Leg Mechanism of a Quadruped Wheeled Robot with a 4-DoF Spherical Parallel Link Mechanism

To develop a quadruped wheeled robot with high mobility, we have designed and developed the leg mechanism of a quadruped wheeled robot, named “MELEW-2LR” (MEiji LEg-Wheeled Robot–No.2 Leg Refined). MELEW-2LR has a total of 4 degrees of freedom (DoFs), which include translational movements of the leg tip in 3 directions (forward/backward, left/right, and up/down) and rotation of the leg tip in the Yaw direction to control the steering angle of the wheel when turning. The leg mechanism uses a 4-DoF parallel link mechanism that combines spherical links and parallel links to achieve high output. In addition, all motors are located at the hip joint to reduce inertia in the leg. Furthermore, a system was constructed to calculate the motor angle from the leg tip position by solving inverse kinematics on PC and to provide the angle command value to the brushless DC motor via a microcontroller. Evaluation experiments were conducted on the leg, and it was shown that accurate position control in the three translational directions and in the Yaw direction was possible, as well as bending and stretching movements with a payload equivalent to the leg mass.