DRIVE UNIT

TECHNICAL FIELD

The present invention relates to a drive unit comprising an electrical motor.

BACKGROUND OF THE INVENTION

In many applications low speed drive units are needed to rotate objects. Then it is often a big advantage to reduce the weight of the drive unit, especially when the drive unit is moved by other parts of the system it works in. Examples of such systems are vehicles, linear guide ways and robots. In the case of industrial robots, the most important issue with respect to weight is to reduce the weight of the wrist, which in turn makes it possible to reduce the power of the main axes and the weight of the moving parts of the robot. Such weight reductions imply lower robot cost, higher safety, easier installation, easier programming and improved performance.

Consequently, there is a need for a lightweight designed drive unit.

SUMMARY OF THE INVENTION

The object of the invention is to design a lightweight drive unit. Another object is to minimize the size of the drive unit.

According to an aspect of the present invention, there is provided a drive unit comprising the characterizing features of claim 1 and in a second aspect by a method for assembling a drive unit in accordance with the independent claim 25.

Preferred embodiments are described in the dependent claims.

The solution according to the first aspect of the invention is to provide a drive unit comprising an electric rotating actuator with a stator and a rotor. The drive unit further comprises a speed reducer. The drive unit is characterized in that the speed reducer comprises a wave generator and a flex spline, and that each of the stator, the rotor, the wave generator and the flex spline is designed with an centre hole and they are all arranged integrated in a common housing such that a tubular passage is provided for through the common housing.

The feature "cables and hoses" are defined as at least one cable and/or at least one hose supplying any energy or medium or transmitting measurement and control signals within and through the drive unit. The provided tubular passage is provided to accommodate the cables and/or hoses arranged within the drive unit and passing through the inside of the drive unit.

In one embodiment, an electric rotating actuator comprises a hollow high speed shaft on which a rotor is arranged.

In one embodiment, an electric rotating actuator comprises a hollow high speed shaft on which both a rotor and a wave generator are arranged.

In one embodiment, a rotor is arranged on a hollow high speed shaft and the wave generator is arranged on the rotor.

In one embodiment, an electric rotating actuator comprises a bearing arranged mounted around and holding the rotor.

In one embodiment, an electric rotating actuator comprises a bearing arranged around and holding the rotor and wherein the wave generator is arranged on the rotor.

In one embodiment, a low speed shaft is arranged journalled in bearings within the high speed shaft.

In one embodiment, a low speed shaft is arranged journalled in bearings within the high speed shaft and the flex spline is arranged on the low speed shaft.

In one embodiment, a low speed shaft is arranged journalled in bearings within the housing and providing the tubular passage.

In one embodiment, a low speed shaft is arranged journalled in bearings within the housing and the flex spline is arranged on the low speed shaft.

In one embodiment, the wave generator is arranged mechanically and rigid connected to the rotor.

In one embodiment, the rotor is arranged on a hollow high speed shaft, the wave generator is arranged on the rotor and the flex spline is arranged fixed on a low speed shaft.

In one embodiment, a flange is arranged to be rotated by the drive unit during operation.

In one embodiment, a flange is arranged to be rotated by the drive unit during operation and the flex spline is arranged fixed on the flange.

In one embodiment, a brake means is arranged integrated in the housing.

In one embodiment, at least one sensor means is comprised in the drive unit.

In one embodiment, the at least one sensor means is arranged for servo control of the drive unit.

In one embodiment, the at least one sensor means is arranged for feed back control of the speed reducer.

The housing of the drive unit comprises a high speed motor compartment for the actuator and a low speed gear compartment for the speed reducer. The low speed gear compartment is arranged sealed with respect to oil leakage from its environment. At least one rotating sealing is arranged preventing speed reducer lubrication from entering the motor compartment. When the gear compartment comprises grease, the sealing a labyrinth sealing is useful, since they are almost free from friction. When the gear compartment comprises oil, an overpressure is created within the compartment and an elastomeric sealing with ultra low friction is useful.

In one embodiment, a tube is mounted inside the tubular passage. One drawback when having cables and hoses in the centre tube is that the tube is rotating with high speed. Therefore an inner protection tube is needed, connected to the centre tube via two bearings. This will give an arrangement similar to Figure 5. However, in Figure 5 the inner shaft has a low speed rotation.

In one embodiment, the flex spline comprises a gable with at least one opening. Since the flex spline is completely comprised within the gear compartment, the opening does not need to be sealed.

