WO2011096888A1

WO2011096888A1 - Permanent magnet motors without magnet back iron

Info

Publication number: WO2011096888A1
Application number: PCT/SG2010/000032
Authority: WO
Inventors: Howe Yuen Lim; Chai Meng Goh; Yeong Tu Chua; Ching Boo San
Original assignee: Akribis Systems Pte Ltd
Priority date: 2010-02-02
Filing date: 2010-02-02
Publication date: 2011-08-11

Abstract

A permanent magnet motor having two or more permanent magnets and two coil assemblies, in which the permanent magnets are positioned between the two coil assemblies, and each of the two or more permanent magnets are not mounted onto any magnet back iron. The permanent magnet motor is used in a permanent magnet linear motor or a permanent magnet rotary motor or a permanent magnet planar motor or a permanent magnet hybrid motor.

Description

PERMANENT MAGNET MOTORS WITHOUT MAGNET BACK IRON

Field of the invention The present invention relates to a new type of permanent magnet motor that does not require the magnets to be attached to any magnet back iron. The motor can be linear or rotary, and it can be an ironless type or with iron core. It can be also be a single phase motor or multi-phase motor. Background and discussion of prior art

The permanent magnet motor has become the de-facto motor for small to medium power range type of applications, such as in the range from 1 W to 3 W. The popularity of the permanent motors stem from its performance, and the development of high energy magnets in the last 20 to 30 years, such as the Neodymium Iron Boron (NdFeB) type of high energy magnets, which was first developed in 1982 and is currently the strongest permanent magnet available in the industry.

Permanent magnet motors have been called many different names in the industry, such as DC brushless motor, coreless motor, ironless motor, AC servo motor, torque motor, voice coil motor etc. Different names are used due to differences in design, such as whether it is single phase, or multiphase, whether it is for rotary or linear motion, and whether the coil is wound around iron laminations or just molded by itself without any lamination. There are many manufacturers of permanent magnet motors, used in all kinds of industries ranging from automation equipment, household appliances, transportation, military, biomedical, chemical industry, space applications etc. Yet in all permanent magnet motor designs, there is one common design feature or similarity. The permanent magnets are always attached to a back iron, which can be a soft magnetic iron material or certain types of stainless steel, which have very high magnetic permeability. The magnet back iron is used to close the magnetic flux path in the magnetic circuit, by allowing the magnetic flux to flow from one magnet to the magnet beside it, which has opposite polarity.

Fig 1 shows a voice coil motor, which is a type of permanent magnet motor,. Permanent magnets la,lb,lc and Id are attached to magnet back iron 2a and 2b. While the permanent magnets used are typically the NdFeB type, other types of permanent magnets can also be used. The polarity of the magnets are indicated in the figure, where N stands for north pole and S for south pole. The coil 3 is formed by a single coil, with a rectangular shape. Since there is only one coil, this motor is called a single phase motor. The flux circuit 4a shows how the magnetic flux flows from permanent magnet la vertically upward in Fig 1, cutting the coil 3 before flowing into magnet lb. The flux then makes a turn and flows through the magnet back iron 2a, and returns from magnet lc, cutting the coil 3 again as it is directed into magnet Id. It then returns to magnet back iron 2b, before finally ending in magnet la again. When a current is fed into the coil, a force is produced in the direction shown in Fig 1. Therefore, it can be seen that the magnet back iron 2a and 2b not only holds the magnets in position, they also act as return paths for the magnetic flux.

The flux pattern is actually more complicated, but for illustration purpose, the flux circuit 4a approximates the pattern fairly well. However, near to the center of the motor, the flux path between the magnets has a distorted shape, as shown by flux circuit 4b. This phenomenon can be observed when analyzing the motor using finite element analysis on a computer. The flux lines that flow from magnet la towards magnet lb are not straight, but are distorted especially near the center of the air gap surrounded by the four magnets. This distortion of the flux path is inevitable and results in weaker flux density in the region near the edges of the magnets. Hence, voice coil motors are known to have weaker force sensitivity when the coil is at the extreme ends of the stroke, in the region where the flux density is weaker. This effect is undesirable because more current will need to be fed into the motor coil to achieve the same amount of force as the motor moves towards the extreme ends. In other words, the controller needs to compensate for this limitation in order to achieve good performance without a large force ripple.

Fig 2 shows an ironless linear motor, which is another type of permanent magnet motor. US patent 6,573,622 B2 describes such a linear motor. This motor uses very much the same design as the voice coil motor described above, except that the coil has typically three phases, although it can have any number of phases other than three. Due to the coil having three phases, there is a need to do commutation, where the coil phases are turned on or off, depending on the position of the coil relative to the magnets. Hence, this type of motor is also called a brushless linear motor, since it does not use brushes for commutation.

The magnets 5a,5b,5c,5d,5e,5f,5g and 5h are attached to magnet back iron 6a and 6b. The coil 7 is drawn as a solid piece for simplicity of illustration. Any person skilled in the art would appreciate that the coil comprises sections corresponding to different phases. In this case, the coil is shorter than the magnet track, which usually indicates that it is a moving coil design, while the magnet track is kept stationary. Flux path 8a has a similar flow direction as the voice coil motor described earlier, cutting coil 7 as it passes through the air gap, producing force in the direction indicated in Fig 2. However, there are 2 more flux paths, 8b and 8c that also cuts through the coil, produced by the interaction of magnets 5a,5b,5c and 5d and the interaction of magnets 5e,5f,5g and 5h respectively. Although not shown in Fig 2, the distortion of the flux path described in the voice coil motor also occurs in this type of linear motor, as well as other types of linear motor. The distortion is caused by the sharp turn of the flux path around the magnet back iron and the interaction of the magnets with opposite polarity.

