Gear encoder

Abstract

The present invention provides a gear-type encoder comprising a read head and a gear. The read head includes a first magnetic sensor corresponding to the Z region of the gear. The first magnetic sensor comprises four groups of magnetic sensing elements arranged in two rows, one above the other, with each pair of magnetic sensing elements forming a half-bridge. The module of the first magnetic sensor is 1.5 to 2.5 times the module of the gear. The four groups of magnetic sensing elements within the first magnetic sensor are equally spaced at a distance of P / 2, such that the phase difference between the two magnetic sensing elements forming the half-bridge is 180°, where P represents the gear tooth pitch. The present invention can filter out background noise, improve the signal-to-noise ratio of the Z signal, and facilitate the extraction of useful signals.

Description

Technical Field

[0001] The present invention relates to the technical field of encoders, and in particular to a gear type encoder. Background Art

[0002] A gear encoder consists of a gear made of magnetically conductive material and a readout head. The readout head includes a magnetic sensor and a magnet corresponding to the gear module. To obtain a spatial magnetic field with uniform intensity and direction, the magnetic sensor must be mounted as close to the center of the magnet's surface as possible. The sensor receives the magnetic field generated by the magnet, with the center of the magnetic sensor facing a point radially to the side of the gear. Due to the magnetoresistance effect, the direction of the magnetic field at the sensor's location changes as the gear rotates, causing the sensor to output a regularly varying electrical signal. The gear acts as a signal modulator, altering the direction of the magnetic field lines of the magnet's spatial magnetic field as it rotates. This changes the direction of the magnetic field received by the magnetic sensor, and the output signal, generating an electrical signal corresponding to the top and bottom of the gear teeth.

[0003] The structure of the gear encoder is as follows Figure 1 As shown, the gear is divided into AB area and Z area. Two magnetic sensors correspond to AB area and Z area respectively. Both magnetic sensors output two differential signals. The two differential signals output by the magnetic sensor corresponding to AB area are A signal and B signal respectively. Of the two differential signals output by the magnetic sensor corresponding to Z area, only one is taken as Z signal.

[0004] The internal structure of the magnetic sensor is as follows Figure 2 As shown, the magnetic sensor has eight magnetic sensing elements, R1-R8, arranged in two rows, one above the other. Each group of two magnetic sensing elements is equally spaced at a pitch of P / 4. The resistance of R1-R8 changes with the external magnetic field. Two magnetic sensing elements form a group vertically, meaning R1 and R3, R2 and R4, R5 and R7, and R6 and R8 are in the same position and sense the same magnetic field. Pins 3 and 4 connect to power and ground, respectively. Pins 1, 2, 5, and 6 output signals V1+, V2+, V1-, and V2-, respectively. The differential between V1+ and V1- forms one differential signal, and the differential between V2+ and V2- forms another differential signal.

[0005] R1-R4 and R5-R8 are arranged in Wheatstone bridge, such as Figure 3 As shown, R1 and R3 experience the same magnetic field at the same position. R1 and R4 form a half-bridge. When R1 increases by ΔR, R4 decreases by ΔR. When R2 increases by ΔR, R3 decreases by ΔR. The same applies to R5-R8. ΔR satisfies the sinusoidal variation within one tooth period, so:

[0006] ΔR=RKsinα;

[0007]

[0008]

[0009] V + -V - =KsinαV CC .

[0010] The Z signal is Figure 4 As shown in the figure, due to the excessive clutter in the Z signal, the background noise is too large and the signal-to-noise ratio is very low, making it difficult to extract the useful signal. Therefore, it is necessary to provide a gear encoder that can improve the signal-to-noise ratio of the Z signal. Summary of the Invention

[0011] In view of the above problems, the object of the present invention is to provide a gear encoder that improves the signal-to-noise ratio by removing the background noise of the Z-phase signal, which is more conducive to the extraction of useful signals.

[0012] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0013] The present invention provides a gear-type encoder, comprising a reading head and a gear. The reading head comprises a first magnetic sensor corresponding to a Z region of the gear. The first magnetic sensor comprises four groups of magnetic sensing elements arranged in two rows aligned vertically, with each two magnetic sensing elements forming a half-bridge. The module of the first magnetic sensor is 1.5 to 2.5 times the module of the gear. The four groups of magnetic sensing elements within the first magnetic sensor are arranged at equal intervals of P / 2, so that the phase difference between the two magnetic sensing elements forming the half-bridge is 180°, where P is the tooth pitch of the gear.

