CA1074393A - Stepping motor using extended drive pulses and method - Google Patents

Abstract

STEPPING MOTOR USING EXTENDED
DRIVE PULSES AND METHOD
Abstract of the Disclosure The present invention relates to a stepping motor and a method of operating same. A unit is provided for selectively energizing each of a plurality of phases in response to a drive pulse, wherein each drive pulse has three successive portions. The energizing unit includes a timer for establishing the delineation between the three portions of the drive pulse so that during a first portion of each drive pulse one other drive pulse for one other phase exists simultaneoulsy, during the second portion of each drive pulse drive pulses for none of the other phases exist, and during the third portion of each drive pulse a second other drive pulse for a second other phase exists simultaneously. The timer provides a series of drive pulses for each phase and the third portions of all pulses in each series is of a variable duration and the total duration of each pulse of each series is fixed.

Description

`' 107~393 This is a division of Canadian patent application Serial No. 275,034 which was filed on 29 March 1~77.
BACKGROUND OF THE INVENTION
This relates to stepping motors and more particularly to a method and drive circuitry for providing increased torque or speed with a minimum increase in power consumption.
Stepping motors are conventionally operated in one of two modes. Single phase operation involves exciting or energizing one of the windings (or phases) of the motor at a time, and stepping is accomplished by sequentially energizing adjacent phases. The alternative mode of operation is dual phase excitation in which two adjacent phases are energized at all times; in the dual phase operation one phase continues to produce torque throughout the first half of the next phase excitation so that maximum performance (torque) from a given size motor is achieved, but this is accomplished only at the expense of excessive power consumption. Thus while the single ;,~ 20 phase excitatiPn consumes less power, more torque is produced by the dual phase excitation.
While high torque characteristics are of course desirable, it is of increasing importance to prevent unnecessary power consumption. Accordingly, it is the object of the present invention to provide improved stepping motor operation, and in particular to tailor the torque-speed characteristic of the stepping motor to the application while minimizing the power consumption.
It is a further object of the present invention to provide an improved stepping motor drive circuit which satisfies these requirements.

It is a still further object of the present invention to provide a stepping motor with efficient performance, especially to tailor the motor torque characteristics to the dynamic load requirements while minimizing the power supply requirements.
SUMMARY OF THE INVENTION
In accordance with one embodiment of the present invention a stepping motor drive circuit creates extended drive pulses to produce an extended single phase excitation.
Each drive pulse overlaps the beginning of the successive drive pulse by a defined time, but the extended pulse is terminated before the subsequent drive pulse is commenced.
Thus, the extended single phase excitation is not a dual phase operation. However, it does have some of the advant-ages of dual phase excitation without its disadvantages.
In particular, higher torque is provided without excessive power consumption.
The extended single phase drive pulse generated in accordance with the present invention continues to provide torque while the current in the next energized phase is being built up. The resultant improvement in speed-torque characteristics of the motor is considerable, but since the simultaneous energization of two phases is terminated when no longer needed, the increase in power consumption is very small.
Stepping motors can be used in two types of operating systems: closed loop and open loop. In closed loop systems the speed and/or position is monitored by a sensor and a feedback signal controls the timing of the drive pulses, hence controlling the speed and the torque.
In an open loop system there is no feedback and speed is established in response to the frequency of an external clock. In closed loop systems using extended drive pulses the duration of the pulse extension (or overlap) may be of fixed duration so that as the speed increases, the relative percentage of the overlap increases, since the real time duration closed loop systems using extended drive pulses the duration of the pulse extension (or overlap) may be of fixed duration so that as the speed increases, the relative percentage of the overlap increases, since the real time duration of the drive pulse decreases. This facilitates higher slew speeds (due to the large drive pulse overlap resulting in higher torque as the speed increases), but minimizes the power - requirements at low ~stepping) speeds where sufficient torque is available to accelerate the load even with a ; small drive pulse overlap. In open loop systems a fixed ,. ,j duration drive pulse overlap may be used to provide higher torque at all times. Alternatively, the overlap may be varied so that the large overlap is provided for acceleration and deceleration (where increased torque is necessary), but the overlap is made small for constant speed operation to conserve power by not energizing the adjacent phase unnecessarily.
The extended single phase excitation is therefore applicable to both open and closed loop systems although its specific implementation may differ slightly in the two systems. In addition, the length of the extended pulse may be selected for each particular application, whether the system is of the open or the closed loop variety.
In accordance with one aspect of the invention there is provided a method for operating a stepping motor having a plurality of individually energizable phases comprising the steps of: sequentially energizing each of a plurality of phases for distinctive intervals of time; the energization interval of each one of the phases overlapping in time with the energization interval of the phase first subsequent thereto for a selected overlap period, the selected overlap period being such that the energization interval of the one phase terminates a selected time prior to the energization of the next subsequent one of the plurality of phases; and wherein the selected overlap period for a given phase is variable~ in duration and the energization interval for that phase is of a fixed duration.
In accordance with another aspect of the invention .:
~ there is provided a multiphase stepping motor having a plurality of individually energizable phases comprising:
means for selectively energizing each of the phases in response to a drive pulse, each drive pulse having three successive portions; said energizing means including timing means for establishing the delineation between the three portions of each drive pulse so that during a first portion of each drive pulse one other drive pulse for one other phase exists simultaneously, during the second portion of each drive pulse drive pulses for none of the other phases exist, and during the third portion of each drive pulse a second other drive pulse for a second other phase exists simultaneously; and wherein the timing means provides a series of drive pulses for each phase and the third portions of all pulses in each series is of a variable duration and the total duration of each pulse of each series is fixed.

