User manual

Barrett Technology, Inc.

BA4-310 System User Manual Version 1.1

-stage cabling in the first three motor axes is similar. The cable attached to the inner motor

pinion connects to the outside termination of the appropriate pulley. The cable attached to the

outer motor pinion connects to the inside pulley termination.

The two 1

-stage cables of the fourth motor axis span a large (~510 mm) distance down the

inside of the inner arm link. Slightly different from the first three drives, the 1

-stage cable on

the fourth motor drive is wound with a right-handed pitch to a termination slot machined into

the side of the pulley.

5.1.2 Second-Stage Cable Path Description

Cable circuits in the 2

-stage consist of cables connecting the two grooved pinions of the

pulley/pinions to the output pulley for that drive. The tension stresses in the 2

-stage are about

three times higher than in the 1

-stage. Therefore, slightly larger-diameter cables are used (in

parallel pairs to double their capacity).

Each parallel pair is actually a single cable that is folded in half so that both termination lugs

are at one end and a U-shaped loop is at the other end. The advantage of using this

configuration, rather than two separate cables, is that, as the parallel pair is pre-tensioned, the

stresses in the two halves of the pair automatically propagate around the loop to share the load

equally. In all four 2

-stages the brass lugs of a cable are attached to two termination slots at

one end of a grooved (pulley/pinion) pinion (1/2 turn apart). The groove is actually a double-

pitch groove to accommodate the parallel pair of cables. U-slots or islands have been machined

into the 2

-stage pulley(s) in order to secure the U-shaped loop.

5.2 Helpful Tools & Tips

Re-cabling can be a difficult task for someone inexperienced with BarrettArm re-cabling. It

requires good mechanical dexterity. If you are re-cabling one of the BarrettArm's cabled drives

for the first time, thoroughly read the sections of this manual on BarrettArm cabling and pre-

tensioning, make sure that you have the proper tools and cable parts, and observe good safety

procedures. The cabling instructions have numbered checkboxes next to each step. These

pages may only be photocopied for use as a re-cabling checklist.

Allow roughly 1-4 hours per motor axis when re-cabling for the first time. Subsequent re-

cablings are generally much shorter (approximately 25 minutes per motor axis). Often not all

of the cables need to be replaced at once, thereby further reducing future re-cabling times.

One important point to keep in mind is that each cable of a given drive must be held in place at

all times until the entire circuit is pre-tensioned. The wrapped cables act like light torsional

springs which, when released even momentarily, may quickly unravel your work back to your

starting point. Pre-tensioning, which prevents this unraveling, cannot be done until all cables in

that circuit have been installed. Regular 1/2-inch masking tape is a tremendous aid in

temporarily preventing this unraveling. As a cable is wound or threaded onto each pulley or