Patent ID: 7079919

Claim:
A method for adjusting the stroke of a press brake comprising a fixed table carrying a die, a moving beam carrying a punch, means of moving the moving beam bearing on uprights fixed to the fixed table, measuring rules for measuring a movement (d) of the moving beam with respect to the uprights, at least one sensor measuring a physical parameter (p) varying according to a force exerted by said punch on a piece placed on said die, and an electronic control device controlling the movement of the moving beam between a top dead center and a bottom dead center (BDC), provided with means of acquiring the movement measurements (d) and the physical parameter (p), and calculation means for correcting a value of the bottom dead center according to the measurements of said movement (d) and said physical parameter (p), wherein the difference in thickness between an actual thickness (e r ) of a sample of the piece to be bent and a nominal thickness (e) of the piece is calculated by comparing an actual position of the movement of the moving beam at which there occurs a predetermined variation Δp in said physical parameter (p) with a theoretical position of said movement (d) where this variation Δp should occur, wherein the electronic control device processes the measurements of said movement (d) and said physical parameter (p), during a plastic deformation phase of said sample of the piece during bending, so as to compare them and determine their differences with reference data pre-recorded during a reference bending operation which made it possible to obtain a set value α c of the bending angle after release of the force exerted by the punch and to determine a reference value of a spring effect correction, and wherein the electronic control device calculates a first correction to the bottom dead center according to said reference value of the spring effect correction and to said differences with the reference data, wherein an instantaneous bending angle α under load of the piece is calculated according to a variation in said movement d, taking account of said difference in thickness (e r −e) and geometric parameters of the punch and die, wherein a bearing force (F) of the punch on the piece is calculated by means of a value of the physical parameter (p), wherein the succession of values of a pair of parameters consisting of instantaneous bending angle and bearing force (α, F) is acquired and compared with a reference curve (α, F) ref pre-recorded during a reference bending operation on a piece of the same material which made it possible to obtain the set value α c of the bending angle after release of the force exerted by the punch, and wherein said electronic control device calculates a correction (A′) of a maximum value of the instantaneous bending angle under load (α max ) ref determined during the reference bending according to the difference between the pair (α, F) issuing from the measurements and the reference curve (α, F) ref in the plastic deformation phase.