In one embodiment, the housing comprises a gable wall with at least one opening. Using a speed reducer comprising a wave generator and a flex spline, e.g. a Harmonic Drive speed reducer, it is very important that the wave generator is accurately mounted relative the low speed components of the speed reducer. To make this possible there is usually a flexible transmission between the motor and the wave generator and the Harmonic Drive speed reducer is mounted independent of the mounting of the motor. In order to minimize the size and weight of the drive unit such a flexible transmission is not possible to use.

The opening/hole in the gable wall of the housing is sealed with a bolt with sealing compound in the thread.

If a wider centre channel is needed for cables and hoses the high speed shaft can have a larger diameter meaning that the rotor parts will come closer to the shaft and that a drum type of brake is probably needed since the radial space for the brake will be reduced. As an alternative the brake can be mounted on the outer part of the rotor giving a larger diameter of the drive unit, compare Figure 2. Simultaneously the central hole in the wave generator must be made bigger as well as the central hole in the flex spline cup. This should be possible, compare with the wave generator design in Figure 7. In principle the high speed shaft diameter could be increased so that the rotor cylinder could be mounted directly on the shaft. However, then the wave generator and the flex spline diameter must have larger diameters, which is actually possible since there is unused space around the Harmonic Drive components. Ideally, the Harmonic Drive diameter should be somewhat larger than the motor diameter, compare Figure 2.

In one embodiment, the drive unit is comprised in an industrial robot. In one embodiment, the drive unit is comprised in a wrist of an industrial robot.

In one embodiment, the drive unit is comprised in a driving wheel of a vehicle. This design makes it possible to make very compact propulsion solutions, especially for small vehicles like small autonomous robots. It could also be used for the rack and pinion application shown in Figure 19, whereby one of the wheels is replaced by the pinion gear.

In one embodiment, the drive unit is comprised in a linear guide way (Figure 18). The more common ball screw arrangement with the drive unit fixed arranged to rotate the screw is also possible. Then the linear cylindrical bearing is mounted on the linearly moving ball bearing unit. Light weight linear motions have many applications in the control of different functions in different vehicles. Examples are flaps and rudders in airplanes, valves, levers and gears in engines, docking equipment in space vehicles.

The solution according to the second aspect of the invention is to provide a method of assembling a drive unit with radial symmetry, comprising mounting an electric rotating actuator with a rotor and a stator axially from a direction A, mounting a speed reducer, with a wave generator and a flex spline, axially from the same axially direction A, rotating the rotor without fastening the wave generator on the rotor and then fastening the wave generator using a tool operating through at least one hole in the low speed compartment.

In one embodiment, the method comprises adjusting the wave generator in radial direction by rotating the rotor such that the vibrations of the gear of the flex spline are minimized when the speed reducer is assembled and the wave generator is free floating in radial direction in relation to a high speed shaft, comprising fastening of the wave generator using a tool operating through holes in the flex spline and providing an integration of the electric rotating actuator and the speed reducer into one unit.

According to the invention, there is at least one hole in the housing and in the flex spline structure to be able to reach a mounting element/tool between the high speed shaft and the wave generator. Examples of mounting methods are screwing, gluing and laser welding.

In one embodiment, the tool is operating through at least one hole in a flange comprised in the drive unit.

In one embodiment, the tool is operating through at least one hole in the wave generator comprised in the drive unit.

In one embodiment, the tool is operating through at least one hole in a gable of the flex spline.

In one embodiment, the tool is a screw driver operating for fastening of the wave generator by tightening at least one screw.

In one embodiment, the method is provided by having holes in the gable of the flex spline through which a screw driver can reach screws that fasten the rotor shaft of the motor directly to the spline generator when this has been adjusted to minimum vibration. This can be seen in for example Figure 12, where the screws 117 can be reached through the screw holes 125 in order to fasten the wave generator mechanics 118 to the motor shaft 105.

In one embodiment, the method comprises mounting the drive unit and then fastening the wave generator using a tool operating through at least one hole in the housing of the drive unit. In one embodiment, the at least one hole is arranged in a gable of a low speed compartment of the housing comprising the gear.

In one embodiment, the method comprises mounting the drive unit, mounting a tool flange comprising at least one hole and then fastening the wave generator using a tool operating at least through the hole in the flange and a hole in the housing,

In accordance with the invention, it is necessary to use a lightweight electrical motor combined with a lightweight speed reducer. These components are tightly integrated together with sensors needed for the control of the drive unit. This integration must be made in such a way that rotating shafts, bearings and housing are minimized by having the motor and speed reducer as close as possible to each other and to design the structure in such a way that the material and the bearings are optimally used. It is also important to make use of a high speed motor together with a speed reducer with high gear ratio. In order to avoid overheating the

motor should have a very low power loss and the gear should be lubricated in an oil chamber to make use of the cooling possibilities obtained from oil flow. The drive unit is designed with two compartments, one motor compartment and one gear compartment. This is to assure that no lubricating oil or grease is entering the motor.

