U.S. patent application number 09/872711 was filed with the patent office on 2002-03-07 for controlled high speed reciprocating angular motion actuator.
Invention is credited to Brown, David C., Nussbaum, Michael B., Stukalin, Felix.
Application Number | 20020027393 09/872711 |
Document ID | / |
Family ID | 22775255 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020027393 |
Kind Code |
A1 |
Brown, David C. ; et
al. |
March 7, 2002 |
Controlled high speed reciprocating angular motion actuator
Abstract
A reciprocating rotary action actuator consisting of a rotor and
stator that can be added to a bi-directional rotary motor or
galvanometer scanner, where the stator has a ring magnet and a pair
of soft iron pole pieces that concentrate the flux of the ring
magnet into a concentric set of narrow, uniformly spaced, axially
oriented, magnetic flux fields intersecting the rotor's field of
travel. The rotor has small permanent magnets embedded in the
periphery of a nonconductive, nonmagnetic rotor core. The rotor
magnets have the same number and spacing as the stator's magnetic
flux fields. The magnet poles are oriented opposite the flux fields
of the stator pole pieces, so that upon rotation, the rotor magnets
encounter the stator flux fields at each end of rotor travel,
creating an opposing force that reverses the angular direction of
the rotor with minimal requirement for actuator current and
generation of thermal losses.
Inventors: |
Brown, David C.;
(Northborough, MA) ; Nussbaum, Michael B.;
(Newton, MA) ; Stukalin, Felix; (Framingham,
MA) |
Correspondence
Address: |
MAINE & ASMUS
100 MAIN STREET
P O BOX 3445
NASHUA
NH
03061-3445
US
|
Family ID: |
22775255 |
Appl. No.: |
09/872711 |
Filed: |
June 1, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60208611 |
Jun 1, 2000 |
|
|
|
Current U.S.
Class: |
310/15 |
Current CPC
Class: |
H02K 33/16 20130101 |
Class at
Publication: |
310/15 |
International
Class: |
H02K 033/00; H02K
035/00 |
Claims
Among our claims are:
1. A device for providing fixed amplitude reciprocating angular
motion to a bi-directional rotary drive mechanism and load,
comprising a stator assembly configured with at least one stator
magnet coupled with at least one pair of upper and lower inwardly
extending pole teeth, said pole teeth configured for concentrating
magnetic circuit flux lines induced by said magnet in a common
direction between respective upper and lower teeth of each said
pair, a rotor assembly sized and configured for rotation within
said stator assembly between said upper and lower pole teeth, said
rotor assembly comprising a corresponding at least one rotor magnet
peripherally configured on said rotor with poles oriented in
opposition to said magnetic circuit flux lines of said stator so as
to have the free rotation of said rotor magnetically opposed by
intersection of said magnet with opposing said flux lines of said
stator.
2. A device for providing fixed amplitude reciprocating angular
motion according to claim 1, said at least one pair of pole teeth
being at least two pairs of pole teeth, the location and spacing of
said pairs about the axis of said rotor configured in conjunction
with the location and spacing of said at least one rotor magnet to
limit the arc of rotation of said rotor to a fixed amplitude.
3. A device for providing fixed amplitude reciprocating angular
motion according to claim 2, said pairs of pole teeth being of
equal spacing about the axis of said rotor assembly.
4. A device for providing fixed amplitude reciprocating angular
motion according to claim 2, said at least one rotor magnet being
equal in number and spacing with said pairs of pole teeth.
5. A device for providing fixed amplitude reciprocating angular
motion according to claim 2 said at least one rotor magnet being at
least two rotor magnets, the spacing of said rotor magnets
configured in conjunction with the spacing of said pairs of pole
teeth to limit the arc of rotation of said rotor to a fixed
amplitude.
6. A device for providing fixed amplitude reciprocating angular
motion according to claim 5, said rotor magnets configured with
equal spacing about the axis of said rotor assembly.
7. A device for providing fixed amplitude reciprocating angular
motion according to claim 5, said at least two pairs of pole teeth
being sixteen pairs of pole teeth.
