Press brake and press brake control method

A press brake comprising:

• an upper table on which a punch is mounted;
• a lower table on which a die is mounted;
• a table lifting mechanism configured to raise and lower the upper table or the lower table;
• an angle sensor configured to measure an angle of a sheet metal, when the table lifting mechanism raises and lowers the upper table or the lower table and bends the sheet metal, while the sheet metal is interposed between the punch and the die;
• and
• a control device configured to calculate a bending angle of the sheet metal based on an angle of the sheet metal measured by the angle sensor and configured to control the table lifting mechanism to lower the upper table or to raise the lower table, wherein
• when the control device controls the table lifting mechanism to lower the upper table or to raise the lower table to bend the sheet metal to have a target bending angle,
• the control device controls the table lifting mechanism to lower the upper table by a first depth value or to raise the lower table by the first depth value such that the sheet metal is bent to have a predetermined temporary bending angle that is wider than the target bending angle during a temporary bending period,
• the control device calculates a first bending angle of the sheet metal bent to have the temporary bending angle based on the angle of the sheet metal measured by the angle sensor,
• the control device, during a load removal period after the sheet metal is bent to have the temporary bending angle, controls the table lifting mechanism to raise the upper table or to lower the lower table to remove a load applied to the sheet metal, while keeping a state in which the punch is in contact with the sheet metal,
• the control device, while the load applied to the sheet metal is removed during the load removal period, calculates a second bending angle of the sheet metal based on the angle of the sheet metal measured by the angle sensor and calculates a spring back amount based on a difference between the second bending angle and the first bending angle,
• the control device calculates a second depth value for bending the sheet metal to have the target bending angle in consideration of the spring back amount during a driving period and controls the table lifting mechanism to lower the upper table by the second depth value or to raise the lower table by the second depth value, and
• the control device, during a final angle measurement period after the sheet metal is bent to have the target bending angle, removes the load applied to the sheet metal, while keeping the state in which the punch is in contact with the sheet metal, controls the table lifting mechanism to raise the upper table or to lower the lower table, and calculates a final bending angle of the sheet metal based on the angle of the sheet metal measured by the angle sensor.