STRAIN WAVE GEAR WITH ENCODER INTEGRATION

Abstract

Described herein is an example a strain wave gear that includes: gear elements, where the gear elements include a circular element with an internally toothed gear and where the gear elements include a flex element with a flexible externally toothed gear arranged in the circular element; a wave generator rotatably arranged in the flex element and configured to flex the externally toothed gear in a radial direction to partly mesh the internally toothed gear and the externally toothed gear; support elements including a bearing input support element and a bearing output support element rotatably coupled to the bearing input support element, where elements of the support elements are fixed to elements of the gear elements; and an encoder arrangement including an encoder track and an encoder reader, where a part of the encoder arrangement is fastened between an element of the support elements and an element of the gear elements.

Claims

1-78. (canceled)

79. A strain wave gear comprising: gear elements comprising: a circular element comprising an internally toothed gear, and a flex element comprising a flexible externally-toothed gear arranged in the circular element; a wave generator rotatably arranged in the flex element and configured to flex the externally-toothed gear in a radial direction to partly mesh the internally-toothed gear and the externally toothed gear; support elements comprising: a bearing input support element, and a bearing output support element rotatably coupled to the bearing input support element, wherein elements of the support elements are fixed respectively to elements of the gear elements; and an encoder arrangement comprising: an encoder track, and an encoder reader, wherein a part of the encoder arrangement is fastened between an element of the support elements and an element of the gear elements.

80. The strain wave gear of claim 79, wherein a part of the encoder arrangement is clamped between an element of the support elements and an element of the gear elements.

81. The strain wave gear of claim 79, wherein a part of the encoder arrangement is in direct contact with an element of the support elements and an element of the gear elements.

82. The strain wave gear of claim 79, wherein the encoder track is fixed to the bearing output support element, and wherein the encoder reader is fixed to the bearing input support element.

83. The strain wave gear of claim 79, wherein the encoder track is fastened between the circular element and the bearing output support element.

84. The strain wave gear of claim 79, wherein the encoder reader is disposed on the bearing output support element.

85. The strain wave gear of claim 79, wherein the bearing input support element is fixed to the flex element, and wherein the bearing output support element is fixed to the circular element.

86. The strain wave gear of claim 79, wherein the bearing input support element and the bearing output support element are configured to support an internal bearing.

87. The strain wave gear of claim 79, wherein an element of the support elements and an element of the gear elements are mechanically fixed to each other by fastening means to fasten a part of the encoder arrangement.

88. The strain wave gear of claim 79, further comprising an output flange.

89. The strain wave gear of claim 88, wherein the output flange is an element of the support elements, and wherein a part of the encoder arrangement is fastened between the output flange and an element of the gear elements.

90. A robot system comprising: a robotic arm comprising a plurality of robot joints mechanically connecting a robot base to a robot tool flange; and a robot controller configured to control movement of the plurality of robot joints and thereby control movement of the robot tool flange, at least one robot joint of the plurality of robot joints comprising a strain wave gear, the strain wave gear comprising: gear elements comprising: a circular element comprising an internally toothed gear, and a flex element comprising a flexible externally-toothed gear arranged in the circular element; a wave generator rotatably arranged in the flex element and configured to flex the externally-toothed gear in a radial direction to partly mesh the internally-toothed gear and the externally toothed gear; support elements comprising: a bearing input support element, and a bearing output support element rotatably coupled to the bearing input support element, wherein elements of the support elements are fixed respectively to elements of the gear elements; and an encoder arrangement comprising: an encoder track, and an encoder reader, wherein a part of the encoder arrangement is fastened between an element of the support elements and an element of the gear elements.

91. A method of assembling a strain wave gear, the method comprising: arranging a flexible externally-toothed gear of a flex element in a circular element with an internally-toothed gear, the flex element and the circular element comprising gear elements; providing support elements, the support elements comprising a bearing input support element and a bearing output support element; and providing a part of an encoder arrangement between an element of the support elements and an element of the gear elements by fixing separate elements of the support elements to respective elements of the gear elements, the encoder arrangement comprising an encoder track and an encoder reader.

