Introduction

ActiNav autonomously does all of the robot motion planning for transporting parts from a bin to their destination.  Since parts may be anywhere in the bin, in any orientation, each path is different.  Typical cable and hose management schemes, which rely on a predictable, contained path, are often insufficient for the wide variety of possible ActiNav movements.  Hoses may become tangled, or may catch on elements in the environment.

This article describes one way of managing hoses using spiral (also known as “coiled”) pneumatic tubing.

Prerequisites

• Spiral tubing. The length of tubing depends on your implementation.

• For bridging the last 2 or 3 wrist joints and the tightest connection to the robot, we recommend two spiral tubes with a 1.5 inch (38 mm) outer spiral diameter, such as the Nitra 1PUxxxC10 (or you can cut a 1PUxxxc20 in half). https://www.automationdirect.com/adc/shopping/catalog/pneumatic_components/flexible_pneumatic_tubing_-a-_hoses/coiled_polyurethane_(pur)_tubing/single_tube
• For longer lengths and wider coils: https://www.festo.com/us/en/p/spiral-plastic-tubing-id_PK_PUN_S

• Straight tubing of the same diameter, such as https://www.mcmaster.com/50315K24 or https://www.festo.com/us/en/p/plastic-tubing-id_PUN/. Length depends on your implementation.

• Deformable PTFE tape. 0045” (0.11 mm) thick is easiest to handle and will last at least a year.  0.0115” (0.3 mm) thick will last indefinitely but needs more careful application. https://www.mcmaster.com/76025A712 or https://www.mcmaster.com/76025A732

• Hose clamps. We recommend stainless steel clamps that are made for soft hose.  These are smooth and have upturned edges, and are less likely to mar the robot finish.

  • For the lower UR5 tube and joints: McMaster-Carr https://www.mcmaster.com/5076K53

  • For the upper UR5 tube: McMaster-Carr https://www.mcmaster.com/5076k54

  • For the lower UR10 tube and joints: McMaster-Carr https://www.mcmaster.com/5076K54 and https://www.mcmaster.com/5076K53 

  • For the upper UR10 tube: McMaster-Carr https://www.mcmaster.com/5076K57

• Pass-through quick-connect connectors for your size tubing, such as https://www.mcmaster.com/5225K62 or https://www.festo.com/us/en/a/558761/

• (Optional) PVC tape, hook-and-loop straps, or rigid plastic tubing, for example https://www.mcmaster.com/53945K14.

• (Optional, depending on your end effector) 90° (elbow) pneumatic fitting. Make sure it can swivel freely!  The Festo QSM series works well, or the Parker-Hannifin W369PLP series.

Determine your configuration

Overall

For ActiNav bin picking, the three wrist joints tend to have the greatest range of movements, and thus need the most flexibility in hose management.  It is generally sufficient to use the spiral tubing just to bridge these last three joints.  A 3 ft (1 m) working length tube, like the Nitra 1PUxxxc20, is about right for this.

It is also possible to use spiral tubing for the entire length of the robot arm, if you anchor it in several places (see below).

Wrist joints

While it is possible to bridge all three wrist joints with one spiral tube, this tends to sag and may interfere with the bin, target, or environment.  It’s better to bridge wrist 2 and 3 with one spiral, and wrist 1 with another section.

The final connection at your end effector should be a 90° swivel.  This will prevent the spiral tube from pinching and preventing air flow.

Install the Wrist Tubing

Protect the rubber flat-rings

The tubing may rub against the rubber flat-rings that seal the robot joints, damaging the rubber.

Protect the flat-rings with a layer of PTFE tape.  Note in the picture which side of the joint to place the tape on, so that the joint isn’t bridged by the tape.  If thicker tape is used, trim the tape ends so they butt together and do not overlap.  The thinner tape is more tolerant of overlap. Do not use PVC tape.  PVC deforms when the joint heats up and may damage it.

Determine where to route the spiral tubing

Determine what the most likely robot pose is for picking and placing, and route the tubing so it is least likely to interfere with the bin, placement target, or environment. This is generally best achieved by routing the tube over the top of the robot when it is positioned over the bin.  You may want to run your ActiNav bin picking program first, to observe typical movements. 

For difficult picks, especially when free spin around the tool Z axis is enabled, the robot may assume a wide variety of poses.  Be sure that, whatever routing you choose, there is enough room for any wrist joint to rotate at least ±180°.

Use of spiral tubing is no guarantee that the tubing will not interfere with the bin, environment, or placement.  The amount of slack required for full joint rotations may protrude or sag.

Fasten two pass-through connectors

Using a hose clamp, fasten a pass-through connector to the robot arm near the wrist, and another one on the wrist joint 2 casting, at the tube anchor points you determined above.  You may optionally use PVC tape to protect the robot from scratches.

Hose clamps may have sharp edges.  Account for this in your risk assessment!  Also, locate the worm drive screws so they are unlikely to contact the tube.  Occasional contact is generally OK.

Connect the tubing

The pass-throughs form a solid anchor point that doesn’t pinch the tube or move along the arm, and makes it easy to replace the tube later.  This method can be used at other points along the arm also.

For the wrists, use two short pieces of spiral tubing, or cut a longer tube in to two pieces. Trim the spiral tube to keep the tube close to the robot arm, but still allow ±180° joint rotation.   Don’t be shy about making the tubing short: it’s quite tough and withstands extensive pulling.  For the Nitra 1PUxxxC20, use about 5 loops for joint-to-arm connection.  For the joint-to-end effector connection, use about 12 loops for the UR5, 15 for the UR10.  Trim the straight ends so they are quite short.

On wrist joint 2 or elsewhere on the robot, you can also anchor a short piece of rigid tube or pipe for a longer spiral tube to pass through.  This is more secure than a hook-and-loop fastener. Spiral tubing tends to not move and abrade against the tube edges.

Test the vacuum

Inserting a coiled section in to a push-to-connect fitting must be done with care to fully seat the tube.  Check for a good vacuum after all connections are made.

Note on Tube Volume and Cycle Time

Spiral tubes are longer than straight tubes, but this has a negligible effect on pressurization or evacuation time. For example, a 1 meter coil across the wrist joints adds less than 10cc of volume.  For even a weak vacuum generator, this additional volume can be evacuated in less than a tenth of a second.

Wear and Replacement

The spiral tube may stretch or abrade over time.  Keep this in mind when routing the tube, and replace it if it gets too long or too worn.  Typical lifetime for abrasion against the robot castings is over a year, but rubbing over sharp edges of the hose clamps may reduce this to three months.