Rotary encoder, robot arm system and a method for detecting a rotary position

Abstract

The invention relates to a rotary encoder (10) with an optical sensor (13) and a first grid scale (11) detectable by the optical sensor (13) and rotatable relative to the optical sensor (13), characterized by a second grid scale (12) which is arranged such that the first and second grid scales (11, 12) overlap to form a moiré pattern which can be detected by the optical sensor (13).

Description

[0001] The invention relates to a rotary encoder with an optical sensor and a first grating scale detectable by the optical sensor and rotatable relative to the optical sensor. Furthermore, the invention relates to a robot arm system with a joint module and a robot arm segment, as well as to a method for detecting a rotational position of a first grating scale rotatable relative to an optical sensor.

[0002] With the advancing automation of, for example, production chains, the demands on the respective mechatronic systems are increasing. In the context of so-called Industry 4.0, the relevance and associated use of robots or robot arms is increasing. For example, so-called six-axis robots should be mentioned here, which are used particularly in high-precision and dynamic production. The control and regulation of such systems requires precise knowledge of the respective movement state, i.e. the kinematics, of the mechatronic components in question in order to ultimately achieve a high level of movement precision in production. The kinematics here includes the position and the adjustment speed of relevant robot modules. The movement of robot arms or the tool center point (TCP) in particular requires a high level of accuracy.Furthermore, the elasticity of mechanical components can make it difficult to determine the kinematic state precisely and thus also to guide the tool precisely.

[0003] For precise movement control of robot arms, it is particularly important to determine the rotational position or the relative angular position of two directly adjacent robot arm segments. Furthermore, the adjustment speed can also be of greater relevance, although slower travel is preferred, particularly for high-precision control of a robot arm. Devices or sensors for determining the rotational position of robot arms are already known in the prior art. These often function using a combination of a light source, an optical sensor, and a rotatable disk with a grid structure. The grid structure can have several slots arranged in the circumferential direction. The disk is arranged between the sensor and the light source, with the light signal being interrupted by the areas between the slots in the disk.This enables a signal readable by the optical sensor, from which the position relative to a starting position can be determined. The disc is mechanically connected directly to a robot arm segment, whose rotational position needs to be determined. The direct connection to the disc provides information about the current position of each robot arm segment.

[0004] A disadvantage, however, is the high demands placed on the production of such a grating structure on the disc in conjunction with a high-resolution light sensor, which can detect even minimal changes in light. Precision depends on the number and thus also the width of the slits in the grating structure on the disc. Each slit is assigned an angular range of the respective connected arm segment. With an increasing number of slits, which in turn must lead to thinner slits, smaller angular ranges enable a more precise determination of the rotational position of a segment. Furthermore, narrower slits also make it more difficult for a sensor to detect changes in light, especially at higher adjustment speeds. Consequently, a high-resolution light sensor is required, which is very expensive.

[0005] Against this background, the task arises to provide an optimized and cost-effective device for determining a rotational position.

[0006] The object is achieved by a rotary encoder with an optical sensor and a first grating scale that can be detected by the optical sensor and rotated relative to the optical sensor, wherein a second grating scale is arranged such that the first and second grating scales overlap to form a moiré pattern that can be detected by the optical sensor.

[0007] The advantage of the rotary encoder according to the invention is that the moiré pattern can be detected with less effort by the optical sensor. The grid created by the moiré pattern is advantageously wider than, for example, the width of the lines of the first grating scale and is thus easier to detect by a light sensor. Furthermore, the periodic grid created by the moiré pattern moves at a higher speed than the adjustment speed of the first grating scale. Thus, the device according to the invention enables cost-effective, simple detection of a faster and wider pattern.