~ _ 4 _ BRIEF DESCRIPTION OF THE DRAWINGS
The present invention taken in conjunction with the invention disclosed in Canadian patent application Serial No. 275,034, filed 29 March 1977, will be described in detail hereinbelow with the aid of the accompanying drawings, in which:
FIG. 1 is a schematic representation of a four-phase stepping motor of a generally conventional design;
FIGS. 2 and 3 illustrate waveforms representative of the driving pulses used for conventional single phase , , ~, and dual phase excitation;
FIG. 4 illustrates waveforms representative of the driving pulses when operating a stepping motor in accordance with the present invention;
FIG. 5 is a schematic diagram of one embodiment of a driving circuit in accordance with the present invention;

.. FIGS. 6 and 7 illustrate waveforms produced at various points in the circuit of FIG. 5;

1~74393 Von Braun 2 1 FIGS. 8A, 8B, 9A, and 9B are graphlcal lllustratlons

2 Or the advantageous characterl~tlcs of operatlon ln accordance

3 wlth the present lnventlon,

4 DETAILED DESCRIPTION
The stepplng motor to whlch thl~ descrlptlon 6 19 dlrected 18 a~sumed to be a varlable reluctance motor 7 wlth rOur stator phase~, Thls motor structure 1~ conven-8 tlonally termed a rour-phase motor and its phases are energlzed 9 ln sequence, If only one phase ls energlzed at a tlme, lt 19 normally referred to as a slngle pha~e operatlon; lf two ll phases are energlzed all tlmes, lt 1~ referred to as a 12 dual phase operatlon, FI~. l 18 a generallzed schematlc 13 representatlon of a conventlonal rour-phase motor structure, 14 but lt 18 understood that the lnvention 19 not llmlted to that speclfic deslgn and the lnventlon 19 equally appllc-16 able to approprlate multlphase (other than, as well a9, 17 rour-pha~e) motors Or dl~ferent deslgn. In the embodlment 18 shown each phase includes two poles (11 and ll', 12 and l9 12', 13 and 13', and 14 and 141, respectlvely). Each pole 1B provlded with a wlndlng or coll 21 through 24 and 21l 21 through 24', and the colls on a glven pole palr (constltut-22 lng one phase) are energlzed together to provlde a rlux 23 path through the magnetlc rotor lO (see for example the 24 North, N, and South, S, deslgnatlon on poles ll and ll').
Whlle the drawlng 19 sultable for explalnlng the modes of 26 energlzatlon found in the prlor art and ln accordance wlth 27 the method of the pre~ent lnventlon, lt 1B repre~entatlve 28 Or many varled deslgns and, as such, a specl~lc connectlon 29 of the wlndlngs on the prlmed poles 19 not shown. However, the swlt¢hes SW-l through SW-4 represent a mechanlsm for 31 energlzlng the re~pectlve pha3es l through 4 (by connect-32 lng both lnterconnected co~ls on the pole palr; l.e. 21 1074393 Von Braun 2 1 and 21' ror phase l, 22 and 22' ror phase 2, etc. to a 2 power supply 27) in the sequence shown by the energlze 3 arrow E. Ad~acent poles are separated by 45 and ad~acent 4 rotor races 15 are separated by 60. Therefore, as the phases l through 4 are energlzed sequentially the rotor lO
wlll advance or step 15 ln the dlrectlon shown by the 7 rotate arrow R as each successlve phase is energlzed.
