Apparatus for clamping workpieces on machine tools

An apparatus (1) for clamping workpieces on machine tools, comprising:

• at least one basic frame (2) fixable to a machine tool (M) for machining a workpiece (P);
• at least one clamping unit (3) associated with said basic frame (2) in a movable manner between a release position and a clamping position of said workpiece (P), passing through a plurality of intermediate transient positions;—at least one hydraulic actuator (22, 23), provided with a fixed portion (24), associated with said basic frame (2), and a movable portion (5), connected to said clamping unit (3), said hydraulic actuator (22, 23) comprising at least a first chamber (26) configured to be supplied with a first pressurized hydraulic fluid to displace said clamping unit (3) from said release position to said clamping position, said first chamber (26) being connectable to a first sensing device (27) for sensing the pressure of said first pressurized-hydraulic fluid;
• wherein:
• said apparatus (1) comprises at least one sensing channel (15) formed on at least one of either said basic frame (2) or said clamping unit (3), configured to be supplied with pressurized air and which is connectable to a sensing sensor (16) for sensing the pressure of said pressurized air, wherein said at least one sensing channel (15) is hermetically sealed when said clamping unit (3) is in the clamping position and is open outwards at least when said clamping unit (3) is in said intermediate transient positions;
• and
• said first sensing device (27) and said sensing sensor (16) are connectable to a control system adapted to authorize a machining of said workpiece (P) when a pressure of said first pressurized hydraulic fluid in said first chamber (26) and a pressure of said pressurized air in said at least one sensing channel (15) are simultaneously higher than their respective threshold values.