CA1145389A - Controller for variable reluctance stepper motor - Google Patents
Controller for variable reluctance stepper motorInfo
- Publication number
- CA1145389A CA1145389A CA000402933A CA402933A CA1145389A CA 1145389 A CA1145389 A CA 1145389A CA 000402933 A CA000402933 A CA 000402933A CA 402933 A CA402933 A CA 402933A CA 1145389 A CA1145389 A CA 1145389A
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- waveforms
- motion
- motor
- teeth
- motor controller
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Abstract
VARIABLE RELUCTANCE STEPPER MOTOR
AND CONTROLLER THEREFOR
ABSTRACT OF THE DISCLOSURE
A variable reluctance stepper motor including cooperating fixed and moving structures having tooth-like patterns of equal pitch but with the fixed and moving teeth having different lengths measured in the direction of movement. The smaller teeth are divided into groups which are offset from one another by fractions of a tooth pitch to provide a bi-directional motor capable of being stepped from one position to the next with the teeth tending to produce force in the desired direction carrying essentially all of the flux and the teeth tending to produce force in the opposite direction carrying essentially no flux. The controller comprises a closed loop control system which senses a voltage indicative of motion on the driven windings, uses this voltage to confirm that motion has ocurred, compares this voltage with one modeled after a waveform indicative of no motion and effects successive changes in the winding drive states at optimum times.
AND CONTROLLER THEREFOR
ABSTRACT OF THE DISCLOSURE
A variable reluctance stepper motor including cooperating fixed and moving structures having tooth-like patterns of equal pitch but with the fixed and moving teeth having different lengths measured in the direction of movement. The smaller teeth are divided into groups which are offset from one another by fractions of a tooth pitch to provide a bi-directional motor capable of being stepped from one position to the next with the teeth tending to produce force in the desired direction carrying essentially all of the flux and the teeth tending to produce force in the opposite direction carrying essentially no flux. The controller comprises a closed loop control system which senses a voltage indicative of motion on the driven windings, uses this voltage to confirm that motion has ocurred, compares this voltage with one modeled after a waveform indicative of no motion and effects successive changes in the winding drive states at optimum times.
Description
~.5~B9 The present invention relates to controllers for variable reluctance stepper-motors. This application is a divisional application of Canadian application Serial No.
326,855, filed May 3, 1979.
One known variable reluctance stepper motor employs a toothed rotor/stator combination in which rotation of the rotor causes a cyclic variation in the reluctance of the magnetic circuit, which includes the rotor and stator teeth and t-he gap therebetween. The gap changes dimension as the rotor and stator move relative to one another. A motor capable of providing continuous stepping motion is comprised of two or more such sets of rotor/stator teeth, as well as separate magnetic circuits extending therethrough, which circuits are capable of being selectively energized. The different rotor/stator teeth are staggered in relative angular positions. By selective energization of the magnetic circuits, the rotor is caused to assume successive positions of least reluctance for the respective magnetic circuits, depending on the magnetic and mechanical variables designed into the motor and the method of controlO In conventional variable reluctance stepper motors, the rotor and stator teeth are of the same or nearly the same width. This configuration produces the greatest possible difference between maximum and minimum reluctanceO
It is also known that stepping motors of all kinds exhibit instabilities at certain combinations of drive, load inertia and operating frequency. These instabilities result from the fact that the force/displacement characteristic at each cardinal position of the stepper is like a spring constant which, mb/ - 2 - ~
~ ~ S~ ~9 acting on the inertia mass of the moving part, results in a ~ highly undamped mechanical resonance. Operation of the stepper 3 at the resonant frequency or at harmonics of this requency will 4 often result in erratic performance, While there are timing 5 methods which will uniformly accelerate and decelerate a stepping 6 motor through its resonance frequencies, these methods are all 7 subject to the requirement that the load must be nearly constant.
8 A well-compensated stepping motor drive system which smoothly 9 accelerates, slews and decelerates a given Load will usually l0 perform very badly if the load is doubled or halved. ' l2¦ Manufacturers and users of s~epping motors have l3,1developed various techniques for controlling stepper motors in i411a closed-loop manner, Feedback stepper controls may be classified l511into two groups: (l) velocity feedback systems, in which a 16~ signal indica~ive of mechanical stepping ra~e is developed and 17 used to modify the drive frequency; and (2) pulse position or 18 timing feedback systems, in which an output is derived from l9 either the motor itself or a separate transducer and used 20 directly to control stepper drive switching. Velocity feed~ack 21 is implicit in the latter systems and the response of the 22 stepper to time varying loads is much more rapid, The most 23 ¦success~ul known method of feedback control involves the addition , 24 of an external position measuring device such as an electro-optica transducer, Signals from the transducer are used to confirm and 26, count steps and in some systems the transducer output is used 271 directly to t~'me driving pulses to the motor, 28, , 291l Investigators have tried to derive feedback signals ' q0' directly from the windings of a stepper motor, The principal , - 3 -s38g l~
- advantage of this approach would be lower costs. A secondary
326,855, filed May 3, 1979.
One known variable reluctance stepper motor employs a toothed rotor/stator combination in which rotation of the rotor causes a cyclic variation in the reluctance of the magnetic circuit, which includes the rotor and stator teeth and t-he gap therebetween. The gap changes dimension as the rotor and stator move relative to one another. A motor capable of providing continuous stepping motion is comprised of two or more such sets of rotor/stator teeth, as well as separate magnetic circuits extending therethrough, which circuits are capable of being selectively energized. The different rotor/stator teeth are staggered in relative angular positions. By selective energization of the magnetic circuits, the rotor is caused to assume successive positions of least reluctance for the respective magnetic circuits, depending on the magnetic and mechanical variables designed into the motor and the method of controlO In conventional variable reluctance stepper motors, the rotor and stator teeth are of the same or nearly the same width. This configuration produces the greatest possible difference between maximum and minimum reluctanceO
It is also known that stepping motors of all kinds exhibit instabilities at certain combinations of drive, load inertia and operating frequency. These instabilities result from the fact that the force/displacement characteristic at each cardinal position of the stepper is like a spring constant which, mb/ - 2 - ~
~ ~ S~ ~9 acting on the inertia mass of the moving part, results in a ~ highly undamped mechanical resonance. Operation of the stepper 3 at the resonant frequency or at harmonics of this requency will 4 often result in erratic performance, While there are timing 5 methods which will uniformly accelerate and decelerate a stepping 6 motor through its resonance frequencies, these methods are all 7 subject to the requirement that the load must be nearly constant.
8 A well-compensated stepping motor drive system which smoothly 9 accelerates, slews and decelerates a given Load will usually l0 perform very badly if the load is doubled or halved. ' l2¦ Manufacturers and users of s~epping motors have l3,1developed various techniques for controlling stepper motors in i411a closed-loop manner, Feedback stepper controls may be classified l511into two groups: (l) velocity feedback systems, in which a 16~ signal indica~ive of mechanical stepping ra~e is developed and 17 used to modify the drive frequency; and (2) pulse position or 18 timing feedback systems, in which an output is derived from l9 either the motor itself or a separate transducer and used 20 directly to control stepper drive switching. Velocity feed~ack 21 is implicit in the latter systems and the response of the 22 stepper to time varying loads is much more rapid, The most 23 ¦success~ul known method of feedback control involves the addition , 24 of an external position measuring device such as an electro-optica transducer, Signals from the transducer are used to confirm and 26, count steps and in some systems the transducer output is used 271 directly to t~'me driving pulses to the motor, 28, , 291l Investigators have tried to derive feedback signals ' q0' directly from the windings of a stepper motor, The principal , - 3 -s38g l~
- advantage of this approach would be lower costs. A secondary
2 ;vantage in high performance systems would be the elimina~ion
3 of the inertia of a separate transducer, which can be a
4' significant part of the total load, The problems most frequently , si~encountered are that the windings of most stepper motors have a 6 high degree of cross-coupling and the feedback signals are small 7 compared with drive voltages, In conventional steppers, as the g,motor speed changes the relative magnitudes of these voltages glflvary significantly. The most successful known system is one "which measures average motor current which is indicative of "average motor speed because the motor back EMF reduces motor 12llcurrent- A~ least one such closed loop motor control system is I ~
,commercially available, The response of such a system to load transients is extremely poor, however, because the averaging ¦¦process involves a long time constant.
19 l 21 ,,, 23 , 261 ., 27 11i 28 ji 29~
~0' , 38~
The invention relates to a motor controller for a variable reluctance stepper motor having at least two windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed wave-forms. The controller comprises: waveform generator means for synthesizing waveforms modeled after the no-motion signals;
comparator means for comparing the synthesized waveforms with the motion-dependent waveforms; and means for controlling the energization of the windings in response to the comparison.
BRIEF DESCRIPTION OF THE INVENTION
Thus, the present invention involves a novel variable controller for a reluctance stepper motor. The variable reluctance stepper motor minimizes undesirable restoring forces and produces a more efficient stepper motor of higher sensitivity. As will be described more fully below, the teeth on one of the cooperating elements of the motor are wider than the teeth on the other cooperating element, while the pitch of the teeth on both elements is the same. In addition, the narrower teeth are divided into groups and are offset with respect to each other by fractions of a tooth pitch.
