supplies 4 83
25. 7 14 1 3 Design 3 14 1 3 1 Objective Design 3 was a refinement of design 2 It retained the same force sensitive handle idea from the previous design which used springs to translate the physical force applied to the handle to displacement Inside the joint of the handle was a rotary potentiometer that measured the rotation of the joint However the electric circuit controlling the motion of the bed was completely changed in order to ensure a large enough current for the motor This circuit used pulse width modulation to control the speed of the DC motor and an H bridge to control its direction Instead of a linear actuator the motor turned a lead screw that was mounted underneath the bed parallel to the ground Attached to the lead screw was a rigid bar that raised the bed back as the nut on the screw was forced backward Rotating the screw in the opposite direction moved the nut forward and thus lowered the bed back The bed s frame was constructed out of 80 20 Aluminum Beryllium 14 1 3 2 Control Lever The control lever will consist of three main parts a lever a potentiometer and two resistance springs The lever will be approximately one foot long and will be in the shape of a flattened S Figure 2 shows the preliminary shape which has been designed to keep the majority of the control lever below the surface of the bed out of the way of both the patient and the care giver while still allowing easy access to the patient w
26. FINAL REPORT Adjustable Back Angle Controller ABAC By Alaena DeStefano Steven Frisk Raymond Pennoyer Team No 8 Funded by Rehabilitation Engineering Research Center Client Contact Information Dr John Enderle University of Connecticut Biomedical Engineering Department Program Director amp Professor of Biomedical Engineering Bronwell Building Room 217C 260 Glendale Road Storrs Connecticut 06269 2247 Voice 860 486 2500 Email jenderle bme uconn edu Website www eng2 uconn edu jenderle BME Program Homepage www bme uconn edu EMB Magazine Homepage www EMB Magazine bme uconn edu Table of Contents Abstract 1 Introduction 1 1 Background 1 2 Purpose of the project 1 3 Previous Work Done By Others 1 3 1 Products 1 3 2 Patent Search Results 1 4 Map for the rest of the report 2 Project Design 2 1 Design Alternative 2 1 1 Design 1 2 1 1 1 2112 2 1 1 3 2 1 1 4 2 1 1 5 2 1 1 6 2 1 1 5 2 1 1 6 2 1 1 9 2 1 1 10 2 1 1 11 24 E17 Objective Control Lever Lever Hydraulic Control Valves Resistance Springs Hydraulic Pump Motor Motor Hydraulic Tubing and Fixtures Pressure Valve Pressure Gauge and Adapter Hydraulic Lift Polycarbonate Box 2 1 2 Design2 2 1 2 1 2 1 2 2 2 1 2 3 2 1 2 4 2 1 2 5 Objective Control Lever Lever Resistance Spring Electric Circuit 2 1 2 5 1 Overview 2 1 2 5 2 Potentiometer 2 1 2 5 8 Inverting Amplifiers 2 1 2 5 4 Dif
27. IEC 60601 1 e EC IR 62296 Considerations of unaddressed safety aspects in the Second Edition of IEC 60601 1 and proposals for new requirements This Technical Report is primarily intended to be used by manufacturers of medical electrical equipment test houses and others responsible for assessment of compliance with IEC 60601 1 and those developing subsequent editions of IEC 60601 1 e IEC 61310 3 Safety of machinery Indication marking and actuation Part 3 Requirements for the location and operation of actuators Specifies safety related requirements for actuators operated by the hand or by other parts of the human body at the man machine interface Gives general requirements for the standard direction of movement for actuators the arrangement of an actuator i relation to other actuators the correlation between an action and its final effects Based on IEC 60447 but is also applicable to non electrotechnical technologies Covers single actuators as well as groups of actuators forming part of an assembly e IEC TR 61258 Guidelines for the development and use of medical electrical equipment educational materials Outlines a generic process for developing materials for education and training of operators of medical electrical equipment It may be used by standards organizations manufacturers regulatory agencies hospital managers physician and nurse educators and others involved directly or indirectly in education and training
28. Therefore the faster the motor spins the faster the load is moved In this design a ball lead screw will be used turned by an electric motor and used to pull together the sides of a scissor jack During this contraction the 58 scissor jack pushes up on the bed back raising the angle This set up is shown in Figure 43 DE Figure 43 Diagram of Scissor Jack Lifting Bed Back ho hi L Figure 44 Free Body Diagram of Lifting System Where hz Raise in bed at 0 degree incline D sin 0 hi Length of Fully Retracted Scissor Jack 0 degree incline in bed back D Distance of connection point from bed joint y degree tilt of actuator at 0 degree incline in bed back tan L h 59 L horizontal displacement of connection point D cos 0 Assuming that the force from the patient s weight is focused at about 1 3 of the length of the bed back 35 inches in length from the joint we assume that F is concentrated at D 15 inches Therefore the actuator will also be placed at this point so that the majority of the weight is directly supported The bed is also projected to lift from 0 degrees to 70 degrees of incline Therefore the actuator will be under the greatest tensile and shear stresses while at its maximum amount of incline To determine the proper material and diameter for the actuator shaft we assume the maximum load of 180 pounds is applied at the connection Knowing the force applied at the join
