as) United States
`a2) Patent Application Publication 1) Pub. No.: US 2011/0133682 Al
`
` Eggeret al. (43) Pub. Date: Jun. 9, 2011
`
`
`US 20110133682A1
`
`(54) METHOD AND DEVICE FOR DETECTING
`STEP LOSSES OF A STEP MOTOR
`
`(76)
`
`Inventors:
`
`Heinz Egger, Grambach (AT);
`Bernhard Heinz, Proleb (AT);
`Jurgen Schuhmacher,
`Linsengericht (DE)
`
`(21) Appl. No.:
`
`12/745,606
`
`(22) PCT Filed:
`
`Dec. 3, 2008
`
`(86) PCT No.:
`
`PCT/EP08/10212
`
`§ 371 (c)(),
`(2), (4) Date:
`
`Feb. 23, 2011
`
`(30)
`
`Foreign Application Priority Data
`
`Dec. 3, 2007
`
`(EP) cesecececsesssssesestesesesnenenes 07023353.1
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`GOSB 19/40
`(52) US. C0. veececescscccsssssssesesssssssssseessessessssssssneeesss 318/685
`(57)
`ABSTRACT
`Foractivating a stepper motor, a pulse-width modulated cur-
`rent is supplied to a coil of the stepper motorandit is deter-
`mined whetherthe current flowing throughthe stepper motor,
`based on a default value, lies within a current bandwidth
`defined by an upper switching threshold and a lower switch-
`ing threshold. The current supply to the coil is switched on
`when the detected current has droppedto the lower threshold
`and is switched offwhen the detected currenthas risen to the
`upperthreshold. In order to detect a step loss, the signal form
`of the current or its change, respectively, is analyzed and
`deviations from desired values or desired value ranges,
`respectively, which have been caused by step losses, are
`detected. The determination of the signal form of the current
`or its change, respectively, may occur indirectly by analyzing
`a corresponding control signal.
`
` 1
`
`APPLE 1040
`
`1
`
`APPLE 1040
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 1 of 13
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`US 2011/0133682 Al
`
`Stator
`
`p
`
`Stator
`
`®
`
`Rotor
`
`Rotor
`
`Fig. 1
`
`Rw
`
`Lw
`
`u|
`
`Im
`
`|Um
`
`Fig. 2
`
`
`
`2
`
`

`

`Patent Application Publication
`
`Jun. 9, 2011 Sheet 2 of 13
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`US 2011/0133682 Al
`
`In
`
`S1
`
`$3 a
`
`Fig. 3
`
`3
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 3 of 13
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`US 2011/0133682 Al
`
`15 V /-
`
` 10V
`
`
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`
` -5V = fe ett
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`
`25ys
`
`30us
`
`35us
`
`40us 45ys 50us
`
`Fig. 6
`
`4
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 4 of 13
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`US 2011/0133682 Al
`
`600 mA
`
`
`
`
`
`1.8ms 2.0ms
`
`
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`Fig. 8
`
`5
`
`

`

`Patent Application Publication
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`Jun. 9,2011 Sheet 5 of 13
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`US 2011/0133682 Al
`
` 1.2
`1.0
`
`0.8
`
`0.6
`
` 0.4
`
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`
`fpr
`
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`
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` 1.0432
`
` 1.025
`
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`
`:
`
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`
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`
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`
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`
`1.01ms
`
`1.02ms
`
`1.03ms
`
`1.04
`
`Fig. 10
`
`6
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 6 of 13
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`US 2011/0133682 Al
`
`400 mV
`
`300 mV
`
`200 mV
`
`
`
`
`
`-200 mV
`
`-100 mV
`
`10us
`
`20us 30ys 40us
`
`50yus
`
`G6GOus 7Ous 80us 90s 100Us
`
`Fig. 11
`
` i it AE
`
`
` OV
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`
`
`
`
`150 us 200us 250us 300s 350s 400s 450 ys 500s 550 ys
`
`Fig. 12
`
`7
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 7 of 13
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`US 2011/0133682 Al
`
`15V
`
`10V
`
`BV
`
`OV
`
`-5V
`
`$7
`
`10s 154s 20us
`
`25u8
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`Fig. 13
`
`45118
`
`50,8
`
`
`
`1600|[ms] 500 stepsisek
`
`1500
`
`1400
`
`1300
`
`1200
`
`
`1|677|1353|2029|2705|3381|4057|4733|5409|6085|6761|7437|8113
`3391015
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`3043-3719 4395
`«5071
`S747
`«6423
`«70997775
`
`Sample
`
`Fig. 14
`
`8
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 8 of 13
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`US 2011/0133682 Al
`
`2700
`
`2500
`
`2300
`
`2100
`
`1900
`
`1700
`
`150
`1300
`
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`Fig. 15
`Samples
`
`10000|[ms]
`9000
`
`8000
`
`7000
`
`6000
`
`5000
`
`4000
`
`3000
`
`2000
`
`Steps/Sek
`1000
`
`00
`1500
`2900
`3500
`4500
`5900
`6500
`7500
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`
`
`1000
`
`2000
`
`3000
`
`4000
`
`5000
`
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`
`000
`
`7000
`
`Fig. 16
`
`9
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 9 of 13
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`US 2011/0133682 Al
`
`[ms]
`
`2500
`
`2000
`
`1500
`
`1000
`
`500
`
`tmax (500mA)
`
`tmax (125mA)
`
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`
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`
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`
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`
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`
`Fig. 17
`
`10
`
`10
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`

