Safety measures for axis commissioning

Axis commissioning includes:

In particular, the knowledge and use of NC security functionalities,
taking the necessary safety precautions and
compliance with a specific sequence of commissioning steps.

DANGER

Danger to life or risk of serious injury or damage to property due to unintentional movements of the axis

When commissioning axes, there is a movement of them and the mechanics coupled to them, which creates a hazard for people and a risk of damage to the machine. The following safety measures provide guidelines for safe commissioning. The actual measures to be taken depend on the axis and its surroundings.

As a general rule, "Don't take an action whose consequence you can't estimate."

General safety precautions

Inform yourself about the safety instructions and commissioning steps of your drive, such as: AX8000 and the NC safety functions and use them.

Handling the emergency stop case is one of the most important and safety-relevant features of a machine. For this reason it is usual for an additional hardware safety circuit to be built on top of all the logical (logical axis enables) and software enables (PLC: controller and feed enables). Extensive statutory regulations exist governing the reaction and the implementation in hardware of the emergency stop system. Here we only make reference to these.

Within the limits prescribed by the statutory regulations, there remains often a degree of free choice as to how, for instance, NC axes are stopped in the event of an emergency stop. In some cases the mechanical properties of the machine mean that it is not always possible to bring axes that are moving to an abrupt halt (e.g. abruptly output of 0.0 V of an analog interface). It is therefore quite common for NC axes to be slowed following special braking ramps in an emergency stop situation, after which they are then electrically and mechanically locked.

One of the first procedures for commissioning a machine is to test the emergency stop circuit. We begin with safe, standard situations (the axes are stationary under emergency stop conditions, although special attention must be paid here to axes that move vertically). The testing then moves on to more complicated cases (axes moving slowly, then axes moving rapidly).

It is possible, in order to test and commission rapidly, to set the logical axis enables (controller and feed enables) and the velocity override of the axes from the TwinCAT development environment via the Axis online dialog for the particular axis*. This is, however, only possible if the axis interface is not involved in cyclical exchange with the PLC (mapping between the NC and PLC tasks). In that case, the single write of information from the development environment would immediately be overwritten again by the cyclic data exchange. It must, however, be pointed out that this procedure can be very dangerous, because the usual safety monitoring and manipulation facilities of the PLC are disabled. Therefore, this feature can be safely used on an axis test rig with endless axes.
*It is extremely inadvisable to use this facility on a real machine.

Essential requirements

The description below covers all the steps of commissioning an axis. Several types of axis and a range of different situations are covered. In each step, all the settings which must be made are mentioned, even when they are identical with the settings of the previous step. In practice, only some of the listed (partial) steps are actually executed for an axis.

Before you can begin the commissioning itself, a number of preparations must be made:

Check their completeness and correctness of all the electrical connections.
All parts of the axis (encoder, drive, controller, PLC interface) must be of appropriate types, and must be provided with the correct resources (PLC variables, I/O hardware in the fieldbus etc.).
The NC architecture must not only be created, but must also be written into the registry, and TwinCAT must be started with it.

Safety precautions

The following safety precautions must be taken:

Ensure that no one can enter or reach into the machine: the machine can behave unpredictably during commissioning.
Isolate those parts of the equipment on which you are currently working. Anything that is not needed must be safely shut down as it may interfere or distract.
Inform all persons in the vicinity that there is an increased risk of accidents and that they must keep the necessary distance from the machine.
Make sure you are alone in the hazardous area. Only necessary and instructed as well as competent persons should be present in case of need.

Sequence

It is necessary to observe a particular sequence, because the individual steps of axis commissioning are built logically on each other. The sequence, however, does depend on the particular axis composition, i.e. on the combination of the encoder, controller and drive types.