Contact force estimation for serial manipulator based on weighted moving average with variable span and standard Kalman filter with automatic tuning

Feng Cao,Paul D Docherty,Xiaoqi Chen

doi:10.1007/s00170-021-08036-9

Abstract

Sensorless contact force estimation methods facilitate the application of the serial manipulators to manufacturing as they enable robots to interact with unexpected collisions at low cost. In this paper, an external force estimation approach with no embedded sensors is proposed. The approach combines a Weighted Moving Average (WMA) with variable span, the standard Kalman filter (SKF), and its tuning routines. Improved confidence in the motor output torque is achieved due to the reduction of the measurement noise in the motor current by the WMA. The span of the filter adapts continuously to achieve optimal tradeoff between response time and precision of estimation in real time. With the comprehensive information of uncertainty in motor current noise and measurement errors of individual joints speed, an automatic tuning algorithm of the SKF is presented. Validation of the presented estimation approach in terms of estimation accuracy and response time was conducted on the Universal Robot 5 manipulator with differing end effector loads. It was found that the combined force estimation method leads to a reduction of the root-mean-square error and response time by 55.2% and 20.8% in comparison with the established method. The proposed method can be applied to any robotic manipulators as long as the motor information (current, joint position, and joint velocities) is available. Consequently, the cost of collision recognition could be reduced dramatically.

Highlights

Industrial serial manipulators controlled in position mode play an important role in the manufacturing field
The proposed contact force estimation method based on the SKFW works effectively in the physical experiments and the response time is reduced by 55.2% on average compared to an established standard Kalman filter (SKF) approach [39]
This paper proposes a novel sensorless contact force estimation method

Summary

Introduction

Industrial serial manipulators controlled in position mode play an important role in the manufacturing field. A major challenge for position-controlled manipulators is the unexpected interaction with the environment, which may damage the manipulator, environment or operator Tasks such as multi-robot cooperation [1], [2], exoskeleton robots [3], [4], physical HumanRobot Interaction [5], [6], polishing [7]-[9], assembly [10], and collision detection [11], [12] require monitoring of the contact force. The nonlinear disturbance observer provided by Chen [20] is widely used [21]-[23] With these model-based approaches, the disturbance estimation accuracy is theoretically guaranteed. A constant disturbance has to be assumed, and that restricts its extensive use beyond research

Methods

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Discussion

Conclusion