Introduction The Adjustable Back Angle Controller (ABAC) will improve upon the

current methods of adjusting a bed. This device will be controlled with a force sensitive handle located on the most accessible side of the bed. The basic concept of adjusting the back angle will take the input force on the handle and adjust the speed proportional to the force applied to the handle, i.e., more force on the handle outputs a faster speed to raise or lower the back angle. This concept works by adjusting the voltage supplied to a linear actuator with a potentiometer in the joint of the handle. This design will accommodate those with limited mobility and control; as well as prevent injuries to caretakers that attempt to sit the patients upright. The variable speed motor will control the actuator from zero to a safe maximum speed. This will allow for a smoother operation while still offering speedy adjustments when necessary. Overall this device will be user-friendly, smoother in operation, and less time consuming, making the operation less stressful.

Design Alternative In this section there is a brief objective describing each design and its

corresponding subunits. The optimal design was chosen instead because the original idea of a hydraulic system is much more expensive than the latest electromechanical system. Also, with the manufacturability of the hydraulic system, it can get really messy and complicated trying to enclose the pipes without any leaks. The sustainability of the system is then weakened and cannot hold the load up with the pressure. In an electromechanical system, the parts are easily acquired and assembled. In addition, the lifting force will not fade because it is dependent on the power source as opposed to hydraulic pressure.

Objective The objective of this first design was to experiment with a hydraulic lever

system. The idea behind this was to have a smooth and quiet operating system with stability to lift the patient. Since hydraulics is used in many industrial settings, there was no doubt in having enough power for this application. However, concerns about the quietness of the motor and cleanliness for hospital operations arose and caused this design to be reevaluated for the future alternative designs.

Control Lever The control lever will consist of three main parts; a lever, two hydraulic

control valves, and resistance springs. The lever will be approximately 2 feet long, and will be in the shape of a flattened “S”. Figure 1 shows the 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 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 bed back.

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 of force to unlock it so that all users will be able to operate it.

Figure 1: Basic Design of Handle

Inside of Box

Safety Switch

Side View

Top View

Safety Switch

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. 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. 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 valve, the pressure difference is regulated to drive the piston at the desired velocity. 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 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 (Δx), and a known spring constant (k), force required to displace the spring-lever is equal to the spring constant times the displacement (F=kΔx).

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 2, next page, 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.

Where:

Fs1=k(L1) Fs2=k(L2) P=input force ΣMA = 0 = P*L+Fs2*l - Fs1*l P = l*(Fs1-Fs2) / L P = l*k*(L1-L2) / L

Figure 2: Free Body Diagram of Lever

Hydraulic Pump/Motor The hydraulic circuit that provides the lifting force to adjust the bed is

powered by the hydraulic pump. A pump creates hydraulic energy by mechanical means. There are a variety of different kinds of pumps, but they share some common characteristics. In order for any pump to work, it must first draw the hydraulic fluid into the pumping chamber by creating a slight vacuum. This allows atmospheric pressure on the open reservoir tank to force the fluid into the pump. Once it is inside the pump, further mechanical operation forces the liquid out the other side, simultaneously drawing more in. One important factor to note is that the pump itself does not create pressure. It merely causes liquid to flow. Pressure is a result of the resistance to that flow that the pump creates, i.e., without a load, pressure at the outlet of the pump is always zero. This means that the pressure in the system will not rise past that which is required to overcome the load. Pumps are categorized as either positive-displacement or non-positive-displacement. Non-positive-displacement pumps are not sealed well internally. This allows some ‘slippage’ of fluid back thru the pump under high pressure. The significance of this is that the pump’s output is reduced as pressure increases. On the other hand, positive-displacement pumps allow insignificant fluid slippage, if any at all, and are as efficient under high pressures as they are at lower pressures.