`

`Patent Application Publication
`
`Jun. 9, 2011 Sheet 10 of 13
`
`US 2011/0133682 Al
`
`In
`
`$1
`
`$3 x
`
`11
`
`11
`
`

`

`Patent Application Publication
`
`Jun. 9, 2011 Sheet 11 of 13
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`US 2011/0133682 Al
`
`
`
`
`
`Oms
`
`20 ms
`
`40 ms
`
`60 ms
`
`80 ms
`
`100 ms
`
`120 ms
`
`Fig. 19
`
`12
`
`12
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 12 of 13
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`US 2011/0133682 Al
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`
`
`13
`
`13
`
`

`

`Patent Application Publication
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`Jun. 9, 2011 Sheet 13 of 13
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`US 2011/0133682 Al
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`
`
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`14
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`

`

`US 2011/0133682 Al
`
`Jun. 9, 2011
`
`METHOD AND DEVICE FOR DETECTING
`STEP LOSSES OF A STEP MOTOR
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`[0001] This patent application is a U.S. national counter-
`part of international application serial no. PCT/EP2008/
`010212 filed on Dec. 3, 2008, which claimspriority to Euro-
`pean Patent Application No. 07023353.1 filed on Dec. 3,
`2007, each of which is hereby incorporated herein by refer-
`ence.
`
`BACKGROUNDOF THE INVENTION
`
`[0002] The stepper motor is a special design of synchro-
`nous machines and is composedofa fixed stator designed
`with several coils and a rotor rotating therein. Depending on
`the mode of construction of the rotor, three basic types of
`stepper motors are differentiated:
`[0003]
`the stepper motor excited by meansof a perma-
`nent magnet,
`[0004]
`the stepper motor with variable reluctance and
`[0005]
`the hybrid stepper motor.
`[0006]
`In the stepper motor excited by means of a perma-
`nent magnet, the rotor consists of a cylindrical permanent
`magnetwith radial magnetization. This means that permanent
`magnetsofdifferent polarities alternate with each other along
`the rotor circumference. The rotor always aligns itself with
`the magnetic field generated by the energization ofthe coils.
`Ifthe coils are switched on one after the other, the rotor turns
`into the corresponding direction. Accordingly, the stepper
`motor performsa revolution if all coils are switched on and
`off one after the other.
`
`In the stepper motor with variable reluctance, the
`[0007]
`rotor consists of a de-energized toothed soft-iron core. With
`this design, the momentarises due to the rotor construction
`which provides a variable magnetic air-gap resistance. The
`rotor follows the stepper field, since it seeks to align itself in
`the stator field such that the magnetic energy in the air gap
`becomes minimal.
`
`[0008] The hybrid stepper motor is a hybrid between a
`stepper motor excited by means of a permanent magnetand a
`variable reluctance stepper motor. It consists of an axially
`polarized permanent magnet at the ends of which toothed
`rotor discs made of a soft-magnetic materialare attached. The
`tworotor discs are biased by the permanent magnet andare
`offset relative to each other by half a tooth width so that the
`north and south poles will alternate. Very small stepping
`angles are possible with the hybrid stepper motor,and it has a
`self-retaining moment. However,
`this is a complicated
`design.
`Stepper motors function according to the synchro-
`[0009]
`nousprinciple. The torque driving the rotor results from dif-
`ferently aligned magneticfields in the stator and the rotor. The
`rotor always rotates such that the largest possible magnetic
`flux will form.
`
`In contrast to other motors, the stepper motor has
`[0010]
`coils only located in the stator. Hence, the rotating motion is
`producedbyselectively activating the individual coil wind-
`ings, which causesthe stator field to be relayed by a particular
`angle after each step pulse. Relaying the stepperfield is also