Simultaneously the drive unit must be designed in such a way that it is easy to mechanically adjust the components for optimal performance and that the assembly can be easily made, preferably automatically.

When designing a lightweight motor for this application it is necessary to have a high density motor with very strong magnetic field in the air gap and to be able to obtain very high motor speed without unwanted heating. One way to obtain these features is to have an ironless thin laminated stator winding and a rotor with magnets generating a strong field across the stator winding. This arrangement can be made by having a cylindrical stator laminate and a cylindrical rotor with a cylindrical slit into which the stator cylinder is mounted. A motor with the rotor and the stator is manufactured by the company Thin Gap and is able to generate a continuous torque of 0.63 Nm and a peak torque of 4 Nm, having a weight of only 0.57 kg (including bearings and housing). Instead of having a cylindrical stator and rotor, these components can also be manufactured as discs, which will give a flat motor design. The motor components are mounted in the motor compartment of the drive unit module. As a lightweight speed reducer the well known Harmonic Drive technology is adopted. The main components of a Harmonic Drive gear assembly are the wave generator on the high speed side and the flex spline on the low speed side. These components are integrated into the gear compartment, which is filled with oil for the lubrication of the gear teeth of the flex spline and of the gear ring outside the flex spline. The Harmonic Drive technology can be developed to have outstanding torque to weight ratios. For example, a version described in the literature with continuous torque of 40 Nm, peak torque of 92 Nm and gear ratio of 160:1 can be manufactured with a weight of only 0.127 kg. Since this type of lightweight speed reducer has a built in flexibility, an encoder is used to increase the stiffness of the drive unit by means of feedback control. The encoder selected for this is a capacitive encoder, which is accurate, light weight, easy to integrate mechanically, robust and of low cost. Of special interest is to use the encoder concept developed by Hexagon Metrology. In this encoder, groups of four transmitting electrodes for each receiving electrode, is used to measure the rotation angle with very high precision. Since rotation angle is also needed to be measured on the high speed side

because of the requirements from the servo control (including motor commutation), capacitive encoders will be mounted both in the motor compartment and on the outgoing mounting flange. The capacitive encoder technology is critical to obtain measurements on the low speed side since no other technology has the needed combination of high precision, robustness, easy to integrate and low cost. The high speed encoder on the motor side can be replaced by for example a resolver type of angle measurement sensor, even if this will be heavier, take a bigger space and be more difficult to integrate into the motor compartment.

Since a brake and capacitive encoder rings with support ring can be mounted after the mounting of the motor and speed reducer it is easy to get access to the fastening site when the wave generator is adjusted on the rotor. See for example the brake 46, 47 and capacitive encoder rings 49, 50 with support ring 51 in Figure 5.

Making the integration between a braking structure and the rotor, it is important to avoid unwanted effects on the rotor from the braking with respect to mechanical stress and thermal effects.

When an absolute measurement encoder is needed on the high speed side, the encoder rings must be broader and the brake must be moved to be outside the rotor cylinder. To avoid too big increase in drive unit diameter then, a drum type of brake could be used with a cylindrical braking track on the outer part of the rotor. An alternative is to mount the rotor in the opposite direction and mount the stator on the gable wall and the encoders on the middle wall of the drive unit. It is however more difficult to mount the stator after the rotor and the mounting of the capacitive encoders will be more tricky.

When an absolute encoder is needed on the low speed side, the face plate flange should be made with a larger diameter. With a bigger change of the mounting of the speed reducer it could also be possible to reduce the inner diameter of the low speed encoder rings.

Dependent on the requirements the design of embodiments, comprising a rotor and a wave generator arranged on a high speed shaft and a flex spline on a flange, can easily be adjusted.

The invention is a general drive unit concept. The description comprises a number of different embodiments and mentions a number of different technical areas, where the drive unit is

usable. These are not limitations. Other possible applications are wheel chairs and other equipment for disabled people, including also robots for feeding and other services. Extremely Lightweight drive units are also very important for autonomous vacuum cleaners and lawn-mowers. In hospitals light weight drive units are needed for lifts to be easily attached to beds. The lightweight drive units will also be valuable for intelligent lifting in industry to be integrated in so called Intelligent Assist Devices (IAD).

