Pilz: How can I prevent my device from starting up unexpectedly?

In the process of adjustment, cleaning, maintenance and repair of mechanical equipment, the unexpected start of equipment due to various reasons is one of the most typical accident causes.

Many companies may also be struggling with how to effectively control unplanned start-ups during maintenance.

ISO 14118:2017 Safety of machinery — Prevention of unexpected start-up (equivalent to GB/T 19670) was developed to effectively control the hazards caused by unintentional start-up.

The "Trident" to prevent accidental activation

According to the results of the risk assessment, the following three measures can effectively prevent accidental start-up:

1. Manually isolate and dissipate energy sources, the machine should be equipped with manually operated devices to isolate and dissipate the energy supply.

Pilz: How can I prevent my device from starting up unexpectedly?

　　2. If the use of manual isolation and energy dissipation is not suitable for frequent short interventions, the designer should provide additional automatic control functions to prevent accidental start-up.

3. When required by the risk assessment, audible and/or visible warning signals and delayed start-up should be provided.

Automatic control function to prevent accidental activation of the "five heavens"

For the use of automatic control functions to prevent accidental start-up, the ISO14118 standard has been refined into 5 different levels, the letters (A→E), the lower the position, the better the effect of protection:

　　Level A prevents accidental start-up by stopping control. For example, the use of lockable position knobs, key switches, lockable mode selector switches, and buttons with covers to prevent false triggering of the start signal.

Level B/C prevents accidental activation by giving a stop signal (Level B) or cutting off the energy source (Level C) by means of an automatic control signal from the machine, such as an interlock switch on a safety door.

Level D prevents accidental activation by mechanically disengaging the power transmission components from the machine's power mechanism, such as a clutch.

Level E prevents the unintentional activation of hazardous movements by means of wedges, struts, latches. The mechanical restraint should be mechanically strong enough to withstand the expected pressure. The diagram shows an example of locking a cylinder to prevent accidental start-up.

Validation is also essential after the controls have been completed to help the user check that the controls are in place.

Isolation from any power supply shall be visible (visible open circuit of the power supply circuit) or indicated by a clear and reliable indication of the effectiveness of the isolation function.

To confirm whether energy is dissipated, it is possible to verify that there is no energy residue in the inside/outside parts of the machine through built-in devices (such as pressure gauges) or test points, and maintenance work can be started.

A "killer feature" to prevent accidental start-ups

If, based on the results of the risk assessment, other measures to prevent unintentional start-up are not feasible, the stop state can also be monitored by using a Class 2 stop device as defined in IEC60204-1. If this stationary monitoring function detects that motion is occurring, it should initiate a stop of category 0.

　　However, it is important to note that the part of the control system that performs the static detection function should be designed to be safety-related.

Pilz: How can I prevent my device from starting up unexpectedly?

Sections viewed

Contact

working hours