Two stage punch press actuator with output drive shaft position sensing

A method of operating a press having a frame, a table mounted on the frame for supporting a die of a tooling set on which may be placed a workpiece, a drive rod mounted on the frame to move toward and away from the table between retracted and extended positions respectively, wherein the drive rod has an end adjacent the table for carrying a punch of a tooling set, and said drive rod is for transferring force to the punch, the method comprising:

• a) providing relatively low force to the drive rod responsive to a start signal, said low force urging the drive rod toward the table, wherein the low force is such that movement of the drive rod is blocked if a human hand or finger interferes with the drive rod;
• b) sensing the position of the drive rod, and providing a continue signal in response to the drive rod achieving a predetermined position between the retracted and extended positions of the drive rod;
• c) supplying relatively high force to the drive rod in response to the continue signal;
• d) generating force to apply to the drive rod with a force generator;
• and
• e) performing the sensing of the position of the drive rod by sensing a position feature of the force generator, wherein:
• the force generator includes a low pressure hydraulic cylinder having an internal piston, said low pressure hydraulic cylinder supplying low pressure hydraulic fluid;
• the position feature comprises a sensing shaft attached to the piston and projecting from the low pressure hydraulic cylinder;
• the force generator comprises an actuator hydraulic cylinder receiving low pressure hydraulic fluid from the low pressure hydraulic cylinder;
• and
• the sensing of the position of the drive rod further comprises sensing the position of the sensing shaft.

A method for operating a punch press comprised of a punch designed to mate in a predetermined manner with a die for forming a workpiece, the method comprising:

• supplying a low pressure hydraulic fluid via a low pressure valve to a fluid port operatively connected to the punch for applying a relatively low force to the punch in accordance with a start signal, wherein the low pressure valve is in an open state, wherein the low force is too low to cause injury if a human hand or finger interferes with the punch;
• detecting if the punch has reached a predetermined intermediate position and generating a continue signal if the punch has reached the predetermined intermediate position, wherein the predetermined intermediate position is such that a human finger located between the punch and the workpiece will apply force to the punch before the punch reaches the predetermined intermediate position;
• and
• supplying a high pressure hydraulic fluid via a high pressure valve to the fluid port for applying a relatively high force to the punch in accordance with the continue signal, wherein the high pressure valve is in the open state and the low pressure valve is in a closed state, wherein:
• the supplying of the low pressure hydraulic fluid further comprises moving a low pressure piston within a low pressure chamber;
• the detecting of if the punch has reached the predetermined intermediate position and generating a continue signal if the punch has reached the predetermined intermediate position further comprises detecting the end of a sensing shaft attached to the low pressure piston as the low pressure piston moves within the low pressure chamber for detecting if the punch has reached the predetermined position and placing a valve operatively connected to the low pressure piston in an open state when the end of a sensing shaft is detected for generating the continue signal;
• and
• the supplying of the high pressure hydraulic fluid further comprises driving a high pressure piston within a high pressure chamber.

A method of operating a hydraulic press, wherein the press includes a hydraulic piston chamber, an actuator piston accommodated in the hydraulic piston chamber, and a tool fixed to the actuator piston, wherein the method comprises:

• in a first stage of operation, supplying fluid at a relatively low pressure to the hydraulic piston chamber in response to a start signal, wherein, in the first stage of operation, the fluid applies a force to the actuator piston that is low enough that a human hand or finger applied to the tool can block movement of the actuator piston;
• sensing the distance between the tool and a workpiece;
• providing a continue signal when the tool is spaced from the workpiece by a predetermined distance;
• in a second stage of operation, supplying fluid at a relatively high pressure to the hydraulic piston chamber in response to the continue signal to perform a pressing operation on the workpiece, wherein the method further comprises:
• supplying the fluid to the hydraulic piston chamber with a low-pressure pump piston;
• and
• performing the sensing of the spacing between the tool and the workpiece by detecting the actual position of the low-pressure pump piston.

A method of operating a hydraulic press, wherein the press includes a hydraulic piston chamber, an actuator piston accommodated in the hydraulic piston chamber, and a tool fixed to the actuator piston, wherein the method comprises:

• in a first stage of operation, supplying fluid at a relatively low pressure to the hydraulic piston chamber in response to a start signal, wherein, in the first stage of operation, the fluid applies a force to the actuator piston that is low enough that a human hand or finger applied to the tool can block movement of the actuator piston;
• sensing the distance between the tool and a workpiece;
• providing a continue signal when the tool is spaced from the workpiece by a predetermined distance;
• in a second stage of operation, supplying fluid at a relatively high pressure to the hydraulic piston chamber in response to the continue signal to perform a pressing operation on the workpiece, wherein the method further comprises:
• supplying the fluid to the hydraulic piston chamber with a low-pressure supply piston;
• and
• driving the low-pressure supply piston pneumatically.