A New Control Method for Backlash Error Elimination of Pneumatic Control Valve

Backlash is a commonly non-linear phenomenon, which can directly degrade the control accuracy of a pneumatic control valve. To explain the cause and law of backlash error, and to propose an effective method, many research works on the modeling of a pneumatic control valve system have been carried out. The currently model of a control valve system can be classified as a physical model, data-driven model, and semi-physical model. However, most models only consider the force-displacement conversion process of a pneumatic diagram actuator in a pneumatic control valve system. A physical model based on the whole workflow of the pneumatic control valve system is established and a control method to eliminate the backlash error is proposed in this paper. Firstly, the physical model of the pneumatic control valve system is established, which is composed of three parts: pneumatic diaphragm actuator model, nozzle-flapper structure model and electromagnetic model. After that, the input–output relationship of the pneumatic control valve system can be calculated according to the established physical model, and the calculation results are consistent with the experimental result. Lastly, a self-calibration PID (SC-PID) control method is proposed for backlash error elimination. The proposed method can solve valve stem oscillation caused by backlash during valve control.

Experimental Validation of the Tactile Exploration by a Manipulator With Joint Backlash

This research investigates using a manipulator to tactilely explore objects and environments when significant backlash affects its joint’s positions. A typical application is the exploration of rough environments, such as oil wells, where the harsh conditions dictate the use of tactile exploration. These conditions can result in large, unknown, and variable backlash in the manipulator’s transmissions, which strongly affects the measurement precision. Here, a method is developed to simultaneously map the unknown surface and identify the joint backlash. The robot probes the surface and uses its encoder readings to construct a partial map of the environment as a combination of geometric primitives. While the surface is built, the same data are also used to estimate backlash in the joints and to correct the surface measurements for backlash error. The effectiveness of the approach is demonstrated in simulation case studies and laboratory experiments.

Modeling and assessment of the backlash error of an industrial robot

SUMMARYThis paper proposes an experimental approach for evaluating the backlash error of an ABB IRB 1600 industrial serial robot under various conditions using a laser interferometer measurement instrument. The effects of the backlash error are assessed by experiments conducted on horizontal and vertical paths. A polynomial model was used to represent the relationship between the backlash error and the robot configuration. A strategy based on statistical tests was developed to choose the degree of polynomial representing the effect of the tool center point (TCP) speed and payload. Results show that the backlash error strongly affects the repeatability of the industrial robot. Statistical analyses prove that the backlash is highly dependent on both robot configuration and TCP speed, whereas it remains nearly unaffected by changes in the payload. It was discovered that the backlash error as measured at the TCP may exceeds 100 μm, and that the positive backlash error increases and the negative backlash error decreases when there is increase in TCP speed.