In a linear embodiment the motor comprises a cylindrical slider and a rod-shaped stator. l'he slider comprises two poles separated by a permanent magnet. Each pole comprises two sets of one or more spiral teeth separated by a winding. Each winding is continuously energized by a current whose direction is controlled. Thus, there are four possible combinations of current directions.
mb/ ; 5 The magnitude of the current is such that the magneto-motive force (MMF) across the teeth on each side of the winding is equal to that produced by the permanent magnet. Current in a given direction will produce a minimum MMF across the teeth on one side of the winding and a maximum MMF across the teeth on the other side of the winding because the direction of the winding MMF aids the permanent magnet MMF on one side and opposes it on the other.
The stator of the linear variable reluctance stepper motor comprises a toothed member having uniformly spaced spiral teeth having a pitch P and a width equal to P/2.
- The spiral slider teeth have a pitch P and a width equal to P/4. The slider tooth sets on each pole are offset from each other by an amount equal to (n + 1~2)P, n being an integer. The poles of the slider are offset from each other by an amount equal to (m + l/4)P, m being an integer.
In a disk, rotary embodiment the motor comprises a rotor and a stator having two poles. Between the stator poles is a disk-shaped rotor having uniformly spaced radial teeth having an angular pitch P and an angular width equal to P/2. Each stator pole comprises two sets of radial teeth, the locus of each set describing a circle with a different radius. The stator teeth have an angular pitch P
and an angular width equal to P/4. Associated with each stator pole is a permanent ring magnet and a winding. The sets of teeth in each stator pole are offset from each other by an angular amount equal to (n + l/2)P, n being an integer. The stator poles are offset from each other by an mb/ - 6 -3~S3B~
angular amount equal to (m + l/4)P, m being an integer.
Each winding is continuously energized by a current whose direction is controlled.
In a cylindrical, rotary embodiment the motor comprises a rotor and a stator having two poles. The rotor is cylindrical and has longitudinally extending teeth with grooves therebetween, the rotor teeth having an angular pitch P and an angular width equal to P/2. The stator is cylindrical and surrounds the rotor. The stator has two annular poles separated by an annular magnet. Each stator pole has two sets of equally spaced, longitudinally extending teeth having an angular pitch P and an angular width equal to P/4. The sets of teeth in each stator pole are offset from each other by an angular amount equal to -(n + 1/2)P, n being an integerO The two stator poles are offset from each other by an angular amount equal to (m + 1/4)P, m being an integer. The sets of teeth in each stator pole are separated by an annular winding which is continuously energized by a direct current, the direction of which is controlled.
The above-described variable reluctance stepper motors are characterized by the production of a motion dependent electrical signal that can be employed in the motor controller of the present invention to time the drive pulses in an optimum fashion so as to achieve reliable stepper operation during acceleration, slewing and deceleration under widely varying load conditions.
mb/', 7 ~ hus, the variable reluctance stepper motors suitable for use with the incremental mGtion motor controller of the present invention comprise a pair of windings continuously energized by direct currents, the direction of which is controlled. The motion dependent signal employed in the incremental motion controller of the present invention is derived from that end of the winding which has most recently switched to the lower (e.g., ground) voltage. In the absence of any motion, the voltage will exhibit an unperturbed waveform which, in the case of a linear variable reluctance stepper motor, may be of the type V = a(l - e-bt~, where a and b are constants. When the stepper motor is allowed to move, however, the change in reluctance induces a transient voltage in the winding which is superimposed on the unper-turbed waveform and results in a perturbed waveform. In the case of a linear variable reluctance stepper motor, the perturbation may be such as might be caused if h in the expression V = a(l - e-bt) were not constant but, for some time t>0, b = b(t), first decreasing and then increasing in value. See, e.g., the lower curves in Figs. 8A and 8B.
As described in greater detail hereinafter, the incremental motion motor controller of the present invention compares the motion-induced (perturbed) signal with a synthesized signal which is modeled after the no-motion (non-perturbed~
waveform and which is offset from the no-motion waveform in the direction of perturbation so as to control the timing of the drive pulses and achieve reliable stepper operation during acceleration, slewing and deceleration under widely varying load conditions.
mb/ - 8 -. . , ~5~
BRIl~F DESCRIPTION OF THE DRAWINGS
3 Figure i is a simplified view in section of a linear 4 variable reluc~ance stepper motor of ~he present invention;
Figure 2 is a simplified plan view, partially 6 sectioned, of a cylindrical, rotary, variable reluctance stepper 7 motor of the present invention;
8 Figure 3A is a simplified view in section of a disk, g rotary, variable reluctance stepper motor of the present lO,iinvention;
Figure 3B is a simpli~ied view of the tooth arrangement i 12ljf the motor of Fig. 3A:
13~1 Figure 4A is a simplified view in section of a slider llelement for the motor of Fig. l;
15 ~ Figure 4B is a simplified partial plan view of a 16 stator for use with the spiral slider element of Figure 4A; 2 17 Figure 5 is a functional block diagram of one 18 embodiment of the motor controller of the present invention;
19 Figure 6 is a schematic diagram of one embodiment of 20 the motor drive circuit of Fig. 5;
21 Figure 7 is a schematic diagram of one embodiment of 22 the function generator and comparator circuits of Fig. 5;
23 Fîgures 8A, 8B and 8G are graphic represen~ations of 24 typical waveforms associated with one embodiment of the motor 25 ! controller of Fig. 5; and 26 Figures 9A, 9B and 9C are flow diagrams of one 27!l,embodiment of the programs for the processor of Fig. 5.
29i _ g _ ~S~B9 ~ DETAILED ~ESCRIPTION
2 - .
3 Fig. 1 is a view in section of a linear, variable 4 reluctance stepper motor 10 in accordance with the present in-
,commercially available, The response of such a system to load transients is extremely poor, however, because the averaging ¦¦process involves a long time constant.
19 l 21 ,,, 23 , 261 ., 27 11i 28 ji 29~
~0' , 38~
The invention relates to a motor controller for a variable reluctance stepper motor having at least two windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed wave-forms. The controller comprises: waveform generator means for synthesizing waveforms modeled after the no-motion signals;
comparator means for comparing the synthesized waveforms with the motion-dependent waveforms; and means for controlling the energization of the windings in response to the comparison.
BRIEF DESCRIPTION OF THE INVENTION
Thus, the present invention involves a novel variable controller for a reluctance stepper motor. The variable reluctance stepper motor minimizes undesirable restoring forces and produces a more efficient stepper motor of higher sensitivity. As will be described more fully below, the teeth on one of the cooperating elements of the motor are wider than the teeth on the other cooperating element, while the pitch of the teeth on both elements is the same. In addition, the narrower teeth are divided into groups and are offset with respect to each other by fractions of a tooth pitch.
In a linear embodiment the motor comprises a cylindrical slider and a rod-shaped stator. l'he slider comprises two poles separated by a permanent magnet. Each pole comprises two sets of one or more spiral teeth separated by a winding. Each winding is continuously energized by a current whose direction is controlled. Thus, there are four possible combinations of current directions.
mb/ ; 5 The magnitude of the current is such that the magneto-motive force (MMF) across the teeth on each side of the winding is equal to that produced by the permanent magnet. Current in a given direction will produce a minimum MMF across the teeth on one side of the winding and a maximum MMF across the teeth on the other side of the winding because the direction of the winding MMF aids the permanent magnet MMF on one side and opposes it on the other.
The stator of the linear variable reluctance stepper motor comprises a toothed member having uniformly spaced spiral teeth having a pitch P and a width equal to P/2.
- The spiral slider teeth have a pitch P and a width equal to P/4. The slider tooth sets on each pole are offset from each other by an amount equal to (n + 1~2)P, n being an integer. The poles of the slider are offset from each other by an amount equal to (m + l/4)P, m being an integer.
In a disk, rotary embodiment the motor comprises a rotor and a stator having two poles. Between the stator poles is a disk-shaped rotor having uniformly spaced radial teeth having an angular pitch P and an angular width equal to P/2. Each stator pole comprises two sets of radial teeth, the locus of each set describing a circle with a different radius. The stator teeth have an angular pitch P
and an angular width equal to P/4. Associated with each stator pole is a permanent ring magnet and a winding. The sets of teeth in each stator pole are offset from each other by an angular amount equal to (n + l/2)P, n being an integer. The stator poles are offset from each other by an mb/ - 6 -3~S3B~
angular amount equal to (m + l/4)P, m being an integer.
Each winding is continuously energized by a current whose direction is controlled.
In a cylindrical, rotary embodiment the motor comprises a rotor and a stator having two poles. The rotor is cylindrical and has longitudinally extending teeth with grooves therebetween, the rotor teeth having an angular pitch P and an angular width equal to P/2. The stator is cylindrical and surrounds the rotor. The stator has two annular poles separated by an annular magnet. Each stator pole has two sets of equally spaced, longitudinally extending teeth having an angular pitch P and an angular width equal to P/4. The sets of teeth in each stator pole are offset from each other by an angular amount equal to -(n + 1/2)P, n being an integerO The two stator poles are offset from each other by an angular amount equal to (m + 1/4)P, m being an integer. The sets of teeth in each stator pole are separated by an annular winding which is continuously energized by a direct current, the direction of which is controlled.
