Safety light curtain vs fixed guard vs safety interlock: which is right for your machine?

You stand in front of a running line. Press, robot cell, fast conveyor.
You know it needs guarding, but do you go with a fixed fence, a door with safety interlock, or a safety light curtain?

Let’s walk through it in simple language, using real shop-floor scenes and some examples from NEW STAR’s product range.

Overview of machine guarding: fixed guard, safety interlock and safety light curtain

For most safety standards and risk assessments, the logic is:

1. Fixed guard – physical barrier, bolted in place.
2. Safety interlock guard – door or cover with interlock switch.
3. Safety light curtain – opto-electronic presence sensing around the danger zone.

You start with the question:

• Can we totally block access to the hazard with metal?
• If not, do people need to walk in or just reach in?
• How often will they go in—once a shift or every 5 seconds?

NEW STAR fits into this picture as a one-stop machine safety sensors manufacturer:

• Safety Light Curtains
• Compact Safety Light Curtain and Front Ultra-Thin models for tight spaces
• Safety Device range with safety interlock switches, safety relays and controllers

Fixed guards usually come from the machine builder or local fabricator, but they work together with these safety sensors.

When to use fixed guards for machine safety

If the hazard is severe and access is rare, the simple answer often works best: fixed guards.

Best scenes

• Back and sides of stamping presses and machine tools
• Covers over belts, couplings, flywheels
• Around saws, milling, wood and panel processing equipment
• Heavy, dirty zones with sparks, chips, hot parts or strong coolant spray

Why fixed guards still win sometimes

• They give a solid barrier against reach-in and climb-in.
• They don’t care about dust, vibration, or light.
• Harder for someone to “cheat” them quickly during a busy shift.

But there is real pain:

• Every die change or mold change means unbolting panels.
• On packaging or logistics lines, fences steal floor space.
• On high-mix production, fixed guards can slow changeover so much that production hate them.

So in many projects you mix:

• Fixed guards at back and side of the machine.
• Interlocked doors and/or light curtains at front loading zone where people actually work.

Fixed guard for presses, metalworking and wood processing equipment

For presses, brakes, shears, saws, long conveyors, a common setup is:

• Fixed guarding behind and below the hazard
• A front window where the operator feeds parts
• Then you choose either a gate with interlock or a safety light curtain at the front

Ultra-slim curtains like Front Ultra-Thin or Compact Safety Light Curtain are handy when the press frame is narrow and you don’t have room for a big door.

When to use safety interlock switches on doors and gates

Safety interlock switches make sense when people actually walk into the cell or stick most of their body inside.

Typical use cases:

• Robot cells with sliding or swing gates
• Injection molding machines with large front doors
• Die-casting machines, CNC cells, welding booths
• Any time you have a “walk-in” area that must stop before you enter

You mount an interlock on the door and wire it through a safety relay or safety controller.
Door open = machine must stop or stay stopped.
Door closed and reset = machine can run.

NEW STAR covers this with the Safety Device family: safety interlock switches plus safety relays.

Why interlocks are a good choice

• Very clear for operators: door open means “safe to go in.”
• Good fit for higher Performance Levels when wired right.
• Easy to include in your lockout/tagout and EHS procedures.

Things to watch

• Classic bypass tricks: spare key in the door, magnet taped over the sensor, bridge wire.
• Mechanical wear: hinges sag, cams misalign, then you get nuisance trips.
• If the guard has big openings, somebody can still reach in while the door is “closed”.

Safety interlock switches on robot cells and injection molding machines

Two quick scenes:

1. Robot palletizing cell
   • Fixed fence on three sides
   • Sliding access door with dual-channel safety interlock
   • Sometimes plus a safety scanner watching the rear of the robot
2. Injection molding machine
   • Large front door with monitored safety interlock
   • Rear guards fixed, maybe with maintenance-only access
   • Light curtain only for special operating modes or semi-automatic loading

Here the interlock handles full-body access, while other sensors are just extra layers.