[0014] Preferably, the reading head further comprises a second magnetic sensor corresponding to the AB region of the gear, and the module of the second magnetic sensor is the same as the module of the gear.

[0015] Preferably, the center lines of the sensing areas of the first magnetic sensor and the second magnetic sensor are respectively opposite to the radius extension line of the gear, and the first magnetic sensor is offset from the second magnetic sensor in the horizontal direction by a distance of mπ / 4, where m is the module of the gear.

[0016] Preferably, the gear is divided into two parts using a line along the tooth width direction as a dividing line, one part is a full-tooth spur gear, and the other part is a single missing tooth formed by removing material from the tooth top to the tooth root on a spur tooth of the full-tooth spur gear.

[0017] Preferably, the distance from the second magnetic sensor to the dividing line is ≥2.5 mm, and the distance from the first magnetic sensor to the dividing line is ≥2 mm.

[0018] Preferably, the side surfaces and front surfaces of the first magnetic sensor and the second magnetic sensor are respectively perpendicular to the mounting surface of the gear.

[0019] Preferably, the tooth tip circle diameter of the gear is ≥20 mm.

[0020] Preferably, the gear tooth top roughness is better than 1.6, the tooth surface roughness is better than 3.2, and the tooth root surface roughness is better than 3.2.

[0021] The present invention can achieve the following technical effects:

[0022] 1. During the processing of single-gap teeth, straight teeth are usually produced by hobbing, and then a portion of the teeth are milled off to form single-gap teeth. The processing cost of this type of single-gap teeth is lower than that of the currently commonly used single-convex and single-concave gears. Compared with single-convex gears, it is easier to process and can save assembly costs compared to single-concave gears.

[0023] 2. The modulus of the second magnetic sensor corresponding to the AB area is the same as the modulus of the gear. The modulus of the first magnetic sensor corresponding to the Z area is 1.5 to 2.5 times the modulus of the gear. When the first magnetic sensor encounters a full tooth part, the tooth pitch is P and a DC signal is generated. When encountering a single missing tooth, the tooth pitch is 2P and a sine wave signal is generated. This is used to filter out background noise, improve the signal-to-noise ratio, and facilitate the extraction of useful signals.

[0024] 3. The first magnetic sensor is offset from the second magnetic sensor in the horizontal direction by a distance of mπ / 4, so that the equal amplitude points of the A and B signals coincide with the maximum amplitude point of the Z signal, satisfying the phase relationship between the A, B and Z signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of a traditional gear encoder;

[0026] Figure 2 It is a schematic diagram of the structure of a traditional magnetic sensor;

[0027] Figure 3 This is a schematic diagram of the positional relationship between the traditional magnetic sensor and the gear;

[0028] Figure 4 This is a traditional Z signal diagram;

[0029] Figure 5 It is a schematic diagram of the structure of a traditional single convex tooth gear;

[0030] Figure 6 It is a schematic diagram of the structure of a traditional single concave tooth gear;

[0031] Figure 7 is a front view of a gear-type encoder according to one embodiment of the present invention;

[0032] Figure 8 is a top view of a gear-type encoder according to one embodiment of the present invention;

[0033] Figure 9 2. It is a schematic diagram of the internal structure arrangement of a gear-type encoder according to one embodiment of the present invention;

[0034] Figure 10 is a schematic diagram of the positional relationship between the first magnetic sensor and the gear according to an embodiment of the present invention;

[0035] Figure 11 is a schematic diagram of the internal structure arrangement of a first magnetic sensor according to an embodiment of the present invention;

[0036] Figure 12 is a schematic diagram of a Z signal according to an embodiment of the present invention;

[0037] Figure 13 FIG. 4 is a schematic diagram of the phase relationship between the A and B signals and the Z signal according to an embodiment of the present invention.

[0038] The reference numerals include: reading head 1, first magnetic sensor 11, second magnetic sensor 12, magnetic sensing elements R1-R8, center line of sensing area 13, gear 2, full-tooth spur gear 21, single missing tooth 22, dividing line 23, radius extension line 24. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0040] The gear encoder provided by the embodiment of the present invention will be described in detail below.

[0041] like Figure 7-Figure 9 As shown, the gear encoder provided by an embodiment of the present invention includes: a reading head 1 and a gear 2, the gear 2 is divided into two areas along the thickness direction, namely, the AB area and the Z area, the reading head 1 includes a first magnetic sensor 11 and a second magnetic sensor 12, the first magnetic sensor 11 corresponds to the Z area, and is used to generate a Z signal, and the second magnetic sensor 12 corresponds to the AB area, and is used to generate an A signal and a B signal.

