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
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.
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.
Ned has a new friend! The HiWonder Xarm is a fun little educational robot which you can buy assembled or in a kit. We thought it would be fun to see if the Xarm is repeatable enough to perform in a video alongside our Niryo Ned. It did very well for the price; at one stage, I needed to reteach some points that “wandered” for some reason but other than that it’s a great little robot. Note, the Xarm is really more of a 5-axis than 6-axis robot; the 6th axis is the gripper jaws, which does limit some of the positioning but Ned was able to work around this.
For props, I designed a simple heart shape with a grip and printed it on our FlashForge Creator Pro. Resized for the smaller heart, repeat. Slicing done on Simplify3d.
In any setup where pre-stage is the locating method, it’s important to know where your robots & parts are. I used a couple of plastic grids which are inexpensive and reusable; they’re sold as quilting accessories.
We repeated the exchanging-of-valentines action over two dozen times; occasionally it didn’t work out (there was some variability where Ned put down the small heart, and occasionally the pencil stuck in his gripper jaws), but overall I was really happy with the sequence. The video featured on RoboFiesta’s Youtube channel was shot on a Samsung Galaxy S21 Ultra 5G, which has awesome media production capabilities. Edited on Adobe’s Premier Pro.
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.
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.
Ok, this one may not be completely intuitive, but there is a difference between precision and accuracy in the world of robotic motion and robotic-aided assembly and manufacturing. A common way to think of the difference between the two is the dart board analogy. As shown below, accuracy can be thought of hitting the exact mark you intended to hit- the very center of the dart board. Precision can be thought of as hitting the same spot every time- repeatability, but not necessarily in the exact spot you intended.
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Sure, there are dozens of contenders in the industrial desktop robotics category, but for professional-grade speed and precision, the Mecademic Meca500 is the hands-down winner. At just over 10lbs with nearly 13″ of reach, it’s diminutive size allows for easy transport and set-up in situations where space is restricted. The quality of construction is apparent right out of the box; it’s a serious, well-constructed machine with an on-board software interface which allows for rapid set-up and use.