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Abstract This work is devoted to computer simulation of electro-pneumatic drives for vertical motion mobile robots. These robots are equipped with suction pads to move on walls and ceiling. An output highlights a conflict between the main requirements to such robot drives: simultaneous ensuring of high speed and smoothness of movement of robots with a considerable mass of moved objects. The low efficiency of traditional cushion systems of cylinders is shown in development of such kind of robots. New structure of electro-pneumatic drive for applications with considerable inertia load is developed. This structure represents mechatronic system and consists from the set of on-off valves and computer control device that operates the valves and reaches the optimum motion control of the object with required smoothness. This could be achieved due to the multistep braking in the end of stroke. The paper also represents the mathematical model of developed drive with description of throttle elements, friction forces and details of computer control systems. Mathematical model realized in computer program allows to simulate processes of movement of electro-pneumatic drives.69498
The results of computer modeling show that developed structure and multistep computer control allows to develop effective electro-pneumatic drives for high-quality and high-speed control of massive objects in the part of vertical motion mobile robots. Developed program represents effective analysis instrument, so it can be used in the process of design engineering.
Keywords: VMMR; electro-pneumatic drive; non-linear mathematical model; computer simulations
1. Introduction
Vertical motion mobile robots (VMMR) are effectively used for inspection and manipulation of objects, which are complicated or impossible to access. The most common design of these robots consists of two mobile platforms connected with each other. Each platform has its own vacuum pads and pneumatic drives to fix pads on the inspected surface [1]. One of the platforms may have a manipulator or measurement equipment. The robot developed in MSTU "STANKIN" can be an example of such kind of VMMR (Fig. 1).
Suction pads allow platforms to fix on various flat surfaces. While the first platform is attached to the surface, the second makes the movement using the electro-pneumatic drive.
After that the second platform attaches to the surface, the first may move by the means of another electro- pneumatic drive. That construction allows robot to move on walls and the ceiling of investigating object. Using of suction pads requires vacuum ejectors and compressed air despite the fact that it is a very expensive working body [2], therefore it is reasonable to use pneumatic cylinders for platforms movement. Considering task preferences and conditions solved by VMMR the binary (on-off) pneumatic drives are preferred.
The efficiency of VMMR increases dramatically with their speed increase. This is achieved through the speed increase of its pneumatic drives. Total time of VMMR movement consists of acting times of every pneumatic drive, mobile platform drives and pad drives. Therefore the time of mobile platforms movement has the greatest influence on the cycle time. For the average robot speed of 50 mm/sec or more with the stroke of 250 mm the longitudinal cylinders movement time must be not more than 1 sec. This allows calculating the average speed of the cylinders, which is 250 mm/sec. That is 5 times greater than average robot speed.
Fig. 1. Example of vertical motion mobile robots.
The first and the most important requirement is to organize the reliable robot fixation. That is why very important to limit dynamic forces, providing smooth starting and braking in the end of the stroke without rebounds and shocks. Ensuring the safe work of the robot requires to limit dynamic forces of one cylinder to 500 N and the speed in the end to 120 mm/sec.