8. A device for providing fixed amplitude reciprocating angular
motion according to claim 1, said stator magnet comprising a ring
magnet within which said rotor assembly operates, said at least one
pair of upper and lower inwardly extending pole teeth comprising
upper and lower pole pieces magnetically coupled to said ring
magnet, said upper and lower pole teeth extending radially inward
from respective said pole pieces.
9. A device for providing fixed amplitude reciprocating angular
motion according to claim 1, said at least one rotor magnet being
wedge shaped.
10. A device for providing fixed amplitude reciprocating angular
motion according to claim 9, said at least one rotor magnet
embedded in a nonconductive, nonmagnetic rotor core material.
11. A device for providing fixed amplitude reciprocating angular
motion according to claim 1, said stator assembly fixed with
respect to the stationary reference frame of a said drive
mechanism, said rotor assembly being attached to the rotary
component of said drive mechanism.
12. A device for providing fixed amplitude reciprocating angular
motion according to claim 11, said rotor assembly attached to a
position detector for determining angular position.
13. A device for providing fixed amplitude reciprocating angular
motion according to claim 11, said drive mechanism being a
galvanometer, said load being a reciprocating scanner mirror.
14. A fixed amplitude reciprocating angular motion drive mechanism,
comprising a bi-directional rotary drive motor, a stator assembly
configured with at least one stator magnet coupled with at least
one pair of upper and lower inwardly extending pole teeth, said
pole teeth configured for concentrating magnetic circuit flux lines
induced by said magnet in a common direction between respective
upper and lower teeth of each said pair, said stator attached to
the housing of said motor, and a rotor assembly sized and
configured for rotation within said stator assembly between said
upper and lower pole teeth, said rotor assembly comprising a
corresponding at least one rotor magnet peripherally configured on
said rotor with poles oriented in opposition to said magnetic
circuit flux lines of said stator so as to have the free rotation
of said rotor magnetically opposed by intersection of said magnet
with opposing said flux lines of said stator, said rotor being
attached to the output shaft of said motor.
15. A fixed amplitude reciprocating angular motion drive mechanism
according to claim 14, said at least one pair of pole teeth being
at least two pairs of pole teeth, the location and spacing of said
pairs about the axis of said rotor configured in conjunction with
the location and spacing of said at least one rotor magnet to limit
the arc of rotation of said rotor to a fixed amplitude.
16. A fixed amplitude reciprocating angular motion drive mechanism
according to claim 15, said pairs of pole teeth being of equal
spacing about the axis of said rotor assembly.
17. A device for providing fixed amplitude reciprocating angular
motion according to claim 16, said at least one rotor magnet being
equal in number and spacing with said pairs of pole teeth.
18. A device for providing fixed amplitude reciprocating angular
motion according to claim 16 said at least one rotor magnet being
at least two rotor magnets, the spacing of said rotor magnets
configured in conjunction with the spacing of said pairs of pole
teeth to limit the arc of rotation of said rotor to a fixed
amplitude.
19. A device for providing fixed amplitude reciprocating angular
motion according to claim 18, said rotor magnets configured with
equal spacing about the axis of said rotor assembly.
20. A device for providing fixed amplitude reciprocating angular
motion according to claim 19, said at least two pairs of pole teeth
being sixteen pairs of pole teeth.
21. A device for providing fixed amplitude reciprocating angular
motion according to claim 14, said stator magnet comprising a ring
magnet within which said rotor assembly operates, said at least one
pair of upper and lower inwardly extending pole teeth comprising
upper and lower pole pieces magnetically coupled to said ring
magnet, said upper and lower pole teeth extending radially inward
from respective said pole pieces.
22. A device for providing fixed amplitude reciprocating angular
motion according to claim 14, said at least one rotor magnet being
wedge shaped.
23. A device for providing fixed amplitude reciprocating angular
motion according to claim 22, said at least one rotor magnet
embedded in a nonconductive, nonmagnetic rotor core material.
24. A device for providing fixed amplitude reciprocating angular
motion according to claim 14, said rotor assembly attached to a
position detector for determining angular position.
25. A device for providing fixed amplitude reciprocating angular
motion according to claim 24, said device being a galvanometer,
said load being a reciprocating scanner mirror.