[0008] The respective grating scales preferably have a scale with a defined width and an alignment, which are particularly preferably arranged on an optical element. The optical element can have a main extension plane and thus preferably be designed with thin walls. Furthermore, the optical element can have any cross-sectional area in the main extension plane, preferably polygonal, round or oval, with the optical element particularly preferably being a disk. It is conceivable for the scale to be a line pattern, with the lines being able to represent either openings, depressions or at least partially reflective elements on the respective optical element.For example, the line pattern can have a combination of black and white stripes, wherein the white stripes at least partially reflect incident light and the black stripes substantially absorb the light. The differences in the reflections can be created solely or additionally by differences in the surface structure. Such lines are preferably printed on a disc, in particular transparent, white or black. The scale can be arranged concentrically on the optical element, in particular on one of the surfaces which extend parallel to the main extension plane, wherein the scale is preferably arranged uniformly in the circumferential direction on a radius at least partially or on the entire circumference. In addition, the respective scale, in particular the lines of the line pattern, can extend outwards in the radial direction. The thickness orThe spacing of the lines and / or the alignment of the lines can vary and is different, in particular, for the first and second grating scales. Furthermore, the cross-sectional area of ​​the lines can be chosen arbitrarily. Each grating scale has an optical element. The superposition of the first and second grating scales then produces the so-called moiré pattern. The first grating scale and the second grating scale are preferably arranged substantially parallel to one another. The moiré pattern according to the invention is an optical effect, wherein a periodic grid is created by the superposition of two regular grids (here the first and second grating scales). A rotatable grating scale is required, wherein, according to the invention, the first grating scale is arranged so as to be rotatable. The relative movement of the first grating scale to the second grating scale can produce the moiré pattern, which is detected by the optical sensor according to the invention.To detect the moiré pattern, the optical sensor is aligned such that the optical sensor detects the first grating scale and the second grating scale, or the moiré pattern resulting from the relative movement of the two grating scales. According to the invention, the moiré pattern arises solely from the superposition of the respective first grating scale and the second grating scale. In particular, the rotary encoder has an evaluation unit that can determine a rotational position from the signal generated by the optical sensor. The optical sensor can, in particular, be arranged substantially perpendicular to the main extension plane of the first and / or second grating scale.

[0009] In an alternative embodiment of the invention, the rotary encoder has at least one further grating scale, wherein at least one further grating scale can preferably be designed to be rotatable.

[0010] In a further alternative embodiment of the invention, the rotary encoder comprises a plurality of optical sensors, wherein the plurality of optical sensors are arranged such that each optical sensor detects a different periodic pattern of the moiré pattern. For this purpose, an optical element can comprise a plurality of grating scales, which are preferably arranged concentrically around the rotation axis of the optical element at a different radius. An optical sensor can then be directed at a respective grating scale on the respective optical element. This advantageously allows an absolute rotational position to be determined.

[0011] According to a preferred embodiment of the invention, the second grating scale is arranged in a rotationally fixed manner relative to the optical sensor. Particularly preferably, the second grating scale is connected directly to the optical sensor, so that no additional holding device is required for the second grating scale. The moiré pattern requires a relative movement of the first and second grating scales to one another. The rotationally fixed arrangement of the second grating scale with the optical sensor can advantageously make an additional holder for the second grating scale obsolete. Thus, the rotary encoder can be designed more compactly.

[0012] According to a preferred embodiment of the invention, the second grating scale is arranged between the optical sensor and the first grating scale. The second grating scale and the optical sensor are thus arranged on one side of the first grating scale. If the second grating scale is designed to be rotationally fixed, the second grating scale can be connected to the optical sensor, thus eliminating the need for an additional mount. At the same time, the first grating scale can be directly connected to an element whose rotational position or angular velocity is to be determined.

[0013] According to a preferred embodiment of the invention, it is provided that the first grating scale is arranged between the optical sensor and the second grating scale.

[0014] According to a preferred embodiment of the invention, the first and second grating scales comprise at least partially transparent material and / or through-openings. The grating scale can each be designed as a line pattern, wherein the lines within the line pattern either reflect, absorb, or transmit incident light. The lines are therefore either applied to the optical element, introduced into the element as a recess or through-opening, or printed on. If a through-opening is involved, the through-opening can also be filled with a transparent material so that the light is transmitted. The respective type of line on the respective grating scale can be selected depending on the relative arrangement of the first and second grating scales and the optical sensor.If the optical sensor is arranged between the first and second grating scales, one grating scale preferably has through-openings, and the respective other grating scale has either light-reflecting or light-absorbing lines. Absorbing lines are only preferably used if the optical element consists of a material that reflects light, in particular a metal. If the optical sensor is arranged outside the first grating scale and the second grating scale, the lines of the two grating scales are designed as through-openings with or without transparent material. The through-openings are preferably filled with transparent material depending on the application. The lines of the respective grating scale preferably influence the incident light so that the optical sensor can detect the differences. The material can preferably be completely transparent.

