- PrototypePicture: Elbow and Wrist Prototype
Gabriela Moya, Stephanie Vásquez,
ABSTRACT
At the beginning of the wrist and elbow rehabilitation therapy, the clients are able to do only slow and short movements of their joints due to the degree of pain and nature of the lesion. The main goal of the first and second phases of rehabilitation is to achieve the full joints mobility. In this project, we have considered the anthropometrics of the human arm, taking into account the movements and angles of the elbow and wrist with the goal of developing a prototype for the first and second phases of rehabilitation. The implementation consists of four different adaptations, one for each movement, a sensors’ interface electronic board, a control board, and a graphical user’s interface where the physiotherapist is able to set up a personalized rehabilitation cycle responding to the client needs. In addition, it incorporates a servo to generate the movements during the rehabilitation process.
INTRODUCTION/BACKGROUND
The great amount of clients with wrist and/or elbow lesions made some physiotherapists suggest us to implement an equipment that allows clients to achieve the maximum potential for function and normal activities of their injured joints. Considering therapeutic robotics accelerates the rehabilitation process due to its accuracy, we have considered the design of a prototype controlled by the computer for the rehabilitation of the wrist and elbow of an adult. The client will exercise in a passive way to achieve the full range of motion of the joints of the elbow and wrist during the first and second phases of rehabilitation.
In order to maintain the safety of the client, the physiotherapist is able to set up the information regarding the area to treat (elbow or wrist), movement to do (flexion-extension, pronation-supination of the elbow, flexion-extension, abduction-adduction of the wrist), the angle of each movement (0°-130°, -90°-+90°, -70°-+70°,-30°-+15°, respectively) and the speed (low-speed, normal-speed, high-speed) according to the client’s progress. The process controls the angle, sense of rotation and position through the communication between Matlab and Arduino.
PROBLEM STATEMENT
Almost all of the elbow and wrist lesions provoke a reduction of the mobility of these joints. Thus, our goal was to design and implement a prototype controlled by the computer able to execute the flexion-extension, pronation-supination of the elbow, flexion-extension, and abduction-adduction of the wrist following its corresponding angular range. A requirement we also had to consider was that this prototype could be used by any adult. In this case, the adaptability property was one of the main aspects of the design for this prototype. The client should be able to regulate the distance of the supports in order to be comfortable during his therapy session.
DESIGN AND DEVELOPMENT
The movements, angles and dimensions of the upper extremity involved in the rehabilitation prototype are shown in the Figure 1.
Figure 1. Anthropomorphic considerations for the design.
The architecture of the rehabilitation system is based on the diagram shown in the Figure 2. The user’s interface allows data input which is transmitted to the Arduino controller. The controller sends the corresponding signal to the actuator and the mechanisms. During the whole process the sensors are controlling the variables in order to execute the rehabilitation properly.
Figure 2. System’s General Diagram.
The prototype is meant to be used by an adult who needs to rehabilitate either the left or right upper extremity. The design contemplates as the minimum dimensions of women and maximum dimensions of men in order to make this prototype adaptable to any kind of client. The dimensions were shown previously in Figure 1 in the corresponding column.
Mechanical Design
To simplify the mechanical design, it was divided into four areas, as shown in Figure 3.
Figure 3. Mechanical Design.
The torque of every movement was calculated in order to select the actuator that will execute the movements. The results for flexion-extension of the elbow is 10.15Nm, pronation-supination of the elbow is 4.19Nm, flexion-extension of the wrist is 1.25Nm and for abduction-adduction is 1.37Nm. All of these results consider the masses of the hand (0.73Kg) and hand and forearm (3.13Kg). For this reason, the Torxis i00600 servo which has a torque of 11.3Nm is the more appropriate for this project.
The Table 1 shows the mechanical design of the prototype pieces and a brief description of each one.
Table 1. Mechanical design of the prototype pieces.
Electronic Design
The electronic design is composed of two main areas. A sensors’ interface electronic board and a control board are in charge of all the actions executed by the actuator.
Figure 4. Electronic Diagram.
The circuits for the signal conditioning of the sensors of the angular position, sense of rotation and limit switches status are in the sensor’s interface board. Meanwhile, the board control is an Arduino board which was selected by the number of I/O pins needed for this project.
Because of the 14 I/O pins and the PWM outputs necessary to control the Torxis servo, the Arduino UNO R3 board was selected to be used as the controller in this project.
