The traverse reaches the wrong point, reverses inconsistently, or drifts away from the spool edge because an encoder count has been treated as a complete position-control system. Start by identifying what the encoder measures and what command the traverse drive accepts. A reliable retrofit needs traverse-position feedback, a repeatable home reference, calibrated distance scaling, endpoint logic, and a defined response to lost feedback.
Reject the usual quick fixes
Do not start by entering a 12-inch target and reversing whenever the displayed count reaches that number. The controller receives encoder pulses, not inches. The required count depends on encoder resolution, mechanical ratio, and how the input mode evaluates the encoder channels.
| Quick fix | Why it fails | Required correction |
|---|---|---|
| Reset the position from the touchscreen | The screen command does not prove that the mechanism is at a known physical point. | Use a physical home switch and reset position only when the traverse is at home. |
| Use the spool encoder as traverse position | Spool rotation indicates material movement, not the carriage location, unless the mechanical relationship is fixed and slip-free. | Use feedback from the traverse for position, or treat spool feedback as a speed or gearing reference. |
| Reverse at a raw count of 12 | Twelve counts and 12 inches are unrelated until the axis is calibrated. | Measure counts per inch and calculate the endpoint count. |
| Change motor speed until the winding looks right | Open-loop adjustment cannot correct missed motion, backlash, or a changing spool diameter. | Calculate the traverse rate from winding pitch, then verify actual motion. |
Check before moving on: identify whether the displayed value changes with traverse travel, spool rotation, or both. Stop here if that relationship is unclear.
Identify the feedback and drive interface
Determine where the incremental encoder is mounted. An encoder on the traverse can measure carriage displacement. An encoder on the spool can provide a master reference for electronic gearing, but it cannot independently prove that the traverse reached an edge.
Next, identify how the traverse motor is driven. A stepper or servo accepting pulse commands requires a different control architecture from a variable-speed motor receiving an analog command. With pulse control, commanded pulses define requested motion while the traverse encoder can verify actual displacement. With analog speed control, the PLC must manage direction and speed while position feedback supplies the stopping and reversal decision.
AXGEAR may be relevant when the traverse must follow a master encoder by a defined ratio. Do not select it merely because an encoder exists. First establish which axis is the master, which is the follower, and whether the drive interface can execute the resulting command.
The winding relationship is:
Required traverse distance per spool revolution = cable outside diameter + pitch adjustment
The adjustment sets clearance or packing. The actual value belongs in a controlled operator setting with practical limits based on the machine.
Check before moving on: manually move the traverse and rotate the spool separately. Confirm which action changes the count connected to X0 and X1, and document the traverse drive command type.
Prove the encoder and home signals
Configure X0 and X1 for the incremental encoder input mode required by the wiring. If the encoder supplies two phase-shifted channels, the configured mode must derive direction from their phase order. A normal discrete-input program that counts individual state changes can lose pulses or interpret direction incorrectly at operating speed.
- Disable automatic traverse motion.
- Observe both input states while turning the encoder slowly.
- Confirm that both channels switch and that neither remains permanently on or off.
- Move the traverse a short distance toward the far edge. Confirm that position changes steadily in the chosen positive direction.
- Move back toward home. Confirm that the same position decreases.
- Reverse the channel assignment or correct the configured direction convention if the sign is wrong; do not hide incorrect direction with scattered arithmetic inversions.
Fit a physical switch at the home end of the traverse. Approach it from a consistent direction, stop the axis, and assign the home position only after the switch is detected. The switch establishes the physical datum; the encoder maintains relative position after that datum is known.
Do not repeatedly reset the count while the switch remains active. Use a homing sequence that recognizes the intended switch transition and completes once. Check before moving on: move away from home, return through the homing sequence, and verify that the same mechanical location produces the same zero reference.
Scale the 12-inch stroke
Calibrate the actual mechanism instead of building the scale from assumed encoder data. Backlash, gearing, coupling arrangement, and the selected encoder evaluation mode all affect the count-to-distance relationship.