[0015] According to a preferred embodiment of the invention, the rotary encoder comprises a light source, in particular an LED. The first grating scale and the second grating scale are preferably arranged between the optical sensor and the light source. Preferably, the first and second grating scales are designed either with through-openings or with through-openings made of semi-transparent or transparent material. In a further alternative embodiment, the optical sensor is arranged on the same side as the light source. In this case, the grating scale arranged between the other grating scale and the optical sensor and the light source can be designed with through-openings or with through-openings made of semi-transparent or transparent material, and the respective other grating scale is designed to be reflective.

[0016] Another subject of the invention is a robot arm system with at least one joint module and at least one robot arm segment, wherein the joint module has an electric motor and at least one rotary encoder according to one of the preceding claims. The robot arm system can also have multiple robot arm segments, wherein the multiple robot arm segments are each connected via a joint module. The joint module can have multiple rotary encoders; preferably, one rotary encoder is arranged on the input side and one rotary encoder is arranged on the output side of the joint module or the robot arm segment.

[0017] According to a preferred embodiment of the invention, the electric motor has a drive shaft, wherein the first grating scale of the rotary encoder is connected to the drive shaft in a rotationally fixed manner. The scale of the first grating scale is preferably arranged concentrically in the circumferential direction around the rotation axis of the drive shaft, wherein the scale is arranged partially or over the entire circumference. The rotational movement of the drive shaft can be detected directly by the rotary encoder due to the rotationally fixed connection of the first grating scale to the drive shaft. Depending on the range of motion of the respective segment of the robot arm system to be driven, the scale can be arranged on the respective optical element partially or over the entire circumference of the optical element.

[0018] According to a preferred embodiment of the invention, the joint module additionally comprises a gear mechanism, wherein the electric motor is connected to the gear mechanism, which comprises an output shaft, wherein the first grating scale of the rotary encoder is rotationally fixedly connected to the output shaft of the gear mechanism. In addition or alternatively to arranging the rotary encoder on the drive shaft of the electric motor, the joint module can comprise a rotary encoder on an output shaft of a gear mechanism. Thus, the input and output rotational positions of the joint module can be determined with high precision.

[0019] Another subject of the invention is a method for detecting a rotational position of a first grating scale that is rotatable relative to an optical sensor, wherein the optical sensor detects a moiré pattern that results from a superposition of the first grating scale with a second grating scale. Due to the rotation of the grating scale in combination with the second grating scale, the moiré pattern can rotate faster than the rotation speed of the second grating scale. Furthermore, the periodic grid, which results from the superposition of the two grating scales and the associated relative movement, can be detected more easily. The resulting grid can be wider than the line width of a single grating scale and is thus easier for an optical sensor to detect.

[0020] The advantageous configurations and features, as well as the technical advantages explained in connection with the rotary encoder, can also be applied, alone or in combination, to the robot arm system and the method. Conversely, the advantageous configurations and features explained, as well as the technical advantages of the robot arm system or the method, can also be applied, alone or in combination, to the rotary encoder.

[0021] Further details and advantages of the invention will be explained below with reference to the exemplary embodiment shown in the drawing. Herein: Fig. 1 a simplified schematic representation of an embodiment of a robot arm system with gearing; Fig. 2 a schematic embodiment of a joint module in connection with a transmission; Fig. 3 an embodiment of a first grating scale overlapping with a second grating scale; and Fig. 4 an embodiment of a rotary encoder with a light source for detecting a rotational position of a first grating scale by an optical sensor.