26. A galvanometer scanner with fixed amplitude reciprocating
angular motion drive mechanism, comprising a bi-directional rotary
drive motor and scanner mirror, and a stator assembly configured
with at least one stator magnet coupled with at least one pair of
upper and lower inwardly extending pole teeth, said pole teeth
configured for concentrating magnetic circuit flux lines induced by
said magnet in a common direction between respective upper and
lower teeth of each said pair, said stator attached to the housing
of said motor, and a rotor assembly sized and configured for
rotation within said stator assembly between said upper and lower
pole teeth, said rotor assembly comprising a corresponding at least
one rotor magnet peripherally configured on said rotor with poles
oriented in opposition to said magnetic circuit flux lines of said
stator so as to have the free rotation of said rotor magnetically
opposed by intersection of said magnet with opposing said flux
lines of said stator, said rotor being attached to the output shaft
of said motor and to said scanner mirror.
27. A fixed amplitude reciprocating angular motion drive mechanism
according to claim 26, said at least one pair of pole teeth being
at least two pairs of pole teeth, the location and spacing of said
pairs about the axis of said rotor configured in conjunction with
the location and spacing of said at least one rotor magnet to limit
the arc of rotation of said rotor to a fixed amplitude.
28. A fixed amplitude reciprocating angular motion drive mechanism
according to claim 17, said pairs of pole teeth being of equal
spacing about the axis of said rotor assembly.
29. A device for providing fixed amplitude reciprocating angular
motion according to claim 28, said at least one rotor magnet being
equal in number and spacing with said pairs of pole teeth.
30. A device for providing fixed amplitude reciprocating angular
motion according to claim 28 said at least one rotor magnet being
at least two rotor magnets, the spacing of said rotor magnets
configured in conjunction with the spacing of said pairs of pole
teeth to limit the arc of rotation of said rotor to a fixed
amplitude.
31. A device for providing fixed amplitude reciprocating angular
motion according to claim 30, said rotor magnets configured with
equal spacing about the axis of said rotor assembly.
32. A device for providing fixed amplitude reciprocating angular
motion according to claim 31, said at least two pairs of pole teeth
being sixteen pairs of pole teeth.
33. A device for providing fixed amplitude reciprocating angular
motion according to claim 26, said stator magnet comprising a ring
magnet within which said rotor assembly operates, said at least one
pair of upper and lower inwardly extending pole teeth comprising
upper and lower pole pieces magnetically coupled to said ring
magnet, said upper and lower pole teeth extending radially inward
from respective said pole pieces.
34. A device for providing fixed amplitude reciprocating angular
motion according to claim 26, said at least one rotor magnet being
wedge shaped.
35. A device for providing fixed amplitude reciprocating angular
motion according to claim 34, said at least one rotor magnet
embedded in a nonconductive, nonmagnetic rotor core material.
36. A device for providing fixed amplitude reciprocating angular
motion to a bi-directional rotary drive mechanism and load,
comprising a stator assembly configured with at least one stator
magnet coupled with a multiplicity of upper and lower outwardly
extending pole teeth, said pole teeth configured for concentrating
magnetic circuit flux lines induced by said magnet in a common
direction between respective upper and lower teeth of each said
pair, a rotor assembly sized and configured for rotation around
said stator assembly between said upper and lower pole teeth, said
rotor assembly comprising a corresponding multiplicity of rotor
magnets configured on said rotor with poles oriented in opposition
to said magnetic circuit flux lines of said stator so as to have
the free rotation of said rotor magnetically opposed by
intersection of said rotor magnets with opposing said flux lines of
said stator.
37. A device for providing fixed amplitude reciprocating angular
motion according to claim 36, said rotor magnets embedded in a
nonconductive, nonmagnetic material.
38. A device for providing fixed amplitude reciprocating angular
motion according to claim 36, said stator assembly fixed with
respect to the stationary reference frame of a said drive
mechanism, said rotor assembly being attached to the rotary
component of said drive mechanism.
39. A device for providing fixed amplitude reciprocating angular
motion according to claim 36, said rotor assembly attached to a
position detect or for determining angular position.
40. A device for providing fixed amplitude reciprocating angular
motion according to claim 39, said drive mechanism being a
galvanometer, said rotor assembly attached to a load, said load
being at least one mirror.
