期刊
MATHEMATICS
卷 8, 期 11, 页码 -出版社
MDPI
DOI: 10.3390/math8112051
关键词
automatic optical inspection; kinetic theory; parallel robots; robust control; sliding mode control
类别
资金
- Basque Government through the project SMAR3NAK [ELKARTEK KK-2019/00051]
- Ministerio de Economia y Competitividad [RTI2018-094669-B-C31]
- Aernnova
- Diputacion Foral de Alava (DFA) through the project CONAVAUTIN 2 (Collaboration Agreement)
The authors introduce a new controller, aimed at industrial domains, that improves the performance and accuracy of positioning systems based on Stewart platforms. More specifically, this paper presents, and validates experimentally, a sliding mode control for precisely positioning a Stewart platform used as a mobile platform in non-destructive inspection (NDI) applications. The NDI application involves exploring the specimen surface of aeronautical coupons at different heights. In order to avoid defocusing and blurred images, the platform must be positioned accurately to keep a uniform distance between the camera and the surface of the specimen. This operation requires the coordinated control of the six electro mechanic actuators (EMAs). The platform trajectory and the EMA lengths can be calculated by means of the forward and inverse kinematics of the Stewart platform. Typically, a proportional integral (PI) control approach is used for this purpose but unfortunately this control scheme is unable to position the platform accurately enough. For this reason, a sliding mode control (SMC) strategy is proposed. The SMC requires: (1) a priori knowledge of the bounds on system uncertainties, and (2) the analysis of the system stability in order to ensure that the strategy executes adequately. The results of this work show a higher performance of the SMC when compared with the PI control strategy: the average absolute error is reduced from 3.45 mm in PI to 0.78 mm in the SMC. Additionally, the duty cycle analysis shows that although PI control demands a smoother actuator response, the power consumption is similar.
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