Linear displacement measuring apparatus for determining an absolute position, and linear guide having such a displacement measuring apparatus

A linear displacement measuring device for determining an absolute position, comprising:

• a) a linear rail which has a longitudinal axis and is composed of a plurality of individual rail segments, which rail segments are arranged next to each other in the direction of said longitudinal axis,
• wherein each of the rail segments has a material measure which comprises at least one first incremental track extending in the direction of the longitudinal axis and having a plurality of equidistantly arranged position markings, and
• wherein the material measure of one of the rail segments has an absolute track located next to the first incremental track of the material measure and having a plurality of position markings for coding a plurality of predetermined absolute positions which lie next to each other in the direction of the longitudinal axis;
• b) a scanning device with a sensor arrangement for scanning the material measures, which sensor arrangement comprises at least a first sensor, a second sensor and a third sensor,
• wherein the first sensor, the second sensor and the third sensor are arranged at intervals to each other and the scanning device is guided, with respect to the rail, to be movable in the direction of the longitudinal axis along a plurality of the rail segments,
• thereby enabling the sensor arrangement to be arranged at each one of the rail segments so that the first sensor and the second sensor are enabled to scan the first incremental track of a respective rail segment in such a manner that the first sensor is configured to detect at least a first one of the position markings of the first incremental track of the respective rail segment and the second sensor is configured to detect at least a second one of the position markings of the first incremental track of the respective rail segment,
• wherein the first sensor is configured to generate a first signal (S1) containing information about a position of the scanning device relative to the first one of the position markings detected by the first sensor, and wherein the second sensor is configured to generate a second signal (S2) containing information about a position of the scanning device relative to the second one of the position markings detected by the second sensor, wherein the first sensor and the second sensor are arranged offset relative to one another by a predetermined distance (D) in the direction of the longitudinal axis, so that the scanning device is enabled to be brought into a position (P1) with respect to in each case two adjacent rail segments, in which position the first sensor detects at least one of the position markings of the first incremental track of the material measure of the one of the two adjacent rail segments, and the second sensor detects at least one of the position markings of the first incremental track of the material measure of the other one of the two adjacent rail segments,
• wherein the third sensor is configured to scan the absolute track of the material measure of the one of the rail segments and to generate a third signal (S3) containing information about a position of the scanning device relative to the predetermined absolute positions;
• c) a first evaluation device for the third signal (S3), which is configured to detect whether the scanning device is located at one of the predetermined absolute positions regarding the one of the rail segments, and is configured, where an evaluation of the third signal (S3) shows that the scanning device is located at one of the predetermined absolute positions (P1) with respect to one of the rail segments at a first time, to determine a first absolute value (AW1) which represents the one of the predetermined absolute positions (P1);
• d) a second evaluation device for the first signal (S1) and the second signal (S2), which is configured to evaluate, after the first time, the first signal and the second signal during a first time interval between the first time and a second time and to determine a position difference (PD) between the position (P1) of the scanning device at the beginning of the first time interval and a position (P2) of the scanning device at the second time at the end of the first time interval;
• and
• e) a computing unit comprising an output interface, wherein the computing unit is configured to calculate, from the first absolute value (AW1) and the position difference (PD) determined by the second evaluation device, a second absolute value (AW2) which represents an absolute position of the scanning device at the second time at the end of the first time interval, and wherein the computing unit is configured to output, via the output interface, the absolute position,
• wherein the material measure of at least one of the rail segments—with the exception of the one of the rail segments which has the absolute track—comprises a second incremental track which extends next to the first incremental track of the at least one of the rail segments in the direction of the longitudinal axis and has a plurality of equidistantly arranged position markings,
• wherein the second incremental track is arranged at the at least one of the rail segments so that the sensor arrangement of the scanning device is enabled to be arranged at the at least one of the rail segments in such a manner that the third sensor of the scanning device is enabled to scan the second incremental track, the third sensor thereby being enabled to detect position markings of the second incremental track,
• wherein the third sensor is configured to generate a fourth signal (S4) having a variation as a function of a position of the scanning device with respect to the position markings of the second incremental track detected by the third sensor,
• wherein the computing unit is configured to compare the fourth signal (S4) with one or more of the first signal (S1) or the second signal (S2), and
• wherein the first evaluation device and the second evaluation device comprise electronic components.