[0022] In Fig. Figure 1 shows a simplified representation of a robot arm system 1. The robot arm system 1 can have at least one robot arm segment 2, a joint module 4, and in particular also a gear mechanism 3. The gear mechanism 3 can have a simple mechanical transmission, which can in particular be a stress wave gear mechanism. Such robot arm systems 1 are versatile and require precise position determination in many applications. High-precision robot arm systems 1 are frequently used in Industry 4.0 and especially in automated production chains.

[0023] In Fig. 1 shows an embodiment with just one robot arm segment 2, as well as one joint module 4 and one gear 3. However, it is conceivable for a robot arm system 1 to have a plurality of robot arm segments 2, preferably three arm segments, whereby the rotation in each axis can thus advantageously be controlled. For this purpose, the robot arm system 1 preferably has a joint module 4 between each respective robot arm segment 2. A joint module 4 can have an electric motor 5 and a rotary encoder 10. The electric motor 5 controls a robot arm segment 2, whereby the rotary encoder 10 according to the invention enables exact positioning to be determined. In addition, each joint module 4 can also have a gear 3. Furthermore, it is conceivable for a joint module 4 to have further elements, such as a torque sensor.

[0024] Fig. Figure 2 shows a schematic structure of an embodiment of a joint module 4 in conjunction with a gear 3. The gear 3 is a stress wave gear. Fig. 2 shows the structure of the electric motor 5, which can have a first and second housing part 5', 5" and the motor 5 itself. Furthermore, the electric motor 5 has a drive shaft 6, which drive shaft 6 establishes a direct mechanical connection to the gear 3. The rotary encoder 10 can be partially arranged on the drive shaft 6, with a first grating scale 11 preferably being arranged on the drive shaft 6. The rotary encoder 10 according to the invention thus enables highly precise determination of the rotational position of the drive shaft 6, wherein the rotational position of the drive shaft 6 allows a direct conclusion to be drawn about the rotational position of the controlled robot arm segment 2.

[0025] It is also conceivable for the gearbox 3 to have an output shaft on the output side. However, the output shaft is not shown here. The output shaft can be connected directly to the robot arm segment 2, whereby the rotation of the electric motor 3 can thus be transmitted to the robot arm segment 2 via the drive shaft 6, the gearbox 3, and the output shaft. Preferably, a rotary encoder 10 is also arranged on the output side to precisely determine the rotational position of the robot arm segment 2; this rotary encoder 10 can be mounted on the output shaft. Thus, misalignments caused by, for example, the gearbox 3 can be detected.

[0026] In Fig. 3 shows an embodiment of a first grating scale 11 and a second grating scale 12. According to the invention, these two grating scales 11, 12 are superimposed in such a way that a moiré pattern is created, which can be detected by an optical sensor 13. The moiré pattern describes an optical effect, whereby the relative movement in conjunction with the superposition of two patterns (here the first grating scale 11 and the second grating scale 12) creates a periodic grid. This grid can be detected by an optical sensor 13. The advantage of the invention is that, as can be seen from Fig. 3 clearly shows that this periodic grid is wider than the slits indicated by the white lines. Thus, a cheaper optical sensor 13 can be used, which requires a lower resolution and sensitivity. Fig. 3 already shows that a periodic grid is created by the superposition of the first and second grating scales 11, 12. With the relative movement of the two scales 11, 12, the grid moves, and these differences can be detected by the optical sensor 13.

[0027] The relative movement of the first grating scale 11 to the second grating scale 12 is achieved according to the invention in that the first grating scale 11 is rotatable. The first grating scale 11 is preferably arranged in a rotationally fixed manner on a drive shaft 6 or output shaft, so that a detected rotational position of the first grating scale 11 corresponds to the rotational position of the drive shaft 6 and thus enables a direct conclusion to be drawn about the position of the respective robot arm segments 2. Furthermore, the second grating scale 12 can be arranged in a rotationally fixed manner relative to an optical sensor 13. Thus, no relative movement can occur between the optical sensor 13 and the second grating scale 12. The first grating scale 11 can be designed to be rotatable relative to the rotary encoder 10 in that the scale 11 is mounted in a rotationally fixed manner on a rotating element.