92. The method of claim 91, wherein providing a part of the encoder arrangement comprises arranging the part of the encoder arrangement at an element of the gear elements prior to fixing separate elements of the support elements to respective elements of the gear elements.

93. A method comprising: using a support element and a gear element to fasten a part of an encoder arrangement in a strain wave gear.

94. The strain wave gear of claim 80, wherein a part of the encoder arrangement is in direct contact with an element of the support elements and an element of the gear elements.

95. The strain wave gear of claim 94, wherein the encoder track is fixed to the bearing output support element, and wherein the encoder reader is fixed to the bearing input support element.

96. The strain wave gear of claim 95, wherein the bearing input support element is fixed to the flex element, and wherein the bearing output support element is fixed to the circular element.

97. The strain wave gear of claim 96, further comprising an output flange.

98. The strain wave gear of claim 97, wherein the output flange is an element of the support elements, and wherein a part of the encoder arrangement is fastened between the output flange and an element of the gear elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0159] FIG. 1 illustrates a simplified cross-sectional view of components of an example strain wave gear;

[0160] FIG. 2 illustrates a simplified cross-sectional view of components of another example strain wave gear;

[0161] FIGS. 3-5 illustrate simplified cross-sectional views of components of other example strain wave gears;

[0162] FIG. 6 illustrates a flow chart relating to assembly of an example strain wave gear;

[0163] FIGS. 7-9 illustrate simplified cross-sectional views of components of example strain wave gears;

[0164] FIG. 10 illustrates a simplified perspective cutaway view of an example strain wave gear; and

[0165] FIG. 11 illustrates an example robot system.

[0166] Like reference numerals indicate like elements

DETAILED DESCRIPTION

[0167] FIG. 1 illustrates a simplified cross-sectional view of an implementation of an example strain wave gear. The strain wave gear 101 includes gear elements 102, 104, a wave generator 106, support elements 107, 108, and an encoder arrangement 109, 110.

[0168] The strain wave gear 101 is approximately rotationally symmetrical around a central axis of the strain wave gear 101. However, some parts of the gear, such as the encoder reader 110, may not extend all the way around a central axis, but may instead only be localized in one side of the strain wave gear. Further, a wave generator 106 in a strain wave gear 101 is typically not perfectly circular symmetrical, it may for example be elliptical.

[0169] The gear elements include a circular element 102 with an internally toothed gear 103 and a flex element 104 with a flexible externally toothed gear 105. The flex element 104 is arranged partly within the circular element 102. The circular element may typically have an annular shaped body. The inner walls of the flex element 104 are formed as a relatively thin hollow cylinder, resulting in significant flexibility. The externally toothed gear 104 is located at the bottom of the inner walls of the flex element 104. The flex element further includes an annular diaphragm which connects the inner walls with an annular boss 125 located at its outer perimeter.

[0170] The wave generator 106 is arranged within the flex element 104 to flex it. That is, the wave generator 106 deforms the shape of the flex element 104. The wave generator 106 may for example have an elliptical shape, which it then transfers onto a part of the flex element 104, namely the part at which the externally toothed gear 105 is located. This flexing or deformation of the flex element 104 partly meshes the externally toothed gear 105 of the flex element 104 with the internally toothed gear 103 of the circular element 102. The rotational orientation of the wave generator 106 is not fixed to the rotational orientation of the flex element 104. For example, when the wave generator 106 is rotated, the flex element 104 is does not rotate with the same angular velocity. Instead, upon rotation of the wave generator 106, the position at which the gears 103, 105 are meshed rotates in a circumferential direction, which in turn causes a relative rotation between the circular element 102 and the flex element 104. The flex element 104 has slightly fewer gear teeth than the circular element 102, which in turn may determine the reduction ratio of the strain wave gear.

[0171] The support elements 107, 108 include a bearing input support element 107 and a bearing output support element 108. These two are rotationally coupled through an internal bearing 111. Further, the bearing input support element 107 is fixed to the flex element 104, and the bearing output support element 108 is fixed to the circular element 102. Thus, the bearing input and output support elements 107, 108 support the relative rotation between the circular element 102 and the flex element 104. Other implementations of the strain wave gear may have additional support elements. The bearing input support element 107 is connected to the flex element 104 via the annular boss 125 of the flex element 104. They may for example be connected via fasteners such as screws, rivets, nails, click/snap mechanisms, adhesive, welding, etc.