Programming
Figure 5. Programming flow diagram.
The user chooses which process to execute. The maintenance process calibrates the servo and verifies the sensors’ status. For further explanation, see Figure 6 that shows the maintenance interface.
Figure 6. Maintenance interface.
To complete the rehabilitation process, the user should follow these steps:
- Zone to rehabilitate (Elbow or Wrist).
- Arm to rehabilitate (Left or Right).
- Movement to execute (Flex-Ext, Pro-Sup, Flex- Ext, Abd-Add).
- Duty cycle input (Minimum and maximum angles, number of sets and repetitions, speed).
- Serial port.
- Duty cycle verification.
- Process execution.
The Figure 7 shows the user’s interface executing a rehabilitation process.
Figure 7. Rehabilitation process execution.
EVALUATION AND RESULTS
Following a test protocol with different tests, the functioning of the prototype has obtained the results detailed in this section.
Table 2. Angular shift in servo tests.
Figure 8. Tendency error vs angular shift.
The greatest angular shift tested in 30 servo mobility essays is 3° which represents an error of 3.3%.
Testing was done on a person who had prior elbow and wrist fractures. This test was repeated for several days in order to obtain the development of the client using the prototype. As shown in the Table 3 and Figure 9, the client increased the mobility of elbow and wrist.
Table 3. Client tests during rehabilitation with the prototype.
Figure 9.Client’s angular mobility per test.
COSTS
The total cost for this device is $900 because of the Torxis servo, mechanic and electronic parts to make this prototype accurate and safe.
The low cost allows any rehabilitation center to invest in this prototype and to recover the investment in a short period of time.
DISCUSSION AND CONCLUSIONS
The prototype achieved the proposed movements. In other words, it is able to execute flexion-extension, pronation-supination of the elbow and flexion-extension, adduction- abduction of the wrist regarding the angular anthropomorphic limits. These angular limits are considered for an adult client to achieve full joint mobility in the first and second phases of rehabilitation.
Electronic circuits were designed to avoid mistaken signals. For this reason, the sensors’ interface board consists of conditioning circuits to determine the sense of rotation and to verify the limit switches’ status. Subsequently, the signals obtained in this board are properly transmitted to the control board.
The application of Guide, graphical Matlab module, permitted the creation of a friendly and easy to understand graphical user’s interface. In addition, through the programming made in this software it is possible to control the signals sent and received from the control board guaranteeing the correct input data, sense of rotation, angle, limit switches status and the current rehabilitation process visualization.
To verify the adaptability of the prototype, several tests were made on healthy males and females of various heights. According to the results of these tests, any adult person is able to use and feel comfortable because of the adjustability of the displacement system and the supports.
From the testing done on a client diagnosed with elbow and wrist fracture test, it may be concluded that the client improved in the mobility of both joints using the rehabilitation prototype, within several days. Therefore, this project fulfilled the goal of progressively improving the mobility of the complete angular range of the corresponding movement. It is important to mention that due to the degree of pain and nature of lesion that the client presented, she could only perform flexion-extension of the wrist and pronation-supination of the elbow.
ACKNOWLEDGEMENTS
We would like to express our gratitude to our families, our teachers, the Medical Center of our University and the client who helped us during the development of this prototype. It was exciting to receive suggestions from specialized physiotherapists to improve our prototype making it more comfortable. We would like to mention Vanessa Argüello, the client who allowed us to do testing on her, for her patience and kindness when we were evaluating the prototype. We can’t forget all the volunteers we had to do testing, we appreciate your help. Our families should also receive special thanks for helping us any moment we needed with transportation, money and support. Last but not least, our teachers and also our tutors who were always ready to help us.
REFERENCES
William, D. (2001). A robot for Wrist Rehabilitation. Springfield.
Wrui, P. (10 de Mayo de 2013). Guía de diseño en movimientos repetitivos. Obtained from Red Cavier:
http://ergonomiavenezuela.org/guia-de-diseno-en-movimientos-repetitivos/
Tilley, A. (1993). The Measure of Man and Woman: Human Factors in Design, The Whitney Library of Design. New York.
Norton, R. (1999). Diseño de Maquinas. México: Prentice Hall.
Arduino UNO R3 (2013). Obtained from: http://arduino.cc/
Contact:
Stephanie Vásquez
vastephanie@hotmail.com
UNIVERSIDAD DE LAS FUERZAS ARMADAS-ESPE