CN103208868B - High torque low inductance rotary actuator - Google Patents

Abstract

An electromechanical rotary actuator includes a rotor and a stator having one or more slots in which one or more coils are positioned. The stator includes a rotor position reset device that overcomes cogging outside of the desired range of rotation. The rotor position reset means may comprise one or more reset magnets or alternatively a cavity of predetermined profile within the stator adjacent the rotor. A stator includes teeth having a pre-contoured end portion forming a portion of a bore in which the rotor operates. The tips of the teeth form a larger gap compared to typical actuators, where the gap is sized to match the rotor magnets. An actuator is provided that is expected to have a higher torque constant, low coil resistance, and low coil inductance.

Description

High torque low inductance rotary actuator

Cross reference to related applications

The present application claims priority from high torque, low inductance rotary actuator device and related method having application number 61/585,721, filed 2012, 1, 12, the disclosure of which is incorporated herein by reference and is commonly owned.

Technical Field

The present application relates generally to limited angle electromechanical rotary actuators and more particularly to actuators for use in the field of optical scanning.

Background

Electromechanical rotary actuators have existed for decades. It is used in a variety of industrial and consumer product applications, but it is particularly useful in the field of optical scanning, where an optical element is connected to an actuator output shaft that is returned to rotate in an oscillating manner.

For example, to make an optical scanning system, it is common to connect a mirror to the output shaft of a rotary actuator. In this application, the actuator/mirror combination can redirect the light beam over a range of angles, or the field of view of the camera so that a wide variety of targets can be viewed.

Other optical elements can also be connected to the output shaft. For example, a prism or filter can be attached to the shaft and rotation of the shaft of the actuator can change the angle of the prism or filter. If a dielectric filter is employed, changing the angle of incidence of the filter can change the bandpass wavelength characteristic higher or lower, thereby allowing the optical system to be tuned to a particular wavelength. Alternatively, the prism or filter can be rotated completely into or out of the optical path, allowing selective filtering of the light beam.

Typical electromechanical rotary actuators used in the field of optical scanning are usually made of some combination of magnets, steel and coils of insulated enameled wire. These components have been arranged in a variety of ways, but over the past two decades the most common arrangement has been the design of simple two-pole rotor magnets, and "toothless" stators.

The rotor in these actuators is typically a solid, cylindrical magnet made of high grade neodymium iron boron that is diametrically magnetized and two shafts are attached to the magnet. One shaft member may be connected to the mirror and the other shaft member may be operated by the position sensor. The shaft is typically supported by ball bearings. For example, the disclosed dimensions may include rotor magnets having a diameter of 0.12 inches (about 3 millimeters) and a length of 1.3 inches (about 33 millimeters).

A review of known actuator technology and a reference to known actuators will help the reader to better understand the needs that are being met by embodiments of the present invention. This description of progressively improved embodiments, achieved primarily through extensive analysis and experimentation, will also be helpful in addressing the technical problems of the art set forth in the background section herein. Therefore, nothing disclosed in this background section should be construed as an admission that such prior art teachings are known.

Figure 1 shows a cross-sectional view of a rotor and stator arrangement in a typical "toothless" optical scanner of the prior art. The stator is tubular in nature. For the diameters of the rotor magnets described above, a typical stator tube may have an outer diameter of 0.5 inches (about 12.7 mm) and an inner diameter of 0.196 inches (about 5 mm), and is typically made of cold rolled steel. The coil of enamel wire is formed and bonded to the inner wall of the stator steel tube, occupying the region of about 90 degrees arc. There is typically a gap of about 0.007 inches between the outer wall of the rotor magnet and the inner wall of the coil, thus allowing the magnet to rotate freely. In fig. 1, the coil regions are designated as "coil +" or "coil-" to represent turns into and out of the page, respectively.

Figure 2 shows the magnetic flux lines in a typical "toothless" optical scanner of the prior art as shown in figure 1. It can be seen that the flux lines must extend through ("jump over") a relatively large gap to reach the stator steel. The coil is located between the magnet and the stator steel. When the coil is energized, lorentz forces are exerted on the coil and the magnet. Since the coils are typically glued to the stator and thus held stationary, all of the force is transferred to the rotor magnets. Since the force is generated on opposite sides of the magnet, the force is in the form of a torque, and the actuator produces a torque and thus a movement.

In this example of the actuator, 50 turns of AWG #33 enameled wire is employed, having a coil resistance (R) of about 2.5 ohms, a coil inductance (L) of about 100 microhenries, and producing a torque with a torque constant (KT) of about 38,000 dyne cm for each ampere of current through the coil.

Toothless devices have benefits. One benefit is the relatively low inductance of the coil due to the coil not completely surrounding a closed steel core. Rather, the entire interior of the actuator is open, including only the rotor magnets, which have nearly the same magnetic permeability as air.

However, the toothless construction is not without disadvantages. One major drawback is the amount of heat generated in the fast/wide angle rotor motion. In addition, the generated heat cannot be effectively removed. These drawbacks stem from the fact that the coil occupies a relatively small space (cross-sectional area) and that it is glued to the inside of the stator tube so that it has a direct connection only on one side (outside of the coil).

Referring again to fig. 1, it can be seen that the left, right, and inner sides of the coil are essentially free of attachment to any face. It is for this reason that the heat generated by the coil can only be removed from one face (the outside). In fact, the heat generated by the inside surface of the coil heats the rotor magnet, which degrades performance and risks demagnetizing the rotor magnet if the heat exceeds about 100 degrees celsius.