8 FIG, 2 represents the drlve waveforms when the 9 motor Or FIG. l 19 operatlng wlth single phase excltatlon, Drlve pul~e Pl (see the waverorm ror phase 1) is produced ll by the closure Or swltch SW-l and thl~ energlzes coils 21 12 and 21', Slmilarly, drlve pulse P2 shown ln the waveform 13 ~or phase 2 (coils 22 and 22') 18 generated by the closure 14 Or swltch SW-2, and drlve pulses P3 and P4 energlze the respectlve c0118 23 and 23', and 24 and 24' upon closure 16 o~ respectlve swltches SW-3 and SW-4. A complete stepplng 17 cycle (rour steps) requlres energlzatlon o~ each of the 18 stator coll palrs one ~fter another, and thus, contlnuous l9 stepplng requlres the sequence of the four drlve pulses Pl, P2, P3, and P4 to be repeated as many tlmes as deslred.
21 Thls 18 a conventional operatlon and, a~ 19 well-known, 22 the greate~t torque requlrements occur at acceleratlon 23 and deceleratlon Or lnertlal loads, 24 FIG. 3 shows the waverorms assoclated with dual phase operatlon, In thls case at least two phases are 26 always energlzed simultaneously. For example, while switch SW-l 27 18 ON causlng the energlzatlon o~ colls 21 and 21~ as repre-28 sented by drlve pulse P'l Or the waverorm Or phase l, swltch SW-2 29 18 closed generatlng drlve pulse P12 and energlzlng colls 22 snd 22' 90 that both phases (1 and 2) are belng drlven slmultane-31 ously, Subsequently when swltch SW-l is turned OFF endlng Von Braun 2 ~~~ 1 pulse P'l, swltch SW-3 18 simultaneously turned ON forming 2 pul9e P~3 vhich is malntalned throughout the remalnder Or 3 the energlzatlon Or coils 22 and 22' (pulse P'2). Subse-4 quently, while P'3 18 ON, colls 24 and 24' are energlzed by the closure Or swltch SW-4 producing drlve pulse P'4 6 at the termlnatlon Or pulse P~2. As thls contlnues two 7 phases Or the stator are energlzed at ~11 times. It 18 8 obvlous that slnce the torque produced by a prevlously 9 energlzed phase, such as phase 1, wlll contlnue durlng the bulldup o~ current in the newly energlzed phase, such 11 as phase 2 (pulse P'2), the torque characterlstlcs Or the 12 dual phase operatlon are slgnlrlcantly better than the 13 slngle phase operatlon Or FIG. 2. However, lt 19 al80 14 evldent that slnce the voltage 18 applled slmultaneously to two phases at all tlmes, a slgnlrlcant power consump-16 tion 18 the prl¢e pald ror thls lncreased tor~ue characterlstlc 17 because current 18 always drawn by two phases.
18 ~IG. 4 lllustrates repre~entatlve waverorms Or 19 drlve pulses ror operating a stepplng motor ln accordance wlth the present lnventlon. In partlcular, the drlve pulse 2L ror each phase, such a~ 20-1 for phase 1, e~tends beyond 22 the normal termlnatlon 25-1, rOr the slngle pha~e opera-23 tlon and extends lnto the tlme slot of the succeedlng pha~e, 24 but lt termlnates prlor to the time 25-2, the end Or the tlme slot dedlcated to the second or subsequent phase (hence 26 pr$or to the turn-O~ of the next subsequent phase such as 27 pulse 20-3 ~or phase 3), As wlll be explained hereinarter 28 in greater detail, thls extension or overlap repre~ented 29 by X-l, X-2, X-3, and X-4 greatly reduces the lost er~lcl-ency (due to acceleratlon and deceleration whlle current 31 19 belng bullt up and decayed in the stator coils) slnce 32 the exlsting torque 19 malntained by the contlnued e~cltatlon ~on ~raun 2 ~074393 1 of the previously energlzed coll whlle the newly energlzed 2 coll current 18 bullt up. However, slnce the drlve pulses 3 of successlve phases are not malntained ln thelr energlzed 4 state perpetually and, ln fact, two pha~es are energlzed only for a short portlon of the overall tlme, the lost 6 power due to common energlzatlon of two p~ase~ (as ln dual 7 phase excitatlon) 18 mlnlmlzed.