`referred to as a commutation process.
`[0011]
`In this way, the sense of rotation and the rotational
`speed of the motor can be controlled most easily. In order to
`
`determine the position of the rotor, it suffices to count the
`steps in a clockwise andin an anticlockwise direction, respec-
`tively, starting from an initial position, and to multiply them
`by the stepping angle.
`[0012] As regards the activation of the motor winding, a
`unipolar and a bipolar activation can be distinguished.
`[0013] With a unipolar activation, each pole has two wind-
`ings or one winding with a centre tapping, respectively. The
`direction of the magnetic field depends on which oneofthe
`two windings is energized. The advantageofthis activation is
`the small electronic expenditure. The disadvantage is a poor
`utilization of the winding space of 50%, since always only
`one winding is used, depending on the current direction.
`Besides, the use oftwo coils per pole results in a larger motor.
`[0014] With a bipolar activation, each pole has only one
`winding. The direction of the magnetic field depends on the
`direction in which the current flows through said one wind-
`ing. This type of activation has the advantage that the entire
`winding spaceis utilized. A disadvantageis the higher elec-
`tronic expenditure.
`[0015]
`Stepper motors can be operated in several ways. The
`most simple mode of operation is the WaveDrive in which
`always only one coil is energized progressively around the
`circumference. The advantage of this mode of operation is
`that it is easy to implement and can berealized easily also
`with very inexpensive microcontrollers. A disadvantage,
`however,is the lower torque, since as always only onecoil is
`energized,it decreases by a factorof 1/V2,i.e., to about 70%
`of the theoretical maximum.
`
`In contrast, in the full-step mode, all winding sys-
`[0016]
`temsare always energized. The rotating motionis achieved by
`selectively changing the current direction in the windings. As
`a result of the fact that all winding systems are always ener-
`gized, the highest possible torque is obtained in this mode of
`operation. The relatively large steps are disadvantageous,
`whereby the motor tends to perform resonancevibrations.
`[0017]
`In the half-step mode, the WaveDrive and the full-
`step mode are combined with each other. In a stepper motor
`comprising two coils, one or both coils is/are thus always
`energized alternately. Thereby, more angular positions can be
`approached. Theresult is indeed a highercircuit complexity,
`but also a higher positioning accuracy. However, the motor
`always“jumps”backto one ofthe full-step positions, as soon
`as the current is switched off. The major advantage of the
`half-step mode is that the motor vibrates significantly less,
`since the rotor is exposed to a smaller numberof impulses. In
`comparison, in the full-step mode and in the WaveDrive, the
`rotor is always pulled from oneposition into the next one and
`vibrates there aroundthefinal position. These vibrations also
`produce vibrations of the casing and the form of torque is
`jerky. The total system is thus relatively noisy. Due to the
`larger numberofpositions in the half-step mode,the stepping
`angles are smaller and, hence, the vibrations decrease. It is
`generally true that, the smaller the steps become, the more
`uniform is the force path and the moresilentis also thetotal
`system. Moreover,a step loss will be less probable, since the
`rotor vibrations decrease.
`
`Ifthe concept of reducing the stepping angles by
`[0018]
`increasing the partial steps is developed further and further,
`the conclusion can be drawnthat a sinusoidal or cosinusoidal
`
`activation, respectively, is the optimum.Inthis case, the force
`path would be uniform,and only the fundamental component
`of the frequency at which the motor is activated would be
`audible. The microstep operation implements precisely that.
`
`15
`
`15
`
`