29. XXX 44400 LXXX RANGA AA Vi be 10 Y Y Wee 6 4 4 ODDO Kat X 20 MM v AX DC Xo de V y AA X X 4 LRL V ROSA a ays 44 E im K MN ve 0 Ki A DH e d e t d A ei x ke Ai A Kal x Ce LX de SN de e x A t Ge 20 e KX D CO DN ne i e14 pag k 558118 t 70 Degrees LC a 34 Overall Back and Side View of Schemat Figure 27 To calculate the required materials for the actuator the following free body diagram and equations are used el P D Fr ba F 2 A o h L Figure 28 Free Body Diagram of Lifting System Where F Weight of Patient 0 45 hz Raise in bed at 0 degree incline D sin 0 hi Length of Fully Retracted Actuator 0 degree incline in bed back D Distance of connection point from bed joint Fa Force applied by actuator y degree tilt of actuator at 0 degree incline in bed back tan E z 7 7 2 FL Component of patient s weight perpendicular to actuator Ei Component of patient s weight parallel to actuator L horizontal displacement of connection point D cos 0 I Area Moment of Inertia of Actuator Shaft a d Diameter of Actuator Shaft c radius of Actuator Shaft A Cross sectional Area of Actuator Shaft T Torque Output by Motor Bending Moment on Actuator in lbs F m F cos y Eq 3 A A 35 Stress due to Bending psi d TK use P 2 10 19 F Dcos 0 Fa 4 O bending I gtd qi q 64 Direct Shear
30. a 8 UU NN 17 Weekly Meeting 1 day 8 00 17 00 put em 3 25 Calculate RPM required by Motor 5 days 8 00 17 00 Steve puer sine IN UN Test Force Required to Extend Jack 5 days 8 00 17 00 Steve n loms PU Ml NU EN Order Springs 1 day 8 00 17 00 Ihnen a 5 NU NN Write Weekly Report 1 day 8 00 17 00 aa usone ERI ED Update Website 1 day 8 00 17 00 Ca vee lia E NN 23 Weekly Meeting 1 day 8 00 17 00 aa ptm em NU NN Receive Framing 5 days 8 00 17 00 as mesma mm LIO anon Measure and Cut Framing 5 days 8 00 17 00 Alaena Lm manresa s IRE en Machine Bed Frame 5 days 8 00 17 00 Alaena ar_ witeweekiyRepot ay Tal oo OO 27 Write Weekly Report 1 day 8 00 17 00 9 Update Website jaa Tal oo OO Update Website 1 day 8 00 17 00 m Weekiy Meeting day Tal oo OO Weekly Meeting 1 day 8 00 17 00 s Receive Springs tay To tro O 30 Receive Springs 1 day 8 00 17 00 A een same Sis R 31 Test Springs 5 days 8 00 17 00 Alaena PICTCREEEEEPTRNUI UU e 32 Machine Handle 5 days 8 00 17 00 Alaena PERENNE UNE PN 33 Develop Test Plan of Circuit 5 days 8 00 17 00 Ray 34 Test Individual Circuit Components 5 days 8 00 17 00 Ray 35 Write Weekly Report 1 day 8 00 17 00 PEORES C NN 36 Update Website 1 day 8 00 17 00 ete 2 2 9 2007 2 9 2007 37 Weekly Meeting 1 day 8 00 17 00 76 38 39 2 12 2007 2 16 2007 Prototype Circuit 5 days 8 00 17 00 Ray openeen Lem RO PN Test Prototype Circuit 5 days 8 00 17 00
31. ack With the implementation of the brush series wound DC motor there are concerns about the longevity of the brushing mechanism However this is not a major issue because it still has a considerable life span especially for this low impact situation With any load bearing device the wear and tear on the screws and fixtures will also be a concern with the devices sustainability Finally the availability of the parts used in manufacturing the device was considered and it will be economically feasible for mass production According to internationally recognized quality and safety standards there are some constraints to consider when designing The International Standards Organization ISO 18 and the International Electrotechnical Commission IEC 66 develops rules to follow in order to reassure that the product is reliable and will meet expectations in terms of performance safety durability and other criteria The following standards were taken from the IEC website because they closely match the building requirements of the adjustable bed design 19 e IEC 60073 Basic and safety principles for man machine interface marking and identification Coding principles for indicators and actuators Establishes general rules for assigning particular meanings to certain visual acoustsic and tactile indications Has the status of a basic safety publication in accordance with IEC Guide 104 e TEC 60364 4 41 Low voltage electrical installation
32. aining box The springs are to be sized such that both springs are stretched an equal amount when the lever is in the zero position By stretching both springs even in at zero makes both springs act equally on the lever at all times Both springs must also be stretched even when the lever is at its maximal displacement to both sides This is required so that the shorter spring does not begin to compress and push back against the lever making calibrations less precise To design the proper control lever the characteristics of the resistor circuit system must be known Once the relationship between the resistance lever displacement and the voltage output by the circuit is known the input to output force can be calibrated With a known hand displacement Ax and a known spring constant k force required to displace the spring lever is equal to the spring constant times the displacement F kAx as shown in Figure 7 page 10 39 For example if the maximum displacement of the springs is four inches and knowing that the maximum force applied is 20 Ibs it can be calculated that the spring constant needed is five The force required to push at the end of the handle P can then be found by drawing a basic free body diagram of the lever with springs as shown in Figure 8 page 10 and describing the moment about point A By solving for P the force to displace the lever some amount x is directly proportional to the force applied To test the spri