8 In summary, operatlon ln accordance with the 9 present lnventlon utlllzes the best characterlstlcs of both the slngle phase and dual phase modes of operatlon 11 and mlnlmlzes the dlsadvantages of both, 12 FIG. 5 1~ a ~chematlc repre~entatlon Or a drlve 13 clrcult utllizlng dlscrete components sultable for genera-14 tlon of the extended drlve pulses necessary for the operatlon ln accordance wlth the waveforms of FIG. 4. However, other 16 clrcult conflguratlons, as well a8 m cro-processors whlch 17 lend themselves to more comple~, tlme varlable pulse exten-18 slon ln more sophlst~cated systems, may also be used. In 19 essence, the motor drlve 36 contalns the stator colls 21 through 24 and thelr interconnected mate~ 21' through 24' 21 (ln ~IG. 1), and the rem~lnder of the clrcult of FIG. 5 22 serve~ a~ the swltche~ SW-l through SW-4 (ln FI~. 1) and 23 the approprlate tlmlng and control 16 (ln ~I~. 1) for these 24 swltches. A clock slgnal Cp (generated by clock pul~e 2~ generator 30) 19 ~ed slmultaneously into a 4 blt ~hlft 26 reglster 31 and a pulse e~tender 32. The ~h~ft regl~ter 31 27 develops for every four pulses o~ clock signal ~p, four 28 output pul~es 18-1, 18-2, 18-3, and 18-4 sequentlally dls-29 trlbuted over the four output termlnsls Ql, Q2, Q3, and Q4. The pulse e~tender 32, whlch may be a monostable Von Br~un 2 1 multivibrator 40 (commonly rererred to a~ a one-shot) and 2 a serles o~ NAND-gates 41-1 through 41-4, develops, ror 3 every clock pulse, output pulses such as 19-1J 19-2, 19-3, 4 and 19-4 which are sequentlally dlstributed over rour out-put termlnals Tl, T2, T3, and T4. The pulse~ 18 and 19 6 are comblned in a loglc comblner 35 to produce the deslred 7 drlve pulses 20 which are used to control energlzatlon Or 8 the indlvidual c0119 (pha9e9 ) 0~ motor drlve 36, 9 In an N-phase motor, one step cycle occurs ror every N clock pulses. Thus, ln a rour phase motor, one 11 step cycle requires rour clock pulses. In the pre~erred 12 embodlment ~or produclng these drive pulses 20 rOr a rOur 13 phase motor, the ~hlrt reglster 31 18 a standard devlce 14 havlng rour stages, one rOr each motor pha~e. For example, it may be a 4 blt shlrt reglster, such as 18 marketed as 16 part number 9300 by Falrchlld Semlconductor o~ Mountaln 17 Vlew, Callrornla, Its stages are arranged ln a continuous 18 loop wlth one output terminal connected to each stage, 19 One stage 18 lnltlally loaded wlth an "ON" pul~e, and thls "ON" pulse 18 then stepped from stage to stage, one stage 21 at a time, for each clock pulse 17 Or clock slgnal Cp.
22 Thus, as the "ON" pulse 18 stepped, an output pulse 18 23 18 produced at each Or the termlnals Ql through Q4. In 24 one cycle (4 step~) one pulse 18 18 sequentlally produced at each terminal, These pulses 18 are assumed to be posltlve 26 ("1" a hlgh state derlnlng the "oN" pulse) and are ~hown ln 27 FIG, 6. Thus, each Or the pulses 18-1 through 18-4 e~lsts 2~ (at it~ respectlve output Ql through Q4), in lts sequentlal 29 tlme ~lot for one quarter Or the step cycle, and each 18 3 ~ynchronized wlth one o~ the clock pulses 17 (also shown 31 ln FIG, 6).