`

`US 2011/0133682 Al
`
`Jun. 9, 2011
`
`In practice, however, the activation is not effected with a
`precisely sinusoidal signal, but pulse-width modulated
`square wave currents having a switching frequency above the
`threshold of audibility are utilized.In doing so, the motorcoil
`itself serves asa filter and smoothes the square wavesignal to
`such an extent that a roughly sinusoidal or cosinusoidal cur-
`rent, respectively, will flow through the windings.
`[0019] As already mentioned, stepper motors are used
`mainly for positioning tasks. The advantage ofthese motorsis
`that the position of the motor can be determined easily by
`taking into account the steps which correspondto a predeter-
`mined quantized motion. Nevertheless, stepper motors are
`used only rarely without a positioning sensor system. The
`reason for this is the possible occurrence of step losses.
`[0020]
`Step losses occur if the rotor can no longer follow
`the rotating magnetic field ofthe stator—the motorstalls. The
`cause ofthis is, in most cases, a load which is too high or a
`mechanical blockade.
`
`For detecting these undesirable step losses and, sub-
`[0021]
`sequently, correcting the positioning error resulting there-
`from, there are basically two possibilities:
`[0022] with the aid of sensors(e.g., measuring the rota-
`tional speed)
`[0023] without additional sensorsacross the electromag-
`netic field of the motor.
`
`generated in the stepper motoris proportionalto the rotational
`speed. The described lagging of the rotorrelative to the mag-
`netic field of the stator under a load results in an enlargement
`of the air gap betweenthe stator andthe rotor through which
`the magnetic flux ® passes, this air-gap enlargementin turn
`leads to a reduction in the inductance L,,.
`[0027] The firm Trinamic Microchips has brought a driver
`for stepper motors to the market under the name of TMC246/
`249, which driveris able to detect a step loss via the generator
`voltage of the stepper motor. However, said driver is usable
`only to a limited extent, since the principle of measurement
`fails in case of small motors androtational speeds because the
`generator voltage is too small for being able to make reliable
`statements aboutthe state of the load.
`
`[0028] The inductance must be measured for an ascertain-
`mentofstep losses based on the load-dependent motorinduc-
`tance. Two methods are available for measuring the motor
`inductance:
`
`via the amplitude of the winding current, and
`[0029]
`via the phase shift between voltage and winding
`[0030]
`current.
`
`In Helmut Oswald, “FPGA Schrittmotorsteuerung
`[0031]
`mit Lastmessung/Schrittverlusterkennung tiber das elektro-
`magnetische Feld des Motors”, Thesis at the Fachhochschule
`Technikum Wien, 2006, the possibilities of an inductance
`measurement have been examined and, based on these find-
`[0024] The use of sensors for the detection of step losses is
`ings, a stepper motor control has been established. The mea-
`well-tried, but expensive, for which reason possibilities of
`suring method proposedin this documentis based on thefact
`avoiding them are being searchedfor.
`that the phase displacement between current and voltage is
`[0025]
`Inthe sensorless step loss detection, the motoritself
`measured andthe inductanceis inferred therefrom. The prob-
`serves as a sensor. This is made possible by particular char-
`lem of this measuring methodis, however, that the effects of
`acteristics of a stepper motor which involvethatthe electro-
`the variations in inductance become very small belowapar-
`magnetic field ofthe motor will change duc to the load put on
`ticular frequency. Therefore, also this measuring methodis
`the motor. In particular, the stepper motor has the character-
`usable only to a limited extent.
`istic that the rotational speed will remain constant underload,
`[0032] Hence, there is still a requirement for an activation
`but a phase shift between the rotor and the rotary field will
`of stepper motors which,at the same time, enables the detec-
`occur. Analogously to the synchronous machine, this phase
`tion of step losses. In particular, such an activation and step
`shift angle is referred to as a rotor displacement angle. The
`loss detection device should have a small installation space,
`lagging of the rotor relative to the stator under a load is
`enable the detection of step losses without external sensors
`explained in FIG.1. In the left-hand image of FIG.1, the rotor
`and thus in a cost-efficient manner, offer high detection pre-
`runsat idle, the rotor displacement angle is zero. If more load
`cision across a large load and rotational speed range (also
`is now putontherotor, it starts to lag after the stator field B,
`with small overall sizes) as well as ensure an operation of the
`which is shown in the right-hand image. Starting from a
`stepper motor which is as smooth and vibration-free as pos-
`particular motor-dependent
`load,
`the rotor displacement
`sible.
`angle will become too large and the magnetic field of the
`following stator coil will be closer to the rotor than the mag-
`netic field whichit currently follows. The rotor will then end
`up in the following magnetic field. This is referredto as a step
`loss. If the load becomestoo large, the rotor will be unable to
`follow any magnetic field, but will only vibrate. In this case,
`the motor continuously loses steps. Precisely this phenom-
`enonalso occurs if the motoris started at a frequency which
`is too high. Dueto the rotor’s momentofinertia, it is unable
`to immediately follow a quickly rotating magnetic field.
`Thus, in order to be able to operate the motor at higher
`frequencies, the motorhasto be started more slowly and then
`has to be accelerated by means of a frequency ramp. The
`frequency at which the motor can just barely be startedis, at
`the sametime, also the one at which the motor comesto a stop
`within onestep, if the current is switchedoff. It is referred to
`as the start/stop frequency.
`[0026] As can be seen in the electrical equivalent circuit
`diagram of the stepper motor according to FIG.2, the motor
`winding consists of an inductive component (L,,) and an
`ohmic resistance component(R,,). The generator voltage U,,
`
`SUMMARYOF THE INVENTION
`
`It is against the above backgroundthat the present
`[0033]
`invention provides
`certain unobvious advantages
`and
`advancements overthepriorart. In particular, the inventor has
`recognized a need for improvements in a process and device
`for detecting step losses of as stepper motor.
`[0034] Although the present inventionis not limited to spe-
`cific advantages or functionality, it is noted that the present
`invention can provide a stepper motorthat is activated here by
`supplying a pulse-width modulated voltage (PWM)to a coil
`of the stepper motor while detecting the current flowing
`through the coil. By way of comparison, it is determined
`whether the detected current, based on a default value, lies
`within a current bandwidth defined by an upper switching
`threshold and a lower switching threshold, wherein the cur-
`rent supply to the coil is switched on when the detected
`current has dropped to the lower threshold and the current
`supply to the coil is switched off when the detected current
`hasrisen to the upper threshold. By meansofthe invention,a
`
`16
`
`16
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`