[0172] In this implementation, the bearing input and output support elements 107, 108 each support a distinct race for the internal bearing 111. In other implementation, these support elements 107, 108 may be manufactured with integrated races, e.g., for an internal hearing 111. In other implementations, more than one internal bearing may be provided.

[0173] Typically, when the strain wave gear 101 is installed, the bearing input support element 107 is fixed to a motor configured to rotate the wave generator 106 through an axle of the motor. The bearing output support element 108 may then be mechanically coupled or fixed to an output, e.g., to rotate a tool or rotate a connection to a neighboring robot joint. The rotation of the motor axle may then be transferred via the strain wave gear 101 with a high torque capability, coaxial input and output, high gear reduction, and minimal backlash.

[0174] The encoder arrangement 109, 110 includes an encoder reader 110 and an encoder track 109. In this implementation, the encoder arrangement is a magnetic encoder arrangement. For example, the encoder track 109 has an alternating magnetic pattern encoded in one or more ring-shaped patterns at its perimeter. The encoder reader 110 is able to measure/read this pattern to determine an absolute or incremental measure of the relative orientation between encoder reader 110 and encoder track 109. It is to be understood that the encoder reader and encoder track alternatively or additionally can be provided as optical or inductive encoders.

[0175] In this particular implementation, the encoder track 109 is fastened between the circular element 102 and the bearing output support element 108. The encoder reader 110 is attached to the bearing input support element 107. Relative rotation between the bearing input support element 107 and the bearing output support element 108 (and similarly, between the flex element 104 and the circular element 102) will thus result in relative rotation between the encoder reader 110 and the encoder track 109 as well. Consequently, the encoder arrangement 109,110 is able to track the relative rotation.

[0176] In this implementation, the bearing output support element 108 has an internal thread (not shown) and the circular element 102 has a matching external thread (not shown). The bearing output support element 108 and the circular element 102 are assembled by screwing these two parts together via their matching threads. Prior to assembling these parts, the encoder track 109 is placed between the two parts, such that assembling the bearing output support element 108 and the circular element 102 results in fastening of the encoder track 109. In this implementation, the encoder reader 110 is attached by screws (not shown) clamping the encoder reader 110 to the bearing input support element 107.

[0177] When the strain wave gear is installed in an application, the encoder reader may output its reading via a communicative coupling to a controller, such as a robot controller. The communicative coupling is typically wired such that no power source is required for the encoder reader, but it may alternatively be wirelessly connected. The controller may control the input (and consequently the output) of the strain wave gear 101 based on the measurements from the encoder arrangement 109,110.

[0178] FIG. 2 illustrates a simplified cross-sectional view of another implementation of the strain wave gear. In this illustration, a central axis 117 of the strain wave gear 101 is indicated. The input and output of the strain wave gear rotate coaxially around this central axis 117.

[0179] Several of the concepts of strain wave gears introduced above apply to the strain wave gear 101 illustrated in FIG. 2, but the individual parts are connected in a different manner.

[0180] In this implementation, the bearing input support element 107 is fixed to the circular element 102, while the bearing output support element 108 is fixed to the flex element 104. The encoder track 109 is fastened between the bearing output support element 108 and the flex element 104, which may be connected by glue, screws, welding, or other fastening means. The encoder reader 110 is attached to the bearing input support element 107.

[0181] In contrast to the implementation illustrated in FIG. 1, the gear elements 102, 104 are thus connected differently to the support elements 107, 108, but nevertheless, a part of the encoder arrangement 109, 110 is still fastened between an element of the support elements 107, 108 and an element of the gear elements 102,104.

[0182] FIG. 3 illustrates a simplified cross-sectional view of a part of another implementation of the strain wave gear. In this particular illustration, the part of the strain wave gear 101 to the righthand side of the central axis 117 has been omitted.

[0183] Several of the concepts of strain wave gears introduced above apply to the strain wave gear 101 illustrated in FIG. 3, but here, the support elements further include an output flange 112.

