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absolute measuring system

By means of the absolute measuring system, a CNC controlled machine can determine it's position.

Machines with absolute measuring system must have determined marks as well as a sensor at the moving axes which reports the machine's real postion on the base of the determined marks.

At the beginning there were only comparitively expensive and complicated sytems. For that reason absolute measuring systems were rarely to be found on wood processing machines. In the 1990s, a new economical system on beamsaws was used for the first time. A magnetic strip, which is fixed on the established machine along the linear axes, carries position parametres. There is a special reading device on the moving machine part, which analizes the data. Since the start of this technology, absolute measuring systems are increasingly used on all CNC controlled machines in the wood processing field.

Advantages:

  • An absolute measuring system does not require a repeated reference determination on the machine, once calibrated.
  • The absolute measuring system always defines the position value absolutely precisely, in contrast to the relative measurement system, where position errors may occure.

Desadvantages:

  • The magnetic strip goes along the whole machine and cannot be covered nor protected, because the sensor must run along the strip. For that reason there is a greater risk of mecanical damage, for example by flying bits of workpieces.
  • The distance between sensor and magnetic strip must be kept exact. If there is mecanical disturbance (e.g. bending of the support, flying bits) changing the distance, the system will not function.
  • If a part of the measuring system is damaged, the machine must be re-calibrated. In many cases, this can not be done by the user (in contrast to the relative measuring system) but only by a service technician.

Images

Magnetstreifen für Positionsmessung
Magnetsensor zum Auslesen der Positionsdaten