Articulated robot arm with thermally conductive member for cooling

Abstract

An articulated robot arm (1) comprising at least a first connecting rod (2-2) and a second connecting rod (2-3) rotatably connected to the first connecting rod (2-2) by a joint unit comprising a shaft (14) received in a housing (4) of the first connecting rod (2-2), rotatable relative to the first connecting rod (2-2) about an axis (3-2), and a driveline unit (9, 10, 18), and a driveline unit (9, 10, 18) mounted inside the housing (4) of the first connecting rod (2-2) and non-rotatably connected to the second connecting rod (2-3), the driveline unit being mounted inside the housing (4) of the first connecting rod (2-2) for rotating the shaft (14), in which an annular gap (20) is formed between the outside of the driveline unit (9, 10, 18) and the inside of the housing (4). At least one heat conducting member (21, 57, 58, 38) is mounted in the gap (20) in thermal contact with the outside of the drive train unit (9, 10, 18) and the inside of the housing (4).

Description

Technical Field

[0001] The invention relates to an articulated robot arm. Background Art

[0002] Conventionally, such a robot arm comprises a plurality of links interconnected by a revolute joint, each revolute joint comprising a transmission unit, which is non-rotatably mounted on a first link of the links and adapted to rotate a shaft relative to the first link about an axis, the shaft being non-rotatably connected to a second link of the links. In operation, the transmission unit generates heat. When the transmission unit is mounted in a housing of the first link, the housing increases the thermal resistance that hinders the heat dissipation of the transmission unit, so that appropriate measures must be taken to prevent the transmission unit from overheating. For example, Ex-air.com proposes a device for cooling the robot motor housing by injecting compressed air, see https: / / www.exair.com / kno wledqebase / applicationsearch / cool-ing-robot-motor-housings.html. In order to cool the transmission unit at the distal end of the robot arm, a compressed air pipeline extending along the robot arm to the transmission unit must be provided. Such a pipe not only increases the complexity of the robot arm, but also increases the volume and increases the power consumption of the transmission unit. Summary of the invention

[0003] An object of the present invention is to provide a robot arm which reduces the risk of overheating by simple and effective means.

[0004] To this end, the present invention provides an articulated robot arm, which includes at least a first link and a second link rotatably connected to the first link via a rotating joint, the joint including a shaft and a transmission system unit, the shaft being rotatable around an axis relative to the first link and being non-rotatably connected to the second link, the transmission system unit being installed inside a housing of the first link for rotating the shaft, wherein an annular gap is formed between the outer side of the transmission system unit and the inner side of the housing, wherein at least one heat-conducting member is installed in the gap and is in thermal contact with the outer side of the transmission system unit and the inner side of the housing.

[0005] Typically, in an articulated robot having a transmission unit located in a housing of a first link, the transmission unit is supported by an end face member of the housing facing the second link. The heat dissipation efficiency via such an end face member is low. One reason is that the transmission unit tends to include a reduction gear between the end face member and the motor, so that the reduction gear will increase the thermal resistance between the motor (usually the most important heat source in the transmission unit) and the end face member. Another reason is that the end face member facing the second link is close and cannot dissipate heat into the surrounding air, but can only conduct the heat to other areas of the housing. In the robot arm of the present invention, the heat-conducting member can transfer heat directly to these areas of the housing, so that the motor can operate continuously at high power.

[0006] In order to enable the heat-conducting member to effectively receive and transfer heat, the thermal contact is preferably a press-fit contact, i.e. the contact of the heat-conducting member against the powertrain unit and the housing. Alternatively, one or more screws can be used to press the heat-conducting member against the powertrain unit or the housing, or the contact can be ensured by a layer of adhesive.

[0007] Where the power train unit includes an electric motor, the heat conducting member should be located near the motor coils in order to effectively dissipate the heat of the motor.

[0008] Where the power train unit further comprises a driver circuit for powering the motor, and where the driver circuit is likely to heat up in operation, the heat conducting member (or another heat conducting member) may be located adjacent to the circuit.