The pump attribute that is most important to the proposed design is its pressure rating. The pressure rating of a pump is the maximum hydraulic pressure that the pump can operate against. Since the weight of the patient on the bed will be acting on the hydraulic piston in a downward direction, it creates a pressure in the closed hydraulic circuit. Taking the cylinder’s bore size and the hydraulic tubing’s diameter into consideration, the pump must be able to exert a constant pressure on the system of around 200 psi in order to lift a patient that weighs 400 pounds. This is a relatively low pressure for hydraulics, since they are mainly used for heavy industrial work such as lifting cars or splitting logs. Because of this, most hydraulic pumps are designed to produce pressures of

around 2000 psi, an order of magnitude higher. However, some commercial pumps designed for use in low pressure systems such as car washes can be used.

One such device is the PROCON series 4 pump, which has a maximum pressure rating of 250 psi. This is approximately what is needed by this device. This pump is a rotary vane type, which is positive-displacement. This sturdy pump is made of brass and is designed to produce a flow rate of 115 to 330 gallons per hour at 250 psi.

Motor The same manufacturer also produces an electric motor to power the

pump. The model 48YZ Frame Motor is suited to this design. It operates at low horsepower, and high horsepower is not needed. Also, it is a clamp-on type motor, which the Series 4 pumps accept. The displacement required from a hydraulic pump is calculated by the

equation ))(()231)((

. pvolp

mp n

QV

η= where Vp is the displacement in in3 per revolution, Qm

is the flow rate in gallons per minute, np is the pump shaft speed in rpm, and ηvol.p is the pump’s volumetric efficiency.

Pressure Valve This is a very important feature to this hydraulic circuit design. In order to ensure safe operation, the system must not be overloaded in pressure. The PROCON pump has an output pressure of 250 psi. After preliminary calculations, it was determined that about a maximum of 60 psi will be needed to lift the back of the bed; therefore the pressure in the system will not need to be much more. This is where the pressure valve comes into the design. It allows the user to set a safe working maximum pressure of say 80 psi. Then the handle or lever described earlier will operate the control valve from zero psi up to the maximum set pressure by this valve. Basically, the pressure valve acts as a safety feature to filter out high pressure so that the patient is not thrown upwards at high pressures. When the pressure valve is dialing down the pressure, one will know the exact pressure in the system by reading the pressure gauge and adapter that will be incorporated into the design. The adapter will fit the hosing at ½” diameter lever fittings.

Hydraulic Lift One of the main components of this automatic lift system is the hydraulic cylinder. It is imperative that this cylinder is compatible with the system. Most cylinders are made for industrial systems that can lift millions of pounds. However, this design 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 pressure, area, displacement volume, flow, speed, and the influence of inefficiencies. The bore size of the cylinder

determines the mechanical advantage because it determines the size of the area that the force is concentrated. It was determined that for this design a bore size of 2 is efficient. Shown below in Figure 3 is the Prince Double Acting Hydraulic Cylinder which has a bore size of 2, stroke length of 18 inches and a maximum pressure of 2500psi. The double acting feature allows for the piston to be forced equally in both directions.

Figure 3: Prince Double Acting Hydraulic Cylinder

The mounting of this cylinder is important to the design because it stabilizes the cylinder throughout its motion and keeps a low profile when the piston is retracted. A pivot joint will also be considered where the cylinder attaches to the back of the bed so that it allows angular movement as the bed raises and lowers. Polycarbonate Box A box will be built out of a durable, clear Polycarbonate 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. The overall schematic of the design is shown next page in Figure 4. 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.

180

Bed Back

Hydraulic Lift

Motor

Bed Hinge

Support Beam

Power Cord

Control Handle

Figure 4: Overall design Schematic Prototype

The aim of this device is to create an easy-to-use extended physiological proprioceptive-based power assist back-angle controller. As with any prototype, this device is built in its rawest form and has room for much improvement. It was built with the intentions to meet the requirements of the RERC competition and to fulfill the needs requested by the clients. These needs varied from weakness in hands due to arthritis, Parkinson’s disease, blindness, to all ages—young and old. There are several ways in which this device accommodates these needs and they are explained in the following description of use.