Description
[0001] This application relates and claims priority for all
purposes to pending U.S. application Ser. No.60/208611, filed June
1, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. TECHNICAL FIELD OF THE INVENTION
[0003] This invention relates to electromechanical reciprocating
rotary motion devices; and in particular to reciprocating angular
motion actuators for producing constant amplitude, variable
frequency, substantially triangular waveform motion profiles
suitable for optical scanning applications.
[0004] 2. BACKGROUND ART
[0005] The use of an oscillating mirror and associated motor
assembly is well known in the art for effecting a beam sweeping
action. A characteristic of such devices, whether the motor
producing the oscillation is a stepper motor or a galvanometer type
motor, as is commonly the case, force, generated by current flowing
through the motor windings must be used to decelerate the scanning
motion and then reverse it. This necessarily generates heat, which
is a significant problem in a very small device such as a
galvanometer scanner. This heating, for a sinusoidal scan waveform,
is proportional to the fourth power of scan frequency, and the
square of the scan angle. 1 position : sin t velocity : sin t
accelleration : - 2 sin t = j = iK 2 i = 2 j K 2 P = i 2 R T = T
case + R th ( 2 j K t ) 2 R coil
[0006] Many mechanical schemes have been employed to reduce the
motor current and associated heat problem.
[0007] In Khowles US4958894, the excitation of an electromagnetic
coil operating on a magnet at the end of a pivot arm extending off
the mirror, is coordinated with the end-of-travel engagement of the
magnet with one or the other of two resilient bumpers between which
it travels, imparting a reversing bounce and resulting in the
oscillation of the pivot arm and mirror. This bumper variation
produces a faster reversal and lowers the required energy.
[0008] In Culp's US5066084, there is disclosed a constant velocity
scanning apparatus in which the mirror oscillations are maintained
with end-of-travel piezo motion actuators in combination with
end-of-travel, resilient "energy absorbing and releasing contacts"
analogous to the rubber bumpers of Khowles. Howe's US3678308,
illustrates another variation on an oscillating scanner that
employs mechanical springs to provide an end-of-travel bounce in
the oscillating motion of the mirror.
[0009] These all involve scanning systems with mechanical springs
defining the end of travel, and demonstrate well the general idea
that opposing springs can be employed to conserve energy within a
mechanically oscillating device. They use varying geometries and
may also use modified motor drive current schemes for a coordinated
effect on reducing average motor current while maintaining a
satisfactory output waveform of the device.
[0010] It is instructive to look at US5424632, as illustrative of a
common moving magnet scanner. The '632 FIG. 1 is described as a
schematic view of a galvanometer used in a laser scanning system,
illustrating the mirror, motor, and a position transducer. In the
'632 FIG. 2, torque motor 17 includes a magnetically permeable
outer housing 28 that holds the stator 51 consisting of windings 31
on bobbin 50. Permanent magnet rotor 100 is rotably mounted within
the stator. Stator windings 31 in the '632 FIGS. 3 and 8 is the
coil where the heat of concern is generated. This heat is
dissipated radially through the device.
[0011] The achievable flux density of the stator magnet 27 as well
as the resistivity of winding 31 are subject to fundamental
material constraints. The achievable acceleration of this system is
a function of the aspect ratio of the magnet (length to diameter)
and proportional to 1/(magnet radius), to first order. This means
that larger structures allow lower RMS (root mean square)
acceleration. RMS acceleration is defined over the relevant thermal
time constants. In other words, it is the maximum acceleration at
which the device can be run without heat-induced damage and
eventual failure. In theory, one can put an arbitrarily large
stator current, ignoring demagnetizing of the magnet, for an
arbitrarily short time, but when attempting to execute a repetitive
waveform, the device would simply reach a certain steady state.
FIGS. 1 and 2 of the '632 disclosure are included herein as prior
art FIGS. 9 and 10 respectively.
[0012] Another area of art which readers may find instructive is
that of resonant scanners. These scanners use a more or less linear
spring, and constitute a mechanical oscillator in which energy is
continually converted back and forth between kinetic energy (stored
in the rotating mass) and potential energy (stored in a torsional
spring). These can achieve very high efficiencies, as the motor
only has to supply system losses, but they have two fundamental
constraints. First, the frequency is constrained to the resonant
frequency of the system. The frequency can be tuned, to some
extent, such as by changing the temperature of the spring or making
other mechanical adjustments to the design. There are patents to
this effect. Second, the mechanical output motion must be
sinusoidal, or very nearly so.