33. and one on it s 55 output Figure 41 is the resulting graph showing the triangle wave in green reference voltage in yellow and comparator output in blue Whenever the triangle wave is higher than the reference voltage the output is high S File Edit View Simulation Trace Plot Tools Window Help S E X Sv sees Gel SCHEMATIC1 bias gt amp Q pee Ej P576 Bed 3 bias dat act s Figure 41 PSPICE Simulation of Comparator Output Once the control half of the circuit was confirmed to be working as planned current markers were placed on the drains of MOSFETs M1 and M3 to confirm that they are switching properly Figure 42 next page shows that they are with M3 staying closed the entire time and M1 opening and closing in response to the comparator s PWM input 56 3 File Edit View Simulation Trace Plot Tools Window Help S S x ar see SCHEMATICT bias gt 39399 D amp B tz RB d 5 a Y j D I 3 bas dat act Figure 42 MOSFET Switching Response to PWM After parts are ordered and are sent the circuit will be physically constructed on a protoboard and it will be tested using a digital multimeter and oscilloscope The multimeter will be used to ensure that the reference voltages are correct and the oscilloscope will display the voltages across the terminals shown in Figure 42 above similar to PSPICE 222 Electric Motor The electric motor used
34. anizations 71 The Adjustable Back Angle Controller will make the lives of many around the world much easier From nurses and aids to patients suffering from a wide range of afflictions ranging from blindness to any number of diseases causing tremors and the lost of motor skills In particular our design is capable of assisting each of our clients and wide range of disabilities Every day people develop back pain as a result of their occupation injury or life style Occupations such as nursing and home aids are of the most likely to develop some kind of back problem This is mostly due to the constant repositioning of patients to prevent bed sores or for therapies With patients suffering from back pain an inclined back position provides some relief as well as helping to improve the patient s condition Persons with obesity can often have trouble breathing while laying fully reclined position however raising their resting angle up will open the air ways allowing for easier breathing It is also difficult for the elderly obese or sufferer of other debilitating conditions to simply get out of bed while laying flat This often means that a nurse of aid must assist the individual in sitting up and stabilize them while getting off the bed An adjustable bed however allows either the patient or the aid to life the patient s back into an inclined position relieving the aid of any strain on their back while bending over the bed and assisting the
35. basic design consists of a lever handle that controls a circuit which powers a mechanical actuator attached to the back of a bed to adjust the angle The actuator will keep a low profile in the back so that it can fit neatly under the back of the bed and still have the bed lie completely flat This is possible with a scissor jack that can collapse easily and it is operated by a motor which turns a screw rod to provide a smooth lift The key features to this device are its safety lock to prevent accidental movement the control lever which increases the speed with the amount of force applied to it and the intuitive approach to operating the handle such that lifting the handle will give the sensation of lifting the back angle upwards and visa versa The handle design itself will be large and easy to grip or find for those with poor vision or arthritis in the hand There is no confusing interface or technology associated with this device The motivation of the project is to build a totally accessible device to anyone using it 13 Introduction Nursing is among one of the highest risk occupations for the development of back pain and injuries Currently 17 of nurses experience chronic back pain due to working in a hospital setting 3676 of these back injuries in nurses can be contributed to patient handling In addition to the back pain women are also twice as likely to contract musculoskeletal disorders from the following work tasks repeatedly lifting
36. basic shape which is designed to keep the majority of the control lever below the surface of the bed out of the way of both the patient and the care giver while still allowing easy access to the patient within the bed The lever will be used to operate the two hydraulic control valves The two valves will control the amount and direction of the flow to the hydraulic piston When the lever is moved one way it will open one of the valves This will allow the flow in the hydraulic lines to travel into the piston driving it in one direction If the lever is moved in the other direction the other valve will be opened causing the piston to be driven in the opposite direction Depending on the amount of deflection on the lever the corresponding valve will be opened to a varying degree This allows for control of the amount of hydraulic flow to the piston which will control the force output 12 of the piston With a greater lever displacement the valve will be opened more forcing the piston up with a greater force The resistance springs serve a two fold function First of all they will return the lever to its zero position which will allow both valves to be completely closed when not in operation Second the springs will provide the proper resistance so that a specific force will be required to displace the lever a specified amount Therefore the greater force applied to the lever the greater opening in the valve and a greater output force to the be