[0184] The output flange 112 facilities the rotational output of the strain wave gear 101. For example, a tool may be connected to the output flange 112, or the output flange may be connected to a neighbouring robot joint in a robot arm.

[0185] The encoder track 109 is fastened between the output flange 112 and an element of the gear elements 102, 104, namely the circular element 102. In other implementations, the encoder track may be fastened between the output flange and the flex element. In other implementations, the encoder reader may be fastened between an output flange and the circular element, or between an output flange and the flex element.

[0186] FIG. 4 illustrates a simplified cross-sectional view of a part of another implementation of the strain wave gear. In this particular illustration, the part of the strain wave gear 101 to the righthand side of the central axis 117 has been omitted.

[0187] Several of the concepts of strain wave gears introduced above apply to the strain wave gear 101 illustrated in FIG. 4. However, in this implementation, both the encoder reader 110 and the encoder track 109 are fastened between elements of the strain wave gear.

[0188] The encoder track 109 is fastened between the flex element 104 and the bearing output support element 108, while the encoder reader 110 is fastened between the circular element 102 and the bearing input support element 107. In other implementations of the strain wave gear, only the encoder reader 110 is fastened between elements.

[0189] The encoder reader 110 is fastened via an encoder reader PCB 113. Generally, the encoder reader 110 may include an encoder reader PCB 113 in addition to an encoder reader head, which defines the point at which the measurement of the encoder track 109 is performed. The encoder reader PCB 113 may hold circuitry necessary for driving and measuring with the encoder reader head.

[0190] The implementation further illustrates that at least a part of the encoder arrangement can be located in an internal enclosure 114. In this, and in other implementations, an internal enclosure 114 has lubrication for movable parts such as the internal bearing 111 and the externally and internally toothed gears 103,105. The extent of the internal enclosure 114 may typically be confined by one or more gaskets for confining lubrication. Wiring for electronics, e.g., for the encoder reader 110 and its encoder reader PCB 113 may be directed through adequate openings in such gaskets.

[0191] FIG. 5 illustrates a simplified cross-sectional view of a part of another implementation of the strain wave gear. In this particular illustration, the part of the strain wave gear 101 to the righthand side of the central axis 117 has been omitted.

[0192] Several of the concepts of strain wave gears introduced above apply to the strain wave gear 101 illustrated in FIG. 5. Moreover, this strain wave gear 101 includes spacer elements 115 and the encoder reader 110 is fixed to the bearing output support element 108.

[0193] More specifically, the encoder reader 110 is fastened between the bearing output support element 108 and the flex element 104. However, the encoder reader PCB 113 of the encoder reader is not in direct contact with the output support element 108, but only in direct contact with the flex element 104 and one of the spacer elements 115. Spacer elements 115 may for example be included to ensure proper spacing between other elements of the strain wave gear 101. They may be fastened using any of the fasteners or fastening techniques described in this disclosure.

[0194] In this implementation, the bearing output support element 108 and the bearing input support element 107 each include a race for an internal bearing 111 which is a cross-roller bearing 116, which is capable of handling large loads from any direction.

[0195] Since the encoder reader 110 is fixed to the output part of the strain wave gear 101, wiring to the encoder reader cannot necessarily be directed to the reader from the input part without restraining the rotational coupling between input and output or implementing a more complex wiring solution. If the strain wave gear is installed in a robot arm, this may for example be solved by connecting the wiring of the encoder reader 110 to a neighbouring robot joint attached to the output of the strain wave gear 101.

[0196] FIG. 6 illustrates an example flow chart relating to assembly of the strain wave gear. Namely, the flow chart relates to a method of assembling a strain wave gear.

[0197] In a first operation S1 of the method, a flexible externally toothed gear of a flex element is arranged in a circular element with an internally toothed gear, wherein the flex element and the circular element constitute gear elements.

[0198] In a next operation S2 of the method, support elements are provided. The support elements include a bearing input support element and a bearing output support element.

[0199] In a next operation S3 of the method, a part of an encoder arrangement is provided between an element of the support elements and an element of the gear elements by fixing separate elements of the support elements to respective elements of the gear elements. The encoder arrangement includes an encoder track and an encoder reader.