To generate less heat, a lower coil resistance is required, and to reduce the coil resistance, thicker wires must be used.

If, for example, AWG #29 wire is used in place of AWG #33 wire and placed in the same coil region, only about 22 turns may be used, providing a coil resistance (R) of 0.48 ohms and a torque constant (KT) of 16,720 dyne cm per ampere. The coil resistance is of course lower (because of the thicker wire) but the torque constant is also lower (because of the fewer turns).

It is useful to use a figure of merit when compared to the motor design. One important figure of merit is known as the motor constant (KM), which represents the amount of heat generated when the actuator produces a given amount of torque. KM can be calculated in several ways, but the simplest way is: KM KT/√ R.

The KM for an original actuator with 50 turns of coil (KT 38,000, R2.5 ohm) is the square root of 24,033 dyne cm per watt. Thus, to produce 24,033 dyne cm of torque, the motor would need to dissipate 1 watt of heat. To produce twice this amount of torque, or 48,066 dyne cm of torque, the motor would need to dissipate 4 watts of heat. Twice the torque output requires twice the current input. Since heat is proportional to the square of the current, this means that twice the current produces four times the heat.

Comparing these values with the same actuator (KT 16,720, R0.48) with AWG #29 having 22 turns indicates that KM is now 24,133 or about the same value as the original.

This represents an important law for moving magnet actuators. KM is determined by the area occupied by the coil. Regardless of how many turns of wire occupy the coil area. If the coil area remains unchanged and is fully occupied by coil turns, KM will remain the same as before.

For this reason, attempts are being made to simply increase the coil area, for example by increasing the outer diameter of the coil (and the inner diameter of the stator tube). However, increasing the diameter of the stator tube will increase the magnetic circuit air gap that the magnetic flux must jump.

Another figure of merit used in magnetic design is known as the Permeance Coefficient (PC), which represents the "operating point" of the rotor magnets. For a simple magnetic circuit consisting of magnets, air and high permeability steel, the permeability coefficient can be obtained by dividing the magnetization length by the total magnetic circuit air gap. For the electromechanical actuator described above-with a rotor diameter (magnetization length) of 0.120 inches and a stator inner diameter of 0.196 inches, the magnetic circuit air gap is 0.196-0.120-0.076 inches. Therefore, the permeability coefficient is approximately 0.120/0.076 to 1.6.

Fig. 3 provides a B/H curve for a typical high performance neodymium iron boron magnet. The X-axis represents the coercivity (H) of the magnet and the Y-axis represents the flux density (B). The numbers near the outer side (starting at 0.1 and ending at 5.0 on the graph) are the permeability coefficients, which represent the "operating point" of the magnet. This figure shows: at a permeability of 1.6 (which is the case for a typical actuator used in the prior art), the magnet operates at a flux density of 8.7 kilogauss at a temperature of 20 degrees celsius.

If the inner diameter of the stator tube is increased to 0.24 inches, for example, this would provide more than twice the coil wire area, easily allowing more than 22 turns of AWG #29 enameled wire to be used. But increasing the inner diameter of the stator tube also increases the magnetic circuit air gap that the magnetic flux must jump. Therefore, the magnetic field becomes weaker. This is represented by a susceptibility of 1.0 in the graph of fig. 4. This weaker magnetic field requires more coil turns to produce the same torque constant. A lower permeability also creates a risk of demagnetization at elevated temperatures.

Analysis and testing has demonstrated that the KM for a toothless actuator remains substantially constant at a magnetic susceptibility between 1.0 and 2.0, and thus, there is essentially no known way to overcome the problem of heat generation in a toothless actuator. Thus if heat generation is a performance limiting factor, another actuator must be sought.

In the past, some companies have sought to overcome the problem of heat generation by employing "toothed" (also known as slotted) actuators. For example, fig. 5 shows a cross-sectional view of such an actuator used in a known optical scanner. In a toothed actuator, the coil is not located between the magnet and the stator steel, but is wound around a steel core forming "teeth" around the magnet. Since the coil is no longer located between the magnet and the stator steel, the stator teeth can be closer to the magnet. Thus, the susceptibility of toothed actuators is much higher than that of non-toothed actuators.

Fig. 6 shows the same magnetic B/H curve as shown in fig. 3 and 4, but also highlights the final flux density when the permeability is 6. Given the same rotor magnets described above, only 38 turns of wire per ampere are now required to produce 38,000 dyne cm, since the magnets operate at a higher magnetic flux density. And thicker wires may be used because the coil area is significantly larger.

Clearly, a "toothed" stator arrangement can solve the problem of heat generation. However, new problems arise, one of which is a significantly increased inductance (L). For an actuator such as that shown in fig. 5, for example, the inductance is greater than 300 microhenries, which is about three times the inductance of a "toothless" actuator having the same torque constant.

Referring again to the graph of fig. 6, the increase in inductance is due to two factors. The first factor is an "outer fringe line" that circulates magnetic flux around the coil, but does not interact with the rotor magnets to produce torque. The second factor is the "tooth-to-tooth" edge line, which circulates the magnetic flux around the gap between the teeth but does not generate torque, as shown with reference to fig. 7.

To eliminate the outer edge lines, the toothed stator may be rearranged as shown in fig. 8. In this arrangement, the coils are wound around teeth positioned to be entirely contained inside the stator, essentially forming a series of magnetic circuits between the two coils. Essentially, this helps to reduce the inductance to about 212 microhenries, but this is still more than twice as large as a toothless actuator producing the same torque.