37. be tests to verify that these requirements are attained IEC 60601 2 46 Medical electrical equipment Part 2 46 Particular requirements for the safety of operating tables Specifies safety requirements for operating tables whether or not having electrical parts including transporters used for the transportation of the table top to or from the base or pedestal of an operating table with detachable table top IEC 61800 1 Adjustable speed electrical power drive systems Part 1 General requirements Rating specifications for low voltage adjustable speed DC power drive systems Applies to general purpose adjustable speed DC driven systems which include the power conversion control equipment and also a motor or motors Excluded are traction and electrical vehicle drives Applies to power driven systems PDS connected to line voltages up to 1 KVAC 50 Hz or 60 Hz IEC 62955 1 Primary batteries Summary of research and actions limiting risks to reversed installation of primary batteries Provides information relevant to the safe design of batteries and battery powered devices together with appropriate cautionary advice to consumers This report is primarily intended to be used by battery manufacturers equipment manufacturers designers standard writers consumer organizations and charger manufacturers This report may also be of assistance to educational authorities users procurement personnel and regulatory authorities 16 Safety Issues
38. ber Aluminum for Handle and N A About 50 Control Box Camping World Scissor 100 98 Jack Digi Key Corp Mosfets 18 60 Lee Spring Compression 68 90 Springs The Home Depot Bed 18 33 Frame Supplies Estimated Total Cost s 81 Refer to 12 2 for PO Requisitions Numbers 19 2 Timeline Table 4 Timeline m taskwame L nsen Start Fish Names Jeepen en a NU NEN Final Report 6 days 8 00 17 00 Fu em NU NNNM Machine Shop Certification 5 days 8 00 17 00 Ca lupins ame NU NNNM Update Website 3 days 8 00 17 00 a Jentgen p Finalize Parts Order 5 days 8 00 17 00 FUCO Jos ZS 7 Prepare Final Presentation 3 days 8 00 17 00 Cm em 5 7 Final Presentation 1 day 8 00 17 00 jOdePas Says e ol 7 Order Parts 5 days 8 00 17 00 amp stanio Receive Pans uer o ol Start to Receive Parts 4 days 8 00 17 00 9 Prototype Bed with Scissor sack Lues 8001 17 00 Steve Prototype Bed With Scissor Jack 4 days 8 00 17 00 Steve 10 orerscissorack uge aoo i Order Scissor Jack 4 days 8 00 17 00 75 1 16 2007 1 19 2007 11 Receive Scissor Jack 4 days 8 00 17 00 EECH NU PN Measure and test Scissor Jack 4 days 8 00 17 00 Steve PROPER IN e 13 Finish Bed Frame Design 1 day 8 00 17 00 Alaena a tte a LO O Order Framing 4 days 8 00 17 00 is roer lia Sg Write Weekly Report 1 day 8 00 17 00 se uate tm IERI A Update Website 1 day 8 00 17 00 Cor vee li
39. ct the path of power from the DC source 8 MOSFETs act like a voltage controlled switch If a voltage is applied to the gate pin current is allowed to flow through the source and drain pins Because the amplitude of the triangle wave cannot be more than the difference between the other inputs on the window comparator both op amps cannot be on at the same time This is important because if they both were on the four MOSFETs would be activated at the same time which would break them A typical MOSFET is shown in Figure 33 page 37 Activating U1D causes a cascade of events that turns MOSFET Q3 on JFET Q2 off and MOSFET Q6 on This allows power from the DC source to run through Q3 the motor and Q6 causing the motor to turn in one direction The length of time that power is allowed to the motor is controlled by the potentiometer input Likewise activating U1C turns O4 on O1 off and finally Q5 on completing a circuit from power through O4 the motor Q5 and then ground This will cause the motor to turn in the opposite direction As stated above both U1C and U1D cannot be activated at the same time which prevents all of the MOSFETs from being on simultaneously The circuit has been built and tested in PSPICE After setting the simulation profile to transient setting the time range and raising the number of iterations voltage markers were placed One was put on the triangle wave generator output one on the other input to comparator UTD
40. d back 14 1 1 3 Lever The lever will be the object moved by the user to operate the Adjustable Back Angle Controller Its shape will be ergonomic so as to make operation of the devise as simple and comfortable as possible One innovation is the S shape which has been incorporated in Figure 5 next page This shape is designed to keep the majority of the control lever out of the way but allow both the patient and caretaker to comfortably work the device This should also help reduce the occurrences of the handle being bumped since only a fraction of it will be above the protection of the bed mattress Another feature is a safety lock which will be built into the handle In the occurrence of the lever being accidentally bumped this safety switch will prevent the bed from operating The safety switch similar in appearance to a hand brake on a bicycle will unlock the lever when it is depressed It will be placed on the under side of the lever so that it will not be accidentally triggered in the event of an accidental force being applied from the top of the handle such as the patient rolling over on it or a visitor sitting on it The safety switch will operate by means of a clamp on the lever to oppose any accidental movements When the safety switch is held down completely this clamp will release the lever allowing the user be it the patient or a caretaker to operate the bed The safety switch will also only require as little as one pound
