DQS Press Photoelectric Safety Guard Hand Protector
DQS Series Products
How Far From the Die Must the Protector Be Mounted?
A press guard does not work because it is fast. It works because it is mounted far enough back that the press has finished stopping before a hand travelling at normal speed can reach the tooling. That distance comes from ISO 13855:
S = K × T + C
| Term | Meaning | Where the number comes from |
|---|---|---|
| S | Minimum distance from the beam plane to the hazard, in mm | The result — what you are solving for |
| K | Approach speed, mm/s | 2000 mm/s for a hand approach; 1600 mm/s may be used once S exceeds 500 mm |
| T | Total stopping performance, in seconds | Press stopping time plus the guard's response time plus the safety relay and contactor response. Measure the press with a stop-time meter — do not use the figure from the machine nameplate, which is what it did when new. |
| C | Intrusion allowance, mm | Depends on beam pitch d: for d ≤ 40 mm, C = 8 × (d − 14), with a minimum of 0. A 30 mm pitch gives C = 128 mm; a 14 mm pitch gives C = 0. |
Worked example — a mechanical press with a 30 mm pitch guard
Suppose the press stops in 180 ms as measured at the clutch/brake, the protector responds in 10 ms, and the safety relay adds 20 ms. Then T = 0.180 + 0.010 + 0.020 = 0.21 s. With a 30 mm beam pitch, C = 8 × (30 − 14) = 128 mm. So:
S = 2000 × 0.21 + 128 = 420 + 128 = 548 mm
The light curtain has to sit at least 548 mm back from the die. Two consequences people miss:
- A faster device buys you very little here. Halving the guard's 10 ms response to 5 ms moves S by 10 mm. Halving the press stopping time moves it by 180 mm. If the required distance is impractical, service the brake — do not shop for a faster curtain.
- A finer pitch shortens the distance. Re-running the same press with a 14 mm finger-protection pitch drops C to 0 and S to 420 mm. That is often the cheapest way to recover 128 mm of bench space.
Also close the gaps around it. If an operator can reach over, under or around the beam plane, or stand between the beams and the die without being detected, the calculation above is irrelevant. Add fixed guarding or a second curtain, and remember that a press whose stroke can be re-initiated by clearing the beams (PSDI operation) has additional requirements in most jurisdictions.
Which DAIDISIKE Device Suits Your Press?
“Press guarding” covers several different machines, and the right device changes with the tooling and the way the operator works:
| Machine / situation | Device | Why |
|---|---|---|
| Mechanical or hydraulic press, hand feeding at the die | DQS press hand protector | Purpose-built for the die opening, single- or double-sided, ≤ 10 ms response. |
| Press brake — the tool itself must pass through the beams | DKE-L3 laser guard | A narrow laser field that tracks with the beam, so bending can continue without muting the whole guard. |
| Guarding where a documented Type 4 / PL e rating is demanded by the customer or the audit | DQT4 series | Use where a rating has to be shown on paper rather than inferred from architecture. |
| The stop circuit behind any of the above | DA31 or DQSRN safety relay | Forcibly guided contacts, so a welded contact is detected instead of failing silently. A light curtain wired straight to an ordinary relay is not a safety function. |
| Removing the hand from the die entirely | Press feeding equipment | Servo roller feeders, decoilers and levellers. The safest press is one nobody reaches into — guarding and automation are usually specified together. |
Stop Nuisance Trips, Keep the Line Running: Troubleshooting & Maintenance for Photoelectric Press Guards (DAIDISIKE DQS Series)
This practical guide helps manufacturing teams stabilize production with DAIDISIKE® DQS photoelectric safety guards on stamping and forming presses. It covers root-cause diagnosis of false trips, mitigation for oil mist and reflections, parameter tuning and a preventive-maintenance schedule that raises OEE while meeting safety expectations.
- Align & secure: verify beam alignment marks and tighten mounts to torque spec; re-check after the first hour of production.
- Tame reflections: angle the receiver / emitter 2–5° off parallel; fit matte shields around highly reflective stock or die faces.
- Beat oil mist: keep a clean-lens policy; consider anti-fog lens covers or an air knife if mist density is high.
- Harden the circuit: clean ground, proper shield termination and stable 24 VDC supply (± 10 % max ripple).
- Tune response: use DQS response filtering conservatively (5–10 ms) to suppress chatter without masking hazards.
- Prove the function daily: run the block test and OSSD stop test at start-up; log results.
1) Typical Root Causes of Nuisance Trips
- Specular reflections & stray light from polished material, die faces or nearby light sources re-enter the receiver path and simulate beam interruptions.
- Oil mist & debris gradually reduce received intensity and cause intermittent beam loss.
- Mechanical drift (vibration, loose brackets) moves optics out of alignment during high-speed runs.
- Electrical noise / grounding: shared returns, long unshielded runs, VFD noise coupling into OSSD or 24 VDC rails.
- Over-aggressive sensitivity or too-fast response in a turbulent environment (air jets, bounce, fine scrap).
