Abstract
Friction can be found in all mechanical systems, and is the cause of control tracking error. In this article, LuGre friction model for symmetric hydraulic cylinder was studied and obtained experimentally. The estimated friction force was applied for reference force compensation. Force tracking performances of PID force control systems with and without friction compensation were tested and compared. Control system with friction compensation outperformed one without in all cases of tracking tests. The best result was found in the square force tracking tests, with an average error at maximum compression force of 86.105 N in the case of with friction compensation compared with error of 511.996 N in the case without. However, the estimated friction achieved in the study was noisy. This is due to the use of noisy numerically differentiated velocity signal in the friction estimation procedure.
Highlights
Electro-hydraulic control systems could be applied for position control, velocity control or force control
It can be seen that the control system with friction compensation performed better when the piston moved in the positive direction
The estimated friction force was applied as compensation to the reference force signal
Summary
Electro-hydraulic control systems could be applied for position control, velocity control or force control. Electrohydraulic force control systems are used various industrial applications such as press machine, earth moving equipment [1] and flight simulator [2]. Hydraulic cylinder is the main actuator used in force control applications. Friction occurs in cylinder at the contact areas between piston seal and cylinder barrel, and between piston rod seal and wiper. Friction depends on surface contact, temperature, lubrication and contact velocities. Friction always occurs in mechanical systems, and leads to control tracking error. Friction compensation is one of most popular method to solve the problem. Various friction models were reviewed in great details in [3] and [4]. The prediction ability of four friction models were compared in experiments [4], and LuGre friction model was found to be the all-round best predictor
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