The ironless linear motor is used widely due to the low moving mass. Very high accelerations can be achieved with this motor, where the coil is moved. However, due to the large number of magnets required, the cost of such a motor is relatively high. Another disadvantage is the need to have a cable that moves with the moving coil. The bending or flexing of the cables can have very high frequency, in terms of millions of cycles per day. High flex cables are typically used, but these cables will always have a limited life span, especially when the cable needs to have a relatively small bending radius. The force that such a motor can produce is also limited. While the force can be increased with a longer coil length, the moving mass also increases correspondingly, since the density of copper is rather high (8.9 g/cm3), and the coils are typically made of copper. Perhaps the biggest limitation of this type of motor is that the heat generated cannot be removed easily. The coil is moving, and the only way for the heat to be removed or transferred effectively is to the load it is carrying. This is often not desirable, as it causes thermal expansion and affects the accuracy of the motion system. Another type of permanent magnet motor, commonly called a coreless linear motor is shown in Fig 3 above. It is similar to the ironless motor described in Fig 2, except that it has only one row of magnets, and the coil 9 is attached to a coil back iron 10. Magnets 1 la and 1 lb, magnet back iron 12, coil 9, coil back iron 10 and flux circuit 13 operate in the same manner as the previous two motors described earlier, to produce force in the direction indicated in the Fig 3. This type of motor has similar characteristics as the iron less motor described above, but the additional coil back iron adds to the moving mass, reducing its performance in terms of acceleration and force to mass ratio. Moreover, there is a strong attraction force between the coil back iron and the permanent magnets. This attraction force is undesirable, as the linear bearings used have to be strong enough to counteract the attraction force. It also increases the static friction of the moving mass, since the attraction force adds to the normal gravitational force of the load.

Fig 4 shows the same type of motor, but with the magnet track shorter than the coil, which means that it is typically used as a moving magnet motor. Magnet 14a and 14b are also attached to a magnet back iron 15. Coil 16 and coil back iron 17 closes the loop of the magnetic circuit 18 formed by the magnets with the magnet back iron. This design eliminates the need for a moving cable as the coil is stationary. However, the total mass of the magnet back iron and the magnets is rather significant and this reduces the performance of the motor as well. The strong attraction force between the coil back iron and the permanent magnets described earlier is also inherent in this design.

Another linear motor commonly used in the industry is the iron core linear motor. US patent 5,910,691 describes such a motor. Fig 5 show a side view of such a motor. Magnets 19a, 19b and 19c are magnets with alternating polarity and are part of a row of magnets which are mounted on magnet back iron 20. The coil assembly comprises coil 21 which are inserted into the slots formed by laminations 22 stacked together. The laminations act as the coil back iron and are used to reduce eddy current losses, although normal magnetic soft iron can also be used. Two magnetic circuits 23a and 23b are shown in the figure, which allows some of the flux to cut through the coils as it circulates around the slots of the laminations.

The advantage of the iron core linear motor is the large force it can generate, compared to the ironless and coreless linear motors. However, the moving mass of the coil is relatively large and this limits the acceleration it can achieve, even without any load. While it is also possible to move the magnets and have the coil stationary, the total mass of the magnets and the magnet back iron is also very significant. Another big disadvantage of the iron core motor is the large attraction force between the magnets and the coil laminations. Due to the small air gap needed for this type of motor to work properly, which is typically in the range of 0.8 mm to 1.1 mm, the attraction force becomes very large. Large bearings with high load rating need to be used to support the motor. Large static friction force is therefore associated with this type of motor system, and this affects the response of the motor during start of motion and end of motion settling performance. In all the linear motors described above, we can see that the magnet back iron is used to return the flux path, so that the magnetic flux path is a closed circuit. It can also be observed that only one face of the magnet is exposed to the air gap, perpendicular to the direction of its polarity, whereas the other corresponding face is always attached to a magnet back iron. The back iron closes the magnet path between one magnet and the magnet next to it, which has an opposite polarity. This is a common design feature of all existing conventional permanent magnet linear motors.

The same is also true for rotary permanent magnet motors, although in the case of rotary motors, the magnets are mounted onto a circular magnet back iron, and this assembly is collectively called a rotor. Fig 6 shows a conventional coreless permanent magnet rotary motor. The design is similar to the linear motor shown in Fig 3, except that the magnet track and coil assembly are rolled into a circular shape without any open end. The magnetic circuit are also similar, with the magnets 24a,24b and 24c being mounted onto a circular magnet back iron 25. Coil 26 is mounted onto the outer shell or coil back iron 27, and magnetic circuits 28a and 28b are indicated to illustrate the flux paths.

The iron core rotary motor is another type of permanent magnet rotary motor. It is probably the most commonly used permanent magnet motor used in the industry. Its power can range from 5W to 3KW or more, with diameters from 10 mm to more than 1000 mm. As shown in Fig 7, it is very much similar to the iron core linear motor described in Fig 5, with the latter being rolled into a circular shape. As in the case of the coreless rotary motor, the permanent magnets 29 are mounted onto a circular magnet back iron 30, and this assembly is called the rotor. The coils 31 are inserted into the slots of the coil back iron 32, typically formed by stacks of lamination, and this assembly forms the stator of the motor.