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained more closely by the description of different embodiments thereof and with reference to the appended drawing in which:

Figure 1 is a drive unit according to an embodiment of the invention,

Figure 2 is the drive unit in Figure 1 in more detail,

Figure 3 is the drive unit in Figure 1 ,

Figure 4 is a two axes drive unit according to an embodiment of the invention,

Figure 5 is a drive unit according to an embodiment of the invention with double shafts,

Figure 6 is a drive unit according to an embodiment of the invention with a single shaft,

Figure 7 is a cross-section of the drive unit of Figure 6,

Figure 8 is an industrial robot wrist assembly comprising three drive units,

Figure 9 is an industrial robot wrist assembly comprising three drive units,

Figure 10-12 is a drive unit according to an embodiment of the invention with a tubular member,

Figure 13 is a drive unit according to an embodiment of the invention with a tubular member,

Figure 14 is a drive unit according to an embodiment of the invention with a disc type motor,

Figure 15a-c is a drive unit according to an embodiment of the invention comprised in a driving wheel for a vehicle,

Figure 16 is a drive unit according to an embodiment of the invention comprised in a vehicle,

Figure 17 is a drive unit according to an embodiment of the invention comprised in a linear guide way.

Figure 18 is a drive unit according to an embodiment of the invention comprised in an arrangement for actuating a linear movement,

Figure 19 is a drive unit according to an embodiment of the invention comprised in a vehicle body.

Figure 1 is a lightweight drive unit 1 comprising a high speed motor compartment 2 and a low speed gear compartment 3. The motor compartment comprises a lightweight rotor 6, a lightweight stator 7 and a first sensor means 8a. The gear compartment 3 comprises a lightweight speed reducer 5. The rotor and the stator are axially mounted from a direction A. The speed reducer with a wave generator and a flex spline are mounted from the same axially direction A.

Further, the drive unit comprises an outgoing mounting flange 4 and a second sensor means 8b. The drive unit is an integration of a lightweight electric motor, a lightweight speed reducer and lightweight sensors. The drive unit also comprises a brake means with a brake disc 15 and a brake shoe 16, which is presented in more detail below.

Figure 2 is a drive unit comprising a thin laminated stator winding 11 mounted on a wall 34 between the high speed (motor) 2 and low speed (gear) compartment 3. A rotor 10 is positioned with high accuracy on the outer shaft 12 to make it possible to rotate the rotor without touching the stator 11 in the thin air gap of the rotor. The rotor shaft 12 is connected to the housing 2 by means of two bearings 13 and 14, which could be ball- or needle bearings to obtain a lightweight wrist.

The drive unit comprises an encoder concept 9 comprising a rotating encoder ring 18 for measuring the angle of rotation of the rotor and is mounted via a mechanical connection 17 on the rotor 10. The encoder concept further comprises a fixed encoder ring 19, which is equipped with wiring connections and which is mounted on the wall 34 between the high speed 2 and low speed 3 compartments. The encoder rings 18, 19 are simply glued to the mechanical connection 17 and the wall 34. Connected to the rotor is also a cylindrical brake disc 15 which can be engaged by a cylindrical brake shoe 16 mounted on the housing wall 35.

The shaft 12, rotating with high speed, is mechanically connected to a wave generator 20. When the wave generator is mounted on the shaft 12, it is important to be able to adjust the wave generator in radial direction such that the vibrations of the gear are minimized. This can be made by rotating the motor when the speed reducer is assembled and the wave generator is free floating in radial direction in relation to the high speed shaft. With such a mounting action the wave generator will automatically find the assembly position for minimum vibrations. The wave generator 20 is then fixed to the high speed shaft 12 by means of screws 20c via a disc 20b fixed to the shaft 12. In order to be able to adjust the wave generator after

the mounting of the motor and speed reducer, there are holes 22b, 33b in the flex spline gable 22a and in the speed reducer housing 33 respectively. The wave generator 20 is fastened using a tool 37 operating through 33b, 22b for mounting a screw 20c in a hole of the wave generator. If a flange is mounted on the drive unit before fastening the wave generator, the flange is arranged with at least one hole too.