[0200] The fixing of separate support elements to respective elements of the gear elements may for example be understood as fixing the bearing input support element to the circular element and fixing the bearing output support element to the flex element. Or, it may be understood as fixing the bearing input support element to the flex element and fixing the bearing output support element to the circular element. It may also include fixing an output flange to an element of the gear elements.

[0201] Thus, the example method described herein enables assembly of a strain wave gear described herein and variants thereof.

[0202] Note that the sequence of operations performed in the method is not restricted to the above example. For example, one or more of the separate support elements can be fixed to respective gear elements prior to arranging the externally toothed gear in the circular element. Furthermore, the method is not restricted to these particular operations but may for example inserting a wave generator.

[0203] FIG. 7 illustrates a simplified cross-sectional view of another implementation of the strain wave gear.

[0204] Several of the concepts of strain wave gears introduced above apply to the strain wave gear 101 illustrated in FIG. 7, but here some optional details are exemplified.

[0205] An input shaft 118 is configured to rotate the wave generator 106 in relation to the flex spline. In such implementations with an input shaft 118, the wave generator 106 can for instance be provided as an elliptical rigid cam, as an elliptical wave bearing. The input shaft can for instance be driven by a motor whereby the strain wave gear forms a transmission system between the motor and output side of the strain wave gear.

[0206] Further, this implementation has an output flange 112, which is manufactured/fabricated as a single part together with the circular element 102. Furthermore, the output flange 112 is an outwardly protruding output flange. It extends outwardly relatively to the circular element 102 and the bearing output support element 108. It extends radially outward to radially overlap at least partly with the bearing input support element 107.

[0207] Additionally, in this and other implementations, a support element serves as a housing of the strain wave gear 101. In this concrete implementation, the bearing input support element 107 serves as housing.

[0208] FIG. 8 and FIG. 9 illustrate simplified cross-sectional views of other implementations of the strain wave gear.

[0209] Several of the concepts of strain wave gears introduced above apply to these implementations as well. In comparison with the implementation illustrated in FIG. 7, these implementations have other techniques for fastening the circular element 102 to the bearing output support element 108. In FIG. 7, these elements are fastened to each other via an external thread on the circular element 102 and a matching internal thread on the bearing output support element 108. In FIG. 8, the circular element 102 is fastened to the bearing output support element 108 by welding. In FIG. 9, the circular element 102 is fastened to the circular element 102 using screws 121. Accordingly, the circular element 102 and the bearing output support element 108 include matching screw holes 120 with internal threads. By insertion of the screws 121 into the screw holes 120, the encoder track is fastened between the circular element 102 and the bearing output support element 108. With such fastening techniques it is further possible to regulate the strain of the encoder track, for example, by screwing the screws 121 more or less tightly into the screw holes 120.

[0210] FIG. 10 illustrates a simplified perspective cutaway view of an implementation of an example strain wave gear haying components of the type described herein. Several of the concepts of strain wave gears introduced above apply to this implementation as well.

[0211] The bearing input support element 107 and the bearing output support element 108 are each formed as an annular shaped body and are rotatably coupled through an internal bearing 111 which is a cross-roller bearing 116. The races of the bearing 111 is integrally formed in the two support elements 107, 108. The bearing output support element 108 is fixed to a circular element 102 and the bearing input support element 107 is fixed to a flex element 104. The flex element 104 includes an externally toothed gear 105 which and is arranged within the circular element 102 which includes an internally toothed gear 103. The flex element 104 is deformed by a wave generator 106, which in turn can be rotated by an input shaft. This deformation partially intermeshes the externally toothed gear 105 with the internally toothed gear 103. The input shaft 118 is configured to rotate the wave generator 106 in relation to the flex element 104 and the wave generator 106 is upon rotation configured to flex the flexible cylindrical body of the flex element in a radial direction to move the positions at which the external toothed gear 105 partially mesh with the internally toothed gear 103. In the illustrated implementation, the wave generator 106 is an elliptical wave generator as known in the art of strain wave gears. The number of teeth of the internal toothed gear and the external toothed gear are different and rotation of the wave generator moves meshing positions of the gears in a circumferential direction causing the inner ring to rotate in relation to the outer ring. The input shaft 118 can for instance be driven by a motor whereby the strain wave gear forms a transmission system between the motor and output side of the strain wave gear.