_g _ 1074393 Von Braun 2 1 The pulse extender 32 is bullt around a one shot 40, 2 whlch may be a commerclally avallable lntegrated circult 3 device, such as part number SN 74123 marketed by T,I, Corpora-4 tlon, The one shot produces a pulse 42 of selected width for each clock pulse 17, Thls serles of pulses, deslgnated S, i8 ~hown ln FIG, 7 along wlth the clock slgnal Cp to whlch lt 18 7 synchronlzed. The tlme duratlon (width) o~ the pulses 42 8 ~rom the one shot 40 is determlned by an RC networ~ 45 9 whlch 19 connected to approprlate plns of the one shot devlce and to a blas voltage deslgnated +Vl, Altering 11 the RC time constant o~ network 45, such as by changlng 12 the value Or the resistance 46 and/or the erfectlve 13 capacltance 47 (by connecting more or fewer parallel capacltors), 14 changes the selected wldth of the one shot pulses 42, These pul~es 42 are applied to each of four two-16 lnput NAND-gates 41-1 through 41-4, The other lnput to 17 each NAND-gate 41 is one of the quarter cycle pulses 18 18 shown ln FIG, 6, The one shot 40 19 assumed to produce 19 a posltlve pulse 42 ("1" or high state de~lning the "ON"
pulse), and therefore the output of each gate 41 wlll be 21 a slgnal havlng only one negatlve pulse every ~our clock 22 pulses, These negat~ve pulses are shown ln FIG, 7 as 19, 23 and one wlll appear at the output o~ each gate (correspond-24 lng termlnals T) durlng the coincldence of the pulse 42 and the speclflc pulse 18 connected to that gate, These nega-26 tlve pulses wlll be staggered ln tlme, and as can be seen 27 from the waveforms of FIGS, 6 and 7, the specific pulse l9 28 produced by the coincldence of pulse 42 and the quarter 29 cycle pulse 18-1 19 designsted 19-4, while.the pulses l9-1, 19-2, and 19-3 are produced re~pectively ln response to 31 pulses 18-2, 18-3, and 18-4, Hence, the output~ Ql, Q2, ~0743~3 Von Braun 2 l Q3, and Q4 Or the register 31, are connected re~pectlvely 2 to NAND-gates 41-4, 41-l, 41-2, and 41-3.
3 As the extenslon Or the drlve pulses 20 19 a 4 dlrect functlon o~ the pulses l9, these negatlve pulses are herelna~ter referred to as extenslon pulses and the 6 wldth Or pulses 42 18 establlshed 90 that each Or the pulses l9 7 1~ of a durat1on less than the quarter cycle tlme slot occupled 8 by each o~ the pulses 18, Networ~ 45 may, of course, be 9 ad~usted to provlde elther rlxed or varlable extenslon for a glven appllcatlon, AB W111 be dlscussed herelnafter 11 a flxed extenBion 1B o~ten preferred ln closed loop ~ys-12 tems; whereas, varlable duratlon extenslons are o~ten better 13 sulted to open loop systems. It 18 also noted that the 14 extenslon provided for dlfrerent phases can be ~ade dif-rerent slmply by approprlately tlmed changes of the tlme 16 con2tant Or network 45, 17 Pulse9 18 at the termlnals Ql through Q4 of register 31 18 and the correspondlng extension pulses 19 at the termlnals Tl 19 through T4 are combined ln the logic combiner 35 ln proper phase rel~tlon to ~orm the ~our extended drive pulses 20-1 21 through 20-4, each at the respectlve output9 El through 22 E4, The comblner 35 slmply adds the extenslon pulse l9 23 to the end o~ the preceding quarter cycle pulse 18; that 24 18, the quarter cycle pulse 18 1~ combined with the exten-sion pulse 19 who9e leadlng edge occurs at the same tlme 26 a~ the trailing edge of the pulse 18, Thus, pulse 18-1 27 19 extended by the addltlon Or (an lnverted) pulse 19-1 28 to form the extended drlve pulse 20-1 and output El, Sim-29 ilarly, extended drive pulses 20-2, 20-3, and 20-4 are formed at their re~pective outputs from the combination 31 of corre~ponding quarter cycle pulses 18 and extension 32 pulses 19. ~lven the polarltles assumed, loglc comblner 35 ~074393 ~ Von Braun 2 ~. .