The above-described variable reluctance stepper motors are characterized by the production of a motion dependent electrical signal that can be employed in the motor controller of the present invention to time the drive pulses in an optimum fashion so as to achieve reliable stepper operation during acceleration, slewing and deceleration under widely varying load conditions.
mb/', 7 ~ hus, the variable reluctance stepper motors suitable for use with the incremental mGtion motor controller of the present invention comprise a pair of windings continuously energized by direct currents, the direction of which is controlled. The motion dependent signal employed in the incremental motion controller of the present invention is derived from that end of the winding which has most recently switched to the lower (e.g., ground) voltage. In the absence of any motion, the voltage will exhibit an unperturbed waveform which, in the case of a linear variable reluctance stepper motor, may be of the type V = a(l - e-bt~, where a and b are constants. When the stepper motor is allowed to move, however, the change in reluctance induces a transient voltage in the winding which is superimposed on the unper-turbed waveform and results in a perturbed waveform. In the case of a linear variable reluctance stepper motor, the perturbation may be such as might be caused if h in the expression V = a(l - e-bt) were not constant but, for some time t>0, b = b(t), first decreasing and then increasing in value. See, e.g., the lower curves in Figs. 8A and 8B.
As described in greater detail hereinafter, the incremental motion motor controller of the present invention compares the motion-induced (perturbed) signal with a synthesized signal which is modeled after the no-motion (non-perturbed~
waveform and which is offset from the no-motion waveform in the direction of perturbation so as to control the timing of the drive pulses and achieve reliable stepper operation during acceleration, slewing and deceleration under widely varying load conditions.
mb/ - 8 -. . , ~5~
BRIl~F DESCRIPTION OF THE DRAWINGS
3 Figure i is a simplified view in section of a linear 4 variable reluc~ance stepper motor of ~he present invention;
Figure 2 is a simplified plan view, partially 6 sectioned, of a cylindrical, rotary, variable reluctance stepper 7 motor of the present invention;
8 Figure 3A is a simplified view in section of a disk, g rotary, variable reluctance stepper motor of the present lO,iinvention;
Figure 3B is a simpli~ied view of the tooth arrangement i 12ljf the motor of Fig. 3A:
13~1 Figure 4A is a simplified view in section of a slider llelement for the motor of Fig. l;
15 ~ Figure 4B is a simplified partial plan view of a 16 stator for use with the spiral slider element of Figure 4A; 2 17 Figure 5 is a functional block diagram of one 18 embodiment of the motor controller of the present invention;
19 Figure 6 is a schematic diagram of one embodiment of 20 the motor drive circuit of Fig. 5;
21 Figure 7 is a schematic diagram of one embodiment of 22 the function generator and comparator circuits of Fig. 5;
23 Fîgures 8A, 8B and 8G are graphic represen~ations of 24 typical waveforms associated with one embodiment of the motor 25 ! controller of Fig. 5; and 26 Figures 9A, 9B and 9C are flow diagrams of one 27!l,embodiment of the programs for the processor of Fig. 5.
29i _ g _ ~S~B9 ~ DETAILED ~ESCRIPTION
2 - .
3 Fig. 1 is a view in section of a linear, variable 4 reluctance stepper motor 10 in accordance with the present in-
5- vention. Stator 11 is an elongated cylindrical rod having
6 teeth 12 and interspersed grooves 13. The ~eeth have a pitch P
7 and a width P/2. Cylindrical slider 14 slides along stator 11
8 on support bearingsl5. Slider 14 comprises poles 16 and 17
9 separated by ring permanent magnet 18, preferably a rare earth
10~ magnet. Pole 16 comprises two annular slider elements 19 and 20 llli!while pole 17 comprises two annular slider elements 21 and 22.
12¦;Slider elements 19 and 20 are separa~ed by winding 23 while ~i 1311slider elements 21 and 22 are separated by winding 24. Between 14!!ring permanent magnet 18 and poles 16 and 17 are flux "regulators7' 15¦ 25 and 26. Annular rings 27 and 28 provide flux paths between 16 slider elements 19-20 and 21-22, respectively.
17 .
18 Whereas the stator teeth 12 have a pitch P and a 19 width equal to P/2, the slider teeth 29 have a pitch P and a 20 width equal to P/4. In addition, the teeth in slider element 19 21 and 20 (as well as the teeth in slider elements 21 and 22) are 22 ofset from each other by an amount equal to (n ~ 1/2)P, n being 23 an integer. The teeth o poles 16 and 17 are offset from each 24 other by an amount equal to (m ~ 1/4)P, m being an integer.
26 Motor 10 is "stepped" rom one linear position to the 2711 next by rever~ing the direction of curren~ in one of the two 28 control windings 23 and 24. There is no tendency for the slider 29 ! to move in the wrong direction. The direction of motion is ~,o dependent solely upon which winding current is reversed. Also, ~ ~ 5~
selectively inactive teeth do not se~ up any fvrces whic'n conClict 2 rth the direction of the desired forces created by the magnetic 3 energization of the active teeth. Thus, the design of Fig. 1 4 enables the motor to be stepped in either direction and with s`good stability.
7 Fig. 2 depicts a cylindrical, rotary v~riable reluctance 8 stepper motor 40 in accordance with the present invention. Motor gj 40 comprises a cylindrical rotor 41 having longitudinally extending , teeth 42 with grooves 43 therebetween. Teeth 42 have a pitch P
and a width equal to P/2. Grooves 43 may be filled with a 121lnon-magnetic material so that rotor 41 presents a smooth outer 13i periphery~ I
141 . , '.
15~ Stator 44 is provided with two poles9 44a and 44b.
16l Associated with each of stator poles 44a and 44b are two sets of 17 longitudinally extending stator teeth 45-46 and 47-48. Positioned 18 between stator teeth 45-46 and 47-48 are control windings 49a and 19 49b, respectively. Stator teeth 45, 46, 47 and 48 have a pitch P
and a width equal to P/4. Sta~or poles 44a and 44b are separated 21 ~rom each other by ring permanent magnet 49. Stator teeth 45 and 22 46 (as.well as stator teeth 47 and 48) are displaced from each 23 ~ other by an angular amount equal to ~n + 1/2)P, n being an 24 I integer. Stator poles 44a and 44b are offset from each other by 25 ! an angular amount equal to (m + 1/4jP, m being an integer.
26 '~ I
271~ Control windings 49a and 49b receive control currents 281 of a magnitude suf~icient to creat an MMF equal to that developed 29' by permanent magnet 49, the direc~ion of current being selected 30' to cause the magnetic flux develo~ed by the control winding ' ' ~ ~ ~5~ ~
1 either to aid or oppose the magnetic 1ux o~ perrnanen~ ma~ne~ 49.
2 ~he four possible combinations of current direction es~ablish 8 flux paths through the rotor and stator teeth which are analogou~
4 to those created in the linear stepper motor of Fig. 1. The 5 rotary stepper motor is stepped by changing the direction of 6 current o~ one of control windings 49a or 49b.
, !
8, Figs. 3A and 3B depict a disk, rotary variable gilreluctance stepper motor 50 in accordance with the present in- j OI,vention The motor comprises a rotor 51 mounted on a non-magnetir lljishaft 51a by means of a central collar 51b upon which is mounted 12llan integral soft iron ring 51c. Two stator poles 52 and 53 are 13lldisposed on opposite sides o~ rotor 51. Stator pole 52 comprises 411two sets of radial, ~edge-shaped teeth 54, 55, the locus of each 15 ¦set describing a circle with a different radius. Stator pole 53 16 ¦comprises two sets of similar stator teeth 56, 57. Associated 17¦ with stator poles 52 and 53 respectively are permanent ring 181 magnets 57 and 58 Surrounding ring magnets 57 and 58 respec-19 tively are eoils 59 and 60 having leads 59a-59b and 60a-~Ob adapted for connection ~o sources of current whose direction is 21 controllable.
Z3 Rotor 51 comprises equally spaced, wedge-shaped radial 24 teeth 61 having an angular pitch P and an angular width P/2.
Stator téeth 54-57 have an angular pitch P and an angular width 26¦ Pl4 Stator teeth 54, 55 (as well as stator teeth 56, 57) are 27¦ioffset from each other by an angular amount equal to (n + 1/2)P, 28lin being an integer. Stator poles 52 and 53 are offset by an 29' angular amount equal to (m + 1/4)P, m being an integer. Fig. 3B
shows the spatial relation between rotor teeth 61 and stator 1 teeth 54, 55. ~ 53 ~9 3 The current applied to control winding 59, 60 is of 4 a magnitude substantially equal to the MMF of ring-shaped 5 permanent magnets 57, 58, either aiding or opposing. Incremental 6 stepping of the disk-type stepping motor is controlled by switch-7 ing current direction as described earlier. Although not sho~m 8, for purposes of simplicity, it should be understood that stator 9I halves 52, 53 are typically enclosed within a non-magnetic lO, housing.
l2~1 Figs. 4A and 4B show a spiral slider element and 13,,stator for use with a linear variable reluctance stepper motor l4i1of Fig. l. Spiral slider element l9 is comprised of a hollow lSIl cylindrical shell 19a having an outwardly extending circular 16 flange l9b provided for mounting purposes. The hollow interior 17 is provided with a tooth pattern comprised of teeth 29 arranged 18 in a regular helix, each tooth having a pitch P and a width l9 equal to P/4. Grooves 30 are three times as wide as teeth 29.