`

`US 2011/0133682 Al
`
`Jun. 9, 2011
`
`“current band guide” is thus realized in which the current
`through the coil can deviate from a default value, which
`preferably is roughly sinusoidal, only within a certain “cur-
`rent bandwidth”.
`
`For a certain current-dependency of the measure-
`[0041]
`mentto be reduced from the result,it is preferred that at least
`twoperiod durations aroundthe zero point of the current are
`measured.
`
`For a precise and easily adjustable control of the
`[0035]
`progression ofthe default value, the use of a digital-to-analog
`converter is suggested which hasthe valuesallocated to it on
`its digital input by a controller, e.g., an FPGA.
`[0036] Due to the improved processability of the signals,it
`is envisaged that the detected current is converted into a
`proportional voltage signal for further processing, which
`voltage signal
`is optionally cleared from high-frequency
`interferences in a low-pass filter.
`[0037]
`In a preferred embodiment of the invention, the
`detected current or the voltage signal proportional to the
`detected current, respectively, is subtracted from the default
`value and optionally amplified prior to a comparison with the
`upper switching threshold and the lower switching threshold.
`The implementation of this function is effected, for example,
`using a differential amplifier.
`[0038] The resulting differential signal has a signal form
`which, reduced by the default value, is proportional to the
`detected current. Preferably, the differential signal is com-
`pared to the upper switching threshold and to the lower
`switching threshold in a Schmitt trigger, preferably a preci-
`sion Schmitt trigger, with the hysteresis ofthe Schmitt trigger
`being representative ofboth switching thresholds. The result-
`ing control signal of the Schmitt trigger activates a driver for
`generating the PWMvoltage for supplying the coil.
`[0039]
`Inone embodimentofthe stepper motor control, the
`sensorless step loss detection 1s effected by measuringtherise
`time of the current from the lower switching threshold to the
`upper switching thresholdorthefall time of the current from
`the upper switching threshold to the lower switching thresh-
`old or the period duration composedofrise time and fall time
`or a multiple thereof, respectively, and comparing it to an
`upper step loss threshold, with a step loss being detected if
`said threshold is exceeded.
`
`[0040] This embodimentfor the detection of step losses is
`based on the fact that the inductance L,, of the stepper motor
`is dependenton thesize of the air gap in the magnetic circuit
`and hence on the load moment, whereas, in the electrical
`equivalent circuit diagram of the stepper motor (see FIG.2),
`the ohmicresistance R,,, the supply voltage U and the current
`I,,can be assumedto be constant and the generator voltage
`U,,1is indeed dependentonthe rotational speed, but not on the
`load, and is thus irrelevant for the proposed measurement.
`Accordingto the invention, the stepper motor is operated in a
`so-called “current band guide”the hysteresis,i.e., bandwidth,
`of which is preset. In other words, the stepper motoris acti-
`vated accordingto the invention such thatthe current through
`the motor coil is kept between a lower and an upper switching
`threshold, which switching thresholds define the maximum
`deviations from a reference current path. The reference cur-
`rent path is preferably sinusoidal(in a stepped form). Therise
`time of the current from the lower to the upper switching
`threshold as well as the fall time ofthe current from the upper
`to the lower switching threshold are proportionalto the induc-
`tance L,,. Thus, the inductance measurement can betrans-
`formed into a time measurement which, with regard to cir-
`cuitry, is feasible very well, e.g., with an FPGA.
`
`Ifthe stepper motor is operated aboveits start/stop
`[0042]
`frequency, it happensin case of step losses that the motor will
`no longerbe ableto start, but will only vibrate, which mani-
`fests itself in a reduced period duration ofthe current. There-