This device operates on a simple principle: the force inputted is directly related to the outputted speed. As a safety precaution, a push button has been installed on the handle to turn the device on before moving the bed back. The extended physiological proprioceptive idea is that if one were to want to be lifted up, they would imagine pulling up on something to do so and visa versa to be lowered. For example, when the user depresses the safety button and pushes the lever down with 50% of the total max force, the bed will lower at half the max speed. This force is felt through a series of torsion springs that resist any force applied to the lever handle. The opposite will happen if the lever were to be pulled upward while pushing the safety button. If the safety push button is not pushed down when moving the handle, nothing will happen. This is to prevent any accidental movements of the bed back should the handle be sat on or rolled onto.

Clear Polycarbonate box w/pressure gauges, motor

and pump inside

Hydraulic Hosing

Technical Description The control box is used to convert the input for on the handle into an

electrical signal which will be used to control the direction and speed of the lifting system. Therefore, this system creates the force feed back, so that the operator feels like the more energy, in the form of force, they put into the handle, the more energy, in the form of lift speed, the bed gives back. In this way the bed demonstrates extended physiological proprioception. Extended physiological proprioception is the perception of the end of a tool. The force feed back is accomplished through the use of springs. Since springs push back with a greater force the more they are displaced, the torsion springs will allow the handle, and therefore a potentiometer attached to it, to rotate a greater amount with a great force input. At the handle’s zero position, the potentiometer will be in the middle of its swing. This way, the potentiometer will be able to measure the movement in both directions as a displacement from its middle range. The box will be set up such that the handle will be attached to an axis which rotates within the box along with the handle. Then the two torsion springs will be around this axis, with one arm held in place by the box, while the other arm is pushed by the handle, winding up one of the springs, as shown next page in Figure 5.

Figure 5: Handle Box Design

The use of two springs will allow the lever to be force in either direction

with a similar force feed back in both directions. Using the equation for the

spring constant of a torsion spring,θ

LFk *= , at a force (F) of 20 lbs, with a

handle length (L) of 10 inches, and a required rotation of θ = 40º, we have

decided to use torsion springs with a spring coefficient of, deg*5 lbin . These

springs will allow for a 40° rotation of the handle in each direction, which allows

the circuit to provide a full variation of speeds. The finished handle and box is shown below in Figure 6.

Figure 6: Control Box with Handle

The circuit utilizes an H-Bridge to control the direction of the motor. It

uses a microcontroller to read an input voltage across a potentiometer. The electric circuit serves to translate the mechanical action on the control handle into action of the linear actuator. The circuit on a PCB is shown in Figure 7, next page. Rather than varying the speed of the DC motor by changing the input voltage, the design uses pulse width modulation (PWM) to control the speed. The microcontroller translates the input voltage to a square wave that ranges from 0V to 5V. The percentage of time that the wave is at the maximum voltage determines the average DC voltage the motor receives, and thus varies its speed. 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. Using a series resistor in this manner also increases the current that the motor draws, which can be a major problem using powerful motors that already require a high current. The circuit also contains three push-to-make switches that limit the motion of the bed.

Figure 7: PCB Board of Completed Circuit in protective box

The potentiometer is directly attached to the handle and acts as an electro-mechanical transducer. In other words, it serves to translate the physical motion that the user puts on the control handle into an electrical signal readable by the rest of the 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. The potentiometer will convert the displacement and direction of the handle into a variation of resistance and as a result varies the voltage on the wiper pin.

For this design, the first pin of the potentiometer is given 5V, the second (wiper) pin is connected to the microcontroller, and the third pin is grounded. In this setup, the wiper acts like a voltage divider circuit, varying the voltage from 0-5V. However, because of the mechanical setup of the design, the wiper’s center location is the ‘off’ state. Moving the potentiometer away from this center causes the motor to move in either direction at a speed determined by how far away from the center the wiper is. For example, turning it slightly to the left causes the motor to raise the bed slowly, while turning it further increases the speed that the bed raises.