[0212] The input shaft 118 is hollow which allows wires to be lead through to neighbouring robot joints or other electronics when installed in a robot arm.

[0213] A part of the circular element 102 extends out of the bearing input support element 107 and includes an outwardly protruding output flange 112. The output flange 112 extends outwardly in relation to the circular element 102 and towards the outer ring.

[0214] The input shaft 118 extends through the flex element 104 and is rotatable supported by the circular element 102 via n shaft bearing 119. The circular element 102 and the input shaft 118 each includes flanges configured to support the bearing 119. This ensures that the input shaft 1111 is arranged, at the correct position inside the strain wave gear.

[0215] The encoder arrangement includes an encoder arrangement flange 124 upon which the encoder track 109 is attached. This encoder arrangement flange 124 is fastened between the circular element 102 and the bearing output support element 108. The encoder arrangement further includes an encoder reader 110, which in turn includes an encoder reader PCB 113. The encoder reader PCB 113 has screw holes allowing attachment to the bearing input support element 107 via screws.

[0216] The strain wave gear 101 further includes an end plate 123 arranged at the input side of the strain wave gear 101 above an annular boss 125 of the flex element. The end plate 123 includes an opening allowing the input shaft 118 to pass through it. The input shaft is rotatably supported by the end plate via shaft bearings 119. The end plate has screw holes for attachment. Optionally, the flex element 104 may be fixed to the bearing input support element 107 via matching screw holes and screws.

[0217] Optionally, a second end plate may be arranged at the output side of the strain wave gear at the end surfaces of the circular element 102 and may include an opening allowing the input shaft 123 and outwardly protruding output flange 112 to pass through the it.

[0218] The implementation of the strain wave gear also includes a gasket/seals 122 in the internal enclosure 114. Optionally, implementations of the strain wave gear may include additional gaskets, for example in the opening between the bearing input support element 107, the bearing output support element 108, and the encoder arrangement flange 124.

[0219] Such gaskets prevent lubrication provided inside the internal bearing 1107 from leaking out. The sealing can be provided as any kind of sealing known from strain wave gears.

[0220] FIG. 11 illustrates an example robot system 1101. The robot system 1101 includes a robot arm 1100 including a plurality of robot joints 1102a, 1102b, 1102c, 1102d, 1102e, 1102f connecting a robot base 1105 and a robot tool flange 1104. One or more of these joints may include a strain wave gear of the type described herein. A base joint 1102a is configured to rotate the robot arm around a base axis 1105a (illustrated by a dashed dotted line) as illustrated by rotation arrow 1106a; a shoulder joint 1102b is configured to rotate the robot arm around a shoulder axis 1105b (illustrated as a cross indicating the axis) as illustrated by rotation arrow 1106b; an elbow joint 1102c is configured to rotate the robot arm around an elbow axis 1105c (illustrated as a cross indicating the axis) as illustrated by rotation arrow 1106c, a first wrist joint 1102d is configured to rotate the robot arm around a first wrist axis 1105d (illustrated as a cross indicating the axis) as illustrated by rotation arrow 1106d and a second wrist joint 1102e is configured to rotate the robot arm around a second wrist axis 1105e (illustrated by a dashed dotted line) as illustrated by rotation arrow 1106e. Robot joint 1102f is a tool joint comprising the robot tool flange 1104, which is rotatable around a tool axis 1105f (illustrated by a dashed dotted line) as illustrated by rotation arrow 1106f. The illustrated robot arm is thus a six-axis robot arm with six degrees of freedom with six rotational robot joints, however the strain wave gear can be included in robot arms having less or more robot joints and also other types of robot joints such as prismatic robot joints providing a translation of parts of the robot arm for instance a linear translation.