In both the coreless permanent magnet rotary motor and the iron core type, the rotor consists of the magnets and the magnet back iron. The rotor inertia is therefore the sum of the moment of inertia of these parts. The magnet back iron is typically made of soft iron, with a density of 7.8 g/cm3, whereas the permanent magnets typically have a density of 7.6 g/cm3. Both materials are relatively dense, so in many motor applications, the rotor inertia becomes a major part of the load, sometimes even exceeding the moment of inertia of the useful load it is carrying. In other words, the motor spends more of its torque moving itself, rather than the load it is carrying.

It is desirable that some of the disadvantages of conventional permanent magnet motors be overcome.

SUMMARY OF INVENTION

A first object of the invention is a permanent magnet motor having two or more permanent magnets and two coil assemblies, said permanent magnets positioned between the two coil assemblies, wherein each of the two or more permanent magnets are not mounted onto any magnet back iron.

A second object of the invention is a permanent magnet motor having an arrangement comprising two or more permanent magnets and two coil assemblies, said two or more permanent magnets positioned between the two coil assemblies, wherein each of the two or more permanent magnets are not mounted to any magnet back iron, and an air gap is formed between a side of each magnet facing a side of the coil assembly, and another air gap is formed between the other side of the magnet facing a side of the other coil assembly wherein the flux flows in straight lines through each magnet, perpendicular to the side of the magnet, said magnet being either flat or curve, and parallel to the direction of the polarity of the magnet.

A third object of the invention is a permanent magnet motor having two or more permanent magnets and two coil assemblies, said one or more permanent magnets positioned between the two coil assemblies, arranged so that each of the two or more permanent magnets are not mounted to any magnet back iron, a face of each of the permanent magnet faces a face of a coil assembly wherein an air gap is formed between a side of the magnet facing a side of the coil assembly and another air gap is formed between the other side of the magnet facing another side of the coil assembly, wherein the flux flows in straight lines through each magnet, perpendicular to each face of the magnet, said magnet being either flat or curve, and parallel to the direction of the polarity of the magnet.

Preferably the two or more permanent magnets are not mounted to any magnet back iron but are positioned between two coil assemblies and wherein the permanent magnets moves while the coil assemblies are stationary.

Preferably the two or more permanent magnets are not mounted to any magnet back iron but are positioned between two coil assemblies and wherein the coil assemblies move while permanent magnets are stationary.

Preferably the two or more permanent magnets are mounted on a support structure which holds the permanent magnets in place. Preferably the support structure is magnetic or non-magnetic.

Preferably the non magnetic support structure is resin material.

Preferably the non magnetic support structure is aluminum.

Preferably the non magnetic support structure is fiber reinforced plastic. A fourth object of the invention is a permanent ^'magnet liner motor having only a single phase type of coil assembly, and one or more pair of permanent magnets can be used with one or more sets of corresponding coils, and the permanent magnets can be moved while the coil assembly is kept stationary, or the magnets held stationary while the coil assembly may be moved.

A fifth object of the invention is a permanent magnet linear motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron without the presence of slots, and the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

A sixth object of the invention is a permanent magnet linear motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto the slots of an iron core, wherein the permanent magnets can be moved with the coil assembly stationary, or the permanent magnets held stationary while the coil assembly may be moved.

A seventh object of the invention is a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron without the presence of slots, and the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

An eighth object of the invention is a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto the slots of an iron core, wherein the permanent magnets can be rotated with the coil assembly stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

A ninth object of the invention is a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and the permanent magnets are arranged in a disk, such that the direction of polarity of the magnets is pointing in the same direction of the axis of rotation, wherein the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

A tenth object of the invention is a permanent magnet rotary motor having a single phase type of coil assembly, wherein the coil assembly comprises one or more coils mounted onto a segment of coil back iron, and the permanent magnets are arranged in as a segment, such that the direction of polarity of the permanent magnets is in the same direction of the axis of rotation, wherein the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated. An eleventh object of the invention is a permanent magnet linear motor having a single phase type of coil assembly, wherein the coil assembly comprises coils mounted onto a coil back iron that is circular in shape, and the permanent magnets are also arranged in a circular manner, such that the direction of polarity of the permanent magnets is in the radial direction, wherein the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved. [

A twelfth object of the invention is a permanent magnet planar motor which produces force in more than one direction, either using a single phase type or multiphase type of coil assembly, wherein more than one set of permanent magnets can be arranged on a single plane and mounted on a same magnet holder, wherein the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

A thirteenth object of the invention is a permanent magnet planar motor which produces force in more than one direction, either using a single phase type or multiphase type of coil assembly, wherein one set of permanent magnets and one set of coils can be arranged on a single plane and mounted on a same holder, wherein the corresponding coil assembly and permanent magnet assembly can be stationary or be moved. A fourteenth object of the invention is a permanent magnet hybrid motor which produces a torque in one direction and a force another direction, either using a single phase type or multiphase type of coil assembly, wherein more than one set of permanent magnets and can be arranged on a single cylindrical holder, wherein the magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

A fifteenth object of the invention is a permanent linear motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two or more rows of permanent magnets can be moved while the coil assembly is kept stationary, or the two or more rows of permanent magnets held stationary while the coil assembly may be moved.

A sixteenth object of the invention is a permanent magnet rotary motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two or more rings of permanent magnets can be rotated while the coil assembly is kept stationary, or the two or more rings of permanent magnets held stationary while the coil assembly may be rotated. A seventeenth object of the invention is a permanent magnet linear motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two rows of permanent magnets are mounted on opposite faces of a supporting structure, which can be made from magnetic or non-magnetic material, wherein the permanent magnets and the supporting structure can be moved while the coil assembly is kept stationary, or the permanent magnets and the supporting structure held stationary while the coil assembly may be moved.