Via a bearing 21 the wave generator engages gear teeth between the flex spline 22 and the gear ring 23. In this way very high gear ratios can be obtained between the wave generator and the flex spline. The flex spline is mounted on an inner shaft 25, which is connected to the housing by means of two bearings 24 mounted on a ring 36 on the housing 35 and 26 mounted on the housing 33. A tubular passage 31 formed by the inner shaft 25 can be used for cables 95. In one end of the inner shaft 25 a flange 29 is mounted with holes 30 for the mounting drive units, tools or other objects that are rotated by the drive unit. A low speed encoder 27, 28 is mounted between the back side of the flange 29 and the gable wall 33a of the low speed housing 33 with the encoder ring 27 having the electrical connections on the gable wall and the other encoder ring 28 on the flange. As for the high speed encoder rings 18, 19 also these encoder rings can simply be mounted by gluing. To prevent dirt and fluid from entering between the encoder rings a sealing should be used between the flange and the gable wall. There is also a need of sealing between the oil- filled low speed compartment and the high speed compartment. One such sealing is symbolized by a ring 32 and if the bearing 14 between the compartments is not tight, a sealing is also needed in connection to this bearing.

It is noted that each embodiment described comprises at least one hole in a gable of the flex spline. This is not shown in all Figures since they are more schematic.

With the design described above it has been found possible to build a drive unit with the performance according to Figure 3.

Figure 4 is a two axes drive arrangement comprising a first Ia and a second drive unit Ib mechanically connected.

By using more elaborated sealing with very low friction as for example a labyrinth sealing, it is possible to further integrate the motor and the speed reducer as illustrated in Figures 5 - 7.

Both the motor and the speed reducer have cylindrical shape, making it possible to let the motor working partly inside the speed reducer. In Figure 5, the rotor 40 is mounted on a shaft 41 in such a way that a flex spline cup 55 will be arranged outside the rotor.

To make this possible the wave generator 55 is mounted directly on the outer part of the rotor 40. The mounting is described in more detail below and in Figure 11. For the self alignment of the wave generator 52 a floating mounting is needed between the rotor and the wave generator. As described for Figure 2, this can be made using a sleeve and screws. Since a brake 46, 47 and capacitive encoder rings 49, 50 with support ring 51 can be mounted after the mounting of the motor and speed reducer it is easy to get access to the mounting site when the wave generator is adjusted on the rotor. In order to seal of the lubricated gear from the rest of the components, sealing rings 66 and 67 are used and sealing will also be necessary for the bearing 57. The stator 45 is mounted on the housing wall 64 and penetrates the air gap of the rotor 40. The rotor must be rigid enough to carry the wave generator 52 when it engages the gears of the flex spline 55 and the gear ring 54 via the bearing 53. The gear ring 54 is mounted on the cylindrical wall 65 of the housing. The rotor also carries a brake disc ring 46 and a capacitive ring encoder holder 51, which is also used for sealing purpose 66. On a mechanical structure 48 on the cylindrical housing wall 65 both the fixed encoder ring 49 and the brake shoe 47 are mounted. The fixed encoder ring is mounted on the capacitive ring encoder holder and is equipped with the electrical connections. In order to hold the rotor shaft and also to make adjustment of it, a cylinder 44 is used for the bearings 42 and 43. The flex spline 55 is mounted on the shaft 56 and this shaft is connected to the housing by means of the bearings 57 (on the wall 64 via the bearing 43) and 58 (on the wall 63). The capacitive encoder rings 62, 61 to measure the angle of the outgoing low speed shaft 56 are mounted on the housing wall 63 and the flex spline 55. A flange 60 is mounted on the low speed shaft, the tubular centre of which 59 can be used for cables and hoses. With this design a shorter and lighter drive unit can be obtained, to be paid with more difficult oil sealing and assembly.

In Figure 5, the mounting of the wave generator 78, 79 is made through holes/openings 55b in the flex spline 81 and holes/openings 63b in the wall 63 on the flange side of the housing. The screw 40b is used to fix the rotor to the high speed shaft 41 after the assembly of the motor and the speed reducer. This makes it possible to adjust the wave generator 55 during rotation of the motor. These holes/openings are used for a fastening tool. In this embodiment,

the wave generator is fastened with screws. A screw driver is inserted through an opening to tighten at least one screw when the drive unit is assembled.

The design with openings/holes in the flex spline is a general solution for all embodiments shown. In the Figures 2 and 5, there is also provided holes/openings in the housing. This design is suitable for all types of fastening mentioned above and the corresponding tools.

A further integration is shown in Figure 6, in which an outer bearing 69 is used for the rotor 68. In this way the double shaft design can be omitted and the diameter of a low speed shaft 82 can be increased, giving more room for cables and hoses. A sealing ring 85 is used between the rotor 68 of the motor and the flex spline 81. It is also necessary that the rotor bearing 69 and shaft bearing 84 are sealed. A disc brake ring 74 is mounted on the rotor bearing 69 using a support ring 77 and on the same support ring an encoder support ring 76 is mounted. Capacitive encoder rings on the high speed side 72, 73 and the low speed side 86, 87 are used in the same way as in Figure 5. One advantage with respect to the encoder rings on the high speed side in Figure 6 is that these are easier to access than in the design of Figure 5.

