Various sensor technologies can give basic grippers the electronic feedback necessary to become smarter workers. The choice of sensor technology depends on what gripper parameter you need to monitor. The three most commonly monitored gripper parameters are jaw open/closed/jaw closed on part, actual jaw position, and part present/absent in jaw.
Gripper jaw position open/closed/closed on part (end-of-stroke) – This parameter is the most basic form of gripper status that is monitored. Discrete on/off signals from sensors confirm that the gripper is mechanically executing control commands as expected. Magnetic field sensors sense magnets internally mounted on gripper mechanism to indicate open or closed position. Failure to confirm gripper status can stop a line and damage work-in-process or production equipment. Reliable gripper status signals can detect gripper faults when they occur, allowing automatic, orderly stoppage of the process so that problems can be corrected before scrap is produced or machinery is damaged. Jaws can be monitored directly or indirectly.
Gripper jaw actual position, absolute analogue position measurement – Absolute analogue position measurement can deliver precise jaw-position feedback signals for higher process speed, improved quality control, and act as an indicator for preventive maintenance. Analogue signals can create multiple software set points in the controller for recipe-driven flexible production systems. Analogue inductive proximity sensors continually track jaw position by reading distance of wedge face from the face of the sensor. These signals can also differentiate between fully gripped objects of different physical sizes. Analogue signals can also monitor the operating efficiency of the gripper mechanics.
Part present/part absent in jaw – The presence or absence of a part in a gripper jaw provides key information about the assembly or production process status. If a gripper expects to pick up a part and does not detect one, it could mean that there is a stoppage farther up the line. It also might mean that the end of the production lot has been reached and the process is ready for shut down. L-shaped photoelectric sensor provides positive part-in-jaw verification. In some cases, multiple grippers must simultaneously grab a large or heavy part. If one or more grippers fail to properly grip the part, the ‘lift and move’ operation could fail, dropping or dragging the part, which can damage the part and the surrounding equipment. Moreover, the time spent clearing the subsequent line jam could incidentally harm work-in-process father up the line.
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