[0013] Dostal's US3609485, is a resonant torsional oscillator for
optical scanning or other vibratory action at a high amplitude and
constant rate. This patent is cited in many torsional resonant
scanners, an example of which is Corker's US3642344, Optical
Scanner Having High Frequency Torsional Oscillator. The problem
with all of the resonant torsional oscillators is that they give
sinusoidal motion, and are essentially constant frequency devices,
being tunable over a narrow range by varying temperature or
otherwise varying the spring rate of the spring.
[0014] In summary, there remains room for improvement in the design
and operation of bi-directional reciprocating galvanometer scanners
and similar reciprocating motion devices to reduce power
requirements and minimize heat generation through the use of design
features that provide for passive energy conservation in the change
of direction phase of motion.
SUMMARY OF THE INVENTION
[0015] The invention may be most simply described as a
reciprocating rotary action actuator consisting of a motor coupled
to a rotor and stator where the stator has a ring magnet and a pair
of soft iron pole pieces that concentrate the flux of the ring
magnet into a concentric set of narrow, uniformly spaced, axially
oriented, magnetic flux fields intersecting the rotor's field of
travel. The rotor has small permanent magnets embedded in the
periphery of a nonconductive, nonmagnetic rotor core, where the
magnets are of the same number and spacing as the stator's magnetic
flux fields, there being at least one and preferably two or more
with equal spacing. The magnets are pole oriented axially opposite
the flux fields of the stator pole pieces, so that upon rotation,
the rotor magnets encounter the stator flux fields at each end of
rotor travel, creating an opposing force that reverses the angular
direction of the rotor with minimal requirement for motor current.
The device can be incorporated into a galvanometer scanner or other
devices with similar reciprocating rotary action requirements.
[0016] More particularly, the invention encompasses a high speed
reciprocating angular motion device, adaptable to electrically
powered optical scanning and other applications where frequency,
amplitude, load moment of inertia, and scan efficiency are
generally limited by thermal considerations of the actuator. The
limitations of the prior art are overcome by combining a
bi-directional, electrical drive actuator for driving a
reciprocating scanner rotor with high efficiency, while a
preferably passive, energy transformation mechanism, the equivalent
of a set of hi-K (spring constant) bumpers or springs, provides for
decelerating, reversing and re-accelerating the rotor motion at
each end of its arc of rotation. The passive reversing function is
enabled magnetically, and may be modified in some embodiments to
provide limited adjustment for tuning and matching of spring set
characteristics.
[0017] The design is a radical departure from the prior art of
scanner actuators. The design calculations for a device of the
invention having the required passive or near passive ability for
repeatedly reversing the rotor, motor and design load direction,
and executing these acceleration changes within a specified small
portion of the rotor arc of travel, with substantially little
contribution from motor current or impact on thermal budget, are
not trivial. However, it should pose no special problem for those
skilled in the art, upon a full and careful reading and
understanding of this disclosure and its priority document, which
is hereby incorporated by reference.
[0018] The motion waveform of the device may be constrained to be
triangular rather than sinusoidal. A triangular scan waveform is
more useful in many cases, as the largely constant velocity aspect
of the rotor motion is often easier to incorporate into component
and system designs, and offers efficiencies over a sinusoidal scan.
The frequency of the reciprocating motion is not constrained by the
invention. What is constrained by the particular design of any
embodiment is amplitude, the useful arc distance of rotor
motion--this is a substantially constant amplitude system whose
frequency can be varied at will.
[0019] Other objects and advantages of the present invention will
become readily apparent to those skilled in this art from the
following detailed description, wherein we have shown and described
only a preferred embodiment of the invention, simply by way of
illustration of the best mode contemplated by us on carrying out
our invention.
BRIEF DESCRIPTION OF THE FIGURES
[0020] FIG. 1 is a plan view diagram of the stator structure of a
preferred embodiment, illustrating the radially inward projecting
teeth that define the radial spacing of the end-of-travel flux
field "bumpers" for reversing the rotation of a similarly sectioned
rotor.