41. ddle terminal varies according to how far the wiper is along the resistor This is shown in Figure 20 page 21 54 The potentiometer is set up as a voltage divider circuit with middle pin connected to the non inverting input of op amp UlA which is an op amp configured as a voltage follower Voltage followers have a gain very close to one and are used to safeguard the rest of the circuit from input extremes 6 For this and all op amps in the circuit the Vcc is supplied by the DC source and Vcc is ground Optimally all four op amps would be integrated into one IC chip such as the LM324 quad op amp shown in Figure 32 page 36 The output from the voltage follower is connected to the non inverting input of U1B which is a triangle wave generator The triangle wave is generated from the charging and discharging cycles of the 10nF capacitor This value and the resistance of R6 create a triangle wave with a frequency of around 270 Hz The Amplitude of the wave is controlled by the voltage follower The triangle wave is output to two op amps U1C and UID set in window comparator configuration It is connected to the non inverting input of UID and the inverting input of U1C U1C is turned on if the triangle wave input is higher than its non inverting input U1D is activated if the triangle wave is below its inverting input The outputs from U1C and UID are used to control four MOSFETs Metal Oxide Semi Conductor Field Effect Transistor that dire
42. ds to withstand a strong support frame for the actuator can be determined The most practical metal to use in this situation is Aluminum Beryllium Al Be 80 20 This is a light weight durable easy to assemble and cheaper way to construct this verse welding steel parts together Figure 30 page 31 is a picture of Al Be 80 20 and chart of its mechanical properties The design of this structure is seen in the overview of the frame on the following pages in Figure 37 and 38 This material will be ordered in the proper sizes and put together in the machine shop Once the frame is finished it will undergo a series of loading tests to test the strength of the structure If failure is to occur reinforcement will be added where necessary The overall schematic of the design as illustrated in the Microsoft VISIO drawings in Figures 37 and 38 demonstrates the pivoting of the actuator to allow for movement as the bed is operated and sustains a low profile when retracted Also the handle is positioned out of the way and designed for easy access All parts are secured with bolts to the frame of the bed or the Aluminum To demonstrate the final workings of this automatic back angle controller it will be fastened to a mock bed platform It can be made out of scrap Al Be 80 20 or welded with steel and have a metal platform attached to mimic the mattress This will allow the device to be tested under the weight of humans lying on the platform 48 spog am
43. e the pressure difference is regulated to drive the piston at the desired velocity 2 1 1 5 Resistance Springs The resistance springs are used in the control lever to bring the lever back to zero when the action is done and to correlate an input force with an output displacement into the valves To zero the lever two springs with identical spring constants k will be attached between the lever and opposite sides of the retaining box The springs are to be sized such that both springs are stretched an equal amount when the lever is in the zero position By stretching both springs even in at zero makes both springs act equally on the lever at all times Both 15 springs must also be stretched even when the lever is at its maximal displacement to both sides This is required so that the shorter spring does not begin to compress and push back against the lever making calibrations less precise To design the proper control lever the characteristics of the hydraulic piston pump valve system must be known Once the relationship between the valve lever displacement and the force output by the hydraulic cylinder is know the input to output force can be calibrated With a known hand displacement Ax and a known spring constant k force required to displace the spring lever is equal to the spring constant times the displacement F kAx as shown in Figure 7 B 3 i F kAx where x2 x1 Ax Figure 7 Calculation of Input Force on Spring
