Getting to Grips with Grippers

In many automated assembly applications, a well-thought-out custom gripper design is essential. In this article I’ll talk about the process and iterations needed to accomplish the Meca 500 Diode Load sequence in RoboFiesta’s Mecademic Meca 500 Diode Loading Demo on YouTube.

Some of the things you’ll need to consider are:

  • What’s being gripped / picked. Dimensions, fragility, prestage setup
  • Speed required for the application
  • Precision / repeatability required for the application
  • Incoming material variability
  • Placement location with regards to EOAT orientation
EOAT will change depending on material being handled, and pick/place location considerations

For a part in a given location / orientation- a diode mounted on a breadboard, for instance- the gripper design would need to change depending on which direction the gripper fingers extend from the gripper mechanism.

It’s a good idea to do some dry runs with mock material to determine the requirements. For the diode handling, we could have picked with the gripper fingers extending in either X or Z from the mechanical gripper body mounted on the robot flange:

Which directions the gripper fingers extend also affects the toolpath you will program. In our diode sequence, the gripper fingers extend down in X from gripper body.

It took several iterations of grippers to develop a design that would firmly grasp the slightly tapered diode body without slipping. The final design featured a small relief or notch feature to accommodate a small lip on the bottom of the diode body.

Gripper with relief feature for diode lip

Finally, having a capable 3D printer like the Flashforge Creator Pro is invaluable for on-the-fly iterations for functionality and changes in setup orientation of your grippers. I’m currently using 1.75mm ABS Transparent filament, it’s a great material for general purpose applications.

Watch a timelapse of a gripper print here.

There are other factors to take into consideration depending on the situation, but those are the basics I start with when making new gripper designs.

Mecademic Diode Load

Precision diode load

With 5um repeatability, the Mecademic 500 is uniquely suited for applications requiring a high degree of precision. Prestaging of components is key, however, when using purely motion with no vision or dynamic location. The CanaKit Raspberry Pi breadboard provides a good stage for this work, which could be adapted for backloading & soldering manufacturing applications. Watch the video here.

Battered Diode

Word of warning- have a few “burner” parts for use during setup. Once the diode legs get bent they are difficult to straighten!

It’s difficult to see, but the robot performs a “shimmy” action as it places the 2 diodes. This utilized the Mecademic’s ability to jog in very fine increments when building the program- in this case, 0.05mm and finer. This motion was to offset the variance in prestage presentation of the diodes, and the spring memory in the fragile diode legs. The program is included below.

Meca 500 placing diode