Four spiral slider elements are employed in each motor lO
21 (elements l9, 20, 21 and 22 of Fig. l). Fig. 4B shows the 22 stator .ll having interspersed teeth 12 and grooves 13. Teeth 12 23 and grooves 13 have a pitch P and a width equal to P/2. Teeth 12 241 of the stator form a continuous helix and have square threads.
261 It should be understood that the tooth arrangements 27l heretofore described may be reversed in that the wide teeth or 28' the narrow teeth may be provided on the fixed or on the moving 29' part, the opposite tooth configuration being placed on the moving and ~ixed parts respectively.
53B~
In addition, although the permanent magnets are 2 referably formed o~ samarium cobalt, they can be formed of 3 any suitable material. Alternatively, they may be electromagnet~.
4 Magnetic paths may be either solid or laminated and the coils j 5 may be located as shown or wound directly around the teeth to 6 provide different coupling for their MM~'s. In the linear 7 embodiment, the cross section of the inner member n~ed not be 8 round but may be square, hexagonal or any other desired shape.
9lAn inner member having a round cross section is preferred because lOI it is easier to manufacture.
111i. ' 12¦l It can be seen from the foregoing description that the 13~present invention provides novel and highly useful variable 14'reluctance stepper motors. Undesirable opposing forces generated 15 Iby those teeth which do not ~orm a portion of the active flux 16 path are minimized, so long as the currents in the control i 17 windings develop an MMF which rreates a balanced condition with -:
18 the MMF of the permanent magnet, thereby resulting in a highly 19 useful orce per unit weight of the reluctance force motor.
21 The number of teeth employed and, therefore, the size 22 of motion increments, is not limited by any ratio or formula 23 involving pole and slot counts as is the case with vernier 24 steppers. If the desired number o~ rotary steps is divisible by four, a motor can be designed to provide directly this capabil-26l ity. If the desired number of steps is divisible by two but not 27li~ by four, then the motor must have two electrical steps per design , step. To provide an odd number of steps per revolution of the 29 motor, the motor must be designed with four electrical steps per ~o design step. In most cases, however, one to three steps can be , . . .
~ - 14 -3 ~
~ added to the design value to simplify the design. On the other ? ~and, linear motors can be designed ~o have any pitch within the 3 practical limits of physical size and gap tolerances. Although 4 gap toler~nces should be close, they fall well within practical 5 ranges.
7l In addition to the above capabilities and variations, 8 other variations are possible. For example, the motors may be g rotary or linear as described above. Alternatively, a rotary stepper may be mounted upon movable elements of a linear stepper,
12¦;Slider elements 19 and 20 are separa~ed by winding 23 while ~i 1311slider elements 21 and 22 are separated by winding 24. Between 14!!ring permanent magnet 18 and poles 16 and 17 are flux "regulators7' 15¦ 25 and 26. Annular rings 27 and 28 provide flux paths between 16 slider elements 19-20 and 21-22, respectively.
17 .
18 Whereas the stator teeth 12 have a pitch P and a 19 width equal to P/2, the slider teeth 29 have a pitch P and a 20 width equal to P/4. In addition, the teeth in slider element 19 21 and 20 (as well as the teeth in slider elements 21 and 22) are 22 ofset from each other by an amount equal to (n ~ 1/2)P, n being 23 an integer. The teeth o poles 16 and 17 are offset from each 24 other by an amount equal to (m ~ 1/4)P, m being an integer.
26 Motor 10 is "stepped" rom one linear position to the 2711 next by rever~ing the direction of curren~ in one of the two 28 control windings 23 and 24. There is no tendency for the slider 29 ! to move in the wrong direction. The direction of motion is ~,o dependent solely upon which winding current is reversed. Also, ~ ~ 5~
selectively inactive teeth do not se~ up any fvrces whic'n conClict 2 rth the direction of the desired forces created by the magnetic 3 energization of the active teeth. Thus, the design of Fig. 1 4 enables the motor to be stepped in either direction and with s`good stability.
7 Fig. 2 depicts a cylindrical, rotary v~riable reluctance 8 stepper motor 40 in accordance with the present invention. Motor gj 40 comprises a cylindrical rotor 41 having longitudinally extending , teeth 42 with grooves 43 therebetween. Teeth 42 have a pitch P
and a width equal to P/2. Grooves 43 may be filled with a 121lnon-magnetic material so that rotor 41 presents a smooth outer 13i periphery~ I
141 . , '.
15~ Stator 44 is provided with two poles9 44a and 44b.
16l Associated with each of stator poles 44a and 44b are two sets of 17 longitudinally extending stator teeth 45-46 and 47-48. Positioned 18 between stator teeth 45-46 and 47-48 are control windings 49a and 19 49b, respectively. Stator teeth 45, 46, 47 and 48 have a pitch P
and a width equal to P/4. Sta~or poles 44a and 44b are separated 21 ~rom each other by ring permanent magnet 49. Stator teeth 45 and 22 46 (as.well as stator teeth 47 and 48) are displaced from each 23 ~ other by an angular amount equal to ~n + 1/2)P, n being an 24 I integer. Stator poles 44a and 44b are offset from each other by 25 ! an angular amount equal to (m + 1/4jP, m being an integer.
26 '~ I
271~ Control windings 49a and 49b receive control currents 281 of a magnitude suf~icient to creat an MMF equal to that developed 29' by permanent magnet 49, the direc~ion of current being selected 30' to cause the magnetic flux develo~ed by the control winding ' ' ~ ~ ~5~ ~
1 either to aid or oppose the magnetic 1ux o~ perrnanen~ ma~ne~ 49.
2 ~he four possible combinations of current direction es~ablish 8 flux paths through the rotor and stator teeth which are analogou~
4 to those created in the linear stepper motor of Fig. 1. The 5 rotary stepper motor is stepped by changing the direction of 6 current o~ one of control windings 49a or 49b.
, !
8, Figs. 3A and 3B depict a disk, rotary variable gilreluctance stepper motor 50 in accordance with the present in- j OI,vention The motor comprises a rotor 51 mounted on a non-magnetir lljishaft 51a by means of a central collar 51b upon which is mounted 12llan integral soft iron ring 51c. Two stator poles 52 and 53 are 13lldisposed on opposite sides o~ rotor 51. Stator pole 52 comprises 411two sets of radial, ~edge-shaped teeth 54, 55, the locus of each 15 ¦set describing a circle with a different radius. Stator pole 53 16 ¦comprises two sets of similar stator teeth 56, 57. Associated 17¦ with stator poles 52 and 53 respectively are permanent ring 181 magnets 57 and 58 Surrounding ring magnets 57 and 58 respec-19 tively are eoils 59 and 60 having leads 59a-59b and 60a-~Ob adapted for connection ~o sources of current whose direction is 21 controllable.
Z3 Rotor 51 comprises equally spaced, wedge-shaped radial 24 teeth 61 having an angular pitch P and an angular width P/2.
Stator téeth 54-57 have an angular pitch P and an angular width 26¦ Pl4 Stator teeth 54, 55 (as well as stator teeth 56, 57) are 27¦ioffset from each other by an angular amount equal to (n + 1/2)P, 28lin being an integer. Stator poles 52 and 53 are offset by an 29' angular amount equal to (m + 1/4)P, m being an integer. Fig. 3B
shows the spatial relation between rotor teeth 61 and stator 1 teeth 54, 55. ~ 53 ~9 3 The current applied to control winding 59, 60 is of 4 a magnitude substantially equal to the MMF of ring-shaped 5 permanent magnets 57, 58, either aiding or opposing. Incremental 6 stepping of the disk-type stepping motor is controlled by switch-7 ing current direction as described earlier. Although not sho~m 8, for purposes of simplicity, it should be understood that stator 9I halves 52, 53 are typically enclosed within a non-magnetic lO, housing.
l2~1 Figs. 4A and 4B show a spiral slider element and 13,,stator for use with a linear variable reluctance stepper motor l4i1of Fig. l. Spiral slider element l9 is comprised of a hollow lSIl cylindrical shell 19a having an outwardly extending circular 16 flange l9b provided for mounting purposes. The hollow interior 17 is provided with a tooth pattern comprised of teeth 29 arranged 18 in a regular helix, each tooth having a pitch P and a width l9 equal to P/4. Grooves 30 are three times as wide as teeth 29.
