Abstract
A magnetic encoder system (2) of a sewing machine drive comprises a disk (5), which is magnetized, an incremental track (8) and a reference track (9). The incremental track (8) extends completely around the disk (5) and has alternating pole elements (10), which serve as incremental markings. The reference track (9) is designed as a ring-shaped section on the disk (5) and has a monopole (11). The result is a magnetic encoder system (2), for example for a servo motor of a sewing machine.
Claims
1.-10. (canceled)
11. A sewing machine drive with a magnetic encoder system (2), comprising: a disk (5) made of magnetic material; an incremental track (8); and a reference track (9), wherein the disk (5) is magnetized, wherein the incremental track (8) extends completely around the disk (5) and has alternating pole elements (10), which serve as incremental markings, and wherein the reference track (9) is designed as a ring-shaped section on the disk (5) and has a monopole (11).
12. The sewing machine drive according to claim 11, wherein the disk (5) has a recess (12) between the incremental track (8) and the reference track (9).
13. The sewing machine drive according to claim 11, wherein the monopole (11) has a first magnetic flux density (B.sub.1) in a first area that is greater by at least a factor of 10 than a second magnetic flux density (B.sub.2) in at least a second area.
14. The sewing machine drive according to claim 13, wherein the first magnetic flux density (B.sub.1) is greater by at least a factor of 20 than the second magnetic flux density (B.sub.2).
15. The sewing machine drive according to claim 11, wherein the monopole (11) extends over a circumference of at least one pole element (10) of the incremental track (8).
16. The sewing machine drive according to claim 11, wherein the reference track (9) has a plurality of monopoles (11) in a circumferential direction.
17. The sewing machine drive according to claim 11, wherein the reference track (9) serves for zero-point referencing.
18. The sewing machine drive according to claim 11, further comprising an evaluation unit (7) with an integrated microcontroller and magnetic sensors.
19. The sewing machine drive according to claim 11, further comprising an additional, separate magnetic sensor.
20. A sewing machine with a sewing machine drive according to claim 19.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Exemplary embodiments of the invention are explained in more detail on the basis of the drawing.
[0024] FIG. 1 shows perspectively an encoder system assembly for mounting on a servo motor of a sewing machine.
[0025] FIG. 2 is a perspective top view of the encoder system assembly.
[0026] FIG. 3 is a perspective detailed view of a magnetic encoder system in accordance with a first exemplary embodiment.
[0027] FIG. 4 is an enlarged view of the magnetic encoder system in the area of the monopole in accordance with FIG. 3.
[0028] FIG. 5 is a process diagram of the magnetic flux density B of the reference track of the magnetic encoder system in accordance with FIG. 3.
[0029] FIG. 6 is a sectional view of the magnetic encoder system in accordance with FIG. 3.
[0030] FIG. 7 is a perspective detailed view of a magnetic encoder system in accordance with a second exemplary embodiment.
DETAILED DESCRIPTION
[0031] With reference to FIGS. 1 to 6, a first exemplary embodiment of a magnetic encoder system for a sewing machine in the form of a sewing machine servo motor is described below.
[0032] FIG. 1 and FIG. 2 show an encoder system assembly 1, which is used to attach a magnetic encoder system 2 to a servo motor for a sewing machine. The servo motor is not shown for reasons of clarity, but its position is indicated by a motor shaft 4 with a shaft axis 4a. In addition to the magnetic encoder system 2, the assembly 1 includes a mounting flange 3, by means of which the magnetic encoder system 2 is attached to the servo motor. Each of the mounting flange 3 and the magnetic encoder system 2 has an opening starting from its center, which allows it to be attached to the motor shaft 4 of the servo motor. The openings are formed to be circular in shape.
[0033] The magnetic encoder system 2 comprises a ring-shaped disk 5 made of magnetic, in particular ferritic material. Thereby, the disk 5 is connected to the motor shaft 4 so that a rotation of the motor shaft 4 simultaneously results in rotation of the disk 5.
[0034] The mounting flange 3 has a plate 6 on the side turned towards the disk 5, by means of which an evaluation unit 7 is attached to the mounting flange 3. The evaluation unit 7 is used to read out an incremental track 8 attached to the disk 5 along with a reference track 9. The mounting flange 3 and the evaluation unit 7 on it are designed to be stationary. This means that a rotation of the motor shaft 4 does not cause rotation of the mounting flange 3 and the evaluation unit 7.
