Enhancement of Robot Accuracy using Endpoint Feedback and a Macro-Micro Manipulator System

The problem of robot positioning accuracy is caused primarily by unmeasured deflections of the structure and poor actuator servo resolution. This is particulary troublesome when large manipulators and payloads are considered. This paper presents an approach to this problem based on the use of a direct enpoint position and orientation measurement. While this insures accurate measurement of endpoint errors, it is still difficult for most manipulators to accurately make fine movements. To address this problem the concept of a micromanipulator mounted on the end of the large manipulator is forwarded. A full scale prototype micromanipulator was fabricated and tested to verify the feasibility of such a device. To make the control of such a device tractable it is proposed to design the control assuming no dynamic coupling between the macro and micro manipulator. This approach was invetigated by simulation and experimentation and it is found to work well provided the bandwidth of the micromanipulator is kept below the fundamental frequency of vibration of the basic robot structure.