Four spiral slider elements are employed in each motor lO
21 (elements l9, 20, 21 and 22 of Fig. l). Fig. 4B shows the 22 stator .ll having interspersed teeth 12 and grooves 13. Teeth 12 23 and grooves 13 have a pitch P and a width equal to P/2. Teeth 12 241 of the stator form a continuous helix and have square threads.
261 It should be understood that the tooth arrangements 27l heretofore described may be reversed in that the wide teeth or 28' the narrow teeth may be provided on the fixed or on the moving 29' part, the opposite tooth configuration being placed on the moving and ~ixed parts respectively.
53B~
In addition, although the permanent magnets are 2 referably formed o~ samarium cobalt, they can be formed of 3 any suitable material. Alternatively, they may be electromagnet~.
4 Magnetic paths may be either solid or laminated and the coils j 5 may be located as shown or wound directly around the teeth to 6 provide different coupling for their MM~'s. In the linear 7 embodiment, the cross section of the inner member n~ed not be 8 round but may be square, hexagonal or any other desired shape.
9lAn inner member having a round cross section is preferred because lOI it is easier to manufacture.
111i. ' 12¦l It can be seen from the foregoing description that the 13~present invention provides novel and highly useful variable 14'reluctance stepper motors. Undesirable opposing forces generated 15 Iby those teeth which do not ~orm a portion of the active flux 16 path are minimized, so long as the currents in the control i 17 windings develop an MMF which rreates a balanced condition with -:
18 the MMF of the permanent magnet, thereby resulting in a highly 19 useful orce per unit weight of the reluctance force motor.
21 The number of teeth employed and, therefore, the size 22 of motion increments, is not limited by any ratio or formula 23 involving pole and slot counts as is the case with vernier 24 steppers. If the desired number o~ rotary steps is divisible by four, a motor can be designed to provide directly this capabil-26l ity. If the desired number of steps is divisible by two but not 27li~ by four, then the motor must have two electrical steps per design , step. To provide an odd number of steps per revolution of the 29 motor, the motor must be designed with four electrical steps per ~o design step. In most cases, however, one to three steps can be , . . .
~ - 14 -3 ~
~ added to the design value to simplify the design. On the other ? ~and, linear motors can be designed ~o have any pitch within the 3 practical limits of physical size and gap tolerances. Although 4 gap toler~nces should be close, they fall well within practical 5 ranges.
7l In addition to the above capabilities and variations, 8 other variations are possible. For example, the motors may be g rotary or linear as described above. Alternatively, a rotary stepper may be mounted upon movable elements of a linear stepper,
11, or vice versa. As a further alternative, in a linear embodiment 121' either the slider or stator or both m2y be driven so as to impart ¦
13l!rotational movement thereto.
15j Fig. 5 is a functional block diagram of one embodiment 161 of the motor controller of the present invention. It comprises 17 a processor 70, motor drive circuits 71, 72, waveform generators 18 73, 74, 75, 76 and comparators 77, 78 79, 80 The motor drive 19 circuits continuously supply direct current to the motor windings 20 which may, for example, be windings 23 and 24 of the linear 21 variable reluctance motor of Fig. 1. Processor 70 may, for 22 example, be a Rockwell 6502 microprocessor. Motor drive circuit 23 71 may; for example, be of the type shown in Fig. 6. Waveform 24 generator 74 and comparator 80 may, for example, be of the type 25 ~shown in Fig. 7.
261, 2711 Each motor drive circuit comprises an H-bridge which 2glldrives its winding with essentially constant current in one of 29! two directions. The feedback signal used to control stepper , 30 timing is derived from the end of ~he winding which has been ~ 15 -. .
r~ f ~ mos~ recently switched to the lower (in this case ground) voltage.
2 ~t the moment of s~7itching the winding produces an EMF tha~ causes 3 the diode in parallel with the lower switching transistor to 4 conduct J and the voltage reaches approximately -1.0 volts. As 5 the energy in the winding inductance is dissipated, this voltage 6 rises above ground and approaches a positive voltage equal to the 7 IR drop of the winding current through the forward resistance of 8 the driving transistor and the resistance of the 1.5 ohm current 9l limiting resistor. In the absence of any motion-produced EMF, the lO,voltage will exhibit an unperturbed waveform which, in the case ~ of a linear variable reluctance stepper motor of the type sho~n 12l~in Fig. 1, may be of the form V = a(l - e-bt), where a and b 13¦,are constants. Such waveforms are shown7 for example, in the 141!upper curves in Figs. 8A and 8B.
16¦ If, however, the stepper is allowed to move in I -~
17 response to the condition described above, then ~he reluctance 18 change at the end of the motor controlled by this winding will 19 produce a momentary EMF, superimposed on the unperturbed waveform.
ZO In the case of a linear variable reluctance stepper motor of the 21 type shown in Fig. 1, the perturbation may be such as might be 22 caused.i~ "b" in the expression V = a(l - e-bt) were not 23 constant but, for some time t~O, b = b(t)~ first decreasing and 24 ¦then increasing in value. Such perturbed waveforms are shown, 25¦¦ for example, in the lower curves in Figs. 8A and 8B. The lower 26' curve in Fig. 8A is typical of the motion voltage produced with 27,~ light load. I the stepper is more heavily loaded, however, the 28, motion voltage will resemble that shown in the lower curve in 29 Fig. 8B. The motion voltage occurs later in Fig. 8B, indicating a slower mechanical response to the reversal of winding current.
, ~ 38~
In the motor controller of ~he present inven~ion a 2 . ignal is synthesized in waveform generators 73-76 ~,lhich is 3 modeled after the no-motion (non-perturbed) waveform and is 4 offset from the no-motion waveform in the direction of the 5 perturbation. The motion-induced (perturbed) signal is compared ! ' 6 with the syn~hesized signal using comparators 77-80. In the case 7,of a linear variable reluctance stepper motor of the type shown 8. in Fig. 1, the synthesized and perturbed waveforms, together wi~
g,ithe comparator output, are shown graphically in Fig. 8C. The .first crossing, indicated by the comparator output going to its low output voltage, occurs at the time which is nearly optimum ,'for acceleration switching. The second crossing, indicated by 3j'the comparator output going to its higher output voltage, occurs l~at a nearly op~imum time for deceleration switching. Depending 5i¦on the desired program of motion, one of these transitions can be 16¦1used to cause reversal of the winding current at the other motor 171 pole so that the next mechanical state is selected. That winding, 18 in turn, will produce a motion control voltage which can be used 19 to time the next reversal of the first winding current, and so on.
.
21 As will be readily appreciated by those skilled in the 22 art, the waveforms o the no-motion signal and the motion-induced ¦
23 signal are heavily dependent on the physical construction of the 24 motor. In the case o other linear embodiments or in the case of rotary embodiments of the variable reluctance stepper motors 26l! disclosed herein, those waveforms may or may not be exponential 27' in character. They might, for example, be parabolic or 28j hyperbolic. They may even take a orm which does not readily 29 lend itself to mathematical expression. Nevertheless, such waveorms can still be synthesized in waveform generators using, for example, piecewise linear approximations) read onl~J
2 ~mories (ROM's), microprocessors or a combination thereof.
4 It will also be understo_d by those skilled in the art 5 that if the stepper motor encounters a hard stop or an excessive 6 load, then the motion voltage and resulting comparator outputs 7 will not be produced and the next state of the windings will no~ !
8 be selected. This condition can be used to signal an overload g'or to stop counting and indicate ~he actual position reached by l0 the stepper. A correct response to a hard stop or an excessive load is possible only with a step by-step feedback technique.
12l,¦It is not possible with a velocity averaging feedback technique.
13i ~, 14l~l With a large but not excessive load the timing of the 15l~!first crossover at the comparator input will be delayed, as shown i 16 in Figs. 8A and 8B, and switching to the next state will be 17 automatically delayed. The stepper will ~herefore automatically 1~ slow down in response to increasing load and speed up when the 19 load is decreased or removed, and this response will occur on a step-by-step basis.
22 . While an incremental motion motor controller could be 23 used to control stepper motion directly, without the counting 24 of steps, by a system which connects the comparator outputs 25 ¦ directly to winding controls, most actual systems will require 26 ' a means of step counting and a method for commanding the stepping 271,' motor to move to various positions according to a fixed or ad-~8, justable sequence. A flexible control device which can produce 29 this type of response is a microprocessor incorporating control programs which select the winding states and feedback signals, , .
1 -~roviding full positioning performance. The flow charts for one 2 suitable program are shown in Figs. 9A, 9B and 9C, with Figs 3 and 9C showing the "STÉPS" and "DELCSN" subroutines respectively.
5.! The value POSNOW is the present position of the stepper 6 motor, counted up and down as the stepper actually moves. POSCOM i 7 is the commanded new position, set at a new value before entering !
8 the program from the Monitor The program starts by computing g the difference between POSNOW and POSCOM The flag indicating the sign of this diference is DIRFLG. The absolute difference 11 is OFFSET, a quantity which will be counted down to zero as
13l!rotational movement thereto.