[0035] FIG. 3 shows the magnetic disk 5 in accordance with the first exemplary embodiment. The incremental track 8 along with the reference track 9 are formed to be circular in shape and extend along the circumference of the magnetic disk 5, wherein the incremental track 8 is attached entirely to the circumference, while the reference track 9 comprises only a partial section of the circumference. The incremental track 8 has alternating pole elements 10. In contrast, the reference track 9 comprises exactly one monopole 11. Both tracks 8, 9 are arranged in a manner coaxial to each other and coaxial to the motor shaft 4. The reference track 9 has a radius R.sub.A that is smaller than a radius R.sub.V of the incremental track 8.
[0036] The evaluation unit 7 is mounted opposite the disk 5 via the plate 6 on the mounting flange 3 and is used to read out the incremental track 8 along with the reference track 9. Thereby, the evaluation unit 7 is arranged in such a manner that a first magnetic sensor detects the incremental track 8 and an additional magnetic sensor detects the reference track 9. The two magnetic sensors are arranged in a manner radially offset to each other and are not shown in the drawings for reasons of clarity.
[0037] From the enlarged view of the magnetic encoder system in FIG. 4, it is clear that the monopole 11 of the exemplary embodiment shown can be understood as a structure of pole elements 10 with a south pole S extending in the circumferential direction of the reference track 9, which is bounded by two opposite and very weakly defined quasi-north pole sections N. The two quasi-north pole sections N represent an opposite pole of the south pole S and together with it form the monopole 11. The structure of the monopole 11 can also be understood in such a manner that the south pole S is composed of two south pole sections, each of which includes one of the quasi-north pole sections N. In the area of the south pole S, there is a strong magnetic field strength H or magnetic flux density B, whereas, in the area of the quasi-north pole sections N, there is only a very weak magnetic field strength H or magnetic flux density B.
[0038] The diagram illustrated in FIG. 5 shows a smoothed curve of the magnetic flux density B (y-axis) over the circumferential extension (x-axis) of the reference track 9 in accordance with the first exemplary embodiment. No magnetic flux density B can be measured in the non-magnetized areas of the reference track 9 beyond the monopole 11. In the circumferential area of the quasi-north pole sections N of the monopole 11, a maximum value of the magnetic flux density B.sub.2 is much weaker than a maximum value of the magnetic flux density B.sub.1 in the area of the circumferential extension of the south pole S of the monopole 11. In accordance with the exemplary embodiment shown, the magnetic flux density B.sub.1 is greater by a factor of 23 than the respective magnetic flux densities B.sub.2. The ratio |B.sub.1|/|B.sub.2| can be greater than 10, can be greater than 15, can be greater than 20 and can also be greater than 23.
[0039] FIG. 6 shows a sectional view of the disk 5 of the magnetic encoder system 2. The disk 5 has a recess 12 in the circumferential direction between the reference track 9 and the incremental track 8. In the exemplary embodiment shown, the recess 12 is formed in a completely circumferential manner and serves to create an air gap between the incremental track 8 and the reference track 9. This counteracts any influence of the two tracks 8 and 9 among each other. In particular, this effectively prevents magnetic field-induced crosstalk between the tracks 8 and 9.
[0040] In the following, with reference to FIG. 7, a second exemplary embodiment of the magnetic encoder system for a sewing machine drive is described. Identical parts receive the same reference signs as with the first exemplary embodiment, the description of which is referred to here. The central difference compared to the first exemplary embodiment is that, on the reference track 9, a plurality of the monopoles 11 is formed in the circumferential direction. Thereby, the monopoles 11 are arranged at a 90 angle to each other. It is also conceivable to have a different number of the monopoles 11 on the reference track 9 instead of four monopoles 11. The monopoles 11 of the reference track 9 have the circumferential extension of a pole element 10 of the incremental track 8. However, the circumferential extensions of such monopoles can differ among each other.
[0041] Various other variants of the encoder system assembly 1 not shown here are conceivable. For example, incremental track 8 can be located on a top side and the reference track 9 can be located on a bottom side of the disk 5. It is also possible to arrange the incremental track 8 and/or the reference track 9 on an outer jacket wall of the disk 5.
