Programming skills in the automatic tool change process of the machining center in the machining center - News - Global IC Trade Starts Here.

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A well-structured PLC program not only ensures the machine operates smoothly but also makes the system easy to understand at a glance. This helps in self-debugging and enables maintenance personnel to quickly identify and resolve issues. In this article, we will discuss the programming techniques used for the robot during the automatic tool change process on the XH756B series horizontal machining center equipped with the SIEMENS 802D CNC system.

First, let’s briefly introduce the basic setup of the tool changer. The tool magazine is a chain-type unit capable of rotating both forward and backward. The robot mounted on the tool changer performs a 15-step process to exchange tools between the magazine and the spindle. Each step involves precise movements to ensure smooth operation. To reduce the tool change time, we implement pre-selection of tools and perform part processing in parallel, which significantly shortens the overall cycle time.

The sequence of the robot's actions is as follows:

Step 1: Move and retract, grab the pre-selected tool from the magazine.
Step 2: Pull out the current tool from the tool holder.
Step 3: Shift position, move away from the tool side, and grab the new tool.
Step 4: Retract the tool and pull it back.
Step 5: Extend the arm and rotate it toward the spindle.
Step 6: Move out and grasp the tool in the spindle.
Step 7: Pull out the tool from the spindle.
Step 8: Rotate forward or reverse to complete the tool exchange.
Step 9: Push the new tool into the spindle.
Step 10: Retract the robot from the spindle area.
Step 11: Retract the arm and rotate it back toward the magazine.
Step 12: Pull out the old tool and prepare to return it to the magazine.
Step 13: Move the robot toward the magazine.
Step 14: Insert the old tool back into the magazine.
Step 15: Retract and move away from the tool side.

These 15 steps can be divided into four main stages:

Stage 1: Grab the new tool. The Txx code rotates the tool magazine to the nearest position where the selected tool is located. Once the position is confirmed, the robot begins its movement. Steps 1 through 4 result in the new tool being gripped and ready for the tool change.

Stage 2: Perform the tool change. When M06 is called, the canned cycle "TOOL" is activated. This cycle moves all axes to the tool change position and triggers the PLC via the M90 signal. The PLC then initiates the tool change sequence, starting from step 5 through step 10, using the in-position signal from step 5 to confirm the correct positioning of the tool magazine relative to the spindle.

Stage 3: Return the old tool to the magazine. After the tool magazine has rotated and reached the correct position (I signal), the robot executes steps 12 through 15, returning the old tool to the magazine and updating the spindle tool number in memory. Once step 11 is completed, the "read-in inhibit" is lifted, allowing the tool parameters to take effect, and the machining program continues alongside the robot operation.

Stage 4: Pre-select the next tool. During the next M06 call, the Txx code indicates the next tool to be used. While the part is still being machined, the tool magazine can start the robot movement from step 1 through step 4 simultaneously, preparing the next tool for quick exchange. This pre-selection method ensures the robot is always ready when the M06 command is executed, significantly reducing the tool change time and improving overall productivity.