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5. Simulation results
A number of computer simulations using the developed model [12] show following results. First of all, in the process of high-speed movement of massive platforms in VMMR velocity of control target is no longer constant like in classic throttle control. Velocity oscillates and the piston can reach standard braking system with uncontrolled value of the speed. When piston with connected massive object enters standard cushion system pressure in the isolated dumping chamber starts to grow very quickly. It causes the acceleration increase and dynamic forces that are influencing the suction pads. For example two standard pneumatic cylinders with vertical installation in VMMR develop acceleration 16 m/s2 (see Fig. 5). If connected platform mass is 70 kg, dynamic force influencing the suction pads is 1120 N. The conclusion – VMMR can’t functional correctly because of force value limits. Besides, there are rebounds and following after that shocks of piston into the cap that can easily damage the cap of the cylinder and connected to it mechanical parts.
Fig. 5. The diagram of dependence of position + velocity in time (left) and acceleration + velocity in time (right), VMMR is moving up on vertical surface.
Analyzing simulation results show that disadvantages of standard cushion systems are caused by several factors.
First of all standard cushion system contains cushion plug and seal, when plug enters the seal the volume of exhaust chamber isolates and decreases in step way that leads to fast increasing of derivative of pressure at the start of the braking process. Length of the brake plug is insufficient and limited for constructive reasons. In this case using of small cylinder with massive object on high-speed control makes us to tight damping screws hardly to decrease the velocity. The result is processed as in Fig. 5. In this conditions using of minimal diameter and massive object not allowed to achieve necessary pneumatic spring rate and damping in the end of the stroke. That is why using of traditional control methods of pneumatic drives increase the risk of fall of VMMR from vertical surface.
In the process of computer simulation of mechatronic electro-pneumatic drive optimal values of strength and control parts of the drive were achieved. Flow rates of throttles according to fig. 3: T1 – 50 Nl/min; T2 – 105 Nl/min; T3 – 45 Nl/min; T4 – 150 Nl/min; T5 – 170 Nl/min; T6 – 30 Nl/min; T7 – 350 Nl/min. Volumes of reservoirs: Res1 – 70 ml (with connecting tubes); Res2 – 100 ml (with connecting tubes).
Coordinates for sensors: 0 mm – position of sensor S3 that signal that piston is at the left cap; 44 mm – position of sensor S2 that signal about switching off the throttle T2 when cylinder is moving in; 150 mm – position of sensor S1 that signal about switching off the throttle T1 when cylinder is moving in; 200 mm – position of sensor S4 that signal about switching off the throttle T4 when cylinder is moving out; 231 mm – position of sensor S5 that signal
about switching off the throttle T5 when cylinder is moving out; 250 mm – position of sensor S6 that signal that piston is at the right cap.
Results of simulation also can be represented in diagrams that are shown on Fig. 6…9. These diagrams correspond to cylinder moving processes with diameter 50 mm, stroke 250 mm, with mass 30 kg (first step of the robot’s moving cycle) and with mass 70 kg (second step of the robot’s moving cycle) with various orientation of the control target. Each cycle as mentioned before consists from two movements with different masses.
Fig. 6. The diagram of dependence of position + velocity in time (left) and acceleration + velocity in time (right), VMMR is moving on vertical surface in horizontal way (moving out, mass 30 kg).