Engineering · Manufacturing
Spring Length Sensing and Cutoff Control
A handbook for controlling spring length with a reflective/visible sensor, aligning the cutoff tool to the arbor, diagnosing incomplete cuts and protecting the relationship between sensor position, program length and mechanical zeros.
Source fidelity and use of values
This handbook page is derived from an anonymised machine-specific operating and setup manual. Numerical settings are retained only where they carry practical technical meaning. They are marked as source examples and are not universal specifications. Machine builders, tooling geometry, wire condition and site safety procedures can require different values.
1. Length is a combined mechanical and control function
The source machine does not rely solely on a fixed feed distance to determine spring length. A visible sensor is positioned above the ejection trough and detects the spring at a known point. The program uses this detection event together with coil/feed commands to control when the cycle progresses toward cutoff. This means finished length depends on both the program and the physical sensor geometry.
A sensor that is electrically healthy can still create incorrect length if its beam is aimed at the wrong location, its height changes, or the background reflection changes. Likewise, a correctly aligned sensor cannot compensate for a cutter that does not sever the spring cleanly.
2. Sensor target geometry
The source instructs the operator to focus the visible beam on the point where the two sides of the spring trough meet. The trough provides a repeatable background surface, while the moving spring becomes the target. The source electrical drawing distinguishes background detection from spring detection using indicator states on the sensor.
Optical safety and practical setup
The source drawing warns not to stare into the laser beam. Align the device by observing the target spot and status indications, not by looking directly into the emitter.
3. Calibration logic from the source drawing
The manual reproduces a calibration method from the machine’s electrical documentation. Without repeating model-specific wording, the sequence can be understood as four stages:
- Position the sensor at the desired length location. The source places the sensor several inches away from the background so the spring can move across the beam laterally.
- Set the background threshold. With no spring present, adjust the sensor until the background is detected reliably.
- Add rejection margin. Continue the adjustment slightly beyond the switching point so vibration or minor background variation does not create nuisance detection.
- Prove target detection. Place a representative spring at the sensing location and verify the target indicator changes state when the spring crosses the beam.
The source says recalibration is normally unnecessary unless the sensor-to-ramp geometry changes. That makes the sensor mounting position a controlled machine setup dimension.
4. Program length and sensor length are not the same thing
The sample program in the source includes a command that sets spring length in coils or repeated feed increments. The sensor provides the physical confirmation point. The exact command syntax is machine-specific, but the broader control model is useful: the program defines how the spring grows, while the sensor confirms when the product has reached the required position in the trough.
If length shifts after a mechanical intervention, check the sensor height and beam location before editing the program. If length shifts only on one product or after a program change, check the programmed feed/coil count and pretension geometry first.
5. Cutter alignment to the arbor
The cutter must sever the wire while the wire is supported against the arbor’s cutting edge. The source adjusts arbor rotation to match the cutter face angle and keeps a small clearance between cutter and arbor. It then uses lateral cutter adjustment so the blade crosses the wire centre rather than glancing off one side.
Source example: the source cutter has a face angle of about 17°. This is retained as a machine-specific geometric reference, not a recommended cutter standard.
6. Establishing cutter home and full stroke
The source creates a reference at maximum cutter stroke and another at the normal home position. During blank-spring setup, the operator moves the cutter close to the wire without cutting, adjusts laterally, then advances it through the wire to prove the cut. After the cut, the machine returns to the stored home position.
A useful quality principle follows: the cutter home position should be stable enough that the spring is still supported at the moment the blade reaches it. A home or zero that is too far forward can let the cutting action push the spring off the end of the arbor, producing an intermittent “bounce” instead of a full cut.
7. Diagnosing incomplete cuts
| Observed symptom | Likely mechanism from source | Checks |
|---|---|---|
| Cutter occasionally does not sever the wire | Coiling-point zero slightly too far forward, allowing spring to be pushed off the arbor during the cut. | Compare current zero with the last proven setup; inspect spring support at the cut instant. |
| Arbor chips during cutoff | Cutter-to-arbor gap too small or cutter alignment incorrect. | Check arbor rotation, lateral cutter position and full-stroke clearance. |
| Wire partly cut / torn | Gap too large, cutting point off-centre or insufficient stroke. | Prove manual cut at slow speed and inspect the blade path through the wire centre. |
| Previously good hook changes after reset | Coiling-point zero shifted, changing the geometry before cutoff and hook moves. | Re-establish mechanical zero from the approved blank-spring setup rather than compensating later in the program. |
8. Why cutter problems can look like spring problems
The spring body is still under forming forces at cutoff. If the cutter pushes rather than shears, the end of the spring can be pulled or distorted. That can affect the next starting coil because the same wire continues into the next cycle. The source therefore recommends generating blank spring after an abnormal stop or disturbance, cutting away the affected section and then restarting. This protects the next hook or body from deformation created by an interrupted cut.
9. Sensor and cutter commissioning checklist
- Sensor beam aimed at the repeatable trough reference, not a moving bracket or reflective edge.
- Background state stable with no spring present.
- Target state changes reliably with a representative spring.
- Sensor mounting height and distance recorded after calibration.
- Program length command matches the intended spring family.
- Arbor cutting edge clean and correctly oriented.
- Cutter laterally centred on the wire.
- Safe clearance exists between cutter and arbor at full stroke.
- Cutter home leaves the spring supported at the moment of cut.
- Manual/slow-speed cuts are complete before production speed is increased.
10. Reset after cutter-axis service
The source later describes a service operation where removing the cutter servo requires recalibration of the cutter/home proximity relationship. The detailed maintenance procedure belongs in the service handbook page, but the operational consequence is important here: after servo or gearbox work, the cutter position must be re-zeroed before a previous production program can be trusted. A program contains relative positions; if the mechanical home reference has changed, the same command values no longer describe the same physical tool path.
11. Measurement and control records
For a repeatable production process, record the spring-length acceptance method, sensor bracket position, background/target status, cutter home reference, full-stroke clearance and the approved first-off length. If the control displays a coil count or sensor-trigger count, capture that as part of the setup sheet. These records make it possible to separate sensor drift from feed-program drift or a physical cutter reset.
12. A robust troubleshooting sequence
When length or cutoff becomes unstable, avoid changing several program values at once. First verify wire feed is not slipping. Second verify sensor target/background behaviour. Third confirm cutter and arbor alignment. Fourth compare the current mechanical zeros with the approved setup. Only after these checks should the length or cutoff commands be edited. This preserves traceability and prevents a mechanical fault from being “programmed around”.