To further reduce the inductance, the edge portions of the teeth to teeth must be reduced and therefore the gaps between the stator teeth must be opened further. For example, if the gap between the stator teeth is increased to 0.050, the inductance becomes 180 microhenries. If the gap between the stator teeth is further increased, even to 0.070, the inductance becomes 157 microhenries. This is still more than 50% higher than a seamless actuator, but this may be tolerable for some applications.

However, increasing the gap between the stator teeth has negative consequences. At the most, the actuator will have a tendency to "cogging" towards an off-center angle because the south and north poles of the rotor magnets will strongly orient themselves in the direction of the stator teeth themselves. A small amount of cogging can be tolerated by the servo system located outside the optical scanner, but a large amount of cogging is detrimental to performance and thus highly undesirable.

For example, for the toothed or slotted actuator described above with reference to FIG. 8, the gap between the teeth is 0.030 inches and the cogging torque at 20 degrees is 14,000 dyne cm. When the gap between the teeth increases to 0.036 inches, the cogging torque at 20 degrees is 22,000 dyne cm. As the gap between the teeth increases to 0.050 inches, the cogging torque increases to 40,000 dyne cm at 20 degrees. As the gap between the teeth increases to 0.070 inches, the cogging torque increases to 85,000 dyne cm at 20 degrees. Cogging torque of 14,000 dyne cm is tolerable, but higher cogging torques cannot be tolerated.

Since limiting the inductance in a toothed actuator also means increasing the cogging torque, this means that a toothed actuator should not be used if the inductance is the performance limiting factor.

It is reiterated that typical toothless actuators are typically not capable of achieving both high torque constants and low coil resistance. And typical toothed actuators cannot achieve low coil inductance. Accordingly, there is a clear need for an electromechanical rotary actuator that can provide a high torque constant, low coil resistance, along with a low coil inductance.

Disclosure of Invention

In accordance with the teachings of the present invention, an electromechanical rotary actuator may include a rotor and a stator including one or more slots having one or more coils disposed therein. The stator may also include a rotor position reset device that overcomes cogging towards being outside the desired range of rotation. In some embodiments, the rotor position reset device may include one or more reset magnets, and in other embodiments the rotor position reset device may include a cavity within the stator adjacent the predetermined contour of the rotor.

One embodiment may include a limited rotation rotary actuator including a stator having a bore extending axially therein and at least two teeth having a pre-contoured end forming at least a portion of the bore, wherein the at least two teeth terminate in a spaced apart relationship forming a gap therebetween. The rotor may have a two-pole radial magnet bi-directionally operable from the stator and extending into the bore of the stator, wherein a space is formed between the magnet and the predetermined contoured end portions of the at least two teeth. At least one electrical coil may extend around at least a portion of one of the at least two teeth, wherein the electrical coil is energizable to provide bidirectional torque to the rotor. A rotor resetting device may be located within at least one of the at least two teeth, wherein the rotor resetting device is positioned for resetting the rotor to the central rotation angle when the current supply to the at least one electrical coil is stopped.

One embodiment may include a non-uniform spacing formed between the magnet and the predetermined contoured ends of the at least two teeth. The non-uniform spacing provides for greater spacing of the central portion adjacent the predefined profile end of the tooth as compared to the spacing adjacent the tip of the tooth. This non-uniform spacing provides a return torque that results in a spring-like return-to-center action of the rotor.

Yet another embodiment may include a limited rotation rotary actuator including a stator having a bore extending axially therein and at least two teeth having a predefined profile end forming at least a portion of the bore, wherein tips of the at least two teeth form a gap therebetween. The rotor may include a bi-directionally operable dipole radial magnet in the bore. At least one first slot may extend longitudinally within the at least one tooth and at least one second slot may extend from the bore into the stator. The at least one second slot is more or less vertically aligned with the at least one first slot. An electrical coil extends within the at least one second slot and is energizable to provide bidirectional torque to the rotor. The rotor reset device is located in at least a single first slot of the at least one first slot. The rotor resetting means is positioned to reset the rotor to a central rotational angle when the current applied to the at least one electrical coil is stopped.

In yet another embodiment, a limited rotation rotary actuator may include a stator having a bore extending axially therein and at least four teeth having a predefined profile end forming at least a portion of the bore. The ends of the at least four teeth are in spaced apart relation thereby forming a gap therebetween. The rotor has a four-pole magnet arrangement extending into the bore. At least one electrical coil extends around at least a portion of one of the at least four teeth. The electrical coil is energizable to provide bidirectional torque to the rotor. The rotor reset device is located in at least one of the at least four teeth. The rotor resetting means is positioned to reset the rotor to a central rotational angle when the application of current to the at least one electrical coil is stopped.