The microcontroller used in the prototype is a PIC16F874A. Its purpose is to convert the analog potentiometer input to digital, decide in which direction and at what speed the motor should turn, and output control commands to the H-bridge based on this. The program also includes overrides based on the three push button inputs.

Port D is used for most of the I/O because its pins do not share special functions. This leaves the specialized pins free for future development. The exceptions are the PWM output to control the motor’s speed, and the A/D input from the potentiometer. Hardware PWM is used because it allows for easier manipulation of the duty cycle. The duty cycle of the PWM is basically the ratio of the CCPRxL register to the PR2 register. Keeping this in mind, the PR2 register was set to 128 in the initialization of the program. This allows for a full duty cycle even when using only half of an 8-bit analog to digital conversion of a potentiometer reading. After converting the analog 0-5V input to a number between 0 and 255, the data is converted so that the middle of the potentiometer is 0 and the two extremes are 128. First the binary number is checked to see if the most significant digit is a 0 or a 1 to decide which direction subroutine to use. For example, if the most significant digit is a 1, then the potentiometer is turned more than halfway to the left, and the program proceeds to the ‘Up’ subroutine. Next the program changes the number into one that is from 0 to 128 by using a combination of the comf and sublw commands. This number is transferred to the CCPRxL register for the specified direction, and the PWM is activated simultaneously with the corresponding high side flat 5V output.

The program includes a series of bit tests to ascertain if the safety button on the handle has been pressed. If it has not, the program does not activate the outputs. There are also 2 tests to see if the motor limits have been reached. If the motor has reached the bottom of its range, it will press a button that prevents the program from lowering the motor any further. The same holds true for the ‘up’ extreme. The flat 5V output from the microcontroller is not sent directly to the H-bridge (Figure 8). Instead, it is sent to a predriver circuit composed of an N-channel MOSFET and two identical resistors. The resistors are in series and are connected from the full voltage input to the drain of the MOSFET. Its source is grounded. In this configuration, the voltage between the two resistors is still the same as power voltage, because the MOSFET is acting like an open switch, so no current can flow. When the microcontroller’s 5V output reaches the MOSFETs gate, the switch closes, current flows across the resistors, and the voltage drop over each of the resistors is half of the supply voltage. In this case that is 15V. This is connected to the P-channel MOSFETs that compose the high side of the H-bridge. In this manner, the 5V output of the microcontroller is converted to a -15Vgs on these FETs, closing them.

Figure 8: Two H-Bridge Predriver

Three buttons were incorporated into the bed prototype. The first one is located on the handle itself, pictured next page in Figure 9. This button is used as a safety, and the bed will not move unless it is pressed. This is so that anyone that accidentally bumps the handle does not move the bed, which could be startling for the patient. The button is extremely easy to press, so that a disabled person can use it easily as long as they can grasp the handle. The button works as a push-to-make switch, meaning that the circuit through it is open until it is pressed. One side of the switch is connected to the 5V power supply in series with a 100kΩ resistor. This side is also connected to the microcontroller, giving it a logic high input. The other side is grounded, and when the button is pressed, it everything after the resistor, including the microcontroller input, becomes 0V. When the microcontroller senses this, it is allowed to enter the A/D subroutine.

It also checks to see if the button is still pressed when the motor control subroutines initiate, so that the motor will stop as soon as the button is released.

Figure 9: Push-to-Make Switch implemented in Handle

The second button is located at the top of the castor wheel’s range of motion on the back of the bed; pictured below in Figure 10. This button operates in a similar manner to the safety button on the handle, but it is interpreted by the microcontroller in the opposite way. Like the safety button, it gives the microcontroller a constant 5V input until it is pressed, when it is grounded. The program checks if the input is logic high in multiple places within the program. If it is, the program proceeds as normal, but if it is low, the program does not enter the ‘Up’ subroutine, preventing the motor from going up any further. Because the button is placed on the track at the top of the wheel’s range of motion, the wheel depresses it when it reaches the top. This automatically stops the bed, preventing damage to the motor or bed, and any injuries to the patient from over extending the scissor jack.