[0009] In the case where the transmission unit includes a reduction gear, the heat conducting member (or another heat conducting member) may extend around the housing of the reduction gear, thereby filling a gap between the gear housing and the connecting rod housing surrounding the gear housing. When the reduction gear is a harmonic drive gear, the housing of the harmonic drive gear preferably includes a rigid wheel.

[0010] Heat may also be generated by the brake, whether through friction, eddy currents, or any other physical effect that the brake may use to slow the relative movement of the first link and the second link, or through operation of an actuator to displace or maintain a movable component of the brake in an appropriate position. Therefore, the thermally conductive member (or another thermally conductive member) may be disposed proximate to the brake.

[0011] In order to achieve effective thermal contact, the heat conducting member may have an outer flange in contact with the housing and / or an inner flange in contact with the power train unit.

[0012] Furthermore, at least one wall extending radially inwardly from the outer flange and / or inwardly from the outer flange may facilitate heat flow.

[0013] Preferably, at least one wall extends in an axial direction parallel to the shaft.

[0014] Alternatively, a braided wire member or some other member formed from multiple flexible elements, such as a multi-lobed member or a multi-strand member, may facilitate heat flow.

[0015] In the case where the heat conducting member is not compressed between the outside of the powertrain unit and the inside of the housing, it can be held in place by locking engagement with the axially extending track of the housing or powertrain unit. In addition, close thermal contact between the mating surfaces of the track and the flange can be ensured by threaded connection.

[0016] The heat conducting member may be manufactured as an extruded profile, and in particular when it has longitudinally extending flanges and walls as described above, its extrusion direction should be parallel to the axis.

[0017] The cross section of the heat conducting member may be circular, forming a collar around the entire power train unit. Preferably, its cross section is an arc of a circle, as the arc is smaller and easier to manufacture, and will allow the heat conducting member to be in close contact with the power train unit or housing, regardless of possible tolerances in the radius of curvature of the power train unit, housing and heat conducting member.

[0018] The heat conducting member will not typically extend along the entire length of the power train unit. Where the power train unit comprises multiple sub-units (such as motors, reduction gears and / or circuit units) having different diameters, any of these units may have a heat conducting member of matching shape associated therewith.

[0019] The thermally conductive member may be a rigid component of a single material (preferably having good thermal conductivity, such as aluminum, copper).

[0020] A single piece of metal would have excellent thermal conductivity if in close contact with the powertrain unit and housing, but would be heavy and expensive. Furthermore, such close contact is often difficult to obtain due to manufacturing tolerances. To reduce weight and / or achieve close thermal contact despite possible dimensional tolerances of the gap that accommodates the thermally conductive element, the thermally conductive member may include a metal frame and a ductile thermal conductor (such as graphite) that fills at least one cavity or recess of the frame. In the frame, the structural element may be thin enough to yield to pressure when inserted into the gap, while the ductile material is held in place by the frame and may have a sufficiently wide cross-section to provide adequate heat flow and improved thermal conductivity.

[0021] Preferably, the frame comprises one or more cavities which may be filled with a ductile thermal conductor.When the frame is formed by extrusion, the cavities will be elongate and may have open ends in the direction of extrusion.

[0022] Preferably, the ductile thermal conductor comprises graphite. Graphite has excellent thermal conductivity and, due to its softness, easily conforms to the shape of the frame or the surface of the powertrain unit and the housing, thereby forming a close thermal contact.

[0023] The heat conducting member may also include a heat pipe. To facilitate the flow of heat radially outward through the heat pipe, the radially inner wall of the heat pipe should be provided with a wicking material, such as sponge or wool, or a wicking structure, such as ribs, which are spaced sufficiently close to each other to capture the liquid heat transfer fluid in the gaps between the ribs by capillary effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features and advantages of the present invention will become apparent from the following description of embodiments with reference to the accompanying drawings.

[0025] Figure 1 is a view of an articulated robot arm to which the present invention is applicable.