Drawings

For a more complete understanding of the present invention, reference is made to the following detailed description, taken in conjunction with the accompanying drawings, which illustrate various embodiments of the invention, and in which:

FIG. 1 illustrates the combination of a stator and a rotor found in prior art gearless actuators;

FIG. 2 shows magnetic flux lines (magnetic flux lines) in a prior art combination of a toothless stator and rotor;

FIG. 3 illustrates B/H curves and related information regarding a magnet used in a typical toothless optical scanner;

FIG. 4 illustrates B/H curves and related information regarding magnets used in a toothless scanner with increased stator inner diameter;

FIG. 5 illustrates the combination of a stator and a rotor found in prior art toothed actuators;

FIG. 6 illustrates B/H curves and related information regarding a magnet used in a toothed actuator;

figure 7 shows the flux lines and edge lines found in a prior art toothed stator;

FIG. 8 illustrates the combination of a stator and a rotor found in another prior art toothed actuator;

FIG. 9 illustrates an embodiment of the present invention, wherein a two-tooth actuator with a reset magnet is exemplary shown;

FIG. 9A is a perspective view illustrating one embodiment of an actuator in accordance with the teachings of the present invention;

FIG. 9B is an exploded view of the stator portions assembled together to form the stator of FIG. 9A;

FIG. 9C is one embodiment of a rotor having magnets and a shaft operable with the embodiment shown in FIG. 9A;

FIG. 10 shows the magnetic flux lines in the embodiment shown in FIG. 9;

FIG. 11 shows another embodiment of the invention in which insulated coils are located in two slots and a reset magnet is employed;

FIG. 12 shows the magnetic flux lines in the embodiment shown in FIG. 11;

FIG. 13 shows yet another embodiment in which the coils are located in two slots but no reset magnet is employed;

FIG. 14 shows the magnetic flux lines in the embodiment shown in FIG. 13;

FIG. 15 shows another embodiment of the invention in which the coils are located in four slots and have reset magnets;

FIG. 16 shows the magnetic flux lines in the embodiment shown in FIG. 15;

FIG. 17 shows another embodiment of the invention in which the coils are located in six slots and a reset magnet is employed;

figure 18 shows the lines of magnetic flux in the embodiment shown in figure 17, and shows the turns;

FIG. 19 illustrates some features of the stator structure of the embodiment shown in FIG. 18;

FIG. 20 shows another embodiment of the invention in which the coils are located in six slots and no reset magnet is employed;

FIG. 21 shows the magnetic flux lines in the embodiment shown in FIG. 20;

FIG. 22 shows another embodiment of the invention in which a four-pole rotor and reset magnet are employed;

FIG. 23 shows magnetic flux lines in another embodiment shown in FIG. 22;

figure 24 shows how the quadrupole embodiment of figure 22 can be wound with four separate coils, one around each tooth;

figure 25 shows how the quadrupole embodiment of figure 22 can be wound with two separate coils wound around alternate teeth;

figure 26 shows how the quadrupole embodiment of figure 22 can be wound in a serpentine fashion with a single coil around alternating teeth;

FIG. 27 illustrates how the stator of a two pole embodiment may be partitioned into segments to facilitate actuator fabrication and assembly, where the segments may include a point-and-socket arrangement of tips and pockets to facilitate alignment;

FIG. 28 illustrates how the stator may be divided into segments in a four-pole embodiment to facilitate actuator manufacture and assembly, where the segments may include an arrangement of tips and receptacles that facilitate alignment;

FIG. 29 illustrates how the segments may also be arranged in alternating layers to form an overlap region that reduces the overall stator reluctance after assembly;

FIG. 30 illustrates the use of a small material web at one end of the slot in which the reset magnet is seated, wherein the material web is made relatively thin, typically about the thickness of the laminations (e.g., 0.014 inches), and is provided to help the stator maintain a precise shape, and wherein the thinness of the material web is such that its magnetic properties are not affected because it becomes magnetically saturated; and

fig. 31 shows how the material connection can be removed to essentially allow the stator to exist in segments, each segment being operatively connected to a reset magnet, wherein with or without the material connection, rotor position reset will occur.

Detailed Description

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

Referring initially to FIG. 9, one embodiment of the present invention is hereinafter described as an electromechanical, limited rotation rotary actuator 100. The actuator, described by way of example herein, includes a stator 102, the stator 102 having a bore 104 extending axially therein and at least two teeth 106, 108, the teeth 106 and 108 having predefined contoured ends 110, 112 forming at least a portion of the bore. The tips 114, 116 of the teeth 106, 108 are in spaced apart relation and form a gap 118 therebetween. For the embodiment described by way of example herein, the rotor 120 includes a dipole radial magnet (diameter magnet)122 that is bi-directionally operable by the stator 102 and extends into the bore 104. A space 124, here an air gap, is formed between an outer surface 126 of the magnet 122 and the pre-contoured ends 110, 112 of the teeth 106, 108. For the exemplary embodiment described herein, two electrical coils 128, 130 each extend around a portion of each tooth 106, 108. The electrical coils 128, 130 are energizable to provide bi-directional torque to the rotor 120. Rotor reset means 132 in the form of reset magnets 134, 136 are disposed in slots 138, 140 in each tooth 106, 108, the slots extending longitudinally toward the bore 104. The rotor reset device 132 may include only one reset magnet. The rotor resetting device 132 is positioned for resetting the rotor 120 to the central rotational angle 142 when the electrical coils 128, 130 are no longer energized. For the embodiment described herein by way of example, the two teeth 106, 108 (although not limited thereto) are radially aligned. The length dimension 142 of the gap 118 is at least forty percent of the diameter of the radial magnet 122.

One simple way to manufacture the rotor 120 is to use a single piece of radially magnetized cylindrical magnet material. The rotor 120 may be made of one or more magnets as long as it provides a north pole diametrically opposite a south pole. For the embodiment exemplarily described herein, the torque, inductance and resistance values are valid for a rotor magnet having a diameter of 0.12 inches, a length of 1.3 inches, and made of a high grade neodymium iron boron material, and a stator having an inner diameter of 0.136 inches.