2) Ten-Minute Diagnosis Workflow (Before You Touch Parameters)
- Visual & alignment check — Confirm emitter / receiver indicators show full scale or “aligned”. Sight along the housing; ensure no die features protrude into the beam window.
- Wiggle test — Lightly bump the frame by hand; if indicators flicker, tighten mounts and add braces; inspect for bent uprights.
- Lens condition — Wipe with lint-free wipes & neutral cleaner; replace scratched covers. Persistent haze indicates oil carry-over.
- Reflection probe — Hold a matte board (or cloth) near reflective surfaces. If trips stop, implement anti-reflection measures (see next section).
- Power & ground — Measure supply at the receiver under load: target 24 VDC ± 10 %, ripple < 200 mVpp. Verify shield drain bonded at one end only.
- Record the conditions — Ambient lights on / off, line speed, part finish, air jets active. These explain intermittent issues.
If the above stabilizes operation, keep default safety timing. Only then consider mild response filtering (Section 4).
3) Environment Mitigation: Oil Mist, Reflections, Vibration, EMC
3.1 Reflections (mirror-like stock, bright dies)
- Skew the line: rotate the emitter / receiver by 2–5° so any specular bounce misses the opposite window.
- Matte shields: add low-gloss guards (black anodized or painted) along shiny edges within 50–150 mm of the beam path.
- Distance & height: keep the beam window clear of tooling hardware; increase standoff if practical.
3.2 Oil Mist & Debris
- Lens policy: schedule clean every shift for heavy mist, otherwise daily; record in PM log.
- Air knife / low-pressure curtain: a gentle, dry air sweep across the lens prevents film build-up without stirring turbulence.
- Anti-fog covers: use replaceable protective films; swap when haze persists after cleaning.
3.3 Mechanical Stability
- Rigid mounting: favor triangulated brackets; avoid long, cantilevered posts.
- Torque & witness marks: paint-pen the fasteners; re-verify after warm-up.
3.4 EMC & Power
- Star ground for safety devices; keep OSSD returns separate from high-power returns.
- Shielded cable with drain bonded at controller end; avoid parallel runs with motor leads (keep > 200 mm separation, cross at 90°).
- Clean 24 VDC: regulated PSU sized to inrush; add input filtering if VFD noise is present.
4) Parameter Tuning for DAIDISIKE DQS
Applies to DAIDISIKE® DQS Punch Press Photoelectric Safety Guard Hand Protector (single-sided and double-sided). Keep safety performance first; do not mask a real hazard.
| Parameter | Purpose | Recommended practice |
|---|---|---|
| Response time / filtering | Suppress micro-chatter from mist or vibration. | Start at 5–10 ms extra filtering. Validate that total stop time still meets your safety distance calculation per ISO 13855. |
| Sensitivity / gain | Compensate mild soiling without false trips. | Keep at factory default. If raised, pair with stricter cleaning and reflection control. |
| Alignment indicator | Quantify optical margin. | Aim for green / full-scale under real production lighting and speed. If amber / red appears intermittently, correct the environment first. |
| OSSD integration | Reliable stop command. | Wire to a safety relay or safety PLC input per CE / EN 61496-1 / -2 best practice; avoid sharing returns with inductive loads. |
If you modify timing, update your risk-assessment file and re-run the functional test (Section 6).
5) Preventive Maintenance Plan (Templates You Can Reuse)
| Task | Why | Frequency | Pass / Fail Criteria |
|---|---|---|---|
| Clean lenses (lint-free + neutral cleaner) | Restore optical margin in mist | Each shift (heavy mist) / daily (normal) | Indicator stable green; no haze |
| Bracket & fastener torque check | Prevent drift under vibration | Weekly; after die change | No movement under wiggle test |
| Alignment verification | Confirm beam parallelism | Weekly; after collision | Full-scale alignment markers |
| OSSD stop test (block test) | Prove stop-path integrity | Daily at start-up | Immediate stop; log time-stamp |
| Power-quality check (24 VDC) | Eliminate ripple-induced trips | Monthly | 24 V ± 10 %, ripple < 200 mVpp |
6) Functional Tests & Records (Audit-Ready)
Daily Block Test
- With press in safe state, insert the test block through the beam window.
- Verify OSSD opens and the machine issues a safe-stop signal.
- Remove the block; confirm reset logic works per your SOP.
- Log date / time, operator, result and any notes.
After Any Adjustment or Die Change
- Repeat alignment and OSSD stop tests.
- Update the safety distance if response timing was changed.
- File photos of brackets and cable routing for traceability.
7) Quick FAQ
Q1. Oil mist still causes occasional trips after cleaning. What else helps?
A. Add a gentle air knife across the lens, angle the optics 2–5° and fit matte shields near shiny edges. Then confirm power ripple < 200 mVpp.
Q2. Can I increase filtering a lot to stop nuisance trips?
A. Keep it modest (5–10 ms). Any change must preserve the required safety distance per ISO 13855. Re-test and document.
Q3. Where should I bond the cable shield?
A. Terminate the drain at the controller end only (single-point). Avoid daisy-chained returns with inductive loads.