In the spot wedling, the electrode force is usually kept constant during a short welding time because of a too low response speed of the air cylinder and it can not satisfy the developing requirements of spot welding technology. A new motion and force compound control cylinder has been developed to control the electrode force at a high speed. It is composed of a motion control piston and force control piston on the same rod.
The optimal structural parameters and operating conditions of the cylinder are analyzed in the paper. Experiments indicate that the response time of the system for a step input is improved from 0.2 [s] for the conventional cylinder to 0.010 [s] for the cylinder developed here, and the bandwidth is improved from 10 to about 100 [Hz]. It will be possible with using this cylinder to avoid spattering during spot welding and to reduce the welding defects, and increase the welding strength. It can also be applied in other fields of fast control.