# Development of Power-Assist Device for a Manual Wheelchair Using Cycloidal Reducer
###### Abstract  
This paper presents the design process and driving performance test results of a power-assist module to which a cycloidal reducer is applied in order to convert a manual wheelchair into an electric wheelchair. The types of electrification modules currently used to electtify manual wheelchairs include front-mounted, rear-mounted, and powered wheels. These assist devices are either difficult to carry and transport independently or require excellent hand dexterity to operate. To overcome this problem, a cycloidal reducer with no pin roller, and a novel cycloidal curve were designed to develop a small and easy-to-handle power-assist module that was tested by installing this reducer to a manual wheelchair. As a result of the test, the maximum speed of the wheelchair was 6 km/h, the maximum slope that this wheelchair can climb is 20%, and 0.358 Ah was consumed while the wheelchair moved 360 m in the current consumption test. This showed that it is possible to develop a small-sized power-assist module. In addition, the user can easily electtify the manual wheelchair by adding a small weight without replacing the manual wheel. The power-assist module consists of a DC servo motor, cycloidal reducer, battery, and joystick. power-assist device; cycloidal gear; manual wheelchair; epitrochoid; tooth thickness ratio  
on the rear axle of manual wheelchairs. SmartDrive [6] is a rear-mounted PAD controlled by a dial. By turning the speed control dial on the wheelchair frame, the user can start the motion, stop the device, and set the speed. The Smoov wheel [7] has a one-wheeled design similar to SmartDrive and a frame-mounted knob to control the wheelchair speed. These products are difficult to brake and stop, and the time required to become accustomed to them is long. Powered wheels can also replace the traditional wheels of manual wheelchairs, and can be controlled interactively using a joystick or direct push rims. Powered wheels, such as E-fix [8], replace conventional wheels and allow users to control a wheelchair using a joystick with ease. [PERSON] [9] designed a small-sized planetary gear and developed a power wheel that can be applied to a manual wheelchair. Pushrim-activated power-assist wheels (PAPAWs) are another type of powered wheels consisting of a built-in force sensor that detects the user input force acting on the pushrims. When the user activates the pushrim, the speed of the wheelchair is proportional to the input force. Examples of PAPAWs include e-motion [10] and JWII [11] wheels. [PERSON] [12] proposed an input force measurement system for PAPAW and the driving torque of the measured force in which the user pushes the handrim using only an angle sensor. A reducer is a type of mechanical energy conversion device that can amplify torque by reducing the rotational speed of the motor. In particular, the reducers in which the input and output shaft are coaxial include harmonic drives, planetary gears, and cycloidal reducers. Cycloidal reducers have been used in power transmissions, boats, cranes, pumps, and prosthetic hands [13]. Cycloidal reducers can feature low backlash, high efficiency, low noise, a high-reduction, and high torque capacity unlike harmonic drives [13; 14; 15]. [PERSON] [16] proposed an exact approach to the cycloid disk by means of the principle of the instant velocity center. [PERSON] [17] presents a method for kinematic error analysis and tolerance design of cycloidal gear reducers. The conventional cycloidal reducer consists of pin rollers, and multiple contacts are established between the pin rollers and cycloidal disks, making it difficult to manufacture. However, because the proposed reducer has a single-contact structure, it is insensitive to tolerances during manufacturing, and the structure of the reducer is simple because there are no pin rollers required.