Figure 10: Top (left) and Bottom (right) safety stop button

The third button (Figure 10 above) is used in the exact same way as the previous one. The difference is that it is located on the bed back at the bottom of the wheel’s range of motion. At this position, the castor wheel hits it when the scissor jack is completely compressed. When it does, the microcontroller program does not allow the ‘Down’ subroutine to run, which prevents the motor from stalling by trying to lower the jack past the lowest point.

The Lifting System is built around an actuator commonly referred to as a scissor jack. This actuator allows for a large horizontal displacement, while

maintaining a low profile while lowered completely. Rather than a piston or lead screw extending downward as much as the actuator extends, the lead screw on the scissor jack is positioned horizontally, allowing the scissor jack to extend horizontally while collapsing.

This feature is particularly important in this design, because of the impracticality of having about a foot of clearance under the bed to provide the lift which is desired. In addition, the scissor jack includes a foot and head plate, which is ideal for affixing it to a flat surface. This allowed us to use a rolling system, so that the top of the jack is not fixed to the bed, but rather allows the bed back to roll along a wheel as it is raised and lowered. This removed many of the complications associated with have the jack rotate on fixed pins at both the bed back, and the base. These problems include, binding at either pin in the case one is askew, added minimal height due to both pin joints, and the potential for the bed sides to be in the way while the jack lowered and extended to the sides.

The motor which is used for the adjustable back angle controller is the MMP S28 150E-48v GP81-014 DC motor from Midwest Motions. This motor is a 48 volt, DC motor, which is capable of drawing a stead maximum current of 8.1 amps. The reason for choosing this motor, is that it provided a high torque, of 72 in-lbs, coupled with a fast maximum rotational speed, of 285 revolutions per minute (RPM). This was originally coupled with a 48v DC power supply, which would convert the incoming AC from the wall, to DC, and step the voltage down to 48 volts. However, this power supply could only output 6.7 amps, which does not allow use to use the motor to its full potential. Although this does not give us the full use of this motor, it does provide a margin of safety so that the motor is not compromised by excess current.

We have run into complications related to the low current draw of this power supply. To control the speed of the motor, we are using pulse width modulation (PWM). This mode of control acts much like many people running into the back of a car to push it. Each person hits the car with as much force as they can every time, however, if one person hits the car every 5 seconds, the average force imparted on the car over a minuet would be less than if the time between hits were to be 1 second. The PWM sends pulses of voltage to the motor. Each of the pulses is the maximum output voltage for the circuit, however, the time between them changes depending on the speed at which the motor needs to be driven. The closer together then pulses, and the longer each pulse, the greater the speed, until at maximum speed the motor is receiving a continuous stream of the maximum voltage of 48 volts. This constant pulse is where the problem lies. With each pulse, the motor acts as if it is being started from a stop, which is similar to a stall condition. In this condition, the motor will draw a much higher current for a split second. When there is little weight on the lifting system, the current draw is much lower, and is within the range of the power supply. Therefore, the lifting system works perfectly while it is lowering, or lifting only about 80 lbs of weight. At any higher load, the current required to

start moving it exceeds that which the power supply can provide. This overload results in a jumpy motion. This is caused by the motor not receiving enough current during the stall state, but then lurching upward once the current draw dies down, until the end of the pulse. In an attempt to remedy this, we tried using a 36 v power supply from within the lab, which can send up to 10 amps of current. This power supply contains a current regulator which creates a short circuit within its self should the current draw exceed this value. Because of the regulator, this power supply caused a similar problem, however it is able to work at higher loads due to the higher potential current it can supply.

To fix this problem completely, the project would require a source of 48 volts which could provide unlimited current. The only source of unlimited current is a battery, which provides a constant voltage with any current which may be drawn from it.