[0026] Figure 2 is the axial section of the robot arm link;

[0027] Figure 3 is the radial section of the connecting rod;

[0028] Figure 4 and Figure 5 is a radial cross-section of a connecting rod showing different types of thermally conductive members; and

[0029] Figure 6 is a perspective view of a heat conducting member. DETAILED DESCRIPTION

[0030] Figure 1 is a perspective view of a robot arm 1 to which the present invention may be applied. The robot arm 1 has a generally cylindrical fixed link or base 2-1 which houses a motor for rotating the other links 2-2 to 2-6 about a vertical axis 3-1. The link 2-2 is also generally cylindrical and houses a motor for rotating all of the more distal links 2-3 to 2-6 about axis 3-2. The link 2-4 has a generally cylindrical portion in which a motor is coupled to the more proximal link 2-3 for rotating the links 2-4 to 2-6 about axis 3-3. The motor in the link 2-5 drives the link to rotate about axis 3-4. The link 2-6 has two intersecting cylindrical portions, one of which houses a motor for rotating the link 2-6 about axis 3-5 and the other of which houses a motor for rotating an end effector (not shown) about axis 3-6.

[0031] Figure 2 3 - 2 is a schematic cross section of the connecting rod 2 - 2 along the axis 3 - 2 . The cross sections of other connecting rods may differ in detail, but the components described below may all be the same.

[0032] The housing 4 of the connecting rod 2-2 comprises a generally cylindrical portion 5 and a cover 6 screwed onto the open end of the cylindrical portion 5. At the other end of the cylindrical portion, a flange 7 extends radially inward along the entire circumference of the cylindrical portion. The flange 7 supports a drive train unit 8, which comprises an electric motor 9 and a reduction gear 10, i.e. a harmonic drive gear.

[0033] The motor 9 is supported by means of a reduction gear 10, wherein a hollow rigid wheel 11 is fixed to the flange 7 by screws 12, and the stator portion of the motor 9 is in turn connected to the rigid wheel 11 by threads. The rotor portion of the motor 9 is connected to the wave generator 13 of the reduction gear 10. The flexible wheel 14 of the harmonic drive gear is attached to the end face 15 of the adjacent connecting rod 2-3, thereby forming an axis through which the motor 9 can rotate the connecting rod 2-3 relative to the connecting rod 2-2.

[0034] A circuit board 18 may be attached to the motor 9 on a side remote from the reduction gear, carrying a motor driver circuit. The motor 9, the circuit and the reduction gear 10 form a drive train unit for driving the connecting rod 2-3 to rotate relative to the connecting rod 2-2.

[0035] A passage 19 extends along axis 3 - 2 through reduction gear 10 , motor 9 and possibly circuit board 18 , serving as a cable conduit for transmitting power and control signals to the motor of a more remote link.

[0036] When the robot is running, Joule heat is generated in the rotor and stator coils 16, 17 of the motor 9, and possibly in the motor driver circuit. The friction between the wave generator 13 and the flexible wheel 14 may be another source of heat. This heat must be dissipated to the environment efficiently enough to prevent the motor and circuit from overheating. Dissipation directly to the cylindrical part 5 and the cover 6 through the air is not efficient. The heat from the motor 9 can be dissipated to the environment through the reduction gear 10, whose huge metal steel wheel 11 is in close contact with both the stator part and the flange 7 of the motor 9. However, the friction heat generated in the flexible wheel 14 will reduce the temperature gradient between the motor 9 and the reduction gear, so when wear causes increased friction in the reduction gear 10, it may cause the motor 9 or the driver circuit to overheat. This is why an additional heat-conducting member is provided in the annular gap 20 between the outside of the transmission unit 8 and the inside of the cylindrical part 5. Figure 2 Such a heat conducting member 21 is shown between the motor 9 and the cylindrical portion 5 , preferably in a position axially overlapping the coils 16 , 17 of the motor 9 .

[0037] The drive train unit 8 may also include a brake 56, which may also be cooled by the heat conducting member 21. The brake may be of any conventional design, preferably operated by friction, and having a brake disc and a brake pad that are constantly pushed toward each other by a spring, and an electromagnetic actuator 57 that is continuously energized to overcome the spring force and keep the brake disc and brake pad apart. Thus, the brake ensures that in the event of a power outage, the robot will remain stationary but will not collapse. In this brake 56, the main source of heat dissipated via the heat conducting member 21 is the actuator 57. In FIG. 2 , the actuator 57 is shown as axially overlapping the heat conducting member 21.