[0221] A robot tool flange reference point 1107 also known as a TCP is indicated at the robot tool flange and defines the origin of a tool flange coordinate system defining three coordinate axis x.sub.flange, y.sub.flange, z.sub.flange. In the illustrated implementation the origin of the robot tool flange coordinate system has been arrange on the tool flange axis 1105f with one axis (z.sub.flange) parallel with the tool flange axis and with another axis x.sub.flange, y.sub.flange parallel with the outer surface of the robot tool flange 1104. Further a base reference point 1108 is coincident with the origin of a robot base coordinate system defining three coordinate axis x.sub.base, y.sub.base, z.sub.base. In the illustrated implementation the origin of the robot base coordinate system has been arrange on the base axis 1105a with one axis (z.sub.base) parallel with the base axis 1105a axis and with another axis x.sub.base, y.sub.base parallel with at the bottom surface of the robot base. The direction of gravity 1109 in relation to the robot arm is also indicated by an arrow and it is to be understood the at robot arm can be arrange at any position and orientation in relation to gravity only limited by the freedom of operation of the robot joints.

[0222] The robot system 1101 includes at least one robot controller 1110 configured to control robot arm 1100 and can be provided as a computer comprising in interface device 1111 enabling a user to control and program the robot arm. The controller 1110 can be provided as an external device as illustrated in FIG. 11 or as a device integrated into the robot arm or as a combination thereof. The interface device can for instance be provided as a teach pendent as known from the field of industrial robots which can communicate with the controller 1110 via wired or wireless communication protocols. The interface device can for instanced include a display 1112 and a number of input devices 1113 such as buttons, sliders, touchpads, joysticks, track balls, gesture recognition devices, keyboards etc. The display may be provided as a touch screen acting both as display and input device. The interface device can also be provided as an external device configured to communicated with the robot controller 1110 for instance as smart phones, tables, PCs, laptops, etc.

[0223] The robot tool flange 1104 includes a force-torque sensor 1114 (sometimes referred to simply as force sensor) integrated into the robot tool flange 1104. The force-torque sensor 1114 provides a tool flange force signal indicating a force-torque provided at the robot tool flange. In the illustrated implementation the force-torque sensor is integrated into the robot tool flange and is configured to indicate the forces and torques applied to the robot tool flange in relation to the robot tool flange reference point 1107. The force sensor 1114 provides a force signal indicating a force provided at the tool flange. In the illustrated implementation the force sensor is integrated into the robot tool flange and is configured to indicate the force-torque applied to the robot tool flange in relation to the reference point 1107 and in the tool flange coordinate system. However, the force-torque sensor can indicate the force-torque applied to the robot tool flange in relation to any point which can be linked to the robot tool flange coordinate system. In an implementation the force-torque sensor is provided as a six-axis force-torque sensor configured to indicate the forces along and the torques around three perpendicular axes. The force-torque sensor can for instance be provided as any force-torque sensor capable of indicating the forces and torques in relation to a reference point for instance any of the force-torque sensors disclosed by WO2014/110682A1, U.S. Pat. No. 4,763,531, US2015204742, the contents of which are incorporated herein by reference. However, it is to be understood that the force sensor in relation to the strain wave gear not necessarily need to be capable of sensing the torque applied to the tool sensor. It is noted that the force-torque sensor may be provided as an external device arranged at the robot tool flange or omitted.

[0224] An acceleration sensor 1115 is arranged at the robot tool joint 1102f and is configured to sense the acceleration of the robot tool joint 1102f and/or the acceleration of the robot tool flange 1104. The acceleration sensor 1115 provides an acceleration signal indicating the acceleration of the robot tool joint 1102f and/or the acceleration of the robot tool flange 1104. In the illustrated implementation the acceleration sensor is integrated into the robot tool joint and is configured to indicate accelerations of the robot tool joint in the robot tool coordinate system. However, the acceleration sensor can indicate the acceleration of the robot tool joint in relation to any point which can be linked to the robot tool flange coordinate system. The acceleration sensor can be provided as any accelerometer capable of indicating the accelerations of an object. The acceleration sensor can for instance be provided as an IMU (Inertial Measurement Unit) capable of indicating both linear acceleration and rotational accelerations of an object. It is noted that the acceleration sensor may be provided as an external device arranged at the robot tool flange or omitted.