One of the largest complications which was encountered during the construction phase of our design, was how to attach the motor to the scissor jack, so that the motor; 1) input all of the torque it generated into driving the scissor jack, rather than spinning its self, and 2) that none of the motor’s weight was supported by the lead screw. The first criterion is somewhat self explanatory that the motor should rotate the lead screw and not it’s self. However, if this were not satisfied fully, the lead screw would either not receive the motor’s full torque, in a case in which the jack did not freely spin but slipped slightly on start up, or the lead screw would not be driven at all, in which the motor would rotate its self rather than the lead screw. To satisfy this criterion, a design was proposed in which the motor would be clamped tight by an apparatus which is it’s self attached to a fixed structure, thus preventing any rotation. The second criteria proved to be somewhat more difficult to solve, and that is that the lead screw should not bare any of the motor’s weight. Should there be any force bending for put on the lead screw by the jack, this could cause the screw to either bind or break. This required an apparatus which would ride with the scissor jack, since the lead screw rides vertically with the jack as it extends and retracts, as well as traveling horizontally as the two arms of the jack are pulled together. This meant that the jack would have to be fixed completely to the jack, however almost every part of the jack is moving with respect to every other, except the two pins which the lead screw travels through. The two pins, labeled Pin 1 and Pin 2 next page in Figure 11, remain in a single horizontal plane; however they do move towards each other while in operation. Pin 1 is located at the motor end of the lead screw, and remains fixed with respect to the hex nut on the end of the lead screw. Pin 2 is located on the opposite side of the lead screw from the motor, and is pulled in toward Pin 1 while the scissor jack rises.

Figure 11: Scissor Jack Pin Locations

It is apparent from the operation of the jack, that Pin 1 is a good

attachment point to prevent the rotation of the motor; however this only satisfies the first criterion. To prevent the lead screw from being loaded by the motor’s weight, a force must be supplied to counter act the motor. This is supplied by attaching a support bar to Pin 2. To do this, we used a long, this plate, which would be able to fit over the pins. We then punched on 1 inch diameter hole at a length of 6 inches from the motor end of the bar. We then milled a 1 inch wide slot from the other end of the bar, for 16.5 inches, in which Pin 2 would be allowed to slide. A second plate was created to the same specifications as the first, to be put on the other side of the jack. They were then each bent away from each other by 0.35 inches. This bend allowed the majority of the two plates to run flush with the sides of the jack, while also providing enough room between them for the rubber coupling which will be used to secure the motor. The punched holes on each of the plates were slide over Pin 1. Then Pin 2 was placed in the slots on each plate. The plate was welded directly to Pin 1 so that it would not be able to slip off. To ensure that Pin 2 would slide within the slot, without allowing the plates to slip off, a washer was welded on the ends of the pin. The second part of the motor support is the coupling. This is simply a rubber tube, with two stainless steel bands of a maximum diameter of about 3.5 inches. As show next page in Figure 12, two small holes were drilled 3 inches apart, on each of the two plates behind the bend. Matching holes were then drilled in opposite sides of the two stainless steel bands such that they line up with the ones on the plates. Small screws were then placed through the steel bands from the inside, and through the plates, and tightened in place by a nut. The reason for putting the screws in from the inside, is so that there will be very little of the screw in the way of the rubber, which is then slide inside the two steel bands. Because of the flexibility of the steel plates, the bands can be tighten down around the motor, securing it in place, and preventing it from sliding away from the lead screw, and preventing the motor from rotating.