Figure 7 shows the low speed shaft 82, the rotor 68 and the stator 71 in between. Further, Figure 7 shows the wave generator 78, 79, the flex spline 81, the gear ring 80 and the housing 91. From assembly point of view it is very important that all the assembly is made axially from one direction. This is made possible thanks to the radial symmetry of the integrated drive unit as seen in Figure 7.

Figure 8 outlines the potential of using three of the drive units described Ia, Ib and Ic as a wrist assembly on the fore arm of an industrial robot. As a comparison a typical high performance robot used in industry today is shown (the ABB IRB2400 with a maximum load capacity of 10 kg). If the fore arm tube 96 connecting the wrist assembly Ia, Ib and Ic with the main axes of the robot is made from carbon reinforced epoxy it will be possible to reduce the total weight of the forearm of a robot of the ABB IRB2400 type with 5 - 10 times. This will drastically reduce the torque and power need of the main axes and the main axes mechanical structure can simultaneously be designed for a much lower weight, giving a cheaper, safer, lighter and easier to control robot. In Figure 8, the drive units are connected by simple plates 93 and 94 and the hollow, tubular centres of the drive units are used for cables

95. An improved mounting of the drive units with respect to the cables are shown in Figure 9. Here the shafts of unit Ia and Ic are in a common plane and drive unit Ib is mounted with an offset relative drive units Ia and Ic in order to make it possible to have the cable 95 pass by drive unit Ib. Unit Ib is mounted on the flange of unit Ia with the plate 98 and unit Ic is mounted on the flange of unit Ib with the simple structure 99. The cable is as before 95 and the carbon tube 96. The cable 95 is arranged straight through the robot wrist, which is an advantage especially when the cables comprises the process cables and/or hoses since they offer resistance to bending and/or turning.

Figures 10 is an elaborated design of a drive unit using two compartments as in figure 2. In Figure 10 it can be seen how the rotor 100, 101, 102 and 103 is mounted on the high speed shaft 105 using a conical bushing ring 106, which is pressed between the rotor part 102 and the shaft 105 using a nut 107a, which is screwed on the shaft 105. Between the nut and the bushing is a washer 107b. In this way, it is very easy to mount the rotor with high precision on the high speed shaft. The high speed shaft 105 is mounted on the housing gable wall 114 via a ball bearing 108a and on the middle section wall via a needle bearing 109. The bearing type in the gable wall 114 is selected to allow accurate adjustment (with for example a ball track bearing) of the shaft 105 without obtaining stress in the shaft or the bearings supporting it. The gable wall bearing 108 is pre stressed between a clip ring 108b and the gable wall 114. In order to avoid the need of lubricating the gable wall bearing this can be a ceramic bearing. The rotor consists of a magnet carrying structure 100, 102 and the magnets 101. It is also equipped with a wall 103, which carries a brake disc, engaged by a magnetic brake 104b using a brake pad 104a. A capacitive encoder ring 112 is mounted on the rotor and the other ring 113 of the high speed encoder is mounted on the gable wall 114. In the air gap of the rotor the stator 111 is mounted and this mounting is made with screws 116, (see Figure 11). The windings from the fixed encoder ring 113 and the stator 111 are situated in the free space 136 outside the rotor part 100 and will get out through a hole (not shown) in the high speed compartment wall.

Figure 11, Figure 10 with more details, shows the wave generator 118 of the Harmonic Drive speed reducer is mounted on the high speed shaft 105 with screws 117. The diameter of the screw holes in the wave generator are made somewhat larger that the diameter of the screws making it possible to adjust the wave generator for minimum speed reducer vibrations. The gear ring 120 of the Harmonic Drive is mounted using screws 121 early in the assembly

sequence. These screws are also used to mount the cylindrical high speed compartment part 115 on the cylindrical low speed compartment part 122. In order to obtain as low weight as possible and in order to match the temperature coefficient of the steel parts of the speed reducer, the low speed compartment part could be manufactured in special Aluminium alloys. The flex spline unit 119 is mounted on the flange 127 and on a bearing 123, preferably of cross track type, by means of screws 125 running into a ring 126 with screw-thread holes. The screws 125 clamp the flex spline 119 between the ring 126 and another ring 124, which in turn is used to clamp the bearing 123 against the flange 127. After trimming the adjustment of the wave generator 118 on the high speed shaft 105 by turning the rotor shaft 105 around, the wave generator screws 117 are tightened by a screw driver using holes in the flange 127 and the flex spline 119. If not all the flex spline screws 125 are used during the adjustment process, the holes for the lacking screws can be used to reach the wave generator screws 117.

