Machinery builders need absolute position feedback

The trend toward increasingly precise and economical products is placing strong pressure on machine tool builders to improve the machining accuracy of their products.

The trend toward increasingly precise and nevertheless economical products is placing strong pressure on machine tool builders to improve the machining accuracy of their products.

Also, during operation the machines must provide the shortest possible non-cutting and setup times, permit a quickest possible restart after trouble, and provide maximum operational safety.

The requirement can be met by using machine tools whose axes are equipped with absolute linear encoders or rotary encoders.

Heidenhain has continued to increase the number of absolute encoders it offers with interfaces for Fanuc and Mitsubishi controls as well as EnDat found in Drives from Siemens and Indramat amongst others.

Unlike incremental encoders, which measure the position value by counting lines, on an absolute encoder the position value is read in the form of a code applied directly onto the scale substrate.

Absolute encoders detect the actual position value immediately upon machine startup and after power interruptions or a fault.

They obviate the reference run required with an incremental encoder and considerably reduce standstill and starting times.

This applies as much to rotary as linear axes.

Eliminating the reference run is particularly advantageous on transfer lines, where each machining station is equipped with up to six axes.

With incremental encoders, after any interruption each axis must slowly and tediously back off from the workpiece and return to its predefined starting position.

Also, the otherwise indispensable mechanical limit switches, which must be periodically checked and serviced, can be eliminated completely because absolute encoders provide a continuously accurate position value both at standstill and at maximum traversing velocity.

The EnDat interface provided with absolute linear and angular encoders from Heidenhain supplies important information on the operational status of the encoder.

This information serves as an aid for preventive maintenance and diagnosis, thereby helping to prevent downtime.

Heidenhain offers for machine tools a wide range of high-accuracy absolute position encoders that are mechanically compatible with previous incremental encoders.

This enables manufacturers to change to absolute encoders without having to redesign the machine.

Absolute linear encoders are available in measuring lengths up to 3 meters.

The smallest possible measuring step is 0.1 micron with accuracy grades per meter measuring length as fine as +/-3 microns.

Absolute angle encoders permit resolutions as fine as 0.00004 deg at accuracy grades to +/-2 arc seconds.

Of course the absolute encoders, like the incremental encoders, fulfil the standard requirements on equipment for use on machine tools.

Absolute encoders therefore contribute to reducing system downtime and increasing availability, which adds up to a significant economic benefit for the user.

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