44. ected to the rest of the electrical circuit The resistance between the two end terminals is constant and is set at manufacturing However the resistance between the middle terminal and either terminal adjacent to it changes as the shaft is rotated A typical potentiometer is pictured in Figure 19 next page 26 Washer Casing Terminals Figure 19 Typical Rotary Potentiometer 2 Inside the potentiometer is a long resistor with its ends attached to either end terminal The middle terminal is connected to a wiper that moves along the resistor The resistance between the end terminal and the middle terminal varies according to how far the wiper is along the resistor This is shown in Figure 20 PIN Rotary potentiometer construction Wiper Resistive strip Figure 20 Internal Workings of Rotary Potentiometer 3 In this design the DC power voltage will be applied to the center terminal In this situation the voltage at either end terminal is related to the amount of internal resistor that is between the wiper and the terminal and the wiper and opposite terminal For example if the wiper is moved as far toward Pn the terminal as possible the voltage at that terminal will be equal to the middle terminal The opposite is also true For this device the default position will be the center where equal voltages will be output to both end terminals When movement of the handle rotates the shaft and thus changes the position
45. enario the output voltage is V see reference in Figure 22 1 next page 5 By varying Rrand R the output voltage can be amplified up to the op amp s control voltage The inverting amps main purpose in this circuit is to 28 amplify the voltage from the potentiometer terminals to a level that can be used by the motor Figure 22 Inverting Amplifier Circuit 5 2 1 2 5 4 Difference Amplifier The two voltages from the inverting amplifiers are then both put into a single difference amplifier in Figure 23 next page The difference amplifier also uses an op amp but the supporting circuit is different In addition to the resistors configured like those in the inverting amplifier there is a resistor between the 2 input voltage and the positive input R2 and another between the ground and the positive input R In this case all of the resistors will have the same value which creates an expression for the output voltageV V V 5 The inverting amp from the potentiometer terminal associated with raising the bed back up will be V1 and connected to the negative input on the difference op amp Since the inverting amplifier had made it negative having a greater V4 will cause the difference amplifier to output a positive voltage This will cause the motor to drive the linear actuator up When Va is higher i e the bed back will be moved down then the output voltage will be negative and the motor will retract the actuator
46. er operation the torque and horsepower need to be calculated and can be determined with Equation 1 torque ft lb angularspeed rpm Ea 1 12 5252 ME Power hp 2 2 2 6 Actuator The actuator converts the rotational motion of the electric motor into linear motion to drive the bed back up and down This is typically done through the use of a lead screw or worm gear drive As shown in Figure 25 page 26 the motor drives the lead screw in a circular motion Due to the threading on the lead screw and the load nut this circular motion is transformed into linear motion as the load inches up the threading with each full rotation of the lead screw The roles of the load nut and the lead screw can be reversed should the operation require it In such a case the motor would rotate a fixed threaded nut in which the lead screw would sit The load would then be placed at one end of the lead screw As the nut is rotated by the motor the lead screw will be forced through it in one direction or the other via the threading on each This in turn would then drive the load upwards The rate of linear motion performed by an actuator such as this is a function of the revolution speed of the motor in revolutions per min rpm and the pitch of the thread in inches per revolution in rev as shown in Eq 2 V threadpitch angularspeed Eq 2 With each turn of the nut the lead screw will travel a distance equal to the pitch value of the thread
47. erate it easily Figure 40 Push to Make Switch and Bracket Representation 2 2 2 2 3 Resistance Springs The resistance springs are used in the control lever to bring the lever back to zero when the action is done and to correlate an input force with an output displacement into the valves To zero the lever two springs with varying spring constants k will be attached between the lever and opposite sides of the retaining box The springs are to be sized such that both springs are stretched an equal amount when the lever is in the zero position By stretching both springs even in at zero makes both springs act equally on the lever at all times Both springs must also be stretched even when the lever is at its maximal displacement to both sides This is required so that the shorter spring does not begin to compress and push back against the lever making calibrations less precise To design the proper control lever the characteristics of the resistor circuit system must be known With a known spring displacement Ax and a known spring constant k the force required to displace the spring lever is equal to the spring constant times the displacement F kAx as shown in Figure 7 page 10 For example if the maximum displacement of the springs is one inch and knowing that the maximum force applied down is 20 lbs plus a small amount of weight from the handle it can be calculated that the spring constant under the handle needed is just ove