An eighteenth object of the invention is a permanent magnet rotary motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two rings of permanent magnets are mounted on opposite faces of a cylindrical supporting structure, which can be made from magnetic or non-magnetic material, wherein the permanent magnets and the cylindrical supporting structure can be rotated while the coil assembly is kept stationary, or the magnets and the supporting structure held stationary while the coil assembly may be rotated.

Preferably the permanent magnet motor is used in a permanent magnet linear motor or a permanent magnet rotary motor or a permanent magnet planar motor or a permanent magnet hybrid motor. BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, its advantages, and the objects attained by its use, reference should now be made to the accompanying drawings. The accompanying drawings illustrate one or more embodiments of the invention and together with the description herein, serve to explain the workings and principles of the invention.

Fig. 1 is a drawing of a voice coil motor, of the prior art, which is a type of permanent magnet motor. Fig 2 is a drawing of an ironless linear motor, of the prior art, which is another type of permanent magnet motor.

Fig 3 is a drawing of an coreless linear motor, of the prior art, which is another type of permanent magnet motor. Fig 4 is another drawing of another type of coreless linear motor, of the prior art, which is another type of permanent magnet motor. Fig 5 is a drawing of an iron core linear motor, of the prior art, which is another type of permanent magnet motor.

Fig 6 is a drawing of a conventional coreless permanent magnet rotary motor, of the prior art, which is another type of permanent magnet motor.

Fig 7 is a drawing of an iron core linear rotary motor of the prior art, which is another type of permanent magnet motor.

Fig 8 is a drawing of an embodiment of the invention.

Fig 9 is a drawing of the magnets inserted into a magnet support structure or holder.

Fig 10 is a drawing of a magnet which is shaped in such a way that it has chamfers on both sides, so that the magnet will not slip out of the magnet holder easily.

Fig 1 1 is a drawing of another embodiment of the invention, in a multiphase slot less linear motor.

Fig 12 is a drawing of another embodiment of the invention, a multiphase slot less linear motor with four magnets.

Fig 13 is a drawing of a further embodiment of the invention, a linear motor.

Fig 14 is a drawing of another embodiment of the invention.

Fig 15 is a drawing of another embodiment of the invention, in a coreless permanent magnet rotary motor.

Fig 16 is a drawing of a further embodiment of the invention used in another design of coreless permanent magnet rotary motor.

Fig 17 is a drawing of another embodiment of the invention,

permanent magnet rotary motor. Fig 18 is a drawing of a motor configuration where the magnets are arranged in such a way that the polarity is parallel to the axis of rotation. Fig 19 is a plan view of the rotor, where the magnets are inserted into the pockets of a disk or magnet holder.

Fig 20 is a drawing of a variation of a motor configuration which is an arc shaped voice coil motor.

Fig 21 is a drawing of a further variation of a motor configuration which is an arc shaped voice coil motor.

Fig. 22 is a drawing of an embodiment of the invention, which is a planar motor.

Fig. 23 is a drawing of another embodiment of the invention, which is a planar motor mounted on one single structure.

Fig. 24 is a drawing of a further embodiment of the invention, which is a planar motor mounted on one single structure.

Fig. 25 is a drawing of an embodiment of the invention, which is a hybrid motor.

Fig. 26 is a drawing of an embodiment of the invention, which is a hybrid rotary motor.

Fig. 27 is a drawing of an embodiment of the invention mounted on a supporting piece.

Fig. 28 is a drawing of an embodiment of the invention being a rotary motor mounted on a supporting piece.

Detailed Description Of Invention

The present invention uses a new approach in permanent magnet motor design, mainly by eliminating the magnet back iron. With this design, the magnetic circuit and flux path is also changed, such that the magnetic flux flows in straight lines through each magnet, parallel to the direction of the polarity of the magnet. Two air gaps are created and the two faces of the magnet perpendicular to the direction of the flux flow magnet are exposed to these air gaps, instead of being mounted onto a magnet back iron in conventional designs. This new design can be used in linear and rotary, ironless or iron core, single phase or multiphase type of permanent magnet motors.

The various drawings commencing from Fig 8 onwards describes various embodiments of the invention, the inventiveness being a permanent magnet motor without a magnet back iron.

Fig 8 shows a voice coil motor using this design approach. The permanent magnets 33a and 33b are positioned in the center of the voice coil, with their polarities indicated in the diagram. Coils 34a and 34b are mounted onto coil back iron 35a and 35b respectively. The flux circuit 36a show how the flux flows and forms a close loop. If we start from magnet 33a, the flux path cuts across coil 34b into coil back iron 35b, then makes a turn and returns through coil 34b. It then goes in straight lines through magnet 33b, cuts through coil 34a, and makes another turn in coil back iron 35a. It then emerges to cut coil 34a again, before it finally reaches magnet 33a where we first started. It should be noted that even near the edge of the magnets, unlike the conventional voice coil design, the flux lines cross the magnets in a straight line. Flux circuit 36b does not have the distortion associated with the conventional voice coil design described in Fig 1. Hence, the force sensitivity of this voice coil will be more constant even near the extreme ends of travel. In this embodiment, it is preferred to move the magnets due to the lower mass of the magnets compared with the coil assemblies. By moving the magnets, there is no need to have a moving cable, as the coil is stationary. Moreover, the coil back iron acts as an excellent heat sink for cooling, thereby increasing the continuous current and continuous force of the motor. Nevertheless, it is obvious that the design also permits holding the magnets stationary and moving the coil assemblies. It is also obvious to anyone skilled in the art that we can increase the force of this motor by adding another set of coils and another pair of magnets. Fig 8 therefore illustrates an embodiment whose features are the subject of Claim 11.

