Article
An Adaptive Sliding-Mode Iterative Constant-force
Control Method for Robotic Belt Grinding Based on a
One-Dimensional Force Sensor
Tie Zhang * , Ye Yu and Yanbiao Zou
School of Mechanical and Automotive Engineering, South China University of Technology,
Guangzhou 510000, China; 201720101200@mail.scut.edu.cn (Y.Y.); ybzou@scut.edu.cn (Y.Z.)
* Correspondence: merobot@scut.edu.cn; Tel.: +86-1366-073-3192
Received: 21 February 2019; Accepted: 3 April 2019; Published: 5 April 2019
Abstract:
To improve the processing quality and efficiency of robotic belt grinding, an adaptive
sliding-mode iterative constant-force control method for a 6-DOF robotic belt grinding platform is
proposed based on a one-dimension force sensor. In the investigation, first, the relationship between
the normal and the tangential forces of the grinding contact force is revealed, and a simplified grinding
force mapping relationship is presented for the application to one-dimension force sensors. Next, the
relationship between the deformation and the grinding depth during the grinding is discussed, and a
deformation-based dynamic model describing robotic belt grinding is established. Then, aiming at an
application scene of robot belt grinding, an adaptive iterative learning method is put forward, which
is combined with sliding mode control to overcome the uncertainty of the grinding force and improve
the stability of the control system. Finally, some experiments were carried out and the results show
that, after ten times iterations, the grinding force fluctuation becomes less than 2N, the mean value,
standard deviation and variance of the grinding force error’s absolute value all significantly decrease,
and that the surface quality of the machined parts significantly improves. All these demonstrate that
the proposed force control method is effective and that the proposed algorithm is fast in convergence
and strong in adaptability.
Keywords:
robot; abrasive belt grinding; constant-force control; adaptive sliding-mode control;
iterative learning
1. Introduction
As a finishing process, abrasive belt grinding not only achieves high material removal rates, but
also can be used to improve the surface roughness of components [
1
]. By integrating a multi-degree
industrial robot as a manipulator, a flexible manufacturing cell can be formed, which is especially
suitable for processing surfaces with complicated geometries, such as turbine blades or faucets [
2
].
It can avoids a series of problems caused by manual grinding and CNC grinding, such as the
health problems caused by the harsh processing environment, low processing efficiency, increasing
labor costs [
3
], poor stability, and insufficient consistency [
4
]. Therefore, there have been many
studies on robotic belt grinding, and some of them have addressed the problems of robotic offline
programming [
5
,
6
] and robotic trajectory planning [
7
–
9
]. These methods can improve the machining
quality of workpieces to some extent. Some related studies have shown that by controlling the required
grinding force, the material removal rate can be indirectly controlled to improve the processing quality
of the workpieces, and the phenomenon of over- and under-cutting of the workpieces caused by an
improper contact force can thereby be avoided [
10
]. These findings indicate that controlling the normal
contact force is also the key to improving the grinding quality of abrasive belt. Thus, an increasing
number of researchers are attempting to achieve the desired force control.
Sensors 2019, 19, 1635; doi:10.3390/s19071635 www.mdpi.com/journal/sensors