Figure 12: Complete Motor Support Assembling, with Motor

The castor wheel allows the bed back to roll along the top of the scissor

jack, while the jack pushes straight up. By implementing a caster wheel, and affixing the base of the jack to a platform, the complications which were associated with fixing both ends of the scissor jack. Since there are less moving parts, this means that less can go wrong. Also, if the jack were fixed at both ends, if the two joints were miss aligned at all, one could bind. The castor wheel was attached to the top of the jack with the use of a PVC (polyvinylchloride) sheet and was placed off center towards the bed back, to ensure that the jack down not rub against the bed back while rising. After understanding all the loads that this device needed to withstand, a strong support frame for the lifting mechanism had to be built. The most practical framing option to use in this situation was to purchase a steel bed frame and modify it. This ensured that the bed would be level and support the full weight. One of the modifications for the frame was moving the cross bar to the middle where the hinge of the bed is located. Since the legs of the bed were moved to the middle, the back end was now unstable. However, this was remedied by constructing four legs on the back end that were affixed to a base plate that was needed to stabilize the scissor jack. In Figure 13, next page, this base plate design can be seen attached to the bed frame. The 4 legs consisted of slotted angle steel, leveled out to balance the back end of the frame. The base is simply laminated plywood and all the parts are assembled with steel nuts and bolts. This base plate is essential to the operation of the bed because the scissor jack needs something solid to push off of as the motor torques the screw and raises the load vertically. If it were not bolted down, there would be a loss of efficiency in the operation. For maintenance purposes, should the scissor jack need to be fixed, the base plate can be easily detached from the frame by unbolting the legs.

Figure 13: Scissor Jack Base Plate

The platform of the bed is constructed of ½” thick plywood upholstered in blue fleece and stuffed with egg crate foam and pillows for added comfort. The platform is divided into two halves, one for the bottom half and one for the top half. The bottom half was simply upholstered then lay down on the frame. The top half was braced with angled steel along the perimeter to ensure it could handle the required weight of 200lbs. Also, to prevent deflection of the back when it was raised, two-2x4’s was nailed on the back of the top half parallel to the hinge of the bed. To ensure that the scissor jack does not lift the bed above or below an unsafe level, two stop buttons have been place along the wheel path. When the wheel rolls onto the stop button, the circuit will shut off the power to the motor and stop the movement of the bed. To finish off the bed, it was upholstered and hinged through the slotted steel and attached to the bed frame with a simple nut and bolt fixture. Figure 14 below illustrates the bed in an upward position with the bed back underside exposed.

Figure 14: Back View of Raised Bed Back

The surrounding base of the frame is covered with a bed skirt to hide the operating components. The UConn Biomedical Engineering emblem is sewn and centered on the bed back above the pillow rest for the head. Pictured next page are Figures 15 & 16 of the finished looks of the bed.

Figure 15: Close up of UConn BME Emblem and Uphostering

Figure 16: Finished Bed Lowered & Raised

Testing the Device This device had to be tested throughout its construction to ensure proper

working order. Even still, there are some tests that failed and unfortunately cannot be resolved due to the time and money constraints of the project. The following client’s disabilities were tested on the prototype device.

Blindness:

This test was performed by blindfolding a subject and having them operate the bed without the aid of others. Figure 17 below demonstrates the subject’s success in identifying and grasping the handle to operate the device.

Figure 17: Blind subject

Use of one arm / paralysis on one side:

This test was performed by tying up one arm of a subject and having them operate the bed without the aid of others. This is possible because the handle is interchangeable to either side of the bed. Figure 18 below demonstrates the subject’s success in identifying and grasping the handle to operate the device.

Figure 18: Paralysis subject

Weakness / Arthritis: This test was performed by having the subject lift the handle with her

pinky finger to show little force being inputted. She was easily able to operate the bed without the aid of others. Figure 19 demonstrates the subject’s success in identifying and grasping the handle to operate the device.

Figure 19: Arthritis subject

With the aid of our Adjustable Bed Angle Controller, these benefits can be

enjoyed by individuals such the clients Matt and Akiko, who have vision problems. With our design, it will be much easier for the blind or visually impaired. This is made possible because the lever will always be in the same position, while still remaining out of the way. In addition, instead of fumbling with button, our design allows the patient to operate the bed by pushing the lever down to lower the bed, and up to raise the bed. This intuitive design will allow all users to operate the bed without the learning curve required to learn where each button is located, and the functions they provide.

