Abstract
Impedance control is an important technology used in the grasping control of a robot hand. Numerous studies related to grasping algorithms have been reported in recent years, with the contact force between robot fingers and the object to be grasped being primarily discussed in most cases. Generally, a coupling effect occurs between the internal loop of the grasping operation and the external loop of the interaction with the environment when a multi-fingered robot hand is used to complete a contact task. Therefore, a robot hand cannot hold an object using a large external force to complete a wide range of tasks by applying the conventional method. In this paper, the coupling of the internal/external forces occurring in grasping operations using multiple fingers is analysed. Then, improved impedance control based on the previous method is proposed as an effective tool to solve the problem of grasping failure caused by single-finger contact. Furthermore, a method for applying the improved grasping algorithm to the admittance control of a robot hand-arm system is also proposed. The proposed method divides the impedance effect into the grasping control of the hand and the cooperative control of the arm, so that expanding the task space and increasing the flexibility of impedance adjustment can be achieved. Experiments were conducted to demonstrate the effectiveness of the proposed method.
Highlights
With the development of robotics technology, the applica‐ tion of manipulators primarily used for industrial produc‐ tion has grown rapidly in the field of living support for humans
Approaches to investigate the stability and dynamic control of an object grasped with two fingers [8,9], and stable grasping based on sensory feedback using a multifingered hand-arm system [10] have been discussed
A grasping control method using impedance control by separately considering the force generated by grasping a rigid body has been exam‐ ined from two aspects: the internal force for the grasping action, and the external force for interaction with the environment [11,12,13]
Summary
With the development of robotics technology, the applica‐ tion of manipulators primarily used for industrial produc‐ tion has grown rapidly in the field of living support for humans. Methods of state transition for grasping using one finger and isolating the external force from grasping have been proposed [14], problems such as unstable grasping caused by the coupling of the internal/external impedance and a small working space still remained. Humans usually move their arms and hands in an efficient manner in order to complete soft manipulation. The improved impedance control algorithm proposed in this paper provides an effective tool to overcome the problem of grasping failure caused by single-finger contact that, could occur while using the previous method described in [12]. Grasping experiments using the robot hand-arm system under different conditions were conduct‐ ed to demonstrate the effectiveness of the proposed algorithms
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