[0038] according to Figure 3 In the first embodiment shown in the middle radial cross-section, the heat-conducting member 21 is an extruded profile, preferably aluminum, and has a concave cylindrical inner flange 22 and a convex cylindrical outer flange 23, the curvature of the concave cylindrical inner flange is closely fitted with the outer side of the motor 9, the curvature of the convex cylindrical outer flange is fitted with the inner side of the cylindrical part 5, and at least one, preferably multiple radially extending walls 24 extending from the inner flange 22 to the outer flange 23.

[0039] Preferably, a layer 25 of thermally conductive paste is provided between the flanges 22, 23 and the surfaces of the motor 9 and the cylindrical portion 5 to ensure efficient heat flow over the entire surface of the flanges 22, 23. Conveniently, the layer 25 may be a graphite layer or a graphite-containing layer, since the lubricating properties of graphite facilitate the introduction of the thermally conductive member 21 into the gap 20 in frictional contact with the surfaces of the motor 9 and the cylindrical portion 5.

[0040] like Figure 3 As shown, the arrangement of the heat conducting member 21 is symmetrical about the axis 3 - 2 to prevent the reduction gear 10 from being subjected to an asymmetric load, causing the transmission ratio of the reduction gear 10 to fluctuate, thereby affecting the operating accuracy of the robot arm 1 .

[0041] exist Figure 3 In the embodiment of the present invention, the four radially extending walls 24 and the flanges 22, 23 of each heat conducting member 21 form a frame defining three longitudinal cavities 26. By filling these cavities 26 with a heat conducting material, the cooling capacity of the heat conducting member 21 can be greatly improved. The heat conducting material can be, for example, graphite or a graphite-containing material for layer 25.

[0042] Figure 4 Two other embodiments of heat conducting members 27 , 28 that may be inserted into the gap 20 between the motor 9 and the cylindrical portion 5 are shown.

[0043] The heat-conducting member 27 comprises a frame formed by a metal (preferably aluminum) extruded profile 29 having a central web 30 extending in a circumferential direction relative to the axis 3-2 when mounted as shown, and ribs 31 extending from the central web 30 toward the motor 9 and the cylindrical portion 5 and inclined relative to the radial direction. The radial dimension of the extruded profile 29 when extruded can be slightly larger than the radial dimension of the gap 20, so that in order to insert the heat-conducting member 27 into the gap, it is necessary to increase the inclination of the ribs 31, so that the central web has a slightly undulating shape as shown in the figure, and the edges of the ribs 31 are pressed against the motor 9 and the cylindrical portion 5, thereby ensuring close thermal contact.

[0044] The grooves between adjacent ribs 31 may be filled with a ductile thermally conductive material 32 , just like the cavities 26 of the component 21 .

[0045] The heat-conducting member 28 comprises one or more sealed cavities 33 filled with a heat-carrying fluid in liquid and gas phases. On the inner side of each cavity 33, facing the motor 9, there is provided a cored layer 34 which tends to absorb the heat-carrying fluid in liquid phase, causing it to evaporate by the heat from the motor 9. The outer side of each cavity 33 is cooled by contact with the cylindrical part 5, causing the vapor to condense there. When a droplet formed on the outer side becomes large enough to be moved by the movement of the robot arm 1, it is absorbed as soon as it reaches the cored layer 34. Therefore, the cored layer 34 is always wet and ensures effective heat transfer to the cylindrical part 5.

[0046] The thermally conductive member 28 may be formed by providing two layers of flexible films of resin material, forming a cored layer 34 by depositing a nonwoven layer of thermoplastic fibers on an inner film 35 of the film, placing an outer film 36 on the cored layer 34 and locally welding the sandwich structure thus obtained to form welds 37, the welds 37 defining the cavity 33, and the fibers of the cored layer 34 being fused to form a sealing layer between the two films 35, 36. The resin material of the films 35, 36 may be any material capable of forming a sealing joint with the material of the cored layer 34.

