Design of an Arduino-Based CPM Elbow Actuator with Optocoupler Angle Sensor: Initial Study with Future Consideration for Rubber and Plastic Components

The hand is a part of the human body that serves various activities. However, if the hand is injured due to an accident, it can result in a disruption of motor function for an individual. Therefore, a Continuous Passive Motion Elbow device is needed to assist in the rehabilitation of an injured hand's elbow. While rubber and plastic materials are commonly utilized in commercial CPM devices—plastic for lightweight and durable casings, and rubber (elastomers) for flexible, skin-contacting components—this study does not yet integrate these materials in its prototype. However, the design opens possibilities for future incorporation of ergonomic plastic and elastomer components to improve user comfort, device safety, and manufacturability. The development of the Continuous Passive Motion Elbow design is necessary to improve the existing design and meet the functional needs of postoperative hand elbow therapy patients. This device is designed using an Arduino microcontroller, a DC motor as the actuator, and an optocoupler sensor as an angle reader. The Optocoupler sensor operates by detecting the gaps in the gear disc located in the device's framework. The photodiode emits infrared light, which is directed towards the phototransistor. This light is then converted into a digital signal by the microcontroller, registering as '1' when the infrared light is obstructed (indicating the absence of light reaching the phototransistor) and '0' when there is no obstruction (indicating the presence of infrared light reaching the phototransistor). These digital signals are subsequently converted into angle values through an Arduino program sketch, and the results are displayed on the LCD. In this research, the device will be tested by comparing the test results with goniometer measurements. The results of these tests will be displayed on an LCD screen. The device works effectively, exhibiting an error accuracy of 0.8%.