Figure 12 shows how the bearing 123 is clamped between the high speed compartment wall 122 and a ring 130 using screws 129. The low speed encoder rings 132, 133 are mounted on the assembly ring 130 and on the back side of the face plate 127 respectively. The holes 137 are used for mounting the objects to be rotated by the drive unit. A tube 135 inside the high speed shaft is introduced to make a sealing of the low speed compartment possible. Thus, the sealing rings 128 and 134 prevent oil from leaking into the centre of the drive unit. Moreover, a sealing ring 110 is used to prevent oil leakage into the motor side and another sealing ring 131 is used to avoid leakage to the low speed encoder.

The prototype design in Figures 10 - 12 can be modified to obtain a larger centre hole for the process cables and to be able to use broader capacitive encoder rings as illustrated in Figure 13. As can be seen in the figure the conic mounting of the rotor 140 is now made directly on the rotor cylinder and the brake 151 - 153 is now of a cylindrical type and the stator is mounted on the outer housing wall 159. Thus, only the encoder rings 155 and 156 occupy the gable wall side and can therefore be made broader to include extra electrodes for absolute angle measurements. Also shown in the figure is a cable protection tube 157, which is fixed to the housing at the high speed compartment gable and mounted on a bearing 180 in the flange part 170. As an alternative to the design in Figure 13 the rotor can be mounted in the opposite direction, meaning that the stator 158 will be mounted on the gable wall and the encoder rings between the rotor and the middle wall of the drive unit. However, then the assembly will be more difficult. In order to be able to use broader encoders 177, 178 also on the low speed side

the flange 170 diameter has been increased and a protection ring with a sealing 174 has been introduced.

At least one rotating sealing (110, 149) preventing speed reducer lubrication from entering the motor compartment is a labyrinth sealing or an elastomeric sealing with ultra low friction.

The components in Figure 13 are:

140: Rotor

141: Rotor magnets

142: Conical bushing ring for high precision mounting of the rotor on its shaft (143)

143: High speed motor shaft

144: Washer

145: Nut for fixing the conical bushing (142)

146: Gable wall for the high speed compartment

147: Bearing for the high speed shaft (143)

148: Circular clip for the mounting of the bearing (147).

149: Sealing to avoid oil leakage from the low speed to the high speed compartment.

150: Needle bearing for the high speed motor shaft (143)

151: Cylindrical braking drum mounted on the rotor (140)

152: Braking pad

153: Magnetic braking mechanism

154: Steel ring for the rotating encoder ring (155)

155: Rotating encoder ring (having no wiring)

156: Fixed encoder ring (with the wiring)

157: Protection tube mounted on the gable (146)

158: The stator

159: High speed compartment housing

160: Sealing for oil

161: Low speed compartment housing

162: Screws for mounting of Harmonic Drive gear ring and for mounting the high speed compartment on the low speed compartment

163: The gear ring of the Harmonic Drive speed reducer

164: The wave generator of the Harmonic Drive speed reducer

165: Screws to mount the wave generator on the high speed motor shaft (143). The hole in the wave generator must have a diameter bigger than the screw to make adjustment possible. 166: The flex spline of the Harmonic Drive speed reducer

167: Ring with screw threaded holes for fastening the flex spline to the flange (170) 168: Ring for the mounting of the flange bearing (171) and the flange sealing (181) 169: Screws for mounting the flex spline (166), the flange bearing (171), the flange sealing

(180) and the flange (170) 170: The flange structure

171: The flange bearing (preferably of cross roller type) 172: Ring for mounting of the flange bearing (171) on the low speed compartment housing wall (161)

173: Screw to mount the flange bearing fastening ring (172) 174: Sealing to avoid dust and fluid entering the encoder rings (177, 178) 175: Protection ring for the encoder rings (177, 178) 176: Metal ring for the mounting of the fixed encoder ring (177) 177: Fixed encoder ring with wiring

178: Rotating encoder ring mounted on the flange structure (170) 179: Mounting screw holes on the face plate of the flange structure (170) 180: Bearing for the protection tube (157) 181: Sealing for oil leakage