[0021] FIG. 2 is a plan view diagram of the rotor of the embodiment
cited in FIG. 1, the permanent magnet wedges with opposing pole
orientation interspersed with non-magnetic material rotor core
sections providing the magnetic bounce when they encounter the
respective bumpers of the stator of FIG. 1.
[0022] FIG. 3 is a partially cut-away side elevation diagram of a
galvanometer of the invention, illustrating the sectioned rotor of
FIG. 2 mounted within the upper and lower pole pieces of the stator
of FIG. 1.
[0023] FIG. 4 is a side elevation cross section close-up diagram of
a pair of stator teeth of the stator of FIG. 1, illustrating the
magnetic circuit associated with the stator magnet, with the rotor
assumed to be in a non-interfering mid range of arc of travel
position.
[0024] FIG. 5 is side elevation cross section close-up diagram of
the stator teeth and magnetic circuit of FIG. 4, but with the rotor
having advanced to end-of-travel where a permanent magnetic wedge
section has encountered the stator magnetic circuit, the opposing
magnetic forces illustrated by the opposing arrows.
[0025] FIG. 6 is a position versus time graph of the rotor for two
cycles of oscillation, illustrating the uniformly triangular
waveform with substantially linear rotational velocity except near
the end-of-travel deceleration/acceleration action.
[0026] FIG. 7 is a scanner current versus time graph for a prior
art scanner with a similar rotor motion waveform as the FIG. 6
graph, illustrating the high current requirement for the
deceleration/accelerati- on action at the rotor end-of-travel
position.
[0027] FIG. 8 is a scanner current versus time graph for the
preferred embodiment scanner, illustrating the substantially lower
peak current requirement of the invention, relative to the FIG. 7
prior art scanner.
[0028] FIG. 9 is a prior art schematic view of a galvanometer,
mirror and position detector as applied in a laser scanning
system.
[0029] FIG. 10 is a prior art longitudinal cross-section of the
prior art FIG. 9 galvanometer and position transducer.
[0030] FIG. 11 is an end view of a core stator embodiment of the
invention, showing the two opposing mounting stanchions between the
motor housing and the stator core.
[0031] FIG. 12 is an end view of the exterior rotor and mirror
assembly that mates with the core stator of FIG. 11, showing the
motor shaft to rotor mounting stanchions.
[0032] FIG. 13 is an end view of the rotor of FIG. 12 assembled
with the stator of FIG. 11.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0033] The invention is susceptible of many embodiments. The
preferred embodiment or best mode for using the invention described
and illustrated herein is in no way limiting of the scope of the
invention, as will be readily evident to those skilled in the
art.
[0034] Referring to FIGS. 1-3, a preferred embodiment device in the
form of a galvanometer scanner 10 consists of a stator assembly 20
and a rotor assembly 40, mounted between the scanner motor 12 and
the mirror 14.
[0035] Referring to FIGS. 2-5, stator assembly 20 is fixed with
respect to the stator of motor 12. Rotor assembly 40 is rigidly
affixed to the output shaft of scanner motor 12, and rotates with
mirror 14 and the scanner motor 12 rotor. Stator assembly 20
consists of a ring magnet 22, and a pair of soft iron pole pieces
24 and 26. The pole pieces serve to concentrate the flux of the
ring magnet into a matched north/south pole set of radially
inwardly extending upper and lower axial stator teeth 28. In this
embodiment, stator assembly 20 is configured with 16 sets of upper
and lower teeth 28, or magnetic pole sets, spaced symmetrically
every 22.5 degrees about the stator, each wedge 28 subtending 2.5
degrees.
[0036] Referring now to FIG. 4, there is shown a partial cross
section view of the stator ring magnet 22 and pole pieces 24 and
26, and the magnetic circuit associated with each upper and lower
tooth set. 2 5 Referring to FIGS. 1, 3, and 5, rotor assembly 40
incorporates a set of wedge shaped permanent magnets 48, radially
dispersed in a nonconductive, nonmagnetic structure 42. Rotor wedge
magnets 48 have the same spacing and number as the stator teeth 28,
but are pole oriented so as to provide a magnetic flux path aligned
opposite that of the stator teeth 28.