- Home the traverse and record zero.
- Move the carriage a measured distance without reaching the far mechanical limit.
- Record the absolute encoder-count change.
- Calculate
counts per inch = count change / measured travel in inches. - Calculate
12-inch endpoint count = 12 × counts per inch. - Repeat the measurement in both directions and compare the results.
A direction-dependent difference points to backlash, compliance, or a loose coupling. A count that changes while the carriage does not move points to feedback mounted upstream of mechanical lost motion. Correct the mechanical problem or account for it deliberately in the endpoint setup; a display offset does not remove it.
Keep the commanded endpoint inside the usable mechanical stroke. The 12-inch spool width may not equal 12 inches of safe carriage travel once guide geometry and edge clearance are included. Check before moving on: home the machine, command a slow approach to the calculated far endpoint, and physically measure the travel.
Command travel and controlled reversal
Build the operating sequence around explicit states: home, travel outward, reverse, travel homeward, and fault. In outward travel, command the selected speed until the calibrated far endpoint is reached. Then decelerate or stop as required by the drive, change direction, and travel toward zero or until the home switch is sensed.
Use the encoder position for normal endpoint control and the home switch for reference recovery. If the home switch activates during the expected return approach, stop and re-establish zero according to the homing sequence. If it activates while moving outward, treat that as an invalid state rather than silently resetting position.
For wire laying, set traverse speed from spool speed and desired pitch. The governing relationship is:
Traverse speed = spool revolutions per unit time × traverse distance per spool revolution
A fixed traverse speed works only while spool speed remains fixed. If spool speed varies, ratio control based on the spool encoder can maintain pitch. Position limits still belong to the traverse axis; gearing does not replace homing or endpoint checks.
Check before moving on: run one slow outward-and-return cycle with no wire. Confirm the commanded direction, count direction, far reversal, home approach, and zero reset.
Verify the complete winding cycle
- Power-cycle the controller and verify that automatic operation remains inhibited until homing establishes position.
- Home the traverse, then measure the zero location against a fixed mechanical reference.
- Run several empty cycles at reduced speed. Record the far reversal point and home return point.
- Run at operating speed and check for endpoint overrun caused by motor deceleration or scan-to-output delay.
- Turn the spool slowly and verify that the traverse advances by the intended cable outside diameter plus adjustment for each spool revolution.
- Stop motion during a traverse and restart through the defined recovery sequence. Do not resume from an untrusted position.
- Disconnect or otherwise simulate loss of encoder feedback only under a controlled maintenance test. Confirm that commanded motion without position change produces a stop or fault response.
If the endpoint shifts only at higher speed, examine input capture, drive stopping behavior, mechanical inertia, and coupling slip. If the pitch changes while endpoint position remains repeatable, examine the spool-to-traverse speed ratio rather than the homing logic. Check complete: production is ready only when repeated cycles return to the same home datum, reverse within the usable spool width, and maintain the required pitch through speed changes.
FAQ
Why does the BRX traverse lose its zero position?
An incremental encoder retains only relative movement; it does not establish the carriage's physical datum after startup or an untracked move. Home against a physical switch and reset the position at that repeatable location.
Why does the traverse reverse before or after 12 inches?
The raw count has not been scaled correctly, or stopping distance and mechanical backlash shift the physical reversal point. Measure counts over a known travel, calculate counts per inch, and verify the endpoint at both reduced and operating speed.
Why does the wire pitch change when spool speed changes?
A fixed traverse-speed command cannot maintain pitch when spool speed varies. Use the spool encoder as the master speed or gearing reference, while retaining traverse feedback and home sensing for position limits.
Stop here and contact official AutomationDirect support if X0 and X1 do not produce stable directional counts after their electrical signals and configuration have been checked, or if the drive interface cannot be identified. Escalate before automatic operation when the controller cannot detect lost feedback, establish a repeatable home, or stop inside the usable mechanical travel.