In an earlier study, a three-fingered robot hand was developed for assembly work. Proportional Integral Derivative (PID) control was used to control the position of a DC micromotor measured by an encoder. However, PID control alone could not cater the nonlinearities due to friction of gears and varying loads applied to the finger. Therefore, in order to develop an intelligent control algorithm in future, the effects of varying PID gains need to be investigated to distinguish the optimal value that could produce the best transient response performance. This paper discusses the effect of varying PID gains on position transient response of the joint motor of robot hand through real-time experiments. Several ranges of KP, KI and KD were identified based on the required transient response parameters such as percentage overshoot (%OS), settling time (TS) of within 2%, steady state error (SSE) and rise time (TR). The gains are tuned across the range by a fixed interval with the tuning order starting from KP, KI and KD. It can be observed that the suitable ranges of PID are 0.3 to 0.5 for KP, 1.15 to 1.45 for KI and 0.10 to 0.14 for KD. Meanwhile, the optimum value of 0.4, 1.45 and 0.10 for KP, KI and KD respectively is found to produce 0 of % OS, 5.09 sec of TS and 2.48 sec of TR. Hence, the gains can be applied to the development of an improved position control using intelligent method for the robot hand in future works.
A prototype of three-fingered robot hand was very rigid in its motion, and prone to damages when dealing with hard surfaces or when subjected to external environmental forces. The robot hand could damage fragile objects during grasping tasks if a position control alone is used. Therefore, this study proposes application of force control to the robot hand to improve its current grasping capabilities. Impedance control that considers the dynamic of the robot to produce the softness like human hand was implemented in this study. The dynamical behaviour of the robot hand strongly depends on the impedance parameters known as virtual mass, damping and stiffness. Therefore, the optimal values of impedance parameters need to be investigated to develop a position-based impedance control for the robot finger. Hence, the objective of this study is to determine the optimal value of impedance parameters to impose desired dynamics to the robot system. A constant force weighing 100 g was used by implementing varying impedance parameters to the tip-end’s position. Three experiments were conducted: first to decide the order of parameters to be adjusted, then to determine the optimal value of impedance parameters, and finally to test the optimal values with random force applied to the robot finger. The determined optimal values are: stiffness=1000, damping=10 and mass=1. Thus, the combined parameters have proven that the modified position is capable of responding according to the exerted contact force.