15j Fig. 5 is a functional block diagram of one embodiment 161 of the motor controller of the present invention. It comprises 17 a processor 70, motor drive circuits 71, 72, waveform generators 18 73, 74, 75, 76 and comparators 77, 78 79, 80 The motor drive 19 circuits continuously supply direct current to the motor windings 20 which may, for example, be windings 23 and 24 of the linear 21 variable reluctance motor of Fig. 1. Processor 70 may, for 22 example, be a Rockwell 6502 microprocessor. Motor drive circuit 23 71 may; for example, be of the type shown in Fig. 6. Waveform 24 generator 74 and comparator 80 may, for example, be of the type 25 ~shown in Fig. 7.
261, 2711 Each motor drive circuit comprises an H-bridge which 2glldrives its winding with essentially constant current in one of 29! two directions. The feedback signal used to control stepper , 30 timing is derived from the end of ~he winding which has been ~ 15 -. .
r~ f ~ mos~ recently switched to the lower (in this case ground) voltage.
2 ~t the moment of s~7itching the winding produces an EMF tha~ causes 3 the diode in parallel with the lower switching transistor to 4 conduct J and the voltage reaches approximately -1.0 volts. As 5 the energy in the winding inductance is dissipated, this voltage 6 rises above ground and approaches a positive voltage equal to the 7 IR drop of the winding current through the forward resistance of 8 the driving transistor and the resistance of the 1.5 ohm current 9l limiting resistor. In the absence of any motion-produced EMF, the lO,voltage will exhibit an unperturbed waveform which, in the case ~ of a linear variable reluctance stepper motor of the type sho~n 12l~in Fig. 1, may be of the form V = a(l - e-bt), where a and b 13¦,are constants. Such waveforms are shown7 for example, in the 141!upper curves in Figs. 8A and 8B.
16¦ If, however, the stepper is allowed to move in I -~
17 response to the condition described above, then ~he reluctance 18 change at the end of the motor controlled by this winding will 19 produce a momentary EMF, superimposed on the unperturbed waveform.
ZO In the case of a linear variable reluctance stepper motor of the 21 type shown in Fig. 1, the perturbation may be such as might be 22 caused.i~ "b" in the expression V = a(l - e-bt) were not 23 constant but, for some time t~O, b = b(t)~ first decreasing and 24 ¦then increasing in value. Such perturbed waveforms are shown, 25¦¦ for example, in the lower curves in Figs. 8A and 8B. The lower 26' curve in Fig. 8A is typical of the motion voltage produced with 27,~ light load. I the stepper is more heavily loaded, however, the 28, motion voltage will resemble that shown in the lower curve in 29 Fig. 8B. The motion voltage occurs later in Fig. 8B, indicating a slower mechanical response to the reversal of winding current.
, ~ 38~
In the motor controller of ~he present inven~ion a 2 . ignal is synthesized in waveform generators 73-76 ~,lhich is 3 modeled after the no-motion (non-perturbed) waveform and is 4 offset from the no-motion waveform in the direction of the 5 perturbation. The motion-induced (perturbed) signal is compared ! ' 6 with the syn~hesized signal using comparators 77-80. In the case 7,of a linear variable reluctance stepper motor of the type shown 8. in Fig. 1, the synthesized and perturbed waveforms, together wi~
g,ithe comparator output, are shown graphically in Fig. 8C. The .first crossing, indicated by the comparator output going to its low output voltage, occurs at the time which is nearly optimum ,'for acceleration switching. The second crossing, indicated by 3j'the comparator output going to its higher output voltage, occurs l~at a nearly op~imum time for deceleration switching. Depending 5i¦on the desired program of motion, one of these transitions can be 16¦1used to cause reversal of the winding current at the other motor 171 pole so that the next mechanical state is selected. That winding, 18 in turn, will produce a motion control voltage which can be used 19 to time the next reversal of the first winding current, and so on.
.
21 As will be readily appreciated by those skilled in the 22 art, the waveforms o the no-motion signal and the motion-induced ¦
23 signal are heavily dependent on the physical construction of the 24 motor. In the case o other linear embodiments or in the case of rotary embodiments of the variable reluctance stepper motors 26l! disclosed herein, those waveforms may or may not be exponential 27' in character. They might, for example, be parabolic or 28j hyperbolic. They may even take a orm which does not readily 29 lend itself to mathematical expression. Nevertheless, such waveorms can still be synthesized in waveform generators using, for example, piecewise linear approximations) read onl~J
2 ~mories (ROM's), microprocessors or a combination thereof.
4 It will also be understo_d by those skilled in the art 5 that if the stepper motor encounters a hard stop or an excessive 6 load, then the motion voltage and resulting comparator outputs 7 will not be produced and the next state of the windings will no~ !
8 be selected. This condition can be used to signal an overload g'or to stop counting and indicate ~he actual position reached by l0 the stepper. A correct response to a hard stop or an excessive load is possible only with a step by-step feedback technique.
12l,¦It is not possible with a velocity averaging feedback technique.
13i ~, 14l~l With a large but not excessive load the timing of the 15l~!first crossover at the comparator input will be delayed, as shown i 16 in Figs. 8A and 8B, and switching to the next state will be 17 automatically delayed. The stepper will ~herefore automatically 1~ slow down in response to increasing load and speed up when the 19 load is decreased or removed, and this response will occur on a step-by-step basis.
22 . While an incremental motion motor controller could be 23 used to control stepper motion directly, without the counting 24 of steps, by a system which connects the comparator outputs 25 ¦ directly to winding controls, most actual systems will require 26 ' a means of step counting and a method for commanding the stepping 271,' motor to move to various positions according to a fixed or ad-~8, justable sequence. A flexible control device which can produce 29 this type of response is a microprocessor incorporating control programs which select the winding states and feedback signals, , .
1 -~roviding full positioning performance. The flow charts for one 2 suitable program are shown in Figs. 9A, 9B and 9C, with Figs 3 and 9C showing the "STÉPS" and "DELCSN" subroutines respectively.
5.! The value POSNOW is the present position of the stepper 6 motor, counted up and down as the stepper actually moves. POSCOM i 7 is the commanded new position, set at a new value before entering !
8 the program from the Monitor The program starts by computing g the difference between POSNOW and POSCOM The flag indicating the sign of this diference is DIRFLG. The absolute difference 11 is OFFSET, a quantity which will be counted down to zero as
12 positioning proceeds If OFFSET is initially zero, the routine
13; returns to Monitor If not, the first step is taken by sub-
14 routine STEPS. After this, the program checks whether 2 steps ls,~remain and, if so, switches to a deceleration routine I~ more 16!jthan 2 steps remain, the DELSCN subroutine examines the selected 17 ¦ feedback comparator for a motion signal When it occurs, the 18 !next step is taken.
19 .
The deceleration routine uses subroutine DELSCN also.
21 But when the comparator has made a transition to æero, the 22 i routine continues by examining the same comparator for a 23 I transition to one. When that occurs, the next step is taken 24~1 and this routine repeats until OFFSET = 00 2s!
26 The STEPS subroutine corrects the value of POSNOW by 27 adding DIRFL~, which is either +1 or -1. The lowestorder 2 bits 28; Of POSNOW are now masked and used to select the state of output 29 Of windings to cause motion to the position POSNOW This is done by using the low order bits of POSNOW as part of an index After !
- 19 - ' ~ 5~
a delay the same bi~s are used to construct another index whic'n 2 ~elects the generator for the comparison transient. Finally, the 3 OFFSET is decremented and ~he subroutine exits.
The DELSCN subroutine initially delays action to allow 6 the winding current transient to die down. Then an index is 7 computed to select the proper input for feedback. The input is 8 repeatedly scanned by a loop whose iterations are counted. If g no feedback has occurred by the time initial value LOOPCT 0 has 10 been decremented to zero, the program exits to Monitor because 11 the stepper has taken too long to move. In so doing, it must 12, correct the stack pointer (SP) because it is jumping out of a 13 subroutine. When the input from the comparator is found to be 14 zero, the subroutine exits normally.
16, The program described is, and will usually be, part of 17¦ an overall control program which communicates with a source o~
18¦1 commanded positions and may feed back condition reports to this lgli source. The routines described are sufficient to provide 20 ~ positioning response to a digital command, however, and comprise 21 I only 180 bytes.
23¦1 Tests with a linear variable reluctance stepper motor ~4il o the type shown in Fig. 1 have demonstrated that under closed 25¦! loop control reliable stepping rates of abou~ 400 steps/second 26 are readily achieved even though in an open loop mode the motor 27 will not reliably step at over about 150 steps/second. Under 28 closed loop con~rol the motor has been shown to be quite 29 insensitive to load, running from 400 steps/second down to less than 50 steps/second with increasing load, and always indicating actual steps completed after a hard stop.
s~
1 l~hile the incremental motion motor controller of the 2 present invention has been described in detail in connection with -3 a linear variable reluctance stepper motor it will be appreciated 4 by those skilled in the art that it is equally applicable to 5 disk, rotary and cylindrical, rotary embodiments as well. In 6 addition, while the program disclosed in Figs. 9A-9C adjusts 7 the timing of current switching on the basis of position, it 8 will be appreciated by those skilled in the art that the timing g of current switching may also be adjusted on the basis of a 10 velocity signal, derived from the time between steps. Even higher 11 speeds may be attained by a control system which commands a 12 position more than one step away from the dynamic position. This 13! technique may be particularly efective where the delay in - !
