Control of an electro-discharge machine tool

Electro-discharge machining apparatus for machining a workpiece comprising:

• a first movable member for carrying an electrode;
• servo control means for controlling the speed of said first movable member in response to the voltage between said electrode and a surface of said workpiece;
• a second movable member against which said first member is located in relative sliding engagement;
• said first and second movable members having overlapping portions for limiting the motion of said first movable member in a direction toward said workpiece and with respect to said second movable member by causing abutting engagement;
• sensing and signalling means coupled to said second movable member for sensing the relative position of said first movable member with respect to said second movable member and generating a position signal related thereto;
• and
• drive means responsive to said position signal for moving said second movable member toward said workpiece at a speed relative to the speed of said first movable member so as to control the abutting of said overlapping portions,
• whereby after the abutting of said overlapping portions, the speed of said first movable member toward said workpiece and the speed of said electrode are controlled by the speed of said second movable member toward said workpiece.