Onboard Sensor and Actuator Calibration of a Tripod Electric Vehicle Using Circular, Linear, and Cornering Motion Tests

This article aims at the calibration of an onboard sensor and actuator parameters as well as the identification of the open-loop transfer function of the steering and traction control systems of tripod electric vehicles (EVs). Tripod EVs are commonly used as forklifts and automatic guided vehicles in a factory or wheelchairs in a hospital. A test procedure called the circular, linear, and cornering motions (CLCM) test is introduced in this article for making the corrections which are caused by many factors including the potentiometer of the steering angle error, hall sensor error of the traction speed, the backlash of the steering system, and the tire slip angle that can lead the tripod EV to deviate from the path. The CLCM test is subdivided into circular, linear, and cornering motion subtasks for each individual identification and calibration purposes. The effect of the CLCM test has been verified by both simulation and experiment via an 8-shape navigation path consisting of all linear, circular, and cornering motions. After the CLCM test, the motor control unit (MCU) was coded with the calibrated transfer function of the tripod EV. As a result, the shift of the rotation center with a radius of 1200 mm during circular motion has been reduced to 50 mm. The deviation of the linear motion test has been confined to 20 mm/10 m at a constant speed. The tripod EV is able to perform a 90° cornering motion with a maximum error θ within 10°. The experimental results show that the CLCM test is applicable to identify the error sources of the tripod EV and estimate the wheel slip angle as well as the backlash.