[0028] The first grating scale 11 and the second grating scale 12 preferably have a line pattern, with the spaces between the respective grating scales 11, 12 (in white) each representing a through-opening, colloquially known as a slit. These slits can also be filled with a transparent material, where transparency refers to the light transmission. Furthermore, the first grating scale 11 and the second grating scale 12 are arranged substantially parallel. Preferably, the optical sensor 13 and the light source are arranged substantially perpendicular to the first and / or second grating scale 11, 12.

[0029] Fig. 4 shows a schematic embodiment of the measuring device of a rotary encoder 10 according to the invention. As already Fig. 3 shown, shows Fig. 4 shows the overlap of the first grating scale 11 with the second grating scale 12. In this embodiment, the light rays 14' generated by a light source 14 are reflected by the overlapping lines (white) so that the optical sensor 13 can detect them. Fig. The advantage of the invention is evident in Figure 4, where the reflective surface is enlarged by the moiré effect. Furthermore, the relative movement and the periodically generated pattern also increase the speed of the signal to be detected. The light source 14 is preferably an LED. Fig. 4, the first grating scale 11 is preferably transparent and the second grating scale 11 is reflective, so that the optical sensor 13 can detect the reflected rays. Alternatively, if the second grating scale 12 is arranged in front of the first grating scale 11, the second grating scale 12 or the line pattern of the second grating scale 12 can be transparent and the first grating scale 11 or the line pattern of the first grating scale 11 can be reflective.

[0030] Fig. Figure 4 shows an embodiment in which the optical sensor 13 is arranged on the same side as the light source 14. In this case, the optical sensor 13 can detect the rotational position solely through the reflection of the first and second grating scales 11, 12 and the resulting moiré pattern.

[0031] Alternatively, the first and second grating scales 11, 12 are preferably arranged between the light source 14 and the optical sensor 13, with both grating scales 11, 12 having through-openings. Here, too, the superposition creates a moiré pattern, which is only perceived on the other side by the optical sensor 13. List of reference symbols 1 robot arm system 2 robot arm segment 3 gearboxes 4 joint module 5 Electric motor 5' first housing part 5" second housing part 6 Drive shaft 10 rotary encoders 11 first grid scale 12 second grid scale 13 optical sensor 14 Light source

Claims

[1] Rotary encoder (10) with an optical sensor (13) and a first grating scale (11) detectable by the optical sensor (13) and rotatable relative to the optical sensor (13), characterized by a second grating scale (12) arranged such that the first and second grating scales (11, 12) overlap to form a moiré pattern which can be detected by the optical sensor (13). [2] Rotary encoder (10) according to claim 1, characterized by that the second grating scale (12) is arranged in a rotationally fixed manner relative to the optical sensor (13). [3] Rotary encoder (10) according to one of the preceding claims, characterized by that the second grating scale (12) is arranged between the optical sensor (13) and the first grating scale (11). [4] Rotary encoder (10) according to one of claims 1 or 2, characterized by that the first grating scale (11) is arranged between the optical sensor (13) and the second grating scale (12). [5] Rotary encoder (10) according to one of the preceding claims, characterized by that the first and second grating scales (11, 12) have at least partially transparent material and / or through openings. [6] Rotary encoder (10) according to one of the preceding claims, characterized by that the rotary encoder (10) has a light source (14), in particular an LED. [7] Robot arm system (1) with at least one joint module (4) and at least one robot arm segment (2), wherein the joint module (4) has an electric motor (5) and at least one rotary encoder (10) according to one of the preceding claims. [8] Robot arm system (1) according to claim 7, characterized by that the electric motor (5) has a drive shaft (6), wherein the first grating scale (11) of the rotary encoder (10) is connected in a rotationally fixed manner to the drive shaft (6). [9] Robot arm system (1) according to one of claims 7, characterized bythat the joint module (5) additionally has a gear (3), wherein the electric motor (5) is connected to the gear (3) which comprises an output shaft, wherein the first grating scale (11) of the rotary encoder (10) is connected in a rotationally fixed manner to the output shaft of the gear (3). [10] Method for detecting a rotational position of a first grating scale (11) rotatable relative to an optical sensor (13), wherein the optical sensor (13) detects a moiré pattern which is produced by a superposition of the first grating scale (11) with a second grating scale (12).

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