Sensors for Detecting Contact with Product

  • Hey all,


    We have two large FANUC Robots that depalletize full layers of liquid in trays of cans or cases of bottles using a global vacuum head. Generally works great.


    But it sometimes happens that the edges of the large end-of-arm-tool head come into contact with misplaced product as the robot is moving downwards to pick the next layer. We have found that the in-built collision detection works best when the collision is near the center of the head, where the force is felt directly by the robot arm moving down. But when it is the edge that collides with product, the Robot keeps going down because of the way the forces act on the frame. This can damage and bend certain components.


    So we'd like to supplement the software collision detection with some simple but robust sensors that could be added to the piece of aluminum that makes contact with the product in these events. We'd program the motion to stop as soon as any of them are activated.


    My question is... do you have any suggestions for types / models of sensors that would be well-suited for this application? We would want something that detects a physical touch, not a capacitive sensor that detects the near-presence of an object, because it often happens that the product is very close to the edge and we don't want false positives - we just want to detect these collisions earlier than with the software collision detection.


    Thanks in advance, gents.

    Phil

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  • HawkME

    Approved the thread.
  • such applications are usually running at top speeds so i would look for a way to detect the product before making contact. this way it is possible to make a decision and react early, long before before product is reached.


    various sensor technologies exist and some may not apply. for example:

    contact sensing is possible with LVDT etc but this adds cycle time.

    inductive is short range and may not work on plastic or cardboard containers.

    capacitive is also short range but can work on non-metal targets.

    optical is longer range but one need to be careful in selection to avoid issues with clear plastic of reflective materials.

    ultrasound should work well, it is also longer range. the only thing to keep in mind is that when more than one sensor is used they need to be synchronized to avoid interference/false signals.


    if you really want contact sensing, maybe add an air cylinder and pressure regulator to adjust contact force. robot can extend the cylinder during approach to feel for obstacles. once it is clear that there is no obstacle, it can be retracted. sensing could be done by a reed switch attached to the side of the cylinder (extended position) or also by a pressure sensor.

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

  • Collision guard is never quick enough. If your payload can play inside the limits, I've had good success with these.

    I like them too. different versions exist (spring, magnet, air). The ones i used are all working with air.

    Just keep in mind that result is different:


    Using these devices is simple. Collisions are not avoided although contact damage is dramatically reduced. The downside is that abnormal cases end up in the collision, production is stopped and human intervention is needed..


    Using sensors one can avoid contact at all and use predefined behavior. When implemented correctly, this can continue to operate completely on its own, without need for human intervention. Creating robust solution using only sensors and software can be challenging.


    The most flexible setup would use both...

    1) read pinned topic: READ FIRST...

    2) if you have an issue with robot, post question in the correct forum section... do NOT contact me directly

    3) read 1 and 2

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