[0042] A line along the tooth width of gear 2 serves as a dividing line 23, dividing gear 2 into a fully toothed portion and a toothless portion. The fully toothed portion is a fully toothed spur gear 21, i.e., region AB, which corresponds to the second magnetic sensor 12. The full teeth in region AB are demodulated by the second magnetic sensor 12 to produce A and B signals. The toothless portion is a fully toothed spur gear 21 with a single toothless portion 22 formed by removing material from the tooth top to the tooth root. Region Z is a fully toothed spur gear 21 with a single toothless portion 22, corresponding to the first magnetic sensor 11. The single toothless portion 22 in region Z is demodulated by the first magnetic sensor 11 to produce a Z signal. The fully toothed portion and the toothless portion have the same module, m.

[0043] When machining the gear 2 , a full-tooth spur gear 21 is firstly produced by gear hobbing, and then a portion of a spur tooth is milled off from the tooth top to the tooth root, thereby forming a single missing tooth 22 .

[0044] In traditional gears, the Z region usually uses single convex teeth and single concave teeth, respectively. Figure 5 and Figure 6 The structures of the single convex tooth and the single concave tooth are described below to illustrate the reason why the present invention adopts the single missing tooth 22 instead of the single convex tooth and the single concave tooth.

[0045] 1. Single convex tooth

[0046] A single convex tooth is a protruding tooth that is identical to a tooth on the standard gear in the AB region. Because gear encoders require high gear precision, casting is not an option. Typically, a standard gear is first machined, and then the excess teeth are CNC-milled off, leaving only a single convex tooth. This method results in high manufacturing costs for single convex teeth, which in turn increases the cost of the gear encoder.

[0047] 2. Single concave tooth

[0048] Single-concave teeth are cylindrical surfaces with a single groove. The diameter of the cylindrical surface is equal to the diameter of the tooth tip circle, and the groove corresponds to a valley on a standard gear in the AB region. Gears with single-concave teeth are typically assembled from two or more parts. The high cost of manufacturing such gears increases the cost of gear encoders.

[0049] To address the high cost of machining single convex and single concave teeth, the present invention takes a different approach. After hobbing a full-tooth spur gear, a portion of one of the spur teeth of the full-tooth spur gear is milled off to form a single missing tooth 22. Compared to a single convex tooth, only half of the tooth needs to be milled off, making machining easier and more cost-effective. Compared to a single concave tooth, the entire assembly is a single part, reducing assembly costs. Therefore, the single missing tooth 22 employed in the present invention can reduce the cost of a gear encoder.

[0050] In an example of the present invention, the tooth top circle diameter of the gear 2 is ≥20 mm, the distance between the second magnetic sensor 12 and the boundary line of the gear 2 is ≥2.5 mm, and the distance between the first magnetic sensor 11 and the boundary line of the gear 2 is ≥2 mm.

[0051] If the distance from the second magnetic sensor 12 to the dividing line of the gear 2 is less than 2.5 mm, the single missing tooth 22 will affect the A and B signals, causing the signal quality to deteriorate. If the distance from the first magnetic sensor 11 to the dividing line of the gear 2 is less than 2 mm, the full tooth will affect the Z signal, causing the signal amplitude to decrease.

[0052] In a specific example of the present invention, the side surface of the first magnetic sensor 11 ( Figure 9 The side of the second magnetic sensor 12 ( Figure 9 The front surfaces of the first magnetic sensor 11 and the second magnetic sensor 12 ( Figure 9 The N side is the surface facing the gear) and is also the mounting surface of gear 2 ( Figure 9 The o plane is vertical.

[0053] This arrangement ensures that the module of the gear corresponds to the module of the first and second magnetic sensors 11, 12, resulting in a signal with good sine and cosine properties. If the positions of the first and second magnetic sensors 11, 12 are offset, the resulting module will decrease, affecting signal quality.

[0054] The module of a magnetic sensor represents the spacing between its internal magnetic sensing elements. When the module of the magnetic sensor is the same as the module of the gear, the four sets of magnetic sensing elements are equally spaced at a pitch of P / 4, where p is the gear's pitch. When the module of the magnetic sensor is twice the module of the gear, the four sets of magnetic sensing elements are equally spaced at a pitch of P / 2.

[0055] In a specific embodiment of the present invention, the tooth top surface roughness of the gear is better than 1.6, the tooth surface roughness is better than 3.2, and the tooth root surface roughness is better than 3.2.