It should be mentioned that the magnets are not free to float in the air, but are mounted on a support structure, just as the coil 3 in Fig 1 must be held with a coil supporting structure. In this new design, the support structure need not and should not be magnetic soft iron. A light weight, non magnetic material, such as aluminum or fiber reinforced plastic or resin material can be used. The material need not be magnetically permeable because this support structure does not close the magnetic flux as in the case of the conventional motor design. The flux flows through each magnet independently, perpendicular to the polarity of the magnets, so the support structure does not play a part in closing the magnetic circuit. The sole purpose of this support structure is to hold the magnets in place. A possible design involves machining pockets that fit the magnets exactly and the magnets are fixed easily into their respective position and orientation. Fig 9 shows magnets 33a and 33b inserted into a magnet support structure or holder 37. The magnet faces may flush with the surface of the magnet holder 37, or the magnets can be slightly thinner than the holder. The magnets can be held onto this holder by means of high strength epoxy. This structure can be mounted to a linear guidance system, to keep it into the center of the motor and allow motion in the desired direction. It should also be noted that such a magnet holder may not be necessary if the magnets can be attached one to another rigidly, side by side, or if a solid piece of magnetic material can be magnetized to provide alternating polarity. The magnets can also be shaped in such a way as to improve its retention in the pocket of the magnet holder. For example, Fig 10 shows magnet 38, shaped in such a way that it has chamfers on both sides, so that they will not slip out of the magnet holder easily.

Fig 11 shows that the same approach can be applied to the multiphase, slot less linear motor. Unlike the conventional ironless linear motor shown in Fig 2, it has only one row of magnets but 2 rows of coil. It is also different from the conventional coreless linear motor shown in Fig 3 and Fig 4, since the magnets are not attached to any magnet back iron. The magnets 39, generate a flux circuit 40 that passes through the coil 41 and coil back iron 42. This design enables us to move the magnets in a very efficient manner, as the moving mass is very low, and no cable is necessary, since the coil is fixed. Very high accelerations can be achieved. Moreover, unlike the coreless linear motor design described in Fig 3 and 4, for this new design, since the magnets are positioned in the center, the attraction force towards the top coil back iron and the attraction force towards the bottom coil back iron is balanced, which means that there is zero net attraction force acting on the magnets. This allows us to use smaller linear bearings as guidance system, and the additional, unwanted static friction caused by the attraction force is eliminated. Fig 11 therefore describes an embodiment whose features are listed in Claim 12.

Moreover, the linear motor is scaleable in the sense that more magnets can be added if necessary, to increase the force of the motor. Fig 12 shows a design with 4 magnets. Also shown in Fig 12 are fins 43 added to the coil back iron, to act as heat sink. This can significantly increase the continuous power of the motor. Other forms of cooling are possible, such as using forced air flow or water cooling agents that passes through channels made in the coil back iron. By moving only the magnets, the heat generated by the coils will not be directly transferred to the load, which will affect the accuracy of the motion system.

While the designs shown in Fig 11 and Fig 12 are the preferred embodiments where the magnets are moved with the coil assembly stationary, it is also possible to move the coil assembly 44 as shown in Fig 13, where the coil assembly comprising top and bottom parts are moved along a row of magnets held by a magnet holder plate which is not shown.

The same design approach can be used on an iron core type of design, as shown in Fig 14. Fig 14 describes an embodiment whose features are the subject of Claim 13. A row of magnets 45 is positioned in the center, between two coil assembly 46a and 46b. The flux circuits 47 also goes through the magnets in the same manner described earlier, with the flux lines flowing in the same direction as the polarity of the magnets, without any magnet back iron necessary. With this design, the usual limitations of the iron core motor, namely the relatively high moving mass of the coil assembly or the magnet track assembly have been lifted. With the coil assembly stationary, very large force and very high accelerations can be achieved by just moving the magnets. No moving cable is also necessary and the heat generated can be easily removed from the coil either through natural convection, heat sinks or other means of cooling. Perhaps one of the biggest advantages of this design compared to the conventional iron core linear motor is the elimination of the attraction force. As in the case of the linear motor described in Fig 1 1 ,12 and 13, the attraction force between the magnets and the top coil assembly is completely balanced by the force of attraction between the magnets and the bottom coil assembly. This allows the use of smaller linear bearings, or even frictionless air bearings. It is needless to say that it is also possible to have the magnets stationary, and to move the coil with this design, although it is not a preferred way unless there is some special reason to do so.

The invention can also be applied to rotary motors. Fig 15 shows a coreless permanent magnet rotary motor. Compared to the one shown in Fig 6, the magnets 48 are centered as a concentric ring between coil 49, which is attached to coil back iron 50, and coil 51 , which is attached to coil back iron 52. The working principle is similar to the case of the linear motor described in Fig 11 and 12, except that in this case the motion is rotary rather than linear. A very significant advantage of this design is the elimination of the magnet back iron, which is typically a significant portion of the rotor inertia of any conventional rotary motor. Fig 15 therefore illustrates an embodiment whose features are the subject of Claim 14.

