Control device and control method for injection molding machine

A control device for an injection molding machine including a cylinder into which a resin is supplied, and a screw configured to move forward and rearward and rotate inside the cylinder, the injection molding machine being configured to perform a metering of the resin while the resin is being melted inside the cylinder, by causing the screw to be moved rearward to a predetermined metering position while being forwardly rotated,

• the control device comprising one or more processors that execute computer-executable instructions stored in a memory,
• wherein the one or more processors execute the computer-executable instructions to cause the control device to:
• acquire a pressure of the resin;
• cause, based on a predetermined reverse rotation condition, the screw to be rotated in reverse, so as to reduce the pressure of the resin, after the screw has reached the predetermined metering position;
• measure an elapsed time or a rotation amount of the screw from when the screw has reached the predetermined metering position;
• initiate sucking back of the screw based on a predetermined rearward movement condition so as to occur in an overlapping manner with the reverse rotation of the screw, in a case that a predetermined rearward movement initiation time has elapsed, or in a case that the screw has been rotated by a predetermined rearward movement initiation rotation amount, from when the screw starts being rotated in reverse in a state where the screw stopped moving rearward;
• judge whether or not the rearward movement initiation time or the rearward movement initiation rotation amount has been set;
• and
• in a case that the rearward movement initiation time has not been set, set the rearward movement initiation time based on a required time period from when the screw has reached the predetermined metering position and until the pressure of the resin reaches a predetermined rearward movement initiation pressure, or, in a case that the rearward movement initiation rotation amount has not been set, set the rearward movement initiation rotation amount based on a required rotation amount of the screw required from when the screw has reached the predetermined metering position and until the pressure of the resin reaches the rearward movement initiation pressure,
• wherein the memory includes a table in which the predetermined reverse rotation condition and the rearward movement initiation pressure are associated with each other, and
• wherein the one or more processors execute the computer-executable instructions to cause the control device to set the rearward movement initiation time or the rearward movement initiation rotation amount based on the rearward movement initiation pressure that is determined based on the predetermined reverse rotation condition and the table.