i', V
1 lncludes lnverters 34-1 through 34-4 each inverting one 2 of the quarter cycle pulses 18, These inverted quarter 3 cycle pulses are each applied to one input o~ a two input 4 NAND-gate 33-1 through 33-4, The other input to each ~AND-gate is the corresponding output pulse 19 from the extender 32, 6 ~or example, the pulse 18-1 is inverted and applied to 7 NAND-gate 33-1 along with pulse 19-1, The output is the 8 extended pul9e 20-1 which i8 then applied to a transistor 9 switch 39-1 which connects coils 21 and 21' of the step-ping motor to a voltage +V, thereby energizing this first 11 phase for the duratlon of the extended pulse 20-1, The 12 remaining extended drive pulses 20-2 through 20-4 are 2im-13 ilarly produced and applied to their respective switches 39-2 14 through 39-4, causing energization of stator coils 22-21' through 24-24', respectively, 16 As can be seen in FIG, 4, the resulting extended 17 drive pulses 20 are each ex~ended (by the width of pulse 19) 18 into the next quarter cycle time slot, This overlap pro-19 vide~ the contlnuation of torque from the last energized phase while the next energized phase is being turned ON, 21 Hence, the motor does not suf~er periodic decelerations, 22 and accelerations as each phase excitation is switched 23 ON and O~F. However, the extended pulse 20 does not extend 24 throughout the next quarter cycle time slot and therefore the periods of dual energlzation are minimized, resulting 26 in economy of power, The actual duration of overlap for 27 any specific application will of course depend upon it~
28 characteristics and lt is assumed that the extension (the 29 width of pulse 19) will be established accordingly, As indicated hereinbefore,stepping motors can 31 be operated in two alternative modes, An open loop sys-, Von Braun 2 10743~3 l of its drive circuitry, require~ a clock source, a shl~t 2 reglster and a power drive clrcult, such as 19 shown gen-3 erally a~ 30, 31, and 36 ln FIG. 5. In the slmplest open 4 loop systems uslng slngle pha~e excltatlon, the motor indexes whenever a clock pulse 19 applied to swltch excltatlon ~rom 6 one pha~e to another. The clock ~requency i9 ~lxed and the 7 ultlmate speed o~ the motor 18 lnherently llmited to less 8 than the motor slew speed, which is defined as that speed 9 at whlch the motor cannot accelerate (or decelerate) to the clock ~requency wlthout mlsslng a step. Whlle this ll limlted operatlng range of the open loop system may be 12 extended by ramping the drlve pulses (expandlng the tlme 13 Or one or more pulses by alterlng the clock frequency) 14 at the beginning and end o~ the drlve pulse sequence, the attalnable speed 1~ lnherently lower than the slew speed 16 posslble with a closed loop system, 0~ course, with dual 17 phase excltatlon, increased tor~ue 1rQ available and thls 18 permlts a substantlal lncrease Or speed. However, the l9 dual phase excltatlon requires a substantlal increase in power supply requlrements, 21 Relative to open loop systems, a closed loop 22 system 18 capable Or much hlgher operatlng speeds, Thls 23 18 accompllshed by monltorlng the posltlon or speed o~
24 the rotor and uslng thls ln~ormatlon to energize the varlous stator c0118 at the preclsely proper tlmes, Most conven-26 tlonally the rotor posltlon 18 sensed by a sensor-encoder 27 mounted on the motor shaft, The slgnals produced by the 28 encoder are red back to the drlve circult to ~witch the 29 energlzatlon ~rom one phase to another, such as by control-llng the output o~ a clock pulse generator 30 (ln FI~, 5) Von Braun 2 as represented by ~eedback slgnal 37. The ~eedback slgnal 2 1~ thus constantly adJusted to provlde mQxlmum torque and 3 hence maxlmum speed, 4 In most appllcatlons where mlnlmlzlng the tlme to traverse a ~peclrled dlstance 18 crltlcal, the closed 6 loop mode 19 used because lt can achleve the greatest slew 7 speed, However, the pulse extenslon o~ the present lnven-8 tlon