[0056] The first magnetic sensor 11 and the second magnetic sensor 12 each include eight magnetic sensing elements, which are arranged in two rows and aligned vertically. The two aligned magnetic sensing elements form a group, and the two groups of magnetic sensing elements are arranged in a Wheatstone bridge. The two diagonal magnetic sensing elements form a half bridge. The four groups of magnetic sensing elements are equidistantly arranged at a tooth pitch of P / 4.

[0057] In the present invention, the module of the second magnetic sensor 12 is the same as the module of the gear 2, that is, the second magnetic sensor 12 is not changed. The second magnetic sensor 12 has the same working principle as the traditional magnetic sensor corresponding to the AB area. The two magnetic sensing elements that make up the bridge have a phase difference of 90°, and the output differential signal is a sinusoidal signal.

[0058] The innovation of the present invention lies in that, without changing the internal structure of the second magnetic sensor 12, the module of the second magnetic sensor 12 is set to 1.5 to 2.5 times the module of the gear 2, so that when the second magnetic sensor 12 encounters a full tooth, the differential signal output by the second magnetic sensor 12 is a DC signal, and when encountering a single missing tooth 22, the output differential signal is a sinusoidal signal, thereby improving the signal-to-noise ratio of the Z signal.

[0059] Figure 10 FIG. 4 shows the positional relationship between the first magnetic sensor and the gear according to an embodiment of the present invention.

[0060] like Figure 10 As shown, the first magnetic sensor 11 includes eight magnetic sensing elements R1-R8, R1-R4 and R5-R8 are arranged in a row, and R1 and R3, R2 and R4, R5 and R7, and R4 and R8 are aligned up and down, respectively. R1-R4 and R5-R8 are arranged in a Wheatstone bridge, respectively. R1 and R3, R2 and R4, R5 and R7, and R4 and R8 sense the same magnetic field.

[0061] When the module of the second magnetic sensor 12 is set to 1.5 to 2.5 times the module of the gear 2, R1 and R2, R2 and R5, R5 and R6, R3 and R4, R4 and R7, and R7 and R8 are arranged equidistantly at a distance of P / 2, where P is the tooth pitch of the gear 2.

[0062] Figure 11 FIG. 4 shows the internal structure arrangement of a first magnetic sensor according to an embodiment of the present invention.

[0063] Since only one differential signal of the first magnetic sensor 11 is taken as the output signal, Figure 11 Only four magnetic induction elements R1-R4 are shown in the figure, R1 and R4 form a half bridge, R2 and R3 form a half bridge, and V+ and V- form a differential signal.

[0064] R1 and R4 form a half-bridge, and the phase difference between R1 and R4 changes from 90° to 180°. When R1 increases by ΔR, R4 also increases by ΔR. Similarly, when R2 increases by ΔR, R3 also increases by ΔR. ΔR satisfies the sinusoidal variation within one tooth cycle, and V+ and V- are calculated using the following formula:

[0065]

[0066]

[0067] Then V + -V - =0.

[0068] When the first magnetic sensor 11 encounters a full tooth, the pitch of two adjacent straight teeth is P, then the phase difference between R1 and R4 is 180°, V + -V - =0, the output differential signal is a DC signal.

[0069] When the first magnetic sensor 11 encounters a single missing tooth 22, due to the lack of a straight tooth, the pitch of the two adjacent straight teeth becomes 2P, then the phase difference between R1 and R4 is 90°, V + -V - =KsinαV CC , the output differential signal is a sinusoidal signal.

[0070] The differential signal output by the first magnetic sensor 11 is as follows: Figure 12 As shown, after the first magnetic sensor 11 selects the module of the gear twice, the background noise of the Z signal is reduced, the signal-to-noise ratio is very large, which is conducive to signal extraction.

[0071] The differential signal output by R5-R8 can be obtained in the same way as that of R1-R4, so I will not go into details here.

[0072] The present invention combines these two designs by setting a single missing tooth 22 in the full teeth of the Z region of the gear 2 and setting the module of the second magnetic sensor 12 to be 1.5 to 2.5 times the module of the gear 2. When the first magnetic sensor 11 encounters a full tooth, the pitch of two adjacent straight teeth is P, the spacing of the four groups of magnetic sensing elements in the first magnetic sensor 11 is P / 2, the phase difference between R1 and R4 is 180°, and V + -V - =0, outputs a DC signal; and when the first magnetic sensor 11 encounters a single missing tooth 22, the pitch of the two adjacent straight teeth is 2P, the spacing of the four groups of magnetic induction elements in the first magnetic sensor 11 is P / 4, the phase difference between R1 and R4 is 90°, V + -V - =KsinαV CC , output a sinusoidal signal to filter out background noise, improve the signal-to-noise ratio, and facilitate the extraction of useful signals.

