Abstract
Abstract. This work presents a detailed design of a three-jointed tendon-driven robot finger with a cam/pulleys transmission and joint Variable Stiffness Actuator (VSA). The finger motion configuration is obtained by deriving the cam/pulleys transmission profile as a mathematical solution that is then implemented to achieve contact force isotropy on the phalanges. A VSA is proposed, in which three VSAs are designed to act as a muscle in joint space to provide firm grasping. As a mechatronic approach, a suitable type and number of force sensors and actuators are designed to sense the touch, actuate the finger, and tune the VSAs. The torque of the VSAs is controlled utilizing a designed Multi Input Multi Output (MIMO) fuzzy controller. The fuzzy controller input is the force sensors' signals that are used to set the appropriate VSA torque. The fuzzy controller parameters are then tuned using a genetic algorithm as an optimization technique. The objective function of the genetic algorithm is to avoid unbalance torque in the individual joints and to reduce the difference between the values of the supplied VSAs torques. Finally, the operation of the aforementioned finger system is organized through a simple control algorithm. The function of this algorithm is to enable the detection of the unknown object and simultaneously automatically activate the optimized fuzzy controller thus eliminating the necessity of any external control unit.
Highlights
The evolution and development of the robot hand has played a strategic role in the robot revolution as it is essential in numerous different applications such as service robots
In the moment of sensing the ball, the Cam Pulley Robot Finger (CPRF) stopped its motion and initialized the adjusting Variable Stiffness Actuator (VSA) torques according to the fuzzy controller rules
A fuzzy logic controller has been suggested to control the VSAs torques according to the contact force values
Summary
The evolution and development of the robot hand has played a strategic role in the robot revolution as it is essential in numerous different applications such as service robots. The large difference between the contact forces on the phalanges results in damage to the grasped objects. The geometry design of finger mechanism parts using kineto-static analysis is presented as a solution to reduce the varying contact forces on phalanges. Force isotropy is an essential property that the finger requires in order to avoid stress concentration which causes damage to the grasped objects during contact. Achieving force isotropy in a full grasping operation wasn’t taken into consideration and it is mentioned as a future work. Dandash et al (2011) introduced a technique to achieve force isotropy property for underactuated fingers of three phalanges. Dandash used cam-tendon mechanism again as in Krut (2005) taking a full grasping operation into consideration.
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