provldes increa~ed torque for both open and closed 9 loop systems and thls lmprovement 19 accompllshed wlthout excesslve power consumptlon, 11 In closed loop ~ystems the extenslon X 19 pre~erably, 12 but not necessarlly, o~ a rlxed duratlon. ~or example, the 13 extension may be rlxed at 300 mlcro~econds and, durlng 14 acceleratlon, the drlve pulses 20 may be appro~imately 3 to 4 mllllseconds. The torque ~ the motor at thls slow 16 stepplng rate 18 more than adequate to accelerate the lner~lal 17 load and the pulse extenslon 18 less than 10% o~ the total 18 drlve pulse 20, Hence as ~hown ln ~IG, 8B, the extended 19 slngle phase excltatlon (E~) requires only a maxlmum power level 52, whlch 18 mlnlmally greater than the power supply 21 capacity 51 re~ulred rOr ~lngle phase excltatlon (10), 22 whereas the dual phase excltatlon (20) would requlre a 23 capaclty 53, dou~le that o~ the slngle phase excltatlon, 24 In fact dual phase operatlon produces appro~lmately 140%
o~ single phase torque whlle lt consumes twice the power, 26 A~ the sy~tem accelerates, the clock ~requency 27 (rate o~ pul~e~ 17) 18 lncreased automatlcally ln response 28 to feedback slgnal 37 ~rom the encoder-sensor, Accordlngly, 29 the pulse extenslon becomes an lncreaslngly slgnl~lcant por-tlon of the drlve pul~e 20, For example, at slew speed, the Von Braun 2 pulse 20 may be approxlmately 700 mlcroseconds (approxlmately 2 2 ~ o~ the pulse wldth durlng acceleration) 90 that the rlxed 3 pulse extenslon o~ 300 microseconds 18 approximately 43% of 4 the total pulse wldth, Thls o~ course malntalns the motor output torque at levels much higher than for the slngle 6 phase excltatlon as shown in FIG. 8A. In ~act the torque 7 produced at hlgh ~peeds rapidly approaches that of the 8 dual phase excitatlon and accordlngly the re~ultant slew 9 speed also approaches that produced by dual phase excltatlon.
The pulse extension, and ln partlcular, the ~lxed 11 duratlon pulse extenslon provldes increased slew speed ln a 12 closed loop system wlthout signl~icantly lncreaslng the 13 power supply requlrements (maximum power levels 51, ~2, 14 and 53) as shown ln FIG. 8, At low speeds when maxlmum 1~ torque i8 available (due to the large drlve pulse wldth) 16 and requlred to accelerate the load, maxlmum power 19 con-17 sumed. ~owever, lncreaslngly less torque ls required as 18 the load accelerate9, and as the step (clock) frequency 19 lncreases, a hlgher slew speed is attalned as a result o~ the higher torque produced (due to the contlnually lncreas-21 lng percentage o~ extended pulse tlme). Advantageously thls 22 lncreaslng overlap occurs when excess power 19 available 23 from the power supply.
24 The extension may not be Or a fixed duratlon 2~ in some appllcatlons, In ~act, ln some complex closed 26 loop systems, there may be no extenslon at the motor start 27 up, but a~ the system ~peeds up, larger and }arger pulse 28 extenslons may be provided, 29 Open loop sy~tems do not use automatlc ad~ustment of the step ~requency as described above, The clock fre-31 quency ls ~ixed, and the applicatlon of the extended slngle 1074393 Von ~raun 2 1 phase excltatlon to such systems 19 there~ore somewhat 2 dirferent, Nevertheless, the incorporatlon of pulse exten-3 slon provldes more torque (and hence extends the operatlng 4 range) than 1B avallable rrom slngle phase excltation and may replace the need for ramplng or, lf used wlth ramplng, 6 rurther lncreases the operating range. Herelnafter the 7 ef~ect~ Or ramping will be ignored since the operatlon 8 and advantages o~ extended single phase excltatlon are 9 appllcable equally to systems operatlng wlth and without ramplng.
11 FIGS. 9A and 9B lllustrate the advantages o~
12 extended slngle phase excitation ln an open loop system 13 The extension (X in ~IG. 4) i9 rirst assumed to be o~ a 14 ~lxed duratlon. The step frequency (rate of pulses 17) is con~tant, and as can be seen ln ~IG. 9A a~ter lncreas- !