When to use safety light curtains for presses, robots and conveyors

Safety light curtains use rows of infrared beams between transmitter and receiver.
If your hand, body or a pallet breaks the beams, the OSSD outputs go low and the machine must stop.

They shine when you need open access plus safe stop:

• Hand-fed presses and press brakes
• Assembly and 3C electronics lines with frequent jig or product change
• Packaging and logistics equipment where operators clear jams all the time
• Robot load/unload stations where people don’t walk deep in the cage
• Conveyor infeed and outfeed points near diverters or pushers

NEW STAR offers many options here:

• Standard Safety Light Curtains
• Slim Front Ultra-Thin models for cramped machine frames
• Multi-side guarding kits under multi-sided access protection using cascaded curtains
• High-precision and measurement lines like Measurement Light Curtains for DWS and size check

What safety light curtains do well

• No door to open/close every cycle → faster takt time.
• Very friendly for high-mix, low-volume production where part size changes a lot.
• Easy to integrate muting, blanking or cascading for pallets and material flow.
• Better ergonomics when operators work in front of the hazard all shift.

Limits of light curtains

• They don’t stop flying parts, sparks, metal chips or hot splash. You still need some steel in the design.
• They need clear line of sight. Dust, oil mist and steam can cause spurious trips.
• Safety distance depends on stop time; you can’t put them right next to a slow-stopping monster press.
• Bad risk assessment or wrong resolution = people can sneak hands between beams.

Safety light curtain use in packaging and logistics conveyors

Imagine a DWS conveyor with automatic weighing and carton measurement:

• Side fences run along the line.
• Safety light curtains protect the dangerous nip points and pushers.
• Measurement Light Curtains measure parcel size and sometimes trigger scanners.
• Standard photoeyes like Photoelectric Sensor detect package presence, and Flow Sensor keep an eye on process media.

Operators walk along the conveyor, clear jams, rework boxes. They don’t want to open a gate every 20 seconds. Here the safety light curtain is basically a virtual gate.

Multi-sided access protection vs single-side guarding with light curtains

Some machines need more than one side covered:

• Robot cells where you have multiple pallet stations
• Wood and panel lines where workers can enter from several sides
• Long metal processing equipment with side loading

In that case you go for multi-sided access protection:

• Cascaded curtains in an L or U shape
• One safety function covering several angles
• Clean wiring back to the controller

Single-side guarding with a single curtain is still fine for:

• Stand-alone presses and brakes
• Benchtop assembly machines
• Simple conveyor ends

Safety light curtain vs fixed guard vs safety interlock comparison table

Here’s a quick table you can drop inside your product page or blog post:

How NEW STAR machine safety sensors support your guarding strategy

Choosing between a safety light curtain, fixed guard, and safety interlock is not just a “parts list” decision. It affects:

• How close your team can safely work
• How often the line stops because of nuisance trips
• How your next customer audit or insurer visit goes

NEW STAR positions as One-Stop Machine Safety Sensors Manufacturer | NEW STAR OEM.
From Type 4 safety light curtains and measurement light curtains to safety interlock switches, photoelectric and flow sensors, you can cover:

• Packaging and logistics equipment
• Stamping and machine tools
• Injection molding and die casting
• Electronics assembly and robot systems
• Woodworking, panel and metal processing
• Automotive, 3C, battery, home appliance, pharma, food and beverage

If your layout is tricky or you’re running OEM machines, you can use their Custom Safety Light Curtain Solutions service for non-standard sizes, mounting or resolution. They handle both small runs and bulk orders for equipment builders.

A simple way to move forward:

1. Map hazards and needed Performance Level.
2. Decide where steel must be (fixed guards).
3. Put interlock doors where people walk in.
4. Use safety light curtains at the busy operator side, so the process stays smooth and safe.

Even a rough sketch plus “here the guy stands, here the robot moves, here the conveyor pinch point” is enough to start a real discussion and get a practical, customizable solution.