[0047] Unlike the members 21, 27, the heat conducting member 28 does not have to be pressed into the gap 20 to ensure close thermal contact. When cool, it can be thinner than the gap 20 and can simply be slid into it. When the motor 9 heats up during operation, the heat conducting member 28 also heats up. The formation of internal steam causes the member 28 to expand, so that the membranes 35, 36 are in close contact with the motor 9 and the cylindrical part 5, thereby ensuring efficient cooling when required.

[0048] Figure 5Two further embodiments of heat-conducting members 42, 43 are shown in FIG. Member 42 comprises inner and outer flanges 44, 45, which may be part of an extruded profile made of a highly heat-conducting metal such as aluminum or copper, and a flexible member 46 of braided wire located between flanges 44, 45. An axially extending track 47 is formed on the outside of the powertrain unit 8, which is capable of engaging the profile (e.g., having a dovetail cross-section) of the inner flange 45. A similar mating profile 48 is formed on the inner side of the outer flange 45 and the housing 4. This enables the heat-conducting component 42 to be installed in the gap 20 in the following manner: at the end of the shell with the cover 6 removed, the flanges 44, 45, the corresponding profiles of the transmission system unit 8 and the shell 4 are matched with each other; the component 42 is shifted along the axis 3-2 until the flat hole 49 on the inner flange 44 overlaps with the threaded hole 50 in the transmission system unit 8 and the window 51 in the shell 4, and the threaded hole 52 of the outer flange 43 overlaps with the flat hole 53 of the shell 4, and then these flanges are securely attached by screws 54.

[0049] The heat conducting member 43 is Figure 4 The core layer 34 is replaced by a core structure 55 that is thin enough to maintain the liquid phase of the heat transfer fluid by capillary effect. The core structure 55 can be, for example, a plurality of closely spaced rib-like or filament-like elements that are integrally formed and protrude from the inner membrane 35 of the component 43 into the cavity 33.

[0050] Figure 6 A heat-conducting member 38 for cooling the circuit board 18 is shown. Here, it is difficult to ensure press contact with the heat-dissipating components on the circuit board 18; therefore, the heat-conducting member 38 is designed to absorb heat from the air near the circuit board through fins 39 extending radially inward from the bottom plate 40. The bottom plate 40 has a curvature that matches the inner side of the cylindrical portion 5. Some of the fins 39 have cutouts 41 for engaging the edges of the circuit board 18, ensuring that when the circuit board 18 is inserted into the cylindrical portion 5 and one or more heat-conducting members 38 engage its edges, the heat-conducting member 38 is firmly held both axially and radially. The fins 39 can have a sandwich structure with metal sheets on both sides and a graphite layer in the middle.

