Safety Laser Scanner Product

Overview

Safety laser scanners are rotating lidar (light detection and ranging) units that continuously map a 270-degree field of view around a robot work cell or hazardous machine zone. The scanner measures distance to all objects within 25 meters, generating a 360-point cloud 25 times per second. Firmware evaluates this cloud against user-defined protective and warning zones. If an object (human, equipment, debris) intrudes into the protective field, the scanner immediately opens dual OSSD relay outputs, stopping the robot or machine within 500 milliseconds.

Unlike light curtains, which detect beam interruptions at fixed locations, the laser scanner is a 2D area-scanning sensor that creates a detailed map of the work cell. It can distinguish between an approaching human hand, a trolley, fallen debris, and stationary equipment—enabling flexible safety zones that adapt to different production scenarios.

Lidar Scanning Mechanism

The Lidar Head contains a pulsed infrared Laser Module emitting 50 W peak pulses at 905 nm wavelength (Class 1 eye-safe per IEC 60825-1). A Motor Drive stepper motor rotates a Mirror Assembly eight-sided polygon mirror at 25 Hz. As the mirror spins, the laser beam sweeps across the work cell in a horizontal plane, illuminating the floor, walls, and any obstacles in sequence.

Each laser pulse is 50 nanoseconds wide and fired 50,000 times per second. The Receiver Photodiode avalanche photodiode collects the diffuse reflections (back-scattered infrared light) from illuminated surfaces. A Time Comparator measures the round-trip light transit time with <2 nanosecond resolution. Since light travels ~0.3 meters per nanosecond in air, this translates to range measurement accuracy of ±50 mm at 5 meters distance.

Over one complete 40 ms rotation at 25 Hz, the scanner collects 720 range measurements (one per 0.375 degrees of rotation). This point cloud is uploaded to the Safety Processor FPGA for real-time evaluation.

Safety Zone Evaluation

The Zone Configuration Module allows facility engineers to define up to 20 independent zones in the scanner's field of view using a computer and Zone Programmer USB configuration tool. Zones are drawn as 2D polygons on a floor plan, imported into the scanner's Zone Memory non-volatile memory.

Two zone types are defined:

• Protective Field: A critical safety boundary. If ANY point in the lidar scan cloud enters this zone, the Safety Processor immediately energizes both OSSD Relay Pair OSSD relays to trip the machine's emergency stop.

• Warning Field: A larger outer perimeter. If object intrusion is detected, the scanner issues a pre-warning signal (siren, yellow beacon) to alert workers that machinery is decelerating. This allows graceful shutdown rather than immediate stop, reducing shock to equipment and product.

The FPGA performs geometric intersection testing: for each of the 720 incoming range measurements, it tests whether the measured point lies inside any of the defined zone polygons. If a protective zone intersection is detected, a fault flag is set within the scan evaluation cycle, and both OSSD relays are immediately de-energized.

Dual-Channel Safety Architecture

The Safety Processor FPGA implements dual-channel independent safety logic with no shared single point of failure. The FPGA design contains two identical processing pipelines:

• Channel 1: Evaluates incoming scan data against zone boundaries.
• Channel 2: Independently re-evaluates the same scan.

Both channels must agree on zone intrusion status. If one channel detects an intrusion and the other does not (due to random bit flip or corrupted data), the discrepancy is flagged as a fault, and both OSSD relays are forced open.

An independent Watchdog Circuit circuit (not part of the FPGA) monitors the system clock. If the FPGA hangs, stops clocking, or crashes, the watchdog pulls both OSSD relay lines open within 5 ms.

Each OSSD relay has independent coil drive circuits; failure of one relay (shorted contacts, stuck armature) is detected by the other channel, and the external safety relay module (downstream) recognizes the asymmetry and triggers a machine stop.