16 lng durlng the translent start-up Or the motor, the torque 17 for slngle, dual and extended single pha3e excitations 10, 18 20, and E~, respectlvely, stablllze at constant levels, 19 Slmllarly, the speed increases and a~ter mlnor o~cillatlon, stablllzes at a constant slew speed, As can be seen ln 21 FIG. 9B, the slgnlrlcantly lncreased torque and spe~d, 22 shown in FIG, 9A to be provlded by extended phase excita-23 tlon, does not require slgnl~lcantly larger power supply 24 capaclty, The maximum power requirement 55 for extended phase operatlon 19 only sllghtly hlgher than that requlred (54) 26 ror ~lngle phase excitatlon but always conslderably lower than 27 the requirement 56 ~or dual phase excltation, which 1B twlce 28 that Or the slngle phase excltatlon.
29 A ~urther lmprovement can be achieved by varylng the pulse e~tenslon on a tlme dependent basls. Thls tech-31 nique enables the motor to be best matched wlth the dynamlc 32 load characterlstics. Prererably long pulse extension Von Braun 2 C 1 should be provlded durlng startlng and stopping when load 2 requlrements are greatest and ~mall extenslon (or none at 3 all) during constant speed operatlon, The effect 18 to 4 slgnl~lcantly reduce the power consumptlon durlng constant speed operatlon, The power spectrum for an extended single 6 phase operation w~th optlmized varlatlon o~ the extension 7 19 deslgnated (E0)' ln FIG, 9B. Sometlmes pulse extension 8 13 completely ellmlnated durlng constant speed operatlon 9 to rurther reduce power consumptlon; however, thls 19 not always deslrable slnce lt does allow higher step rates to 11 be achleved. In any event the requlred tlme-dependent 12 varlatlon of the extension can be accomplished by approprl-13 ately altering the characterlstlcs of pulse ex~ender 32 14 (such as by varylng the tlme constant of the RC network 45 ln ~IG, 5), 16 In all cases it is to be under~tood that the 17 above descrlbed arrangements are merely lllustratlve of 18 a small number o~ the many posslble appllcatlons o~ the 19 prlnclples o~ the present inventlon, Numerous and varled other arrangements ln accordance wlth these principles 21 may readlly be devlsed by those skllled in the art wlth-22 out departlng from the splrlt and scope of the inventlon,

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for operating a stepping motor having a plurality of individually energizable phases comprising the steps of:
sequentially energizing each of a plurality of phases for distinctive intervals of time;
the energization interval of each one of the phases overlapping in time with the energization interval of the phase first subsequent thereto for a selected overlap period, the selected overlap period being such that the energization interval of the one phase terminates a selected time prior to the energization of the next subsequent one of the plurality of phases; and wherein the selected overlap period for a given phase is variable in duration and the energization interval for that phase is of a fixed duration.

2. A multiphase stepping motor having a plurality of individually energizable phases comprising:
means for selectively energizing each of the phases in response to a drive pulse, each drive pulse having three successive portions;
said energizing means including timing means for establishing the delineation between the three portions of each drive pulse so that during a first portion of each drive pulse one other drive pulse for one other phase exists simultaneously, during the second portion of each drive pulse drive pulses for none of the other phases exist, and during the third portion of each drive pulse a second other drive pulse for a second other phase exists simultaneously; and wherein the timing means provides a series of drive pulses for each phase and the third portions of all pulses in each series is of a variable duration and the total duration of each pulse of each series is fixed.