The rotor can be designed in many different ways. One example is shown in Fig 16, where pockets are made in the rotor 53, to fit in the permanent magnets 54. The rotor can be made of light weight material, such as aluminum, plastic, fiber reinforced plastic or resin or any other suitable low density materials.

Fig 17 shows a iron core type of permanent magnet rotary motor. The working principle is similar to the case of the linear motor described in Fig 14, except that in this case the motor is rotary instead of linear. The permanent magnets are attached to a rotor, similar to the one shown in Fig 16, and positioned between the inner coil assembly 56 and the outer coil assembly 57. Without any magnet back iron, this motor has very high torque to rotor inertia ratio. Fig 17 therefore illustrates an embodiment whose features are listed in Claim 15.

While the motor shown in Fig 17 does not have extended teeth associated with the slots, it is also possible to apply such teeth design with this invention, to reduce cogging torque. While the magnets shown in Fig 16 and 17 are aligned parallel to the axis to rotation, it is also possible to have skew magnets, in order to reduce cogging torque. The coil laminations can also be skewed instead of the magnets, to achieve the same purpose of reducing cogging torque. Any person skilled in the art will know that all these are conventional practices which can be applied easily.

A performance comparison was made between linear motors using our invention versus the conventional design. The linear motor corresponding to the conventional design is shown in Fig 4, whereas the new linear motor according to our invention is illustrated in Fig 11. The investigation was carried out on a computer using finite element analysis. The two permanent magnets used for both motors are identical, with a length of 50.5 mm, width of 24.2 mm and thickness of 8.2 mm. The amount of coil used and the coil size were also identical, so as to make a fair comparison. The moving mass of the conventional motors includes the magnets and the magnet back iron. The moving mass of the new motor includes the magnets and a magnet holder made of aluminum, which has the same size as the magnet back iron of the conventional motor.

Table 1

We can observe from Table 1 that the new linear motor according to our invention produces higher force, even with the same magnets and amount of coil. The force constant is 24.1 N/A, versus that of 22.9 of the conventional motor. More importantly, the moving mass of the new motor is significantly lower than that of the conventional motor. Consequently, the force to mass ratio of the new motor is 0.134, compared to 0.067 for the conventional motor (about 2 times). This means that the maximum acceleration achievable for the new motor is twice that of the conventional motor, based on the moving mass of the motor parts alone.

Another performance comparison was made between rotary motors using our invention versus the conventional design. The rotary motor corresponding to the conventional design is shown in Fig 6, whereas the new rotary motor according to our invention is illustrated in Fig 15. Again, the permanent magnets and the copper coil used for both motors are identical. The rotor inertia of the conventional motors includes the magnets and the magnet back iron rotor. The rotor inertia of the new motor includes the magnets and the magnet holder made of aluminum.

From Table 2, we can see that the rotor inertia of the new motor is significantly lower, at 0.314 mKgm2, compared to 0.462 mKgm2 for the conventional motor. This corresponds to a 32% reduction in rotor inertia. In fact, in this case we are using an aluminum magnet holder to mount the magnets for the new motor. If an even lighter material, such as fiber reinforced resin or plastic is used, the rotor inertia can be reduced further. Even with this aluminum rotor, the torque to inertia ratio for the new motor versus the old motor is about 1.6 times. This will allow us to achieve much higher performance in terms of angular acceleration for the motor. With itself being lighter, more of the torque can be used for the load, or a heavier load can be used with the same motor.

It should be noted that the different linear and rotary motor configurations described are examples of the present invention. Many other configurations can be designed using this invention.

For example, Fig 18 shows a motor configuration where the magnets are arranged in such a way that the polarity is parallel to the axis of rotation. The rotor is also made without any magnet back iron. Fig 18 therefore illustrates an embodiment whose features are the subject of Claim 16. Fig 19 shows a plan view of the rotor, where the magnets are inserted into the pockets of a disk or magnet holder.

Another variation of this embodiment is an arc shaped voice coil motor, as shown in Fig 20, which is essentially a section of the motor shown in Fig 18. In this design, there is only one coil shaped like a fan on top of the magnet and another similar coil below the magnets, and a pair of magnets in between. This constitutes a single phase, permanent magnet motor with limited angle rotation. Fig 20 therefore illustrates an embodiment whose essential elements are stated in Claim 17.

Fig 21 shows another variation of how the invention may be used. The magnet 64 can be circular in shape or may be formed by arc segments, and this magnet ring is positioned between outer coil and inner coils 65, which are attached to coil back iron 66. Fig 21 therefore illustrates an embodiment whose features are the subject of Claim 18.

This invention can also be applied to a planar motor, where the motor is designed to produce force and motion in more than one axis. Fig 22 shows the configuration of the magnets of a XY planar motor. Fig 22 therefore illustrates an embodiment whose features are stated in Claim 19. As before, the magnets are not attached to any magnet back iron, but are held by a magnet holding structure. There is a first row of magnets 67, which interacts with the coils (not show) to produce a force in the X direction, and another pair of magnets 68, which also interacts with its corresponding coils (not shown) to produce a force in the Y direction. Both sets of magnets are held by the magnet holder 69. The coils used can be with or without slots or laminations.

It is also possible to combine a set of magnets 70 with a set of coil 71 to form a planar motor, mounted on one single structure 72, as shown in Fig 23. Such a design uses a combination of the conventional moving coil, and moving magnets based on the new invention. In this case, the magnets 70 will be positioned between two sets of stationary coils while the coil 71 is positioned between two sets of stationary magnet. This is simply a variation of the invention, and stills falls within the scope of this invention. Fig 23 describes an embodiment whose features are listed in Claim 20.