[0051] Reference numerals

[0052] 1 Robotic Arm

[0053] 2 Connecting rod

[0054] 3 Axis

[0055] 4 Housing

[0056] 5 Column part

[0057] 6 Cover

[0058] 7 Flange

[0059] 8 Powertrain unit

[0060] 9 Electric Motor

[0061] 10 Reduction gear

[0062] 11 Steel Wheel

[0063] 12 Screws

[0064] 13 Wave Generator

[0065] 14 Flexspline

[0066] 15 End face

[0067] 16 Rotor Coil

[0068] 17 Stator coil

[0069] 18 Circuit Board

[0070] 19 access

[0071] 20 Gap

[0072] 21. Heat-conducting components

[0073] 22 Inner flange

[0074] 23 External flange

[0075] 24 wall

[0076] 25 Thermal Conductive Layer

[0077] 26 Cavity

[0078] 27 Heat conducting components

[0079] 28 Heat conducting components

[0080] 29 Extrusion Profiles

[0081] 30 Center web

[0082] 31 Ribs

[0083] 32 Thermally conductive materials

[0084] 33 Cavity

[0085] 34 With core layer

[0086] 35 Intima

[0087] 36 outer membrane

[0088] 37 Weld

[0089] 38 Heat conducting components

[0090] 39 fins

[0091] 40 Base Plate

[0092] 41 Incision

[0093] 42 Heat conducting components

[0094] 43. Heat-conducting components

[0095] 44 Inner flange

[0096] 45 outer flange

[0097] 46 Flexible components

[0098] 47 tracks

[0099] 48 Profiles

[0100] 49 Flat hole

[0101] 50 threaded hole

[0102] 51 Window

[0103] 52 threaded holes

[0104] 53 Flat hole

[0105] 54 Screws

[0106] 55 Core structure

[0107] 56 Brake

[0108] 57 Actuator

Claims

1. An articulated robot arm (1), comprising at least a first link (2-2) and a second link (2-3) connected to the first link (2-2) via a rotary joint, the joint comprising a shaft (14) and a transmission unit (9, 10, 18), the shaft being rotatable relative to the first link (2-2) about an axis (3-2) and being non-rotatably connected to the second link (2-3), the transmission unit being mounted inside a housing (4) of the first link (2-2) for rotating the shaft (14), wherein an annular gap (20) is formed between the outer side of the transmission unit (9, 10, 18) and the inner side of the housing (4), characterized in that At least one heat conducting member (21, 57, 58, 38) is mounted in the gap (20) in thermal contact with the outside of the power train unit (9, 10, 18) and the inside of the housing (4).

2. The articulated robot arm according to claim 1, wherein the first link (2-2) has an end surface member (7) facing the second link (2-3) and supporting the transmission unit (9, 10, 18).

3. The articulated robot arm according to claim 1 or 2, wherein the thermal contact is at least one of: a press-fit contact, a threaded contact, and an adhesive contact.

4. An articulated robot arm according to any one of the preceding claims, in The drive train unit (9, 10, 18) comprises an electric motor (9), and the heat conducting member (21, 27, 28) is located near the coils (16, 17) of the motor (9), or wherein The power train unit (9, 10, 18) further comprises a driver circuit associated with the motor (9), and the thermally conductive member (38) is located adjacent to the circuit. The transmission unit (8; 9, 10, 18) comprises a reduction gear (10), and the heat-conducting member (21, 27, 28) extends around a housing of the reduction gear, optionally, the reduction gear (10) is a harmonic drive gear, and the housing comprises a rigid wheel (11) of the harmonic drive gear, or wherein The power train unit (8; 9, 10, 18) comprises a brake, and the heat conducting member (21, 27, 28) is located near the brake.

5. The articulated robot arm according to any one of the preceding claims, wherein the heat conductive member (21, 38, 42) has at least one of the following: an outer flange (23, 40, 45) in contact with the housing (4) and an inner flange (22, 44) in contact with the drive train unit (8; 9, 10, 18).

6. The articulated robot arm according to claim 5, wherein the heat conductive member (21, 38) comprises at least one radially extending wall (24, 39), optionally wherein the at least one wall (24, 39) extends in a direction parallel to the axis (3-2).

7. The articulated robot arm according to claim 5, wherein the heat conductive member (42) comprises at least one of the following: a braided wire member (46), a multi-leaf member or a multi-strand member.

8. An articulated robot arm according to claim 6 or 7, wherein the at least one flange is in locking engagement with an axially extending track of the housing or the drive train unit.

9. The articulated robot arm according to any of the preceding claims, wherein the heat conducting member (21, 27, 38) comprises an extruded profile (29), the extrusion direction of which is optionally parallel to the axis (3-2).

10. The articulated robot arm according to any one of the preceding claims, wherein the cross section of the heat conducting member (21, 27, 28, 38) is circular or arc-shaped, the arc preferably extending over an angle of less than 180°.

11. An articulated robot arm according to any one of the preceding claims, wherein the thermally conductive member (21, 27) comprises a metal frame and a ductile thermal conductor (32) filling at least one cavity or recess of the frame.

12. The articulated robotic arm of claim 9, wherein the ductile thermal conductor (32) comprises graphite.

13. The articulated robot arm according to any one of the preceding claims, wherein the heat conducting member (28, 43) comprises a heat pipe.

14. The articulated robot arm according to claim 13, wherein the wall at the radial inner side of the heat pipe is provided with a cored material (34) or structure (55).

15. The articulated robot arm according to claim 13 or 14, wherein the wall of the heat pipe is made of a flexible resin film (35, 36).

Images