Amirul Syafiq Sadun

Adaptive friction compensation for hand grasping and compliant control

Attaining a good positioning control is an important step to be achieved for a robotic hand to safely grasp an object. The safety of the grasped object can be enhanced by providing a compliant control strategy. This paper presents a model reference adaptive compliance controller where a mass spring damper system can be introduced. The performance of model-based adaptive controller with the effect of friction and stiction is investigated. A few mathematical models of friction are considered i.e. static friction (stiction), coulomb friction (dry friction), viscous friction, drag friction and square root friction. It is observed that a good positioning and compliant control are feasible in the presence of friction and stiction in simulation. It is evident that the level of compliant control can be achieved during the object grasped.

Force control for a 3-Finger Adaptive Robot Gripper by using PID controller

In order to ensure that a robotic hand can successfully grasp objects without damaging them, an active compliance control can be a very useful technique to provide a safe grasping. In particular, this paper establishes a direct force control for a 3-Finger Adaptive Robot Gripper by using a PID control. A modified FSR force sensor where a plastic cover is used to ensure the contacted force during grasping can be measured and recorded. A series of grasping tests were performed to observe the performance of PID control. The experimental results show that the PID control can be a simple and reliable control scheme to provide an active compliance control through direct force control. In addition, different compliance level is feasible particularly for a stiff spongy ball.

Force Sensing Resistor (FSR): a brief overview and the low-cost sensor for active compliance control

Force Sensing Resistors (FSR) sensors are devices that allow measuring static and dynamic forces applied to a contact surface. Their range of responses is basically depending on the variation of its electric resistance. In general, Flexiforce and Interlink are two common types of FSR sensors that are available, cheap and easily found in the market. Studies have shown that the FSR sensors are usually applied for robotic grippers and for biomechanical fields. This paper provides a brief overview of the application of the FSR sensors. Subsequently, two different set of experiments are carried out to test the effectiveness of the Flexiforce and Interlink sensors. First, the hardness detector system (Case Study A) and second, the force-position control system (Case Study B). The hardware used for the experiment was developed from low-cost materials. The results revealed that both FSR sensors are sufficient and reliable to provide a good sensing modality particularly for measuring force. Apart from the low-cost sensors, essentially, the FSR sensors are very useful devices that able to provide a good active compliance control, particularly for the grasping robotic hand.

Model Identification of a 3 Finger Adaptive Robot Gripper by Using MATLAB SIT

This paper presents the method of finding the estimated plant transfer function of the 3 Finger Adaptive Robot Gripper by using the MATLAB System Identification Toolbox (SIT). The robot gripper consists of 3 under actuated fingers, where the active joint is driven by a DC motor and the passive joint is driven by the underactuated mechanism (elastic tendons). To simplify the study, the model identification only considers the single angular joint of each finger. The approach of fast variable step input (i.e. stairs input) and slow variable step input (i.e. slope input) was introduced while the output of the robot gripper is referring to the motor encoder position of each finger. The best estimated modelling of the gripper is obtained by selecting the transfer function that has the most similar performance (in term of position control) compared to the actual system. Moreover, the result shows that the transfer function obtained by using fast variable step input is sufficient to represent the 3 Finger Adaptive Robot Gripper. Additionally, the PID position control was employed and the result shows that the gripping performance is satisfactorily achieved in simulation and experiment.

Grasping analysis for a 3-Finger Adaptive Robot Gripper

A 3-Finger Adaptive Robot Gripper is an advanced robotic research that provides a robotic hand-like capabilities due to its flexibility and versatility. However, the grasping performance has to be analyzed and monitored based on the motor encoder, motor current, and force feedback so that the finger position and grasping force can be effectively controlled. This paper provides an open-loop grasping analysis for a 3-Finger Adaptive Robot Gripper. A series of grasping tests has been conducted to demonstrate the robot capabilities and functionalities. Different stiffness levels of the grasped objects have been chosen to demonstrate the grasping ability. In the experiment, a Modbus RTU protocol and Matlab/Simulink are used as communication and control platform. A specially modified interlink FSR sensor is proposed where a special plastic cover has been developed to enhance the sensor sensitivity. The Arduino IO Package is employed to interface the sensor and Matlab/Simulink. The results show that the significant relationships between finger position, motor current, and force sensor are found and the results can be used for a proper grasping performance.