Many people suffer from conditions which affect their motor skills. Conditions such as severe arthritis as well as Parkinson’s disease greatly diminish an individual’s manual dexterity as well as their ability to grasp small object. The operation of a handle which requires minimal grasping power, and no dexterity to move, as opposed to a wired remote control with numerous small buttons required to operate the bed, would be of great benefit to individuals such as our client Lakisha who suffers from Parkinson’s disease.

This device has proven to be accessible to the client’s disabilities. It was difficult to show the device under the circumstances where a person has Parkinson’s disease, therefore it was tested by having a subject pretend to have a tremor and operate the handle. It worked fine even though the user had gross motor movements. Knowing this, it can be assumed that all ages—young and old—can operate this lever without confusion. It is also useful and convenient for the caretaker to operate the bed because the position is easy to reach without bothering the patient.

Budget Analysis

Date Company Parts Description Subtotal S & H Tax Total Price

1/5/2007 Lee Spring 10 Compression Springs $71.00 $0.00 $4.26 $75.26

1/5/2007 Digi-Key Corporation 6 Mosfets $13.60 $9.80 -- $23.40

1/5/2007 Camping World Scissor Jack Pair $94.43 $16.00 -- $110.43

2/20/2007 Midwest Motion

Motor Unit & Accessories $990.00 $43.00 -- $1,033.00

2/23/2007 Affordable Beds Bed Frame $69.00 -- -- $69.00

3/21/2007 Mansfield Supply

Steel Hardware Parts $72.59 -- -- $72.59

3/30/2007 Mansfield Supply Hardware Parts $31.58 -- -- $31.58

4/4/2007 Digi-Key Corporation Mosfets $41.59 -- -- $41.59

4/6/2007 Machine Shop Labor $10.00 -- -- $10.00

4/16/2007 Digi-Key Corporation Mosfets $59.91 -- -- $59.91

4/23/2007 Express PCB PCB Board $92.66 -- -- $92.66

4/25/2007 Digi-Key Corporation Mosfets $27.40 -- -- $27.40

4/25/2007 Network in One

Electrical Component box $19.99 -- -- $19.99

4/27/2007 Machine Shop Labor & Parts $33.15 -- -- $33.15

Starting Budget: $2,000.00 Total Spent $1,699.96 Remaining Budget: $300.04

Price of Prototype: 1 Scissor Jack $55 Electrical Components $25 Bed Framing $69 Motor Unit $625 Miscellaneous hardware + $30 ESTIMATED TOTAL COST: $804

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 $804 (refer to budget above). A standard bed (e.g., manual crank lift by A1 Adjustable Beds) is listed as $712. 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. Installing our automatic lift mechanism on new standard hospital beds vs. purchasing a deluxe hospital bed is estimated to be $1624 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 $24,360. 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 organizations.

Conclusion

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.

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 work mechanically identical to the hydraulic cylinder except in a quieter and cleaner fashion. In the optimal design, a scissor jack was implemented in much the same way as the linear actuator was in the second design. This allowed for the direct push-pull action on the bed, but less room is required for the scissor jack to operate under the bed since it collapses as it retracts.

The manner by which the lifting jack will be operated also evolved since the first design, but mostly due to the switch from hydraulic to electric. Initially, the control would call for multiple valves to be operated in order to vary the flow of the hydraulic system. However, once the system was changed to electric, a simple potentiometer and circuit could be used to vary the speed and direction of the electric motor. Additionally, this electric circuit allowed for the implementation of a safety switch which would break the circuit unless the bed was meant to be operated. Also, the handle its self was changed from a straight design to an S-shape which would be easier to operate as both a patient and a caretaker. In all, the optimal design offers the safest, cleanest and most reliable system to provide a variable speed and intuitive operation of an adjustable bed. Because of the easy operation, and minimal required force to operate, patients and caregivers of all ability levels and strength will find the ABAC adjustable bed the best choice for all applications.