[0037] Referring to FIGS. 3 and 5, when galvanometer scanner 10 is
assembled, rotor 40 will occupy the axial space between upper and
lower stator teeth 28. Upon rotation, when individual rotor magnets
48 closely approach alignment with respective upper and lower
stator teeth 28, an opposing electromagnetic `spring` force will be
generated between the opposing flux fields. These opposing magnetic
fields create a circumferential spring force, symmetrically applied
around the rotor axis without bearing bias, which will attempt to
repel and reverse the rotation of the rotor until its magnets 48
are repelled from the gap defined by the upper and lower stator
teeth. For this particular spacing of teeth 28 and magnets 48,
ignoring fringing effects, there are about 20 degrees of free rotor
motion available to the system in between the effective zones of
magnetic spring action. This is the arc of bi-directional linear
motion available to the device of this embodiment. This embodiment
is particularly suited for combination with a bi-directional motor
and position detector similar to the FIG. 9 device, as a
galvanometer for a scanning system.
[0038] It will be readily apparent to those skilled in the art that
the total arc length or degrees of rotation is a function of the
number of teeth and wedge sets, or magnetic poles; being
specifically 360 degrees divided by the number of pole sets. While
one set of stator teeth and matching rotor wedge opposing poles
would theoretically provide a 360 degree arc of reciprocating
motion, having at least two pole sets provides balance to the
reversing mechanism. Also, more poles provide more "bounce"
capability so that the percentage of arc travel consumed by the
change of acceleration is smaller, leaving a larger percentage of
arc for useful, bi-directional, linear motion.
[0039] Referring to FIGS. 6-8, the performance of the device is
depicted in two of three of these graphs. FIG. 6 shows a typical
triangular scan position waveform 60, with a relatively high scan
efficiency, where the acceleration and deceleration at either end
occupy a small portion 62 of the active scan cycle.
[0040] Referring now to FIG. 7, there is illustrated the resulting
scanner current 70, proportional to acceleration, of a prior art
device without the magnetic spring feature of the invention.
Scanner current 70 can readily be seen to sharply increase at 72 to
accomplish the deceleration and acceleration of the rotor reversal.
Motor heating is proportional to the square of this current, and is
thus significantly affected by this current profile.
[0041] Referring now to FIG. 8, there is shown the resulting
scanner current 80 in a device incorporating the invention, where a
substantially lower motor current peak 82, in the order of a
10.times. reduction over the current peak 72 of the FIG. 7 device,
due to the magnetic spring energy conservation feature. As will be
readily apparent to those skilled in the art, heating due to
electrical current is reduced to in the order of {fraction (1/100)}
of its FIG. 7 value.
[0042] Referring to FIGS. 11-13, there is shown an alternative
embodiment with a core stator and external rotor upon which mirrors
are mounted. Stator core magnet 24 is configured with upper and
lower outwardly projecting pole teeth 28, which provide for
concentration of flux lines as described above. Stator 20 is
mounted to the housing of motor 12 by open stanchions 13,
permitting room for attaching external rotor assembly 40 to the
shaft of motor 12 with open stanchions 11. Rotor assembly 40 has
embedded rotor magnets 48 and rotates in reciprocating fashion
around stator 20 within upper and lower pole teeth 28, so that
magnets 48 intersect with the flux lines of teeth 28 as described
in other embodiments, causing the reversal in direction of
rotation. This embodiment is configured for about 90 degrees of arc
or amplitude; the design being adaptable to other arc lengths as
described in other embodiments, subject to mounting stanchion size
and clearance requirements. The number and arrangement of mirrors
14 or other configuration of load is preferably minimal and
balanced.
[0043] As will be readily apparent to those skilled in the art, the
invention is susceptible of many variations of which the preferred
embodiment is illustrative but not limiting. For example, there is
within the scope of the invention, a device for providing fixed
amplitude reciprocating angular motion to a bi-directional rotary
drive mechanism and load, that consists of a stator assembly and
rotor assembly. The stator assembly is configured with at least one
stator magnet coupled with at least one pair of upper and lower
inwardly extending pole teeth, where the pole teeth are configured
for concentrating magnetic circuit flux lines induced by the magnet
in a common direction between respective upper and lower teeth of
each pair of teeth. While the preferred embodiment has multiple
sets of teeth equally spaced about the axis of the device, a single
set of teeth generating a respective set of flux lines, provides a
magnetic bumper to stop the free rotation of a rotor of the
invention.