Referring again to fig. 9, the illustrated stator 102 comprises stator steel with teeth 106, 108, each tooth 106, 108 providing a uniform circular spacing 124 (air gap) around the rotor magnet 122, which may have a smooth circular cross-section or may include multiple facets-by way of further example without departing from the teachings of the present invention. When compared to known actuators, the gap 118 is relatively large (about 40% or more of the magnet diameter), which typically causes the magnet 122 to experience a strong cogging effect (cogging) toward being outside of the desired range of rotation. The reset magnets 134, 136 are inserted into slots 138, 140 in the teeth 110, 112 of the steel stator 102 to bias the upper portion 146 of each tooth 106, 108 to a "south pole" and the lower portion 148 of each tooth to a "north pole" as described herein with reference to fig. 9. The north pole of the rotor magnet 122 is attracted uniformly between the south poles of each reset magnet 134, 136, and likewise the south pole of the rotor magnet is attracted uniformly between the north poles of each reset magnet. This overcomes the cogging effect and keeps the rotor magnets 122 oriented toward the center 141 of the rotational angle range. It should be noted that the lines that appear to separate the north and south poles are merely illustrative and are not intended to limit the magnets to distinguish the separation of the poles.

The stator 102 shown in cross-section in fig. 9 has a cylindrical shape. It should be understood by those skilled in the art that alternative shapes may be employed without departing from the teachings of the present invention, such as the rectangular cross-sectional shape of the actuator 100A shown in fig. 9A. Further, the actuator 100, 100A may include a plurality of stator portions 150, 152. Further, the stator 102 may be formed from laminations 154, as shown with continued reference to fig. 9 and now with reference to fig. 9B. For the embodiment described by way of example herein, rotor magnet 122 comprises a neodymium-iron-boron material. The rotor magnet 122 may be formed integrally with a shaft 156 that carries an optical element 158 carried by the shaft, as shown in accordance with fig. 9C. The optical elements may include mirrors, prisms, or filters that are usefully employed in optical scanners.

With continued reference to fig. 9A, 9B, and 9C, the shaft 156 may be made of stainless steel, although virtually any material can be used so long as the material is capable of withstanding the torque generated by the actuator 100, 100A and any external loads connected to the actuator in a working environment. As described above, the shaft 156 may be formed integrally with the rotor magnet 122 or attached thereto using an adhesive such as epoxy. Referring to fig. 9A, 9B, the stator 102 shown therein comprises a plurality of thin metal sheets, referred to herein as laminations 154 as described above. The laminations 154 may be assembled into the stator portions 150, 152 to form the desired shape. The shape of each lamination 154 may be formed by metal stamping, laser cutting, photo etching, water jet cutting, or other known methods of forming from sheet metal. As described in U.S. application serial No. 13/446,500, which relates to an electromechanical limited rotation rotary actuator, the disclosure of which is incorporated herein in its entirety, laminations 154 may be made of a silicon steel material known as M-19, a material that is specifically used to fabricate electric motors and transformers. However, many different materials will be possible as long as the material is magnetically permeable. Some possible alternative materials include cold rolled steel (e.g., Q-195) and magnetic stainless steel (e.g., stainless steel 416). The tips 160 and receptacles 162 of each lamination 154 alternate across the lamination layers, creating overlapping regions 164 between the laminations 154. As a result, the air gap is effectively filled with magnetically conductive lamination material on adjacent layers due to the overlap region.

Fig. 10 shows flux lines 150 between rotor magnet 122 and reset magnets 134, 136. When current is passed through coils 128, 130, each tooth effectively becomes an electromagnet, which helps to generate torque and motion of rotor magnet 122.

By way of example, for the actuator shown in FIG. 9, with an AWG #25 enamel wire having 19 turns around each tooth, the torque constant (KT) is about 38,000 dyne cm per ampere, the coil resistance (R) is 0.1 ohm, and the coil inductance (L) is about 157 microHenries.

Referring now to fig. 11, an embodiment of the actuator 100 may include a single electrical coil 128 extending around a portion of each tooth 106, 108 and extending near the gap 118 formed between the tips 114, 116 of the opposing teeth. A coil slot 152 is formed in the stator 102 and terminates at the gap 118, resulting in a single coil extending in the coil slot 152. Alternatively, as shown in fig. 11, a single coil may extend in each of the two coils 152, 154, with opposing coil slots 152, 154 formed on opposite sides of the rotor magnet 122 having the single coil 128 extending therein. The individual coils 128 are closely packed into the coil slots 152, 154 to transfer heat generated in the coils 128 to the stator 102.

Therefore, the coil 128 is disposed closer to the rotor magnet 122 than the embodiment of fig. 9 as described above. With continued reference to fig. 11, there may be a wide gap 118 between the teeth 106, 108 formed by the coil slots 152, 154. The wide gap 118 can have a dimension of about 40% magnet diameter 144 or greater. The reset magnets 134, 136 are placed outside of the rotor magnet 122 and are effectively embedded in the steel stator 102 using the slots 138, 140 in the teeth 106, 108, as described above. Fig. 12 shows the magnetic flux lines 150 between the armature magnet 122 and the reset magnets 134, 136 of the embodiment of fig. 11.

For the actuator 100 shown with reference to fig. 11, 38 turns of AWG #31 enamel wire are provided in each coil region, the torque constant (KT) is about 38,000 dyne cm per ampere, the coil resistance (R) is 1.25 ohms, and the coil inductance (L) is about 120 microhenries. It is noted that it produces the same torque constant (KT) and similar coil inductance (L) as a toothless actuator, but the coil resistance is only half. It should also be noted that for the embodiment shown herein, the coil slot surface 156 surrounds the coil 128 on three of the four sides, thus providing a desired, improved heat transfer path to remove heat from the coil.