The similar idea can be applied to a hybrid motor, where 2 sets of magnets 73 and 74 are mounted onto a magnet holder 75, to form a rotor that can rotate as well as move linearly along its axis of rotation. This is shown in Fig. 24 and describes an embodiment whose features are listed in Claim 21. A person skilled in the art will appreciate that the magnets 73 can produce a torque about the axis of rotation of the motor, and the magnets 74 can produce a force along the axis of rotation, with coils placed appropriately according to this invention.

Another variation of this invention is to have two rows of magnets 76, as shown in Fig 25. The flux circuit 77 is shown to move across each magnet in a straight line according to the description of this invention given earlier, except that it now cuts across four sets of coils. With this configuration, almost twice the amount of force can be achieved. The features of the embodiment, in Fig 25 which are the subject of Claim 22. This variation can also be applied on a rotary, as shown in Fig 26. There are two concentric rings of magnets 78 and the flux circuit 79 operates in the same manner as in Fig 25, except that the motor is now rotary in shape. Again Fig 26 therefore illustrates an embodiment whose features are stated in Claim 23. Fig 27 shows yet another variation of this invention where a pair of magnets 80 is mounted onto a supporting piece 81 , which can be made from magnetic or non-magnetic material. Since the flux has to flow through this material, if it is made of non-magnetic material, it has to be very thin to allow the magnet flux to flow through properly without any significant losses. Another pair of magnets 82 is mounted onto the opposite face of the supporting piece 81. Together with coil 83 and coil back iron 84, the magnetic flux circuit 85 can be closed, and a force is produced in this motor. Although the magnets are mounted onto a piece of supporting structure, it can be observed that the polarity of the magnets are similar to a single pair of magnets as described in this invention. Therefore, such a configuration is just an adaptation of the present invention which is the subject of Claim 24.

Such a variation described above can also be applied on a rotary motor, as shown in Fig 28, where one set of magnets 86 is mounted on the outer diameter of a holding material 87, which may be made of magnetic or non-magnetic material, and another set of magnets 88 is mounted on the inner diameter of the holding material 87. The flux flow is shown on the flux circuit 89. Again the features of this variation is the subject of Claim 25. ^"

Having described different configurations and embodiments of the invention with reference to the accompanying drawings, it is to be understood that the invention is not limited to those configurations and embodiments, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined in the claims. Advantageous Effects of the Invention

This invention opens a new way of designing permanent magnet motors without any magnetic back iron for the magnets. With the elimination of the magnet back iron, many more types of materials can be explored for holding the magnets, since these materials are no longer limited to having high magnetic permeability. Aluminum or other light and stiff non-metallic materials, such as fiber reinforced resin or plastic materials can be used. This results in the reduction of moving mass, for the moving magnet design in linear motors, and the reduction of rotor inertia in rotary motors. Hence, higher accelerations can be achieved or more force or torque can be used to move the useful load in an application.

With this invention, the flux lines flow in straight lines through the magnets. This reduces any distortion of the magnetic flux circuit, thereby giving more constant force throughout the entire desired travel.

It has also been shown that the invention allows us to produce higher force with a linear motor and higher torque with a rotary motor for the same size of magnets and same amount of coil used to make a motor. With a corresponding reduction in the moving mass, the performance of the motor is greatly enhanced.

In the case of the iron core type of linear motor, as well as the coreless type of linear motor, with this new design, there is no net attraction force on the magnets. This allows us to use smaller linear bearings in the system design, and simplifies the assembly process. The elimination of the attraction force also improves the motor system performance, since the static friction is greatly reduced. Response time during the start of motion and the end of travel settling times will be shortened.

With this new design, unlike the conventional moving coil design, a moving cable is no longer necessary, since the coils are stationary. This improves the reliability of the motor, since the motor cables will be fixed and there will not be any constant bending of the cables. A moving cable also creates a drag force, or opposing force when it is bent during motion. With this invention, this problem is eliminated completely.

With the coil mounted to a coil back iron, the heat generated by the coils can be removed easily from the motor. Additional heat sinks can be added, or cooling fluids can be used to further improve the cooling of the coils, thereby increasing the continuous current and continuous force of the motor. By moving only the magnets, the heat generated by the coils will not be directly transferred to the load, which will affect the accuracy of the motion system.

Claims

Claims:

1. A permanent magnet motor having two or more permanent magnets and two coil assemblies, said permanent magnets positioned between the two coil assemblies, characterized in that each of the two or more permanent magnets are not mounted onto any magnet back iron.

2. A permanent magnet motor having an arrangement comprising two or more permanent magnets and two coil assemblies, said two or more permanent magnets positioned between the two coil assemblies, characterized in that the each of the two or more permanent magnets are not mounted to any magnet back iron, and an air gap is formed between a side of each magnet facing a side of the coil assembly, and another air gap is formed between the other side of the magnet facing a side of the other coil assembly wherein the flux flows in straight lines through each magnet, perpendicular to the side of the magnet, said magnet being either flat or curve, and parallel to the direction of the polarity of the magnet.

