Auto Tool-Changer Post-processing and Assembly

The Auto Tool-Changer (ATC) is an end-effector platform (EEP) that’s used to grasp, use, and release tools available to it in the workstation.

ATC_assembly_complete-w-2-cables1Auto Tool-Changer (ATC)

It has three tool-docking stations—or ports—that are activated programatically.

The mechanical portion of the ATC consists of a floor and crown (bottom and top piece), each with three tunnels for connection to the Z-axis of the Visible Robot, three solenoids for grasp/release activation, three 3-pronged camming parts, nine cammed “teeth,”—three at each port for gripping the tool, and three faces used to couple the tool with the Visible Robot.

atc-all_parts2ATC component parts

The faces—called the “robot_side_coupler” in the parts documentation, should be printed at a slow speed with substantial fill in your printer’s slicer setting. This, because the parts are quite thin and have relatively fine features. The ATC’s “floor” and “crown” parts of the tub can be printed at a more normal speed and with less fill.

ATC_Design_html_46376ffBack-to-back coupler faces

ATC_Design_html_m529c388b

ATC Crown

ATC_Design_html_m302f3cad

ATC Floor

Post-processing

Carefully use a sharpened knife to remove the plastic skirt and brim from the parts. The parts fit tightly together, so it’s important to remove all the plastic that doesn’t belong to the parts.

 

rstc_post-processing_removing-brimRemoving excess plastic with a sharp knife.

Use a progressive drilling technique with the floor and crown to drill out the holes use to mount the various parts. Start will smaller size drill bits than the final hole diameter and work up to the diameter needed.

The holes on the floor that will be used to mount the leadscrew capture part (the 4 holes forming a square around the center hole with the shorter columns) are drilled out to 7/64” (or 2.5mm if you don’t have inch drill bits). These holes are used as locknuts. The holes for the screws fastening the solenoids should allow the screws (M3 x 20) to pass through easily. Drill these out to 1/8” (or 3.5mm).

The three large holes used to retain the Z-axis shafts are drilled out to 8mm. (Because of the torque—twisting force—the drill bit makes when it takes a “big bite” of the plastic, these holes benefit from having both inch and metric drill bits on hand. The .5mm jump between the 7.5mm and 8mm drill sizes doesn’t seem like much, but the torque from that small “bite” is enough to wrench the part out of your vise (or hand). I found that progressive drilling with the 19/64” and 5/16” bits reduced the torque effect a lot.Drilling at a controlled slow speed helps too.

The holes to be used for the M3 setscrews in the crown should be drilled to 2.5mm. This, to provide a secure locking fit for the setscrews.

Finally, the six holes in each of the floor and crown that will hold the robot-side coupling parts are drilled to 5.5mm (or 7/32”). (The former is preferred as it will hold the coupler tighter).

 

Assembly
Fit the coupler faces
A trick I’ve used to prevent the two coupler pieces from sliding apart, preventing them from seating in the holes is to temporarily screw them together with M3 (3mm x 12) screws and nuts. Once the coupler faces are fit, the screws can be removed.

 

rstc_post-processing_fastening-for-assyTemporary fastening with bolts and nuts for easier assembly

Because different printers and settings will give slightly different results in terms of as-built part dimensions, Try, after each progressive drilling, to fit the parts. You may find that small bits of plastic from the first or last layers printed, or some un-removed chaff from drilling are preventing the fit. A small effort to remove the offending plastic will generally give a nice fit.

    rstc_assembly_3couplers2floorCoupler faces fit to ATC floor

Be sure to orient the coupler faces properly. The “shelf” used to hold the USB Type-C plug goes on the right. This is the shelf with the more rounded corners. The squarish shelf goes to the left. It will be used to hold a USB Type-A Micro plug.

Drill out the center hole of the 3-post camming part to the diameter of your solenoid. If you used the solenoid I did (part no. ZYE1-0826), the diameter is 7.5mm. Put an M3 x 12 through the hole in the plunger and slip the plunger with the screw through the center hole of the camming part.

tcsa_assembly_w-plungerSolenoid plunger mounted to 3-posted camming part

Insert the plunger into the solenoid and mount the solenoid using two M3 x 20 screws. Do the same with the other solenoids.

atc_assembly_all-solenoids-mounted

 

Lightly press the crown onto the posts of the coupler faces, leaving room to fit the USB cables.

atc_assembly_atc-assembled-earlyCrown lightly fit to assembly

Pull one of the solenoid plungers back slightly so that you can fit a cammed tooth into each of their recesses. The cam of the 3-post camming part should fit into a recess on the top of the cammed teeth, with the “tooth” feature to the outside and pointing inward to the center hole. Do the same for each of the other two tool-coupling ports.

atc_assembly_fitting-cammed-teethFitting the cammed teeth into the coupler face

atc_assembly_complete-wo-usb-cablesCammed teeth fit into all coupler ports

Again, being careful as to the orientation of the cables—USB Type-C on the right and the USB Type-A Micro on the left and turned such that the wider part of the USB Micro plug is toward the crown—mount the cables and press the crown fully into its seated position.

NOTE: The orientation of the USB Micro cable is important because the tools that interface with it are all going to expect that orientation. The USB-C doesn’t matter as the interface is the same, up or down.

ATC_assembly_front_closeup2  USB-Micro (L) and USB Type-C (R)

The coupler faces are all now captured, so the holes for fastening the floor and crown can now be drilled. Being careful that plastic bits from the drilling won’t land in places you won’t like, use a 7/64” drill to bore out the holes for the floor-to-coupler face and crown-to-coupler face screws.

atc_post-processing_drilling-out-floor-to-crown-connecting-tunnelsDrilling out the coupler tunnels

Using flat washers with M3 screw fasten the crown and floors onto the couplers both top and bottom. I used twelve M3x25 screws, An alternative is to use six M3x65 or M3x70 screws with nylon locknuts.
NOTE: M3 screws can be easily cut to size with a boltcutter—often found on wire-strippers.

ATC_assembly_complete-w-2-cables1

ATC_Complete_side-bottom-viewFinished assembly

Finally, use six M3 setscrews to set the positions of the USB plugs.
Mechanically, the assembly is done,

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