A Productivity HSO Simple Move can command a target using HSO position tracking, but encoder correction during that same move must be verified in the installed software and module documentation before you design around it. If the mechanism stalls or slips, the commanded position alone does not prove that the load reached its target.
Read the commanded and measured positions first
Do not start by adding pulses, increasing the move distance, or treating a registration input as feedback. Those changes can hide a mechanical or scaling problem while leaving the axis open loop. First compare the HSO position value with an independent measurement from the mechanism, such as an encoder display or a measured travel distance.
- If the HSO count reaches the target while the load falls short, the output command completed but the mechanism did not follow it. Check coupling, load, binding, and whether the motor or drive lost motion.
- If both the HSO count and measured travel are wrong, check the move command, scaling, direction, and output behavior before changing feedback logic.
- If the load reaches the target consistently but a jam or load change must be detected, define a position-deviation limit and a fault response. A move completing normally is not itself proof that the machine remained healthy.
The HSO position tracking described for this application is useful for knowing the commanded position. It does not independently measure the real-world position of the load. That distinction determines whether the next check belongs in the mechanics, the encoder path, or the motion controller.
Compare the symptom with the likely failure
| Observed reading | Likely cause to check | Next check |
|---|---|---|
| Command count reaches target; load stops short | Missed motor motion, slipping coupling, jam, or an unverified feedback path | Measure motor and load position separately; inspect mechanics and drive status |
| Encoder changes in the wrong direction or not at all | Wiring, encoder configuration, signal compatibility, or scaling error | Check encoder counts while moving slowly in each direction and compare with the manual |
| Position is correct at one speed but wrong at another | Pulse or encoder input rate limits, missed transitions, or a drive response limitation | Read the module and encoder specifications; repeat at a lower speed |
| Position is correct without load but deviates under load | Torque limit, mechanical slip, jam, or motor/drive following error | Check the drive's status and feedback diagnostics under the same load |
| Registration occurs, but later travel still deviates | A registration event is being mistaken for continuous position feedback | Test encoder tracking throughout the move independently of the registration event |
Use the trend between command, encoder, and load readings to choose the next branch. A correction to move distance is appropriate only after confirming the scale and mechanics; it is not a substitute for detecting lost motion.
Check that the HSO can read the selected encoder
The proposed arrangement uses the HSO general-purpose inputs for quadrature encoders and selects one encoder as feedback for a move channel. Six GP inputs may appear sufficient for two quadrature encoders, but input count alone does not establish encoder decoding support, usable input frequency, channel assignment, or feedback association with a particular output channel.
- Read the installed HSO module manual and software help for supported input modes. Confirm that the specific GP inputs can decode the encoder type used by the machine.
- Check the encoder's electrical interface, supply, signal levels, and maximum output rate against the module specifications. Do not wire an encoder based only on the number of available terminals.
- With motion inhibited or at a controlled low speed, observe the encoder count while moving forward and reverse. Confirm direction, repeatability, and counts per unit of travel.
- Confirm that the software exposes the encoder value to the intended motion channel and explains how the value is scaled and used during a move.
If the manual or installed software does not show an encoder feedback mode for the HSO, stop that branch. Do not assume that naming GP inputs as encoder tags creates a hardware decoder or a closed-loop motion function. Use a supported feedback-capable drive or motion controller, or obtain confirmation from the product manufacturer.
Keep registration separate from continuous feedback
A registration input marks a reference event, such as a sensor transition during travel. Continuous feedback compares measured position with commanded position throughout motion. These functions can use related hardware, but they answer different questions: registration identifies where a mark occurred; feedback detects whether the axis continues to follow its target.
Placing an encoder option near the registration settings may make the configuration easier to find, but the menu location does not define the control behavior. Before using any such option, identify whether the controller reads feedback continuously, corrects the move, stops on deviation, or only captures a position at an event. Read the feature description and test the behavior at a low-risk operating point.
For jam detection, decide whether the machine needs an alarm, a controlled stop, or a move correction. Correction can be unsafe or unstable if the load is blocked; continuing to add pulses against a jam can increase mechanical stress. A deviation fault with a defined stop response is often the more direct diagnostic when the requirement is to detect lost motion.