Fig. 13 shows another embodiment of the present invention. This embodiment is similar to that shown in fig. 11, with only a single coil region on each side of the rotor magnet. However, in this embodiment, there is no reset magnet as shown in the embodiment shown with reference to fig. 11. Instead, the rotor position return 132 is provided and improved by the inner shaping of the stator steel, which is referred to herein as the return slot region 166, which is actually a structure disposed at a 90 degree angle relative to the "coil +" and "coil-" of the coil 128. As long as the width 168 of this reset slot region 166 is made larger than the gap 118 between the teeth 106, 108 and the depth 170 is larger than 25% of the gap between the rotor magnet 122 and the stator bore effective inner diameter (effective inside diameter)172, there is a resetting effect-when no current is applied to the coils, this effect will reset the rotor 120 to the central range of rotational angles. The reset groove region 166 may not have a symmetrical or uniform surface but may be oval-shaped, with a width 168 that effectively continuously increases to the left and right as shown with continued reference to fig. 13. Thus, the reset means 132 includes a non-uniform spacing formed between the magnet 122 and the predetermined contoured ends of the teeth 106, 108 that results in a greater spacing in the central portion adjacent the arcuate ends of the teeth as compared to the spacing adjacent the distal end portions of the teeth; this non-uniform spacing provides a return torque that results in a spring-like return-to-center action of the rotor. The width 168 is greater than the gap 118, wherein the shape of the region 166 may be further illustrated with reference to the dashed lines of FIG. 13.

Figure 14 shows the magnetic flux lines 150 of the embodiment of figure 13.

By using a radially magnetized cylindrical rotor magnet 122, a sinusoidal flux versus angle profile is obtained from the magnet. This in turn produces a substantially sinusoidal profile of the actuator output torque versus angle (when current is applied to the coil). In addition, a magnetic circuit air gap, such as an oval shaped region 166, is employed, the width 168 of which continuously increases from top-to-bottom toward left-to-right, resulting in a generally sinusoidal spring-like return-to-center torque. Under this configuration, since the shape of the output torque-angle curve (when current is applied to the coil) is the same as the return torque-angle (return to the center) curve like a spring, the end result is that the output angle versus input current curve is approximately linear within about +/-60 mechanical degrees — which is the desired result.

In embodiments of the present invention, a reset magnet or a reset slot is employed to improve the torque output of the actuator. For a given number of coil turns, embodiments of an actuator that do not employ a reset magnet as its rotor position reset means will generally have a torque constant (KT) that is about 8% to 10% lower.

For example, for the actuator shown with reference again to FIG. 13, 38 turns of AWG #31 enameled wire are placed in each coil region, the torque constant (KT) is about 34,200 dyne cm per ampere, the coil resistance (R) is about 1.25 ohms, and the coil inductance (L) is about 120 microHenries. It is noted that this achieves nearly the same torque constant (KT) and similar coil inductance (L) as a "toothless" actuator, but only half the coil resistance. It should also be noted that the coil area surrounds the coil on three sides, providing a very good heat dissipation path to remove heat from the coil.

Fig. 15 shows yet another embodiment of the present invention. In this embodiment, the actuator 100B includes two coil slots 152A, 152B, 154A, 154B on each side of the rotor magnet 122, all located in close proximity to the magnet. The reset magnets 134, 136 are placed in slots 138, 140 located outside the rotor magnet 122, as described above, and are effectively embedded in the stator steel. Coil 128 extends into slots 152A and 154A. Coil 130 extends into slots 152B and 154B. The benefit of this arrangement is that the torque-position curve is desirably flatter than all other actuators (both existing and the embodiments described herein). Fig. 16 shows the lines of magnetic flux between the rotor magnet and the reset magnet of the embodiment of fig. 15.

For the actuator shown in fig. 15, 19 turns of AWG #31 enamel wire are placed in each coil region, the torque constant (KT) is about 38,000 dyne cm per ampere, the coil resistance (R) is 1.25 ohms, and the coil inductance (L) is about 120 microhenries. It is noted that this provides the same torque constant (KT) and similar coil inductance (L) as a "toothless" actuator, but only half the coil resistance. It should also be noted that the coil area surrounds the coil approximately entirely, providing a very good heat dissipation path to remove heat from the coil.

Fig. 17 shows yet another embodiment of the present invention. In this embodiment, the actuator 100C includes three coil slots 152A, B, C and 154A, B, C on each side of the rotor magnet 122, all located in close proximity to the magnet. Fig. 18 shows the magnetic flux lines between the armature magnet 122 and the reset magnets 134, 136 of the embodiment of fig. 17. Fig. 18 also shows respective turns 174 in coils 176A, B, C. In fig. 19, these coil slots are designated as slot 1p, slot 2p, slot 3p, slot 1m, slot 2m, and slot 3 m. Slot 1 p/slot 1m and slot 3 p/slot 3m each comprise a single coil 176A, 176B. Slot 2 p/slot 2m includes two coils 176C, 176D. By dividing the coil into three separate regions (coil slots), the heat accumulated in each coil is minimized and any heat accumulated is more easily removed. Fig. 19 also shows by way of example the angle between the grooves. The angle between the groove 1p and the groove 2p is made substantially the same as the angle between the groove 2p and the groove 3p, and the same as the angle between the groove 1m and the groove 2m and the angle between the groove 2m and the groove 3 m. Any angle between 0 and 90 degrees will be feasible. However, angles between 15 degrees and 45 degrees may achieve the desired performance, but are not intended to be limited to such ranges. From a manufacturing point of view, when the angle is about 22 degrees, it is easy to insert the coils into the slot 1 p/slot 1m and the slot 3 p/slot 3 m.