[0073] Without the missing tooth 22 in the full teeth of region Z, the tooth pitch at a specific location within the full teeth cannot be changed, and thus the phase relationship between R1 and R4 cannot be altered. Furthermore, without setting the module of first magnetic sensor 11 to twice the module of gear 2, the pitch of the magnetic sensing elements cannot be set to P / 4. Therefore, both the missing tooth 22 and the module change of first magnetic sensor 11 are essential for filtering background noise.

[0074] In order to meet the phase relationship between the encoder A, B signals and the Z signal, the current common method is to adjust the phase of the Z signal by delaying the Z signal. The present invention adopts a physical method to offset the first magnetic sensor 11 relative to the second magnetic sensor 12 in the horizontal direction by a certain distance to meet the phase relationship. When the center line 13 of the sensing area of ​​the first magnetic sensor 11 and the second magnetic sensor 12 are both located on the radius extension line 24 of the gear 2, the phase relationship is as follows Figure 13 As shown, the phase difference is T / 4. The arc length of the corresponding gear 2 tooth top is mP / 4. By moving the first magnetic sensor 11 by a distance of mP / 4, the point where the A and B signals have equal amplitudes coincides with the point where the Z signal has the highest amplitude, thus satisfying the phase relationship between the A, B, and Z signals.

[0075] In the description of this specification, the reference terms "one embodiment", "another embodiment", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0076] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

[0077] The above specific embodiments of the present invention do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the scope of protection of the claims of the present invention.

Claims

1. A gear encoder comprising a reading head and a gear, wherein the reading head comprises a first magnetic sensor corresponding to the Z region of the gear, wherein the first magnetic sensor comprises four groups of magnetic sensing elements arranged in two rows, one above the other, with each two magnetic sensing elements forming a half bridge, and wherein: The module of the first magnetic sensor is 1.5 to 2.5 times the module of the gear. The four groups of magnetic sensing elements inside the first magnetic sensor are arranged at an equal interval of P / 2, so that the phase difference between the two magnetic sensing elements forming the half bridge is 180°, where P is the tooth pitch of the gear. The gear is divided into two parts using a line along the tooth width direction of the gear as a dividing line, one part being a full-tooth spur gear, and the other part being a single-missing tooth formed by removing material from the tooth top to the tooth root on a spur tooth of the full-tooth spur gear; When the first magnetic sensor encounters a full tooth, the pitch between two adjacent straight teeth is P, the spacing between the four groups of magnetic induction elements in the first magnetic sensor is P / 2, the phase difference between the two magnetic induction elements forming a half bridge is 180°, and a DC signal is output. When the first magnetic sensor encounters a single missing tooth, the pitch between two adjacent straight teeth is 2P, the spacing between the four groups of magnetic induction elements in the first magnetic sensor is P / 4, the phase difference between the two magnetic induction elements forming a half bridge is 90°, and a sinusoidal signal is output. The reading head further includes a second magnetic sensor corresponding to the AB region of the gear, wherein the module of the second magnetic sensor is the same as the module of the gear, and the module of the magnetic sensor is characterized by the spacing between internal magnetic sensing elements.

2. The gear-type encoder according to claim 1, wherein: The center lines of the sensing areas of the first magnetic sensor and the second magnetic sensor are respectively opposite to the radius extension line of the gear, and the first magnetic sensor is offset from the second magnetic sensor in the horizontal direction by a distance of mπ / 4, where m is the module of the gear.

3. The gear-type encoder according to claim 1, wherein: The distance between the second magnetic sensor and the dividing line is ≥2.5 mm, and the distance between the first magnetic sensor and the dividing line is ≥2 mm.

4. The gear-type encoder according to any one of claims 1 to 3, wherein: The side surfaces and the front surfaces of the first magnetic sensor and the second magnetic sensor are respectively perpendicular to the mounting surface of the gear.

5. The gear-type encoder according to any one of claims 1 to 3, wherein: The tooth tip circle diameter of the gear is ≥20mm.

6. The gear-type encoder according to any one of claims 1 to 3, wherein: The tooth top roughness of the gear is better than 1.6, the tooth surface roughness is better than 3.2, and the tooth root surface roughness is better than 3.2.

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