Machine Design

Sensor Sense: Clamp action sensing

Clamping applications often rely on sensors to ensure parts are in place and jaws or grippers are in proper orientation and position. Though other methods can report open and closed clamps, only sensors near the application can provide true reports on clamp operation.

Clamp sensors are often found in robotic environments like those in automotive assembly. Robotic arms manipulate parts, either welding pieces together or holding them in place until other actions are carried out. The arms are typically programmed to grip several different objects per application.

Sensors placed near the cylinder on the arm mechanism of a robot detect piston movement within the cylinder. The position of the piston corresponds to the location of the arm or the open/closed condition of the jaws or grippers. This technique lets the gripper open to the precise position required for a specific part. One drawback, though, is that the gripper cannot sense whether the part is actually in the gripper or even at the proper position.

Another sensing method used in clamping applications detects part in place — that is, whether the object or part is truly in the grippers. A sensor mounts in the groove of the actual jaw or gripper. In so doing, the sensor can now detect whether the part is physically in the gripper, the clamp is in the right position, and that the part is moving to the proper location. The sensor mounts in such a way that the process damages neither part nor sensor. Though not widely used, this method proves effective in applications where a robot performs multiple part-in-place operations.

A sensor placed in the jaw or gripper does not affect the open/closed function. Rather, this technique is used in addition to cylinder position sensors that gauge whether the gripper is open or closed. These sensing methods provide an increased measure of assurance that processes are functioning properly.

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