`fore, incase ofhigh rotational speeds, it is suitable to measure
`the rise time or the fall time or the period duration of the
`current or a multiple thereof, respectively, and to compareit to
`a lower step loss threshold (tmin), with a step loss being
`detected if said thresholdis fallen short of.
`
`[0043] The upper step loss threshold (imax) and/or the
`lower step loss threshold (tmin) depend on the motor speed,
`the motor type and the ratio between the nominal current and
`the actually supplied current strength. It is therefore envis-
`aged to consider these parameters for the selection of the
`respective step loss thresholds, wherein the appropriate val-
`ues are stored in multidimensional lookuptables ina memory
`or are calculated by a controller, e.g., an FPGA, as functions
`or as functions which have been piecewise assembled.
`[0044]
`In an alternative embodimentof the invention, the
`step loss detection is effected by sampling the control signal
`at a predetermined clock frequencyandfiltering the sampled
`values. The filtered signal is then stored after each microstep.
`From two sections each ofthe filtered signal, a differential
`signal is calculated and compared to a step loss threshold,
`with a step loss being detected if said threshold is reached.
`This embodimentprovides the advantagethat the inclusion of
`two-dimensional motor data is not required.
`[0045] A differential signal formation which makes small
`demandson the computing poweris realized, for example, by
`calculating the differential signal in each case via a summa-
`tion of the first half-wave and the second half-wave of the
`sameperiod ofthefiltered signal S8.
`[0046] A significantly smoother differential signal can be
`obtained if the difference formation meanscalculate the dif-
`
`ferential signal on the basis of a subtraction ofthe full wave of
`one period from the full-waveof the preceding period of the
`filtered signal.
`[0047]
`Ina further alternative embodimentofthe invention,
`the step loss detection is effected by guiding the control signal
`through a first low-pass filter and, optionally, smoothing it
`further in a second low-pass filter and, subsequently, supply-
`ing the filtered and smoothed signal to arithmetic means in
`which it is subjected to a curve discussion calculation, in
`particular a gradient analysis, from which it is detectable
`whether a step loss has occurred. This embodiment of the
`invention enables an extensive evaluation of signal forms of
`the filtered signal, whereby borderline cases ofthe occurrence
`of step losses can also most likely be detected correctly.
`[0048] These and other features and advantages of the
`present invention will be more fully understood from the
`following detailed description of the invention taken together
`with the accompanyingclaims. It is noted that the scope ofthe
`claims is defined by the recitations therein and not by the
`specific discussion of features and advantagesset forth in the
`present description.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0049] The following detailed description of embodiments
`of the present invention can be best understood whenread in
`
`17
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`US 2011/0133682 Al
`
`Jun. 9, 2011
`
`conjunction with the following drawings, where like structure
`is indicated with like reference numerals and in which:
`
`the dimensions of someof the elements in the figures may be
`exaggerated relative to other elements to help improve under-
`standing of the embodiment(s) of the present invention.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`FIG. 1 showstheprinciple of rotor lagging relative
`[0050]
`to the stator field undera load;
`[0051]
`FIG. 2 shows an electrical equivalent circuit dia-
`gram of a motorcoil;
`In order that the invention may be morereadily
`[0073]
`[0052]
`FIG. 3 showsa block diagram of a stepper motor
`understood, reference is made to the following examples,
`loss detection circuit according to the invention;
`whichare intendedto illustrate the invention, but not limit the
