Method and apparatus for reproducing a reference position in an incremental measuring device

In an incremental path measuring system for measuring the relative position of first and second relatively movable components, said system comprising a carrier coupled to the first object, which carrier defines a measuring graduation and at least one reference mark having a predetermined absolute position with respect to a zero point of the measuring graduation, and a scanning unit coupled to the second object for scanning the graduation and the reference mark, the improvement comprising:

• means for decoupling the scanning unit from the second object;
• drive means for shifting the scanning unit from a starting position to at least a scanning position, at which the reference mark is scanned, and back to the starting position;
• and
• means for counting increments of the measuring graduation during the return movement of the scanning unit from the scanning position to the starting position with reference to the predetermined absolute position of the reference mark in order to determine the absolute position of the starting position with respect to the zero point of the measuring graduation.

In an incremental path measuring system for measuring the relative position of first and second relatively movable components, said system comprising a carrier coupled to the first object, which carrier defines a measuring graduation, a plurality of reference marks, each having a respective predetermined absolute position with respect to a zero point of the measuring graduation, and a plurality of code marks, each associated with a respective one of the reference marks and indicative of the respective predetermined absolute position, and a scanning unit for scanning the measuring graduation, the reference marks and the code marks and coupled to the second object, said scanning unit comprising a light source, a scanning plate, and at least one photosensor, the improvement comprising:

• means for decoupling the scanning plate from the second object;
• drive means for shifting the scanning plate from a starting position to at least a scanning position, at which a next one of the reference marks is scanned, and back to the starting position;
• means for holding the light source and the photosensors fixedly in place with respect to the second object, the one of the photosensors aligned with the reference marks extending over a length at least as large as the separation between adjacent ones of the reference marks;
• means for counting increments of the measuring graduation during the return movement of the scanning plate from the scanning position to the starting position with reference to the predetermined absolute position of the scanned one of the reference marks in order to determine the absolute position of the starting position with respect to the zero point of the measuring graduation.

In an incremental path measuring system for measuring the relative position of first and second relatively movable components, said system comprising a carrier coupled to the first object, which carrier defines a measuring graduation and at least one reference mark having a predetermined absolute position with respect to a zero point of the measuring graduation, and a scanning unit coupled to the second object for scanning the graduation and the reference mark, the improvement comprising:

• means for coupling the carrier which defines the measuring graduation to the first object to transmit motion in a first direction from the first object to the carrier while permitting relative movement therebetween in a reverse direction;
• a drive unit coupled to move the carrier in the reverse direction, said drive unit being reversable in direction of movement;
• and
• means for fixedly joining the scanning unit with the second object.