4-energizing windings becomes a significant limiting factor in
19 .
The deceleration routine uses subroutine DELSCN also.
21 But when the comparator has made a transition to æero, the 22 i routine continues by examining the same comparator for a 23 I transition to one. When that occurs, the next step is taken 24~1 and this routine repeats until OFFSET = 00 2s!
26 The STEPS subroutine corrects the value of POSNOW by 27 adding DIRFL~, which is either +1 or -1. The lowestorder 2 bits 28; Of POSNOW are now masked and used to select the state of output 29 Of windings to cause motion to the position POSNOW This is done by using the low order bits of POSNOW as part of an index After !
- 19 - ' ~ 5~
a delay the same bi~s are used to construct another index whic'n 2 ~elects the generator for the comparison transient. Finally, the 3 OFFSET is decremented and ~he subroutine exits.
The DELSCN subroutine initially delays action to allow 6 the winding current transient to die down. Then an index is 7 computed to select the proper input for feedback. The input is 8 repeatedly scanned by a loop whose iterations are counted. If g no feedback has occurred by the time initial value LOOPCT 0 has 10 been decremented to zero, the program exits to Monitor because 11 the stepper has taken too long to move. In so doing, it must 12, correct the stack pointer (SP) because it is jumping out of a 13 subroutine. When the input from the comparator is found to be 14 zero, the subroutine exits normally.
16, The program described is, and will usually be, part of 17¦ an overall control program which communicates with a source o~
18¦1 commanded positions and may feed back condition reports to this lgli source. The routines described are sufficient to provide 20 ~ positioning response to a digital command, however, and comprise 21 I only 180 bytes.
23¦1 Tests with a linear variable reluctance stepper motor ~4il o the type shown in Fig. 1 have demonstrated that under closed 25¦! loop control reliable stepping rates of abou~ 400 steps/second 26 are readily achieved even though in an open loop mode the motor 27 will not reliably step at over about 150 steps/second. Under 28 closed loop con~rol the motor has been shown to be quite 29 insensitive to load, running from 400 steps/second down to less than 50 steps/second with increasing load, and always indicating actual steps completed after a hard stop.
s~
1 l~hile the incremental motion motor controller of the 2 present invention has been described in detail in connection with -3 a linear variable reluctance stepper motor it will be appreciated 4 by those skilled in the art that it is equally applicable to 5 disk, rotary and cylindrical, rotary embodiments as well. In 6 addition, while the program disclosed in Figs. 9A-9C adjusts 7 the timing of current switching on the basis of position, it 8 will be appreciated by those skilled in the art that the timing g of current switching may also be adjusted on the basis of a 10 velocity signal, derived from the time between steps. Even higher 11 speeds may be attained by a control system which commands a 12 position more than one step away from the dynamic position. This 13! technique may be particularly efective where the delay in - !
4-energizing windings becomes a significant limiting factor in
15~' stepper performance. Under these circumstances, the feedback 16l, signal will have to be measured on the other winding and a delay 1711 adjustment may be necessary to avoid producing reverse forces 18¦l or torques.
Although two waveorm generators are shown in Fig. 5 21 for each winding, it will be appreciated by those skilled in the 22 art that where the no-motion waveform produced when one end of 231 a winding is switched to the lower potential is substantially 24¦l the same as when the other end of the winding is switched to the 251¦ lower potential, then only a single waveform generator is needed 26. for each winding. Similarly, only one comparator would be 27 required for each winding i it were time shared. When employing 28 integrated drcuits, however, it is often simpler to avoid time 29 sharing and to use multiple components, the additional size and cost being nominal.
~ 53 Although this invention has been described with respect 2 ~o its preferred embodiments, it should be understc,od that many 3 variations and modifications will now be obvious to those skilled 4 in the art. Accordingly, the scope of the invention is limited, 5 not by the speci~ic disclosure herein, but only by the appended 6 claims.
8 What I claim is:
g 10`
12'i', 13,.
; .
` 18 , 11 22231 .
224l 26"
. 29 .
~ ~ 22 - .
. . : . ~ .
;
, .
Although two waveorm generators are shown in Fig. 5 21 for each winding, it will be appreciated by those skilled in the 22 art that where the no-motion waveform produced when one end of 231 a winding is switched to the lower potential is substantially 24¦l the same as when the other end of the winding is switched to the 251¦ lower potential, then only a single waveform generator is needed 26. for each winding. Similarly, only one comparator would be 27 required for each winding i it were time shared. When employing 28 integrated drcuits, however, it is often simpler to avoid time 29 sharing and to use multiple components, the additional size and cost being nominal.
~ 53 Although this invention has been described with respect 2 ~o its preferred embodiments, it should be understc,od that many 3 variations and modifications will now be obvious to those skilled 4 in the art. Accordingly, the scope of the invention is limited, 5 not by the speci~ic disclosure herein, but only by the appended 6 claims.
8 What I claim is:
g 10`
12'i', 13,.
; .
` 18 , 11 22231 .
224l 26"
. 29 .
~ ~ 22 - .
. . : . ~ .
;
, .
Claims (33)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A motor controller for a variable reluctance stepper motor having at least two windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms, said controller comprising:
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
2. A motor controller according to claim 1 wherein said means for controlling the energization of said windings comprises:
means for determining the difference between a desired motor position and the present motor position;
means for determining the direction for stepping; and means for stepping said motor so as to reduce said difference to zero.
means for determining the difference between a desired motor position and the present motor position;
means for determining the direction for stepping; and means for stepping said motor so as to reduce said difference to zero.
3. A motor controller according to claim 2 wherein said synthesized waveform is offset in the direction of perturbation,
4. A motor controller according to claim 2 wherein said no-motion signal has an exponential waveform.
5. A motor controller according to claim 2 wherein said no-motion signal has an exponential waveform of the general type V = a(1 - e-bt), where a and b are constants.
6. A motor controller according to claim 5 wherein said motion-dependent signal has a perturbed exponential waveform of the general type V = a(1 - e-bt), where for some t>0, b = b(t), first decreasing in value and then increasing in value.
7. A motor controller for a DC variable reluctance stepper motor having first and second windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms, said controller comprising:
first and second motor drive circuits connected, respectively, to said first and second windings for energizing same;
first waveform generator means for synthesizing waveforms modeled after said no-motion signals produced by said first winding;
second waveform generator means for synthesizing waveforms modeled after said no-motion signals produced by said second winding;
first comparator means connected to said first winding and to the output of said first waveform generator means for comparing the synthesized waveforms modeled after said no-motion signals produced by said first winding with said motion-dependent waveforms produced by said first winding;
second comparator means connected to said second winding and to the output of said second waveform generator means for comparing the synthesized waveforms modeled after said no-motion signals produced by said second winding with said motion-dependent waveforms produced by said second winding; and processor means connected to said first and second motor drive circuits, said first and second waveform generator means and said first and second comparator means for controlling the energization of said first and second windings in response to said comparisons.
first and second motor drive circuits connected, respectively, to said first and second windings for energizing same;
first waveform generator means for synthesizing waveforms modeled after said no-motion signals produced by said first winding;
second waveform generator means for synthesizing waveforms modeled after said no-motion signals produced by said second winding;
first comparator means connected to said first winding and to the output of said first waveform generator means for comparing the synthesized waveforms modeled after said no-motion signals produced by said first winding with said motion-dependent waveforms produced by said first winding;
second comparator means connected to said second winding and to the output of said second waveform generator means for comparing the synthesized waveforms modeled after said no-motion signals produced by said second winding with said motion-dependent waveforms produced by said second winding; and processor means connected to said first and second motor drive circuits, said first and second waveform generator means and said first and second comparator means for controlling the energization of said first and second windings in response to said comparisons.
8. A motor controller according to claim 7 wherein said processor means comprises:
means for determining the difference between a desired motor position and the present motor position;
means for determining the direction of stepping; and means for stepping said motor so as to reduce said difference to zero.
means for determining the difference between a desired motor position and the present motor position;
means for determining the direction of stepping; and means for stepping said motor so as to reduce said difference to zero.
9. A motor controller according to claim 8 further including means for decelerating said motor when said difference has been reduced to a predetermined value.
10, A motor controller according to claim 8 wherein said first and second motor drive circuits each comprise a four transistor X-bridge connected across the winding, said four transistors being selectively energized in pairs under control of said processor means to effect current reversal through the winding and stepping of said motor.
11. A motor controller according to claim 8 wherein said first and second waveform generator means each comprises two waveform generators and wherein said first and second comparator means each comprises two comparators.
12. A motor controller according to claim 8 wherein said no-motion signals have exponential waveforms.
13. A motor controller according to claim 12 wherein said synthesized waveforms are offset in the direction of perturbation.
14 . A motor controller according ~o claim 12 wherein said exponential waveforms are of the general type V = a(l - e-bt), where a and b are constants.
