Pilz: Overrun measurement – for safe distances

On machines with electrosensitive protective devices (e.g. laser scanners or light curtains), safety is ensured by the distance between hazardous movements and electrosensitive protective devices. Where there is intervention/access to the danger zone, there will be no more runaway movements.

Overrun is the time and/or distance it takes for a hazardous movement to stop after a shutdown:

Total overrun time = reaction time of the controller + stop time of the mechanical system

Put simply, overrun measurements are metrological evidence of maintaining the necessary safety distance.

The result of the overrun measurement is the safety distance, measured in millimeters. After the measurement is completed, it is necessary to check whether the distance between the field dimensions of the electrosensitive protective device/scanner and the hazardous movement corresponds to the measurement results.

Pilz: Overrun measurement – for safe distances

　　Why do we need out-of-limit measurements?

For mechanical protective devices, such as light curtains, scanners or two-hand controllers, the Machinery Directive requires that the moving parts cannot be touched by personnel while they are moving. This requirement is guaranteed by maintaining a safe distance between hazardous movement and protective devices.

That's why machine builders have to determine overruns and use them to calculate the required safety distance. These results must be stated in the operator's manual. The method described in EN ISO 13855 can be used for this calculation.

One of the obligations of the machine operator is to provide a safe machine for employees, so when checking safeguards, the machine must also be monitored for compliance with the safety distance. The safety functions of all safety components and their combination with the controller, as well as tamper protection, must be tested before the initial commissioning and, where appropriate, at defined intervals. The usual practice for this type of examination is to repeat it every year.

Procedures for out-of-limit measurements

To perform out-of-limit measurements, a sensor (e.g., a wire-actuated encoder), the out-of-limit measurement device itself, and an actuator (e.g., a hand simulator) are required. The hand simulator is mechanically attached to the guard on the application/machine. When the application is at its highest speed, the hand simulator interrupts safeguards (such as light curtains). Activating safeguards triggers a machine shutdown. Using a pull cable, from this point, the overrun distance and the required time are calculated by taking into account the position and speed of the dangerous movement.

This process is repeated 10 times in a row. The worst of these 10 repetitions is the minimum safety distance between the guard and the dangerous movement.

Periodic inspection of safeguards

Pilz has an independent inspection body that carries out the required legal checks for safeguards, which is accredited by DAkkS in accordance with ISO IEC 17020. Accreditation means an assessment and regular monitoring of the technical competence, reliability, independence and completeness of the Pilz inspection bodies in the public interest.

After the inspection, which includes an out-of-gauge measurement, the user will receive a detailed inspection report. If the inspection is successful, the machine is also stamped with the Pilz seal.

Pilz: Overrun measurement – for safe distances

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