Each slot (slot 1p, slot 1m, slot 2p, slot 2m, slot 3p, slot 3m) is wide, which results in that the coil resistance and the inductance of each coil placed in the slot are low. By way of example, the width of slot 1 p/slot 1m and slot 3 p/slot 3m is 0.026 inches, and the width of slot 2 p/slot 2m is 0.048 inches. Furthermore, the total width of all slots is such that the magnetic circuit exhibits a large total tooth gap of 0.1 inch. Since the rotor magnet diameter is 0.12 inches in this example, the total gap between teeth around the magnet is greater than 80% of the rotor magnet diameter. Due to this very wide effective interdental gap, this embodiment has the lowest inductance in all the previously described embodiments.

With continued reference to fig. 17, the reset magnets 134, 136 are placed outside of the rotor magnet 122, but are effectively buried in the stator steel, as previously described. A benefit of this embodiment is that as the coils are spread, heat can be easily removed from these spread coils. Furthermore, the dispersion grade provides an actuator with a very low inductance.

For example, the actuator shown in fig. 17, 10 turns of AWG #29 enameled wire (total 40 turns connected in series) were placed in the region designated as coil 1 +/coil 1-, coil 2 +/coil 2-, coil 3 +/coil 3-, coil 4 +/coil 4-, with a torque constant (KT) of about 38,000 dyne cm per ampere, a coil resistance (R) of about 1.0 ohm, and a coil inductance (L) of about 94 microhenries. It is noted that this yields the same torque constant (KT) as a toothless actuator, but only approximately one-third of the coil resistance and lower coil inductance (L). Each coil region surrounds the coil on three sides, providing a desired, efficient heat dissipation path to remove heat from the coil. These performance parameters are far superior to the toothless actuator.

Fig. 20 shows another embodiment of the present invention. This embodiment is similar to that shown in fig. 17, with three coil regions on each side of the rotor magnet. However, in this embodiment, there is no reset magnet. Instead, the rotor position return 132 is provided by the inside shape of the stator steel-it is not round, but has a return slot area 166. When the slots of the coil (slot 1p, slot 1m, slot 2p, slot 2m, slot 3p, slot 3m, slot 4p, slot 4m) are evenly distributed around the inner diameter of the stator while leaving room for the reset slot region 166 (as shown on the left and right in fig. 20 and 21), the rotor position will be reset to center as long as the reset slot width 168 is wider than the width of slot 2 p/slot 2m (which is located at 90 degrees relative to the reset slot region) and the reset slot region depth is greater than or equal to about three times the distance of the gap between the rotor magnet and the stator teeth. In the case of the exemplary actuator 100, the rotor magnet diameter is 0.120 inches and the stator inner diameter is 0.136 inches, providing a 0.008 inch gap between the rotor magnet and the stator steel, the width of the reset groove region 166 is 0.050 inches, and the depth 170 of the reset groove region 166 is 0.024 inches. As described above, the reset groove region 166 may be modified to appear more like an ellipse rather than more like a groove-similar to the embodiment of FIG. 13 and still be within the scope of the present invention. Fig. 21 shows the magnetic flux lines 150 of the embodiment of fig. 20.

Fig. 22 shows another embodiment of the present invention. In this embodiment, the actuator 100 includes a four-pole rotor magnet 180. In the past, typical quadrupole actuators were manufactured for use in the optical scanning field, but cogging torque was intolerable and inductance was not satisfactory. Therefore, the four-pole actuator has never gained popularity. However, with the stator arrangement shown in fig. 22, cogging torque is completely cancelled by the reset magnets.

With continued reference to fig. 22, the actuator 100 may be described as including a stator 102 having a bore 104 extending axially therein and four teeth 106, 108, 106A, 108A, the four teeth 106, 108, 106A, 108A having a pre-contoured end 110, 112 forming a portion of the bore. The ends 114, 116, 114A, 116A of the four teeth are in spaced relation to form a gap 118, as described above. The rotor 120 employs a four-pole magnet arrangement, described herein as a four-pole magnet 180 extending into the bore 104, wherein a gap 124 is formed between the magnet 180 and the predetermined contoured end of the at least four teeth 106, 108, 106A, 108A. Electrical coils 128, 130 extend around at least a portion of the four teeth. The rotor return device 132, here the return magnets 134, 136, 134A, 136A, is arranged in the grooves 138, 140, 138A, 140A of the teeth. The two coils 128, 130 substantially fill the space between the four teeth to transfer heat generated in the coils to the stator through thermal contact with the teeth. The gaps 118 between the stator teeth are also open and allowed to be made wider, providing an actuator with a very low inductance. Figure 23 shows the magnetic flux lines 150 of the embodiment of figure 22.

For the quadrupole actuator 100 described herein with reference to 22, the coils 128, 130 can be wound in several ways. For example, as shown in fig. 24, four separate coils may be wound around the four teeth in the embodiment of fig. 22. Alternatively, as shown in fig. 25, two coils may be wound, including a coil around alternating teeth. As yet another alternative example, a single coil may be wound around all of the teeth — in a serpentine fashion, as shown with reference to fig. 26. The advantage of winding a single coil around each tooth is that the end-turns do not take up too much space and, therefore, the axial length of the motor can be reduced. The benefit of winding two coils on alternating teeth is that the number of coils is half that when compared to placing a single coil on each tooth. The advantage of the serpentine winding is that only a single coil is required for all teeth.