15. A motor controller for a linear, variable reluctance stepper motor comprising:
a first cylindrical motor member having a plurality of regular helical teeth with grooves therebetween, said teeth having a pitch P and a width equal to P/2;
a second cylindrical motor member surrounding at least a portion of said first member, said second member comprising two annular poles separated by an annular magnet, each pole having two annular elements separated by an annular winding, each element having a set of regular helical teeth with grooves therebetween, said teeth having a pitch P and a width equal to P/4, the sets of teeth in each pole being offset longitudinally from each other by an amount equal to (n ? 1/2)P, n being an integer, said poles being offset from each other in the longitudinal direction by an amount equal to (m ? 1/4)P, m being an integer, said windings characterized by no-motion signals having unperturbed waveforms and by motion-dependent signals having perturbed waveforms;
waveform generator means synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized wave-forms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
a first cylindrical motor member having a plurality of regular helical teeth with grooves therebetween, said teeth having a pitch P and a width equal to P/2;
a second cylindrical motor member surrounding at least a portion of said first member, said second member comprising two annular poles separated by an annular magnet, each pole having two annular elements separated by an annular winding, each element having a set of regular helical teeth with grooves therebetween, said teeth having a pitch P and a width equal to P/4, the sets of teeth in each pole being offset longitudinally from each other by an amount equal to (n ? 1/2)P, n being an integer, said poles being offset from each other in the longitudinal direction by an amount equal to (m ? 1/4)P, m being an integer, said windings characterized by no-motion signals having unperturbed waveforms and by motion-dependent signals having perturbed waveforms;
waveform generator means synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized wave-forms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
16. A motor controller according to claim 15 wherein said second motor member includes annular flux "regulators"
disposed on each side of said magnet and between said magnet and each pole, the cross section of said flux "regulators"
narrowing from said magnet toward each of said poles and wherein said magnet is a rare earth permanent magnet.
disposed on each side of said magnet and between said magnet and each pole, the cross section of said flux "regulators"
narrowing from said magnet toward each of said poles and wherein said magnet is a rare earth permanent magnet.
17. A motor controller according to claim 15 wherein said synthesized waveform is offset in the direction of perturbation.
18. A motor controller according to claim 15 wherein said no-motion signal has an exponential waveform.
19 A motor controller according to claim 18 wherein said no-motion signal has an exponential waveform of the general type V = a(l - e-bt), where a and b are constants.
20. A motor controller according to claim 19 wherein said motion-dependent signal has a perturbed exponential waveform of the general type V = a(l - e-bt), where for some t>o, b = b(t), first decreasing in value and then increasing in value.
21. An incremental motion motor controller for a disk, rotary, variable reluctance stepper motor comprising:
a disk-shaped rotor mounted on a shaft and having a plurality of wedge-shaped, radially extending equally spaced teeth having an angular pitch P and an angular width equal to P/2;
a stator comprising two poles, one disposed on each side of said rotor, each stator pole having two sets of wedge-shaped, radially extending, equally spaced teeth having an angular pitch P and an angular width equal to P/4, the locii of said sets of stator teeth describing circles having two different radii, the sets of teeth in each stator pole being offset from each other by an angular amount equal to (n ? 1/2)P, n being an integer, the two stator poles being offset from each other by an angular amount equal to (m ? 1/4)P, m being an integer, each stator pole also including an annular magnet and an annular winding, said windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms;
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
a disk-shaped rotor mounted on a shaft and having a plurality of wedge-shaped, radially extending equally spaced teeth having an angular pitch P and an angular width equal to P/2;
a stator comprising two poles, one disposed on each side of said rotor, each stator pole having two sets of wedge-shaped, radially extending, equally spaced teeth having an angular pitch P and an angular width equal to P/4, the locii of said sets of stator teeth describing circles having two different radii, the sets of teeth in each stator pole being offset from each other by an angular amount equal to (n ? 1/2)P, n being an integer, the two stator poles being offset from each other by an angular amount equal to (m ? 1/4)P, m being an integer, each stator pole also including an annular magnet and an annular winding, said windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms;
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
22. A motor controller according to claim 21 wherein said rotor further includes an annular-shaped iron ring disposed between said shaft and said rotor teeth to conduct flux between said stator poles and wherein said magnet is a rare earth permanent magnet.
23. A motor controller according to claim 21 wherein said synthesized waveform is offset in the direction of perturbation.
24 An incremental motion motor controller for a cylindrical, rotary variable reluctance stepper motor comprising:
a cylindrical rotor having a plurality of longitudinally extending teeth with grooves therebetween, said rotor teeth having an angular pitch P and an angular width equal to P/2;
a cylindrical stator surrounding said rotor, said stator having two annular poles separated by an annular magnet, each stator pole having two sets of equally spaced, longitudinally extending teeth having an angular pitch P and an angular width equal to P/4, the sets of teeth in each stator pole being offset from each other by an angular amount equal to (n ? 1/2)P, n being an integer, the two stator poless being offset from each other by an angular amount equal to (m ? 1/4)P, m being an integer, the sets of teeth in each stator pole being separated by an annular winding, said windings characterized by no-motion signals having unperturbed waveforms and motion dependent signals having perturbed waveforms;
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
a cylindrical rotor having a plurality of longitudinally extending teeth with grooves therebetween, said rotor teeth having an angular pitch P and an angular width equal to P/2;
a cylindrical stator surrounding said rotor, said stator having two annular poles separated by an annular magnet, each stator pole having two sets of equally spaced, longitudinally extending teeth having an angular pitch P and an angular width equal to P/4, the sets of teeth in each stator pole being offset from each other by an angular amount equal to (n ? 1/2)P, n being an integer, the two stator poless being offset from each other by an angular amount equal to (m ? 1/4)P, m being an integer, the sets of teeth in each stator pole being separated by an annular winding, said windings characterized by no-motion signals having unperturbed waveforms and motion dependent signals having perturbed waveforms;
waveform generator means for synthesizing waveforms modeled after said no-motion signals;
comparator means for comparing said synthesized waveforms with said motion-dependent waveforms; and means for controlling the energization of said windings in response to said comparison.
25. A motor controller according to claim 24 wherein said magnet is a rare earth permanent magnet.
26. A motor controller according to claim 24 wherein said synthesized waveform is offset in the direction of perturbation.
27. A method for controlling a variable reluctance stepper motor having first and second windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms, said method comprising the steps of:
(a) synthesizing waveforms modeled after said no-motion signals;
(b) comparing the synthesized waveforms with the motion-dependent waveforms; and (c) controlling the energization of said windings in response to said comparisons.
(a) synthesizing waveforms modeled after said no-motion signals;
(b) comparing the synthesized waveforms with the motion-dependent waveforms; and (c) controlling the energization of said windings in response to said comparisons.
28. The method of claim 27 further including the step of offsetting the synthesized waveforms in the direction of perturbation.
29. The method of claim 27 wherein said synthesized waveforms are exponential waveforms.
30. The method of claim 29 wherein said exponential waveforms are of the general type V = a(l - e-bt), where a and b are constants.
31. A method for controlling a variable reluctance stepper motor having first and second windings characterized by no-motion signals having unperturbed waveforms and motion-dependent signals having perturbed waveforms, said method comprising the steps of:
(a) determining the difference between a desired motor position and the present position;
(b) determining the direction of stepping;
(c) synthesizing waveforms modeled after said no-motion signal;
(d) comparing the synthesized waveforms with the motion-dependent waveforms;
(e) controlling the energization of said windings in response to said comparisons; and (f) stepping said motor so as to reduce said difference to zero.
(a) determining the difference between a desired motor position and the present position;
(b) determining the direction of stepping;
(c) synthesizing waveforms modeled after said no-motion signal;
(d) comparing the synthesized waveforms with the motion-dependent waveforms;
(e) controlling the energization of said windings in response to said comparisons; and (f) stepping said motor so as to reduce said difference to zero.
32. The method of claim 31 further including the step of decelerating said motor when said difference has been reduced to a predetermined value.
33. The method of claim 32 wherein said synthesized waveforms are exponential waveforms.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000402933A CA1145389A (en) | 1978-07-20 | 1982-05-13 | Controller for variable reluctance stepper motor |
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US926,311 | 1978-07-20 | ||
| US05/926,311 US4286180A (en) | 1978-07-20 | 1978-07-20 | Variable reluctance stepper motor |
| US002,797 | 1979-01-11 | ||
| US06/002,797 US4234838A (en) | 1979-01-11 | 1979-01-11 | Incremental motion motor controller |
| CA000326855A CA1142581A (en) | 1978-07-20 | 1979-05-03 | Variable reluctance stepper motor |
| CA000402933A CA1145389A (en) | 1978-07-20 | 1982-05-13 | Controller for variable reluctance stepper motor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145389A true CA1145389A (en) | 1983-04-26 |
Family
ID=27426147
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000402933A Expired CA1145389A (en) | 1978-07-20 | 1982-05-13 | Controller for variable reluctance stepper motor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1145389A (en) |
-
1982
- 1982-05-13 CA CA000402933A patent/CA1145389A/en not_active Expired
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