[0225] Each of the robot joints includes a robot joint body and an output flange rotatable or translatable in relation to the robot joint body and the output flange is connected to a neighbor robot joint either directly or via an arm section as known in the art. The robot joint includes a joint motor configured to rotate or translate the output flange in relation to the robot joint body, for instance via a gearing or directly connected to the motor shaft. The robot joint body can for instance be formed as a joint housing and the joint motor can be arranged inside the joint housing and the output flange can extend out of the joint housing, Additionally, the robot joint includes at least one joint sensor providing a sensor signal indicative of at least one of the following parameters: an angular and/or linear position of the output flange, an angular and/or linear position of the motor shaft of the joint motor, a motor current of the joint motor or an external force, and/or torque trying to rotate the output flange or motor shaft. For instance, the angular position of the output flange can be indicated by an output encoder such as optical encoders, magnetic encoders which can indicate the angular position of the output flange in relation to the robot joint. Similarly, the angular position of the joint motor shaft can be provided by an input encoder such as optical encoders, magnetic encoders which can indicate the angular position of the motor shaft in relation to the robot joint. It is noted that both output encoders indicating the angular position of the output flange and input encoders indicating the angular position of the motor shaft can be provided, which in implementations where a gearing has been provided makes it possible to determine a relationship between the input and output side of the gearing. The joint sensor can also be provided as a current sensor indicating the current through the joint motor and thus be used to obtain the torque provided by the motor. For instance, in connection with a multiphase motor, a plurality of current sensors can be provided in order to obtain the current through each of the phases of the multiphase motor. It is also noted that some of the robot joints may include a plurality of output flanges rotatable and/or translatable by joint actuators, for instance one of the robot joints may include a first output flange rotating/translating a first part of the robot arm in relation to the robot joint and a second output flange rotating/translating a second part of the robot arm in relation to the robot joint.

[0226] The robot controller 1110 is configured to control the motions of the robot arm the robot joints by controlling the motor torque provided to the joint motors based on a dynamic model of the robot arm, the direction of gravity acting 1109 and the joint sensor signal.

[0227] One or more of the robot joints 1102a-1102f includes a strain wave gear if the type described herein or variants thereof. Consequently, the robot arm 1100 may potentially be operated more accurately and/or precisely.

[0228] Descried herein are example implementations of a strain wave gear, a robot arm with a strain wave gear, a method for assembling a strain wave gear, and use of certain elements to fasten a part of an encoder arrangement in a strain wave gear. By utilizing components of a strain wave gear, it is potentially possible a obtain a more well-defined positioning of parts of the encoder arrangement or of the entire encoder arrangement. Further, it may potentially be possible to reduce undesired wobbling of parts of the encoder arrangement. Further, since standard-components may be utilized, assembly of the strain wave gear may be simplified in comparison with conventional solutions.

[0229] The example implementations of a strain wave gear, robot, methods, structures, and components thereof described herein have been described for the purpose of illustration rather than limitation with reference to specific examples of strain wave gears, methods, and systems. Details such as a specific method and system structures have been provided in order to understand implementations described herein; for instance, it is to be understood that the implementations disclosed in the different figures and corresponding description can be combined in any way. Note that detailed descriptions of well-known systems, devices, circuits, and methods have been omitted so as to not obscure the description of the strain wave gear, robot, methods, structures, and components thereof described herein with unnecessary details. It should be understood that the strain wave gear, robot, methods, structures, and components thereof described herein are not limited to the particular examples described above and a person skilled in the art can also implement the strain wave gear, robot, methods, structures, and components thereof described herein in other implementations without these specific details. Particularly, it is clear that the concept of fastening a part of an encoder track between two elements of a strain wave gear can be implemented using many different approaches as exemplified in the above description. As such, the strain wave gear, robot, methods, structures, and components thereof described herein may be designed and altered in a multitude of varieties within the scope of the appended claims.

[0230] Elements of different implementations described may be combined to form other implementations not specifically set forth previously. Elements may be left out of the systems described previously without adversely affecting their operation or the operation of the system in general. Furthermore, various separate elements may be combined into one or more individual elements to perform the functions described in this specification.

[0231] Other implementations not specifically described in this specification are also within the scope of the following claims.