Although not intended to be limiting, the stator steel can be any magnetically permeable material, but is preferably a motor grade silicon steel. Further, the shape of the stator can be made using any known manufacturing technique, but it has been found that the stator is most easily manufactured by forming thin laminations, such as 0.014 inch thick M-19 material, by blanking, laser cutting or photo etching, and then stacking the laminations to achieve the desired axial motor length.

It is also noted that the laminations 154 forming the stator 102 described above with reference to fig. 9A may be manufactured as a single solid layer or alternatively as separate sections, as shown in fig. 27 and 28, and then assembled together to form the final desired shape. The segments or stator portions 150, 152 can also include overlapping portions on alternating lamination layers to reduce the overall reluctance of the magnetic circuit, as shown in fig. 29 and described above.

It should be noted that the rotor magnet 122 and the reset magnets 134, 136, 134A, 136A can be made of any magnet material, and the reset magnets can be made of a different material than the rotor magnet. However, the highest performance currently available is generally obtained by using neodymium-iron-boron N48H or better as the rotor magnet.

It is noted that in all embodiments where two or more separate coils are provided, it is possible to wind and/or provide current to only a single coil and still be within the scope of the present invention. However, while actuators employing more than one coil often connect the coils in series, it is also possible to connect the coils in parallel or in series plus parallel, and still be within the scope of the present invention.

As noted above, in all embodiments employing a reset magnet, only a single reset magnet may be employed to overcome cogging torque and still be within the scope of the present invention. However, the use of only one reset magnet also produces a radial force on the rotor magnet, effectively attracting the rotor magnet toward the reset magnet. This may be advantageous in applications where radial preload is employed for the support bearing.

The amount of rotor position reset depends on the width and length (in the direction of magnetization) of the reset magnet. If the width or length is increased, a greater degree of reset (torque towards the center of the range of rotational angles) is provided.

Further modifications may be employed in accordance with the teachings of the present invention. For example, referring now to fig. 30, which shows a small material connection 182 at the magnetic ends of the slots 138, 140, the reset magnets 134, 136 may be placed in the slots 138, 140, as set forth earlier with reference to fig. 11. The material bonds 182 may be made very thin, typically about the thickness of the laminations 154 (e.g., 0.014 inches). This helps the stator 102 to maintain a precise shape, wherein the thickness dimension of the material connection 182 (i.e., its thinness) makes it substantially non-influential for magnetism as it becomes magnetically saturated. In addition, and as shown with reference to fig. 31, material connections 182 can be removed, allowing stator 102 to exist in sections 150, 152, with each section effectively connected with reset magnets 134, 136. The reset will occur with or without the material connection 182.

Those skilled in the art will appreciate that multiple magnets may be employed, so long as they are magnetized and aligned to provide lines of magnetic flux in a desired orientation, as will be described in greater detail herein, with the benefit of the teachings of the present invention. Further, while the exemplary embodiment employs two-pole magnets, rotor magnets having a greater number of poles may also be employed, as will be illustrated later herein.

Although a detailed description and illustration of the present invention is provided above, it should be understood that the scope of the present invention is not limited thereto. Moreover, those skilled in the art will recognize many modifications and other embodiments of the invention, which will come to mind to one skilled in the art to which this invention pertains having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed.

Claims (6)

1. A limited rotation rotary actuator comprising:

a stator having a bore extending axially therein;

two diametrically opposed reset slot regions extending from the bore into the stator interior, the stator having four pairs of teeth with a predefined profile end forming at least a portion of the bore, wherein there are four respective teeth on each side of the two diametrically opposed reset slot regions, wherein a gap is formed between the tips of two adjacent teeth on each side;

a rotor having a bi-directionally operable radial magnet in the bore, wherein a space is formed between the magnet and the predetermined profile ends of the four pairs of teeth, respectively;

a first opposing slot pair, a second opposing slot pair, and a third opposing slot pair partially defined by the four pairs of teeth, wherein an angle between the first opposing slot pair and the second opposing slot pair is equal to an angle between the second opposing slot pair and the third opposing slot pair, wherein the angle is in a range of 15 degrees to 45 degrees, and wherein a width of the second opposing slot pair is greater than a width of the first opposing slot pair and the third opposing slot pair;

said two diametrically opposed reset groove regions are positioned substantially perpendicular to said second opposed pair of grooves;

an electrical coil extending in each of the first, second and third opposing slot pairs, wherein the electrical coil is energizable to provide bi-directional torque to the rotor;

wherein there is an electrical connection between the electrical coils.

2. The limited rotation rotary actuator of claim 1, wherein the two diametrically opposed reset slot regions comprise two opposed reset slots, and wherein the two opposed reset slots are configured to reset the rotor to a central rotational angle when current applied to the electrical coil is stopped.

3. The limited rotation rotary actuator of claim 2, wherein the limited rotation rotary actuator comprises two electrical coils extending in the second opposing slot pair.

4. The limited rotation rotary actuator of claim 1, wherein each of the two diametrically opposed reset slot regions comprises a non-uniform curvature of stator material.

5. The limited rotation rotary actuator of claim 1, wherein the two diametrically opposed reset slot regions have a width dimension greater than a dimension of the gap.

6. The limited rotation rotary actuator of claim 1, wherein the electrical coils are connected in series.

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