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Frequently Asked Questions

Troubleshooting Compu-Dobby® III

With all its benefits, the Compu-Dobby III comes with a new learning curve and thus a different set of troubleshooting techniques.

Compu-Dobby III Installation/Troubleshooting/Adjustment Guide

The Compu-Dobby III has been factory adjusted and tested to operate with the matching Dobby Head. Both assemblies work as a set, and no necessary mechanical or electrical adjustments (aside from rotating the connection between the Berkely Snaps and the Harness Cables as discussed below) should be required.

In the event of any Compu-Dobby III servicing (repair or upgrade) some sections may necessitate dis-assembly or replacement, in which case, minor mechanical adjustments may be needed. This troubleshooting guide will attempt to cover all potential mis-alignment problems and descriptions on how to correct discrepancies.

The following excerpts from our loom manual will guide the operator on the installation, troubleshooting and adjustment procedures relative to potential setup problems with AVL’s Compu-Dobby® III.


Compu-Dobby III Installation

Once the loom is completely assembled, the last step will be attachment of the Dobby Head/Compu-Dobby III to the side of the loom (on WDL type looms, the Dobby is factory pre-installed). In order to install the Dobby, please perform the following steps:

a)   Visually inspect the Dobby Assembly for potential shipping damage in the form of bent Dobby Rods and/or kinked Dobby Cables – Report any discrepancies to AVL.

b)   If the loom is a WDL type, then proceed to step (f) below.

c)   Taking precautions not to place any weight on the Dobby Rods (protruding through the bottom of the Dobby Assembly), place the Dobby Head on its face on a flat surface, and temporarily release the mounting Hex Nuts, Lockwashers, and Flat Washers from the mounting Carrige Bolts on the back of the Dobby Head.

d)   Ascertain that the Dobby Cables hang from the front of the Dobby Head so as not to be trapped during installation of the Dobby Head.

e)   Complete Dobby Head attachment to the loom by aligning the mounting bolts with the holes on the Side Frame, and securing with the Flat Washers, Lockwashers, and Hex Nuts (3 places) on the mounting bolts.

f)     Attach the Treadle (or E-Lift) Cables to the Slide Plate – Right Treadle Cable attaches to the Eye Screw on the bottom of the Slide Plate, and the Left Treadle Cable is guided around the Pulley located at the top, right side of the Dobby, and downwards to the Eye Screw on the rear of the Slide Plate.

g)   Cut and remove the factory installed strap that holds the Slide Plate from movement during shipping transit.

h)   Connect all Dobby Cables by routing over the Harness Pulleys and attaching to the Berkley Snaps of the Harness Cables.

i)     Hang the Harnesses at this point.

j)     Perform a few Treadle cycles to “seat and settle” the Harness Cables (all Harnesses should lift). If any Harness fails to lift, release the Dobby Cable from the Harness Cable (detach from the Berkely Snap) rotate the Dobby Cable 90 degrees and re-attach to the Snap. Repeat the process for any and all failed Harnesses until all Harnesses lift consistently.

k)   Unpack the Compu-Dobby III Assembly and inspect for lose Magnet Bracket (located on right side of the Slide Plate). The Magnet can be discerned by a dark rectangular Magnet (approximately ¾” x 1” in size) having a small, flat head philips screw at the center - The thickness of the magnet (about 3/16”) should extend beyhond the slide plate, and the magnet should be parallel to the face of the Slide Plate.

l)     Manually rotate all Solenoid Tips (round plastic components having a concave curvature at the front end) such that the curvature is oriented vertically.

m) Take the Compu-Dobby III along with the four mounting Thumb Screws to the loom, register the top of the Compu-Dobby against the Harness Pulley Support cross members, and slide forward towards the Dobby Head. While supporting the weight of the Compu-Dobby III box, insert the mounting Thumb Screws through the side of the Housing and into the wood Dobby Head.

n)   While supporting the Compu-Dobby III box, temporarily slide out both top Thumb Screws and peering down from the top, confirm that the Dobby Rods are centered on the Solenoid Tips (Rods should be aligned with the center of concave area).

o)   Connect the Compu-Dobby III to both power and computer, and execute a few cycles of a simple pattern comparing to the proper action of the shafts. If any shaft(s) is intermittent in its operation, detach the Dobby Cable from the Berkely Snap, rotate 90 degrees, and re-attach to the Snap. Repeat process until shaft action is correct.

Abbreviated Compu-Dobby III Theory of Operation

In order to better understand the Compu-Dobby III, it is necessary to explain certain key characteristics of the design and operation. First, the Compu-Dobby III is referred to as a 'Negative Dobby'. What 'Negative Dobby' means is simply, that all solenoids are, normally active (extended position - to maintain the shed closed), and each solenoid de-activates to cause that specific Shaft to raise.

