A high-accuracy trajectory following controller for pneumatic devices

Abstract

The use of pneumatic devices is widespread among different industrial fields, in tasks like handling or assembly. Pneumatic systems are low-cost, reliable, and compact solutions. However, its use is typically restricted to simple tasks due to the poor performance achieved in applications where accurate motion control is required. This paper presents a novel nonlinear controller, using neural network-based models, that allows the use of common industrial servopneumatic components in applications where fine trajectory following tasks is required. Furthermore, several experimental trials show that the system is highly robust to payload variation without any controller retuning. These results encourage the use of pneumatics actuators in a set of applications for which they have not been traditionally considered.

Accurate motion control of a servopneumatic system using integral sliding mode control

“…Furthermore, the controlled system was highly robust to parameter variation since high accuracy results were obtained without any controller retuning even though the payload varied from 2.6 to 13.1 kg. Using an enhanced version of the controller developed in [18], the authors of this study also showed in [19] that good results may be achieved in the micrometre range. Indeed, in [19], the positioning error obtained from a control perspective was only limited by the encoder resolution, 1 μm, in any position of the piston stroke and when carrying loads of 3 and 8 kg, without any controller retuning.…”

“…This was the path followed by the authors of this study in previous works [18,19]. In fact, in [18,19], the disturbances were tackled using a friction model to handle friction disturbance and a sliding-based control law to handle not only the payload variation but also the friction model errors.…”

“…In fact, in [18], errors of only a few millimetres were obtained for sinusoidal position references with an amplitude of 0.16 m and varying frequency up to π rads −1 (corresponding to piston velocities of ca. 1 ms −1 ).…”

“…A potential downside of sliding mode approaches like the one followed in [18,19] lies on possibly excessive control activity. Although this problem may be partially mitigated by using models of the system, so that the uncertainty is lowered and therefore discontinuous terms are reduced, this leads to another potential problem: the dependence of the proposed solution on the models used in the particular experimental setup.…”

“…This is particularly relevant regarding friction force, which is well acknowledged as one of the main difficulties to surpass when controlling pneumatic systems. Another cause of excessive control activity of the controllers developed in [18,19] is the fact that the pressure dynamics is viewed by the motion controller as unmodelled dynamics. This prevents perfect sliding mode to occur [20], and consequently, complete disturbance rejection cannot be implemented in practice, causing the well-known chattering phenomenon.…”