48. est for Obese Person Accessibility 5 days 8 00 17 00 wetten oos 3 5 87 Test for Young Person Accessibility 5 days 8 00 17 00 EECH 88 Test for Elderly Person Accessibility 5 days 8 00 17 00 Test for Limited Mobility Dexterity Person 4 2 2007 4 6 2007 Accessibility 5 days 8 00 17 00 La lena A i le E Write Weekly Report 1 day 8 00 17 00 La inopi ee A i k NEN Update Website 1 day 8 00 17 00 78 4 6 2007 4 6 2007 92 Weekly Meeting 1 day 8 00 17 00 als O 7 e NEN Cosmetics 5 days 8 00 17 00 mE Las li ie NEN Troubleshooting Catchup 5 days 8 00 17 00 Las labe ie D ir E Write Weekly Report 1 day 8 00 17 00 ak tidied A T T NEN Update Website 1 day 8 00 17 00 or meoo sam RR 97 Weekly Meeting 1 day 8 00 17 00 oa oie cnn sane B NN Write User Manual 5 days 8 00 17 00 oe rior sane LS NN Final report 5 days 8 00 17 00 wm FinalPresentaton luan sool tof Final Presentation 1 day 8 00 17 00 20 Team Member Contributions to the Project 20 1 Team Member 1 Alaena DeStefano Alaena has a concentration in biomaterials and has studied the importance of material selection therefore her main contribution to this project is concerning the materials being used She will primarily be responsible in the design and framework around the PCB handle and scissor jack as well as provide a prototype bed to mount this device to Her work closely with her teammates will be important to the success of this project
49. f a power loss a back up battery will be implemented per the safety standards of IEC 62955 1 The circuit has also been carefully designed so that the motor cannot draw a dangerous amount of current from it and in worst cases become a fire hazard So all precautions have been taken to ensure that the patient is protected from the electricity Also if power is lost the bed will remain in its current position instead of suddenly falling to horizontal This 69 is an advantage to a mechanical actuator because it will not budge from its position unless a voltage is applied to the motor to give it power again Of course before any product is marketed there are a series of validation steps that include vigorous testing procedures specifications and standards to be met in order for the product to be considered safe for public use The IEC has set some recommended guidelines to be followed for the Technical Reports TR to ensure it is tested properly Below are a few safety issues in compliance with the standards mentioned above to be considered during development especially if this device is marketed e ISO IEC GUIDE 46 Comparative testing of consumer products and related services General principles e IEC TR 62354 General testing procedures for medical electrical equipment This Technical Report applies to medical electrical equipment as defined in IEC 60601 1 Its object is to provide guidance on general testing procedures according to
50. ference Amplifier 2 1 2 5 5 Filter 2 1 2 6 2 01 24 2 1 2 6 Electric Motor Actuator Support Frame 2 1 8 Design 3 2 1 9 1 2 1 3 2 Objective Control Lever 7 61 7 45 7 18 7 8 8 9 9 10 10 11 12 13 13 14 14 15 15 15 17 17 18 18 32 18 18 19 19 19 20 20 25 20 21 21 23 23 24 24 25 25 25 26 26 31 32 33 45 33 33 Div hie 2 1 3 3 Lever 2 1 3 4 Resistance Spring 2 1 8 5 Electric Circuit 2 1 8 5 1 Overview 2 1 3 5 2 Potentiometer 2 1 3 6 Electric Motor 2 1 9 7 Actuator 2 1 8 5 Support Frame 2 2 Optimal Design 2 2 1 Objective 2 2 2 Subunits 2 2 2 1 Control Lever 2 2 2 2 Lever 2 2 2 3 Resistance Springs 2 2 2 4 Electric Circuit 2 2 2 4 1 Overviews 2 2 2 4 2 Circuit Components 2 2 2 5 Electric Motor 2 2 2 6 Actuator 2 2 2 7 Support Frame 2 2 3 Testing the Design Realistic Constraints Safety Issues Impact of Engineering Solutions Life long Learning Budget and Timeline 7 1 Budget 7 2 Timeline Team Member Contributions to the Project 8 1 Team Member 1 Alaena DeStefano 8 2 Team Member 2 Raymond Pennoyer 8 3 Team Member 3 Steven Frisk Conclusion 10 11 12 References Acknowledgements Appendix 12 1 Updated Specification 12 2 Purchase Requisitions and FAX quotes 34 34 35 35 38 35 36 37 38 38 39 39 43 43 45 46 61 46 46 59 46 47 47 48 48 49 49 52 49 49 52 52 53 53 59 59 59 61 61 63 63 66 66 68 68 70 70 74 70 70 74 74
51. g new standard less expensive beds and installing the lift mechanism The availability of our automatic lift mechanism for standard hospital beds in clinics or hospitals around the world can positively affect the health care setting in terms of allowing the patient more independence from the caregiver supervision The societal common good would be served by narrowing the gap between basic health care equipment in the U S versus that in third world countries Our design or product s cost impact to health care facilities exiting and new is exemplified per the following Our design has the estimated retail price of less than 313 refer to budget Table 1 A standard bed e g manual crank lift by A1 Adjustable Beds is listed as 712 22 The price of a deluxe hospital bed model number SS3TPKGTM by A1 Adjustable Beds with the automotive lift mechanism as well as other possibly unnecessary features is listed as 3200 23 Installing our automatic lift mechanism on new standard hospital beds vs purchasing a deluxe hospital bed is estimated to be 2175 cost savings Savings can be considerable for a small clinic purchase of 15 new basic beds and the automatic lift mechanism will yield an estimated savings of 32 621 If use of existing standard beds is possible purchase of only the lift mechanism is necessary to receive the same The savings of course can be used to purchase other equipment or supplies especially beneficial for non profit org
