CROSS-REFERENCE TO PRIOR APPLICATION

Priority is claimed to German Patent Application No. DE 10 2018 209 136.6, filed on Jun. 8, 2018, the entire disclosure of which is hereby incorporated by reference herein.

FIELD

The present invention relates to a position measuring device and to a method for operating a position measuring device. In particular, the invention relates to the determination of collision events in a position measuring device.

BACKGROUND

Many processes in automation technology are based on the movement of machine parts driven by electric motors. The position of the machine parts is determined by position measuring devices. Thus, rotary encoders or angle measuring devices measure rotational movements, for example, of rotating shafts. Length measuring devices on the other hand measure linear displacements of machine parts movably arranged relative to one another.

Particularly in the case of complex systems, such as machine tools or production robots in which movements in several movement axes are possible, there is the risk of collisions. Collisions occur when a moving part strikes an obstacle in an unplanned manner. A typical example for machine tools is if the tool spindle in which a machine tool is arranged hits the workpiece to be machined or a clamping means during a positioning operation. The cause can be that the workpiece or the clamping means is not located at the position at which it should be according to the machining program, or that a movement path incorrectly leads to the collision during the programming of a machining program. In the case of production robots, the behavior is similar; in this case, for example, an incorrect movement of a robot arm or a part to be machined (or other obstacle) which is located in the movement path can trigger a collision.

In the case of collisions, rapid accelerations occur which can damage the components involved in the collision. In addition to direct damage to the machine or the obstacle, initial damage can also occur in machines which at first goes unnoticed, and only after a certain time leads to a failure of the machine. However, a correlation of the failure with a collision can then no longer be detected. For this reason, attempts are made to recognize and log collisions so that, in the event of damage, the cause of the fault or the causative agent can be identified. Also, the detection of a collision also allows preventive maintenance of the machine so that a later failure is prevented.

Thus, WO 03/023528 A2 proposes providing a separate monitoring device which detects collisions by evaluating sensor data and then transmits the sensor data to a machine control for permanent storage. In addition to an additional device, this solution also requires additional cabling effort, as well as a suitable interface with the machine control.

SUMMARY

In an embodiment, the present invention provides a position measuring device including a scale carrier with a measuring scale. A scanner is configured to generate position signals by scanning the measuring scale. A processor is configured to process the position signals into a digital position value. An interface is configured to communicate with downstream electronics. At least one collision sensor is assigned to the position measuring device, and is configured to generate analog or digital measured values from a time characteristic of which collision events are determinable. The measured values are fed to an evaluator configured to determine the collision events by evaluating the time characteristic of the measured values in a controller.