The Compu-Dobby III has a 'Power-On Test Sequence' which causes all solenoids to temporarily activate when power is first applied. The test sequence causes one solenoid to activate in each set of 8 shafts, thus, a 24-shaft Compu-Dobby III will first simultaneously activate Shafts 1, 9, and 17 followed by activation of Shafts 2, 10, 18 etc, until the last cycle comprising of Shafts 8, 16, and 24. Therefore, regardless of the number of total Shafts of the system, a set of 8 'clicks' should be audible each time the unit is powered on.

Following the completion of the test sequence, the Compu-Dobby III is ready to accept data from the computer (provided that both proper 'COM PORT' and 'COMPU-DOBBY TYPE' are selected).

The Shaft configuration is set so that Shaft 1 resides closest to the front of the loom with subsequently numbered Shafts progressing towards the rear of the loom.

The mechanical operation of each solenoid (Shaft Control) requires that the solenoid be de-activated (retracted position) in order to allow the Dobby Rod(s) to idle through the center of the Slide Plate Insert (Slotted Bar atop the Slide Plate) for that particular Shaft to be raised.
When the Right Treadle is depressed, it causes the Slide Plate to travel downwards and 'catch' the nico on all de-activated Shafts, thus causing the Harnesses to raise.

If the design being executed dictates that any particular Shafts are to remain in the down position, those equivalent solenoids are activated (extended position), which, in turn push-out, or deflect the specific Dobby Rod away from the slot, so when the Slide Plate is pulled downwards will cause the nico to not be caught to keep the shaft from rising.

One important characteristic to keep in mind is that if, for any reason a Dobby Rod is bent, operation of that particular shaft will be erratic.

As mentioned, the Treadle actions cause the Slide Plate to move down (right Treadle) and up (left Treadle). Movement of of the Slide Plate places the attached Magnet to be sensed to indicate the weaving cycle. Each cycle consists of the Magnet being detected at the fully down position and returned to the fully up position at which time the Compu-Dobby indicates to the computer to send new solenoid information consisting of the pattern for the subsequent pick.

If the Dobby Rods do not align with Solenoid Tips

This possibility is common especially when the Compu-Dobby has been serviced. To align, use a philips screwdriver to losen (do not remove) the two largest screws located on the back of the Compu-Dobby III. While supporting the weight of the Compu-Dobby III box, slide out both top Thumb mounting screws, and using the tip of the screwdriver engaged on the screw head, force the Solenoid assembly sideways until alignment is achieved. The Dobby Rods must idle with the center of the concave curvature of the Solenoid Tips! Be sure to tighten both screws once the alignment has been performed.

If the shafts raise or do not raise in error

a) Detach the Berkely Snap from the Haness Cable, rotate the Dobby Cable 90 degrees, re-attach to the snap and test. Repeat at 90 degree increments (in same rotation direction) for 180, and 270 degree positions.

b) Remove the Compu-Dobby III from the loom. On the Compu-Dobby III side, verify that the Solenoid Plunger (Solenoid Shaft holding the curved Solenoid Tip) is not bent or stuck. Gently pull on the Solenoid Tip ‘feeling’ for rough or grinding areas throughout the pull travel. Release the Tip, and confirm that it retracts fully. Repeat the process by rotating the Tip and releasing after rotating to 90, 180 and 270 degree rotations.

c) On the loom side (Dobby Head), verify that the Dobby Rod for the Shaft(s) in intermittent or error operation travels relatively straight downwards, and that the Rod resides approximately half-way into the slot of the Slide Plate Insert.

d) Ascertain that the tension necessary to deflect the cable is not excessive due to curvature of the rod towards the (eventual) solemoid direction - Compare to adjacent Rods as too much tension will cause the solenoid to only activate partially.

e) Bend the Rod slightly by gripping the nico with a needle-nosed pliers, and with a finger, deflect the Rod towards the corrective position at either side of the nico. Test by manually pressing on the Slide Plate downwards to engage the adjusted Rod ( may need to release other Rods from engaging the slots by pressing those Rods slightly towards the loom to minimize the required downwards force).

If the pick does not advance

a) Ascertain that computer communication is establish by confirming operation of both proper ‘Communications Port’ and ‘Compu-Dobby Type 3’.

b) Peering from the bottom of the Compu-Dobby III box, verify that the Magnet is parallel to the Slide Plate plane, and that it travels at a distance no greater than 1/8” from the ‘U-Channel’ bracket containing the Magnet Sensors (located on the inside, right side of the Compu-Dobby III box).

c) As a last resort, remove the Compu-Dobby III from the loom, place on a work surface, and acquire a magnet. Apply power, and connect to the computer. Set the weaving software in ‘Weave Mode’ and slide the magnet up and down the Sensor Bracket (polarity of the magnet is critical, so it may be necessary to offer the opposite magnet side to the sensors) on the inside left wall of the Compu-Dobby III box. Repeat as necessary, and verify that the two small green lights (LED’s) on the Printed Circuit Board illuminate alternately. This confirms proper operation and sensing of the Treadle cycling.