Research On Synchronized Control Of Multi-fingered Anthropopathic Dexterous Robot Hand

Dexterous robot hand which has the function of multiform perception is main aspects of robot research. Based on national high technique program (863)"Research on new genetation five-fingerd anthropopathic dexterous robot hand and its cooperative control", it is the improvement of HIT/DLR I robot hand, and the aim is to accomplish the five-finger HIT/DLR II dexterous robot hand that resembles the human hand regarding size and movability (HIT/DLR I robot hand about 1.5 the size of human hand with only four fingers). The dissertation emphasizes on position control and compliance control of a finger and coordinated grasping manipulative strategy of multiple fingers.To replace human hand, the robot has to fulfill the following requisites: first the robot hand must resemble the human hand regarding size and movability. This determines the hardware, i.e. the mechanical structure, actuator and sensor system. Second the robot hand must have skills and a sleight of hand comparable to the human hand. For example, the hand must be both have enough position accuracy in fine grasping manipulation, and enough force accuracy when grasp fragile object. Moreover, it requires the ability of anti-interference in uncertain environment. This determines the software, i.e. the desired performance of the control system.In order to develop five-finger dexterous robot hand with high integration, a DSP&FPGA-based multilevel control system is developed for multi-sensory and multi-DOF dexterous robot hand, in which the drive, control and sensor systems are integrated in the finger. So the five-finger HIT/DLR II dexterous robot hand that resembles the human hand regarding size and movability is realized. To accomplish the phase current detection of the motor, a single direct current link current sensor is used to measure and reconstruct the three phase currents, and stable current signal is measured by optimizing sample instant. To solve the problem of efficient and reliable communication between finger DSP and FPGA, a kind of multi-interrupt differential communication system based on serial communications interface (SCI) and RS485 bus using first in first out (FIFO) registers is designed. To enhance the levels of intelligence manipulation, HIT/DLR II robot hand is equipped with multiple sensors, and all the analog signals are converted in-situ into digital signals to minish noise interference.To solve the problem that the working distance of traditional giant magnetoresistance (GMR) sensor must be more than 1.5 mm, or else it maycause severe disorientation of the angular measurement or permanently damage the sensor element. Based on 3D static magnetic analysis technique, a method for the modeling of ferromagnetic component of the sensor system is presented, and the ultra-miniature giant magnetoresistance sensor system with only 0.5 mm working distance is newly developed for highly integrated HIT/DLR II five-finger dexterous robot hand. The experimental results show an angular accuracy of less than±1°with only the residual offset compensation of ultra-miniature GMR sensor system is obtained. It also has the qualities of simple structure, low cost, ultra-miniature size, and high accuracy, all of which makes up for the shortcomings of traditional measurement sensors.According to the finger structure, a cross-couple synchronized error expression in drive space and master-slave synchronized error expression in joint space are built for HIT/DLR II robot finger. Then a synchronized position control approach is present, including feedbacks of synchronous errors and position errors, and a smooth robust nonlinear feedback compensator. According to Lyapunov stability analysis, it is proved that the proposed method can guarantee both synchronization and position errors converge and asymptotical stability of the system. Compared with conventional non-synchronized PD friction compensation and trajectory tracking control, experimental results demonstrate the proposed control strategy improve the trajectory tracking precision of finger tip in free space.By translate the information of joint torque sensor into position vector, and a cross-couple synchronized error expression in drive space and master-slave synchronized error expression in joint space are built for HIT/DLR II robot finger. Then a synchronized impedance control approach is present, including feedbacks of synchronous errors and position errors, and a smooth robust nonlinear feedback compensator. According to Lyapunov stability analysis, it is proved that the proposed method can guarantee both synchronization and position errors converge and asymptotical stability of the system. Compared with conventional non-synchronized PID impedance control, experimental results demonstrate the validity of the proposed control strategy. And in interaction of robot finger with a person, it generates compliance and smooth movement according to the joint torque, which demonstrates that the ideal joint impedance performance is successfully achieved. All this will provide a good base of multi-finger grasping manipulation and human-robot coordinating manipulation.When the dexterous hand works in uncertain environment, the finger may encounter obstacle or disturbance, which may cause release or damage the grasped object. To solve this problem, the synchronized error expression between multiple fingers is built in Cartesian space, and then a synchronized impedance control approach in Cartesian space is present. The main idea is cooperates the undisturbed fingers with the disturbed finger, which keep relative balance of grasping manipulation. According to Lyapunov stability analysis, it is proved that the proposed method can guarantee asymptotical stability of the system. The experimental results demonstrate the proposed control strategy can avoid damaging or releasing the grasping object, and enhance the anti-interference ability of the dexterous robot hand.