52. greater than 7 lbs lifting patients more than 10 times per hour making beds normally or often and pushing beds or trolleys more than 10 minutes per day 1 These daily tasks cannot be avoided however by the implementation of an automatic adjustable bed nurses will incur less stress on their back during the adjustment of the patient Patients that suffer from back pain obesity and other debilitating diseases require an inclined bed back to relieve pain or provide easy access to the bed Current technology includes an adjustable bed back with a remote control that is accessible for both the patient and the caretaker However this does not accommodate users of all disabilities For example a patient with limited sight may find it difficult to find the remote or press the correct buttons to operate the bed Some of the current beds that may operate at higher speeds are rough or jerky when stopped in position This erratic movement also occurs in beds that have more than one speed Start Force Applied to Handle Potentiometer Adjusted No Action Handle Direction Resistance to Down Terminal Decreased Resistance to Up Terminal Decreased Comparator U1C Activated Comparator U1D Activated MOSFETs Q4 and MOSFETs Q3 and Q5 Activated QO Activated Motor Turns Counterclockwise Motor Turns Clockwise Screw Lead Lowers Bed Sc
53. handling to help the patients sit up right in bed This client has mild hearing loss and suffers from carpal tunnel syndrome The second client is a 69 year old retired woman that sleeps in a hospital bed She has Parkinson s disease with some tremors and as a result has limited mobility and dexterity The third client is a 31 year old lady who was recently in an automobile accident that resulted in partial paralysis of her right side This is inconvenient because she is right handed and she doesn t want a lot of complicated medical devices in her room The fourth client is an 86 year old that is deaf has severe arthritis and heart problems so that she is confined to a bed Her 11 year old grandson has a fascination with electronics and helps her with her therapy and helps her sit up in bed The last few client restrictions are that they are visually impaired These clients have difficulty finding and using the current full electric hand pendant Figure 2 due to its small size and confusing interface All of the clients must be able to operate this prototype device with ease 13 2 Purpose of the project A large number of people encounter difficulty adjusting themselves in hospital beds due to their physical limitations This would apply to those patients with limited mobility and dexterity associated with conditions such as Parkinson s disease paralysis arthritis obesity and other disabilities The problem with current powered hospital beds is
54. hat if a no load condition occurs zero torque speed the motor could accelerate beyond its mechanical design limit and fail 6 However this will never happen in this device because there will always be some load on the system due to the weight of the bed back In choosing a motor it will have the appropriate rotations per minute RPM and be able to handle the voltage outputted by the circuit This can be tested by supplying a range of DC power to the motor and measuring the 30 RPMs by hooking up a tachometer to verify its speed For proper operation the torque and horsepower need to be calculated and can be determined with Equation 1 SERIES L FIELD INPUT VOLTAGE Figure 24 Circuit for a Series Wound DC Motor 7 torque ft Ib angularspeed rpm Power hp SE Eq 1 8 2 1 2 7 Actuator The actuator converts the rotational motion of the electric motor into linear motion to drive the bed back up and down This is typically done through the use of a lead screw or worm gear drive As shown in Figure 25 next page the motor drives the lead screw in a circular motion Due to the threading on the lead screw and the load nut this circular motion is transformed into linear motion as the load inches up the threading with each full rotation of the lead screw The roles of the load nut and the lead screw can be reversed should the operation require it In such a case the motor would rotate a fixed threaded nut
55. he input voltage to a square wave that ranges from OV to a maximum voltage determined by the surrounding circuit The amount of time that the wave is at the maximum voltage is controlled by the input voltage For example a wave generated by a maximum input will spend the maximum length of time at the high voltage The opposite is also true The main advantage of a PWM controlled motor is that it saves power compared to changing the voltage with a resistor which creates an excessive amount of heat under high current levels 2 2 2 4 2 Circuit Components The potentiometer is directly attached to the handle A potentiometer is a variable resistor that acts as an electro mechanical transducer This means that it converts mechanical stimuli into electric effects The potentiometer will convert the displacement and direction of the handle into a variation of resistance within a circuit A potentiometer has three terminals that can be connected to the rest of the electrical circuit The resistance between the two end terminals is constant and is set at manufacturing However the resistance between the middle terminal and either terminal adjacent to it changes as the shaft is rotated A typical potentiometer is pictured in Figure 19 page 21 Inside the potentiometer is a long resistor with its ends attached to either end terminal The middle terminal is connected to a wiper that moves along the resistor The resistance between the end terminal and the mi
56. ign is much lighter only about 180 pounds of lifting force is needed There are many things to consider when choosing the correct cylinder such as the relationships between p