Apparatus including mutually communicating hydraulic cylinders for even distribution of blank-holding force on pressing machine

A balancing apparatus for a pressing machine, including force generating means for generating a force during a pressing operation, and a plurality of balancing hydraulic cylinders having respective oil chambers communicating with each other and including respective pistons that are moved to neutral positions thereof during the pressing operation, for evenly distributing said force, said balancing apparatus comprising:

• a connecting passage connecting said oil chambers of said balancing hydraulic cylinders to each other;
• discharge control means connected to said connecting passage, for inhibiting, prior to said pressing operation, a discharge flow of a working fluid from said balancing hydraulic cylinders and thereby holding said pistons of all of the balancing hydraulic cylinders at upper stroke ends thereof, and for permitting, during said pressing operation, said discharge flow of the working fluid, thereby to permit said pistons to be moved to said neutral positions;
• a cushion platen on which said balancing hydraulic cylinders are disposed;
• a pressure member for holding a blank during said pressing operation on said blank;
• and
• a plurality of cushion pins having upper ends supporting said pressure member and lower ends associated with said pistons of said plurality of balancing hydraulic cylinders, respectively;
• said force generating means comprising a cushioning pneumatic cylinder supporting said cushion platen and generating a blank-holding force during said pressing operation, said blank-holding force being transferred to said pressure member through said cushion platen, said balancing hydraulic cylinders and said cushion pins, for holding said blank;
• and
• said discharge control means being disposed on said cushion platen together with said balancing hydraulic cylinders.

A balancing apparatus for a pressing machine, including force generating means for generating a force during a pressing operation, and a plurality of balancing hydraulic cylinders having respective oil chambers communicating with each other and including respective pistons that are moved to neutral positions thereof during the pressing operation, for evenly distributing said force, said balancing apparatus comprising:

• a connecting passage connecting said oil chambers of said balancing hydraulic cylinders to each other;
• and
• discharge control means connected to said connecting passage, for inhibiting, prior to said pressing operation, a discharge flow of a working fluid from said balancing hydraulic cylinders and thereby holding said pistons of all of the balancing hydraulic cylinders at upper stroke ends thereof, and for permitting, during said pressing operation, said discharge flow of the working fluid, thereby to permit said pistons to be moved to said neutral positions;
• said discharge control means comprising a plurality of discharge control cylinders disposed in parallel connection with each other and connected to said connecting passage, each of said discharge control cylinders including a piston and elastic means for producing a biasing force for biasing said piston so as to hold said piston at an original position thereof prior to said pressing operation, said piston receiving a hydraulic pressure in said balancing hydraulic cylinders through said connecting passage so that said piston is moved from said original position against a biasing force of said elastic means when said hydraulic pressure is raised during said pressing operation, whereby said discharge control cylinders permit said discharge flow of the working fluid from said balancing hydraulic cylinders into said discharge control cylinders through said connecting passage, by an amount corresponding to a distance of movement of said piston from said original position, during said pressing operation.

A balancing apparatus for a pressing machine, including force generating means for generating a force during a pressing operation, and a plurality of balancing hydraulic cylinders having respective oil chambers communicating with each other and including respective pistons that are moved to neutral positions thereof during the pressing operation, for evenly distributing said force, said balancing apparatus comprising:

• a connecting passage connecting said oil chambers of said balancing hydraulic cylinders to each other;
• and
• discharge control means connected to said connecting passage, for inhibiting, prior to said pressing operation, a discharge flow of a working fluid from said balancing hydraulic cylinders and thereby holding said pistons of all of the balancing hydraulic cylinders at upper stroke ends thereof, and for permitting, during said pressing operation, said discharge flow of the working fluid, thereby to permit said pistons to be moved to said neutral positions;
• said discharge control means comprising at least one discharge control cylinder connected to said connecting passage, each of said at least one discharge control cylinder including a piston and elastic means for producing a biasing force for biasing said piston so as to hold said piston at an original position thereof prior to said pressing operation, said piston receiving a hydraulic pressure in said balancing hydraulic cylinders through said connecting passage so that said piston is moved from said original position against a biasing force of said elastic means when said hydraulic pressure is raised during said pressing operation, said piston being moved to a position of equilibrium between said biasing force which increases as said elastic means is elastically deformed during a movement of said piston from said original position and a force based on said hydraulic pressure which corresponds to said force generated by said force generating means, said at least one discharge control cylinder permitting said discharge flow of the working fluid from said balancing hydraulic cylinders into said at least one discharge control cylinder through said connecting passage, by an amount corresponding to a distance of said movement of said piston from said original position, during said pressing operation.

A balancing apparatus for a pressing machine, including force generating means for generating a force during a pressing operation, and a plurality of balancing hydraulic cylinders having respective oil chambers communicating with each other and including respective pistons that are moved to neutral positions thereof during the pressing operation, for evenly distributing said force, said balancing apparatus comprising:

• a connecting passage connecting said oil chambers of said balancing hydraulic cylinders to each other;
• and
• discharge control means connected to said connecting passage, for inhibiting, prior to said pressing operation, a discharge flow of a working fluid from said balancing hydraulic cylinders and thereby holding said pistons of all of the balancing hydraulic cylinders at upper stroke ends thereof, and for permitting, during said pressing operation, said discharge flow of the working fluid, thereby to permit said pistons to be moved to said neutral positions;
• said discharge control means comprising a discharge control cylinder device and biasing means connected to said discharge control cylinder device, said discharge control cylinder device including a cylinder body, and a stepped piston slidably and movably received within said cylinder body and having a large-diameter portion and a small-diameter portion, said large-diameter portion cooperating with said cylinder body to define a first chamber communicating with said connecting passage, said cylinder body cooperating with at least said small-diameter portion to define a second chamber filled with a control fluid which biases said stepped piston toward said first chamber so as to hold said stepped piston at an original position thereof prior to said pressing operation, and wherein said cylinder body has a hole which communicates at one end thereof with said second chamber when said stepped piston is placed in said original position, said hole being closed at said one end by said small-diameter portion when said stepped piston is moved by a predetermined distance from said original position toward said second chamber;
• and
• said biasing means being connected at the other end of said hole for introducing said control fluid into said second chamber through said hole so as to hold said stepped piston at said original position prior to said pressing operation, said biasing means permitting said stepped piston to be moved from said original position against a biasing force of said control fluid when a hydraulic pressure in said balancing hydraulic cylinders is raised during said pressing operation, said biasing means absorbing a portion of said control fluid discharged from said second chamber through said hole during a movement of said stepped piston from said original position.