3. A permanent magnet motor having two or more permanent magnets and two coil assemblies, said one or more permanent magnets positioned between the two coil assemblies, arranged so that each of the two or more permanent magnets are not mounted to

any magnet back iron,

a face of each of the permanent magnet faces a face of a coil assembly characterized in that an air gap is formed between a side of the magnet facing a side of the coil assembly and another air gap is formed between the other side of the magnet facing another side of the coil assembly, wherein the flux flows in straight lines through each magnet, perpendicular to each face of the magnet, said magnet being either flat or curve, and parallel to the direction of the polarity of the magnet.

4. An arrangement for a permanent magnet motor as claimed in any one of Claim 1 to Claim 3 wherein the two or more permanent magnets are not mounted to any magnet back iron but are positioned between two coil assemblies and wherein the permanent magnets moves while the coil assemblies are stationary.

5. An arrangement for a permanent magnet motor as claimed in any one of Claim 1 to claim 3 wherein two or more permanent magnets are not mounted to any magnet back iron but are positioned between two coil assemblies and wherein the coil assemblies move while permanent magnets are stationary.

6. An arrangement for a permanent magnet motor as claimed in any one of Claim 1 to Claim 3 wherein two or more permanent magnets are mounted on a support structure which holds the permanent magnets in place.

7. A support structure for holding one or more permanent magnets in place as claimed in any of the preceding Claims, wherein the support structure is magnetic or nonmagnetic.

8. An non magnetic support structure for one or more permanent magnet, as claimed in Claim 7, said non magnetic support structure is resin material.

9. An non magnetic support structure for one or more permanent magnet, as claimed in Claim 7, said non magnetic support structure is aluminum.

10. An non magnetic support structure for one or more permanent magnet, as claimed in Claim 7, said non magnetic support structure is fiber reinforced plastic.

1 1. A permanent magnet motor as claimed in any of Claim 1 to Claim 3 used in a permanent magnet liner motor having only a single phase type of coil assembly, and one or more pair of permanent magnets can be used with one or more sets of corresponding coils, and the permanent magnets can be moved while the coil assembly is kept stationary, or the magnets held stationary while the coil assembly may be moved.

12. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet linear motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron without the presence of slots, and the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

13. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet linear motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto the slots of an iron core, wherein the permanent magnets can be moved with the coil assembly stationary, or the permanent magnets held stationary while the coil assembly may be moved.

14. A permanent magnet motor as claimed in Claim 1 to claim 3 used in a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron without the presence of slots, and the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

15. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto the slots of an iron core, wherein the permanent magnets can be rotated with the coil assembly stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

16. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet rotary motor having a multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and the permanent magnets are arranged in a disk, such that the direction of polarity of the magnets is pointing in the same direction of the axis of rotation, wherein the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

17. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet rotary motor having a single phase type of coil assembly, wherein the coil assembly comprises one or more coils mounted onto a segment of coil back iron, and the permanent magnets are arranged in as a segment, such that the direction of polarity of the permanent magnets is in the same direction of the axis of rotation, wherein the permanent magnets can be rotated while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be rotated.

18. A permanent magnet motor as claimed in Claim 1 to claim 3 used in a permanent magnet linear motor having a single phase type of coil assembly, wherein the coil assembly comprises coils mounted onto a coil back iron that is circular in shape, and the permanent magnets are also arranged in a circular manner, such that the direction of polarity of the permanent magnets is in the radial direction, wherein the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

19. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet planar motor which produces force in more than one direction, either using a single phase type or multiphase type of coil assembly, wherein more than one set of permanent magnets can be arranged on a single plane and mounted on a same magnet holder, wherein the permanent magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

20. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet planar motor which produces force in more than one direction, either using a single phase type or multiphase type of coil assembly, wherein one set of permanent magnets and one set of coils can be arranged on a single plane and mounted on a same holder, wherein the corresponding coil assembly and permanent magnet assembly can be stationary or be moved.

21. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet hybrid motor which produces a torque in one direction and a force another direction, either using a single phase type or multiphase type of coil assembly, wherein more than one set of permanent magnets and can be arranged on a single cylindrical holder, wherein the magnets can be moved while the coil assembly is kept stationary, or the permanent magnets held stationary while the coil assembly may be moved.

22. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent linear motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two or more rows of permanent magnets can be moved while the coil assembly is kept stationary, or the two or more rows of permanent magnets held stationary while the coil assembly may be moved.

23. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet rotary motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two or more rings of permanent magnets can be rotated while the coil assembly is kept stationary, or the two or more rings of permanent magnets held stationary while the coil assembly may be rotated.

24. A permanent magnet motor as claimed in Claim 1 to claim 3 used in a permanent magnet linear motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two rows of permanent magnets are mounted on opposite faces of a supporting structure, which can be made from magnetic or non-magnetic material, wherein the permanent magnets and the supporting structure can be moved while the coil assembly is kept stationary, or the permanent magnets and the supporting structure held stationary while the coil assembly may be moved.

25. A permanent magnet motor as claimed in Claim 1 to Claim 3 used in a permanent magnet rotary motor having a single phase type or multiphase type of coil assembly, wherein the coil assembly comprises coil mounted onto coil back iron with or without the presence of slots, and two rings of permanent magnets are mounted on opposite faces of a cylindrical supporting structure, which can be made from magnetic or non-magnetic material, wherein the permanent magnets and the cylindrical supporting structure can be rotated while the coil assembly is kept stationary, or the magnets and the supporting structure held stationary while the coil assembly may be rotated.

26. An arrangement for a permanent magnet motor as claimed in Claim 2 wherein said permanent magnet motor is used in a permanent magnet linear motor or permanent magnet rotary motor or permanent magnet planar motor or permanent magnet hybrid motor.