[0044] The rotor assembly is sized and configured for rotation
within the stator assembly between the upper and lower pole teeth.
The rotor assembly has a corresponding at least one rotor magnet
peripherally configured on the rotor with its magnetic poles
oriented axially in opposition to the magnetic circuit flux lines
of the stator so as to have the free rotation of the rotor
magnetically opposed by intersection of the magnet with the
opposing flux lines of the stator. In it's most minimal
configuration, a rotor with one magnet working within a stator with
one set of teeth will have a substantially 360 degree arc or
amplitude between reversals. Of course, the stator's at least one
pair of pole teeth may be two pairs of pole teeth or more. The
location and spacing of these teeth pairs about the axis of the
rotor, can be configured in conjunction with the location and
spacing of the at least one rotor magnet, to limit the arc of
rotation of the rotor to a fixed amplitude or arc of less than 360
degrees.
[0045] Of course, other design parameters make it problematic to
concentrate the required repelling force into a single point of
intersection as between the rotor and the stator flux lines. For
that reason, the numbers of pairs of stator teeth are two or more,
and the number and spacing of rotor magnets is preferably equal to
the number and spacing of pairs of pole teeth, and oriented so that
there are intersecting magnets and flux lines at two or more
equally spaced points about the rotor. This avoids the bearing load
of the single point example above. The number, location and spacing
of these teeth pairs about the axis of the rotor, can be configured
in conjunction with the number, location and spacing of the at
least one rotor magnet, to limit the arc of rotation of the rotor
to a fixed amplitude and provide the maximum number of points of
intersection, thereby distributing the concentration of repelling
force as much as possible.
[0046] The stator assembly magnet may be a ring magnet within which
the rotor assembly operates, magnetically coupled to upper and
lower pole pieces from which the upper and lower radially inwardly
extending pole teeth project.
[0047] The stator assembly may be fixed with respect to the
stationary reference frame of a drive or actuator mechanism or
motor, with the rotor assembly attached to the rotary component of
the drive mechanism. The rotor assembly may be attached to a load.
The drive mechanism may be a galvanometer. The load may be
reciprocating scanner mirror.
[0048] As illustrated in the preferred embodiment, there is a
device for providing fixed amplitude reciprocating angular motion
where the stator has sixteen pairs of equally spaced pole teeth,
and the rotor has an equal number of magnets. The magnets are wedge
shaped, and embedded in a nonconductive, nonmagnetic rotor core
material.
[0049] As another example, there is a device for providing fixed
amplitude reciprocating angular motion to a bi-directional rotary
drive mechanism and load, consisting of a stator assembly
configured with at least one stator magnet coupled with a
multiplicity of upper and lower outwardly extending pole teeth,
where the pole teeth are configured for concentrating magnetic
circuit flux lines induced by the stator magnet in a common
direction between respective upper and lower teeth as in the prior
embodiments. The rotor assembly is sized and configured for
rotation around the stator assembly between the upper and lower
pole teeth, and has a corresponding multiplicity of rotor magnets
configured on the rotor with poles oriented in opposition to the
magnetic circuit flux lines of the stator so as to have the free
rotation of the rotor magnetically opposed by intersection of the
rotor magnets with the opposing flux lines of the stator. The drive
mechanism may be a galvanometer. The load may be one or more
mirrors mounted directly on the rotor or elsewhere attached to the
rotary elements of the galvanometer. The rotor may have a
multifaceted exterior to which the one or more mirrors may be
attached.
[0050] In summary, the invention is a dramatic departure from the
present art of optical scanners and bi-directional rotary motors
generally. In a bi-directional, electrically powered rotor, magnets
in the rotor, upon nearing the end limit of the rotor's range of
rotation, encounter stator flux wedges which create an opposing
`spring` force that very efficiently reverse the rotation of the
rotor. This significantly reduces the peak electrical load and the
related thermal limitations of the actuators of the prior art,
unleashing collateral opportunities for optimizing the performance
of the motor in triangle wave form applications including but not
limited to galvanometer scanners.
* * * * *