If the cylindrical motor design used up to now is exchanged to a disc type motor design the drive unit can be made shorter, which is an advantage for example for the unit Ib in the figures 9 and 10. Thus, Figure 14 shows a drive unit design with a disc type motor having a narrow air gap. Since the low speed side of the design is the same as in Figure 13, this will be left out in the following description. The rotor now consists of 2 discs 182a, 182b and the rotor has to be assembled during the assembly of the drive unit. At first the inner rotor disc 182a, mounted on its holder 184, is mounted on the high speed shaft 188 using the conical bushing 187. Then the stator disc 201 is mounted on the outer housing wall 185 and at last the second rotor disc 182b with its magnets 183 is mounted on the first rotor disc 182a. The ring 197 for holding the rotating encoder ring 198 is mounted on the outer rotor disc 182b via an offset structure 200. The brake disc 194 is also mounted on the outer rotor disc 182b.

The components in Figure 14 are:

182: Rotor parts (182a, 182b) 183: Rotor magnets 184: Rotor holder

185: High speed compartment housing 186 Needle bearing for the high speed motor shaft (188)

187: Conical bushing ring for high precision mounting of the rotor on its shaft (188) 188: High speed motor shaft 189: Sealing

190: Protection tube for the process cables and hoses 191: Circular clip for the mounting of the bearing (192) 192: Bearing for the high speed shaft (188) 193: Gable wall for the high speed compartment 194: Braking disc mounted on the rotor (182b) 195: Braking pad

196: Magnetic braking mechanism 197: Steel ring for the rotating encoder ring (198) 198: Rotating encoder ring (having no wiring) 199: Fixed encoder ring (with the wiring) 200: Offset structure for the encoder mounting ring (197) 201: Stator disc

Figure 15 shows the use of the drive unit for driving a wheel of a vehicle, for example an autonomous vehicle to be used in for example in space missions or in security guard tasks. The compact high power drive unit gives the possibility to make a highly integrated traction system for the vehicle. Thus, as shown in figure 15b, the motor 241 is mounted inside a tube shaft 244, which is connected mechanically to the wheel hub 242 by means of a bearing 243. The mounting of these components can also be seen in the cut A-A in figure 15c. The hub is mounted on the output flange of the drive unit using for example nuts, for which holes 246 are made in the hub. Other holes 247 in the hub are used to mount the tire on. With this highly integrated shaft/drive/hub concept a traction module is obtained, which can be used also for two wheel arrangements in for example bikes and two wheels on and shaft vehicle with built in balancing control, see figure 16.

Figure 16 is a vehicle that makes use of the lightweight drive unit concept. Two integrated shaft/drive unit/hub/wheel modules 248 and 249 according to Figure 15 are mounted on a common shaft 250 and on this shaft a platform 252 with a handle 253 are mounted via a box 251. In this box the battery and all the electronics to control the balance, the speed and the speed difference between the wheels can be integrated. The driver stands and travels on the platform 252. The handle 253 has control levers for vehicle speed and motion direction. It shows how high integration can be obtained with the drive unit and it is easy understand how other types of vehicles with one or more wheels can easily be designed in a modular way.

Figure 17 exemplifies the use of the drive unit for a linear guide way. On the support beam 254 two guide ways 255 and a rack 256 are mounted. A cart 259 slides on the guide ways by means of bearings 258. In order to actuate the cart a pinion 257 is used, fixed to the cart by a shaft 244 using a shaft holder 260. The drive unit is integrated into the pinion in the same way as it was integrated into the hub according to Figure 15. This is also shown by the inserted Figure 17b. In this way a very lightweight rack- and pinion cart is obtained for low cost and high performance applications.

Figure 18 shows an arrangement for actuating a linear movement using a ball screw solution. The ball bearing unit 262 is rotated by the output flange of the drive unit 263. Rotating the ball bearing unit around the screw 261 gives rise to a translation of the ball bearing unit and the drive unit since the drive unit cannot rotate because of a linear cylindrical bearing with a cylindrical beam 264 and a linear bearing unit 265, mounted on the drive unit. This can be used either with the screw fixed or the drive unit fixed, dependent on the application.

Figure 19 is an embodiment, where the hollow shaft of the drive unit is used for the mechanical design of a driving equipment. Instead of a screw as in figure 20, a shaft 268 is here inserted into the hollow drive unit 266. The shaft connects two wheels 267 and 269 with each other and one of the wheels 267 is driven by the output flange 271 of the drive unit. The vehicle body 270 is connected to the housing of the drive unit 266 by a mechanical part 272.