Choose where the position loop closes
A closed-loop system needs a feedback sensor, a controller that reads it at a suitable rate, a position scale, a comparison between target and measured position, and a defined response to error. Merely selecting an encoder does not supply those functions.
- Drive-based loop: A closed-loop stepper or servo drive uses its supported feedback and control functions. Check its position-error or alarm reporting and decide how the PLC will react to those signals.
- Controller-based loop: Use this only when the motion hardware and software support coordinated encoder acquisition and position control for the selected axis. Confirm update behavior, error limits, correction limits, and fault handling in the product documentation.
- Open-loop pulse move: Keep the Simple Move approach only where the application tolerates possible lost motion and a separate method detects unacceptable deviation.
A PLC that sends additional or fewer pulses during a move needs more than a signed position difference. The design must define when feedback is sampled, how much correction can be applied, what happens at the move's acceleration and deceleration transitions, and when error becomes a fault. If these behaviors are not provided by the supported motion function, do not improvise them by issuing competing pulse commands to the same axis.
Restore production with a controlled procedure
For a temporary restore, return the axis to its last known supported configuration. If the machine was designed to run open loop, use that configuration only after checking the mechanical condition and confirming that the process can tolerate undetected position loss. Keep the machine's established interlocks and stop functions active. Do not mask a jam or deviation alarm by widening an error band without a documented acceptance limit.
For a permanent feedback repair or redesign, work through this sequence:
- Record the move target, HSO commanded position, independent encoder position, travel direction, and load condition for a repeatable test.
- Verify mechanical coupling, free travel, motor and drive status, and the encoder's direction and scale before enabling correction.
- Confirm from the manuals that the selected hardware supports the encoder signal rate and the requested feedback function on that motion channel.
- Configure the supported feedback path and its position scaling, deviation limit, and fault response. Use manufacturer-defined settings; read their actual values from the installed software and documentation.
- Test at reduced speed and load. Compare commanded and measured position across repeated moves in both directions, then test the defined deviation response without creating an uncontrolled jam.
- Restore production speed and load only after the axis repeats within the machine's documented tolerance and the fault response stops motion as intended.
Keep the temporary restore distinct from the permanent repair in the maintenance record. Note which feedback path is active and which test demonstrated that it detects or corrects position error.
Verify position and jam response before releasing the axis
At the end of each test move, compare the commanded target with the encoder and an independent load-position check. Repeat in both directions; a single direction can conceal backlash, sign, or coupling problems. Repeat under the load condition that produced the deviation, then confirm that the chosen error limit triggers the intended machine response.
For a drive-based loop, read the drive's feedback and fault diagnostics during the test. For an HSO feedback function, read the configured encoder value and the motion status values identified by the software manual. If the encoder count freezes, changes direction unexpectedly, or diverges from measured travel, stop the test and correct the feedback path before returning the machine to automatic operation.
FAQ
How do I tell whether the HSO position is actual or commanded?
Compare the HSO position value with an independent encoder or measured load travel while the axis moves. A command count that reaches target while the load falls short indicates lost motion or a separate feedback problem.
Can Productivity HSO use its six GP inputs for two encoders?
Six inputs do not by themselves confirm quadrature decoding or channel assignment. Check the installed HSO manual and software help for supported encoder input modes, input rates, and association with the move channel.
How do I use registration for closed-loop positioning?
Treat registration as a reference event and continuous feedback as ongoing position comparison. Verify that the installed motion function explicitly reads encoder position during the move and defines correction or fault behavior.
How do I detect a jam when a move still completes?
Compare command and measured position during travel, then configure a supported deviation limit and stop or alarm response. Test that response under a controlled condition before relying on it in production.
When should I stop and contact official support?
Stop commissioning if the manual does not confirm encoder compatibility, the encoder rate exceeds a documented limit, or the feedback behavior cannot be tied to the intended motion channel. Contact the product manufacturer's official support with the module and software details, wiring, and command-versus-encoder readings from the test.