Response Time and Latency

Total response time from object intrusion to OSSD relay opening is <100 ms in optimized configurations:

• Laser scan propagation: <5 ms (scanner operating at 25 Hz; worst-case latency is 40 ms if object enters between scan frames)
• FPGA zone evaluation: <20 ms
• OSSD relay pull-in: <20 ms
• Total: ~65 ms typical case, ~100 ms worst case

The external machine controller then receives the OSSD open signal and halts servo enable within additional 100–400 ms depending on servo architecture. ISO 13849-1 defines safe stopping distance; for a typical 0.5 m/s robot arm, stopping within 200 ms results in <0.1 m travel—negligible for most applications.

Protective Field vs. Stationary Obstacles

A critical safety challenge is distinguishing between a worker's hand (requiring immediate stop) and a stationary object (tooling, safety barrier) that should not trigger an alarm.

The scanner solves this by comparing consecutive point cloud frames (25 Hz scan rate = 40 ms intervals). If a region of the point cloud is identical between frame N and frame N+1, it is classified as static (no motion). If point cloud regions suddenly appear or move significantly (>50 mm per frame), they are classified as dynamic (moving object, likely a person).

Only dynamic intrusions into protective fields trigger the OSSD alarm. Static intrusions are logged but do not stop the machine (they are obstacles known to the work cell). This allows robots to operate within a protective field that includes stationary equipment, as long as humans are detected.

The system can be configured to trigger an alarm only for moving objects (e.g., in a cell with fixed tooling) or for any intrusion regardless of motion (more conservative, e.g., in high-hazard operations).

Zone Configuration and Maintenance

Zones are defined graphically using zone-programmer software running on a Windows PC connected via USB to the scanner. The engineer:

1. Uploads a floor plan image (CAD drawing or photograph).
2. Draws protective and warning zone polygons directly on the image.
3. Assigns names and response actions to each zone (e.g., "Protective Zone: Immediate Stop" vs. "Warning Zone: Pre-Warning Only").
4. Uploads the zone definitions to the scanner's flash memory.

A Configuration LCD optional 3.5 inch LCD touchscreen on the scanner itself allows field personnel to view the current point cloud in real time and verify that zones are correctly configured. The live visualization shows the laser scan as a radial plot: distance rings at 5, 10, 15, 20, 25 meters, and zone overlays shown as colored contours.

Self-Diagnostics and Fault Handling

The scanner continuously monitors its own health:

• Laser Power: Measures back-scattered signal strength; low signal indicates dirt on window or failing laser.
• Motor Speed: Encoder feedback verifies mirror rotation rate stays at 25 ±1 Hz.
• FPGA Clock: Watchdog ensures system clock oscillator is running.
• Relay Continuity: OSSD coils are monitored for open or short circuits.

If any fault is detected, the scanner logs a timestamped fault code to internal flash memory and immediately opens both OSSD relays, placing the machine into safe state. Fault codes can be read via USB or Ethernet for remote diagnostics.

Environmental Tolerance

The scanner is IP67 rated: it tolerates water jets and dust, but should not be submersed. The transparent Lidar Housing window is coated with anti-reflection (AR) coating to minimize back-scatter noise from the window itself. In very dusty environments (e.g., sandblasting area), the window may require quarterly cleaning.

Infrared laser light is scattered by smoke, fog, and steam. In high-fog environments (e.g., steam rooms, food processing), the scanner's range is reduced. A fog compensation algorithm adjusts sensitivity and detection thresholds based on measured ambient signal levels.

Regulatory and Standards

Safety laser scanners fall under ISO 13849-1 (Safety of Machinery) and ISO 13855 (Opto-Electronic Protective Devices). This design achieves PLd Performance Level, equivalent to IEC 61508 SIL 2. CSA Z434 and ANSI B11.1 recognize laser scanners as acceptable robot safeguarding when properly configured.

Certification is typically via notified body (TÜV, DEKRA, UL, NFPA). The scanner manufacturer provides certification documents; the end-user is responsible for integrating the scanner into their safety-rated control system (typically via a monitored safety relay module) and conducting hazard analysis (ISO 12100) to confirm that zone definitions are appropriate for the specific application.

Some jurisdictions require that the protective field include a safety-certified bumper or mat as a redundant physical barrier, in addition to the laser scanner electronic barrier. This N+2 redundancy ensures that if the scanner fails completely, the machine still cannot harm a worker who contacts the physical barrier.