`
`[0053] FIG. 4 showsacircuit diagram of a motorcoil driver
`scopethereof.
`according to the stepper motoractivation of the invention;
`[0074]
`It is noted that terms like “preferably” and “typi-
`[0054]
`FIG. 5 shows a time-dependency diagram of the
`cally”are not utilized herein to limit the scope of the claimed
`control signals for the motor coil driver as well as of the
`invention or to imply that certain featuresare critical, essen-
`current band guide according to the invention;
`tial, or even important to the structure or function of the
`[0055]
`FIG. 6 shows a time-dependency diagram of a sec-
`claimed invention. Rather, these terms are merely intended to
`tion ofthe pulse-width modulated output current signal of the
`highlight alternative or additional features that may or may
`motorcoil driver;
`not be utilized in a particular embodiment of the present
`[0056]
`FIG. 7 shows the current path through the motor
`invention.
`coil;
`[0075]
`For the purposes of describing and defining the
`[0057] FIG.8 showsthe current path through the motorcoil
`present invention it is noted that the term “substantially”is
`in an enlarged illustration, depicted as a signal converted into
`utilized herein to represent the inherent degree of uncertainty
`a voltage signal;
`that may be attributed to any quantitative comparison, value,
`[0058] FIG.9 showsthe voltage signal correspondingto the
`measurement, or other representation. The term “substan-
`current path through the motor coil and a reference voltage
`tially”is also utilized herein to represent the degree by which
`whichis sinusoidal in a stepped form, which are applied as an
`a quantitative representation may vary from a stated reference
`actual value and as a desired value, respectively, for differ-
`without resulting in a change in the basic function of the
`ence formation to the inputs of a differential amplifier of the
`subject matter al issue.
`stepper motor activation according to the invention;
`[0076] Based on the block diagram of FIG. 3, a detailed
`[0059]
`FIG. 10 showsan enlargedillustration ofa detail of
`description of a motor control 1 according to the invention
`the signals of FIG.9;
`comprising a step loss detection for a stepper motor, in par-
`[0060]
`FIG. 11 showsthe output differential signal of the
`ticular for a hybrid stepper motor, now follows. Fortheillus-
`differential amplifier;
`tration of said exemplary embodiment, it is assumedthat the
`[0061]
`FIG. 12 showsthe input signal and a reference volt-
`motorcontrol is designed for a two-phase motor, wherein two
`age signal on the precision Schmitt trigger according to the
`coils 3 offset relative to each other by 90° are arrangedin the
`stepper motoractivation of the invention;
`stator, with each coil comprising twopartial windings located
`[0062]
`FIG. 13 showsthe control signal of the precision
`opposite to each other with respect to the rotor. In FIG. 3, a
`Schmitt trigger, which is a PWMsignal;
`motorcoil 3 with its electrical equivalent circuit diagram R,
`[0063]
`FIG. 14 showsa diagram ofthe period duration of a
`and L,,-1s illustrated. It must be emphasized that the invention
`plurality of measured values of the PWM signal as a function
`is suitable for stepper motors with any numberof phases.
`of the motor load at a motor speed of 500 steps/sec;
`[0077] Themotorcontrol 1 implements a so-called “current
`[0064]
`FIG. 15 showsa further diagram ofthe period dura-
`band guide” in which the current I,, through the respective
`tion of a plurality of measured values of the PWM signalas a
`motorcoil L,is kept within a lower switching threshold UG
`function of the motor load at a motor speed of 3000 steps/sec;
`and an upper switching threshold OG,as is evident from the
`[0065]
`FIG. 16 shows a diagram of the average period
`upperline ofthe signal/time diagram of FIG. 5. The activation
`duration ofthe PWMsignal as well as ofupper and lowerstep
`is effected by a pulse width modulated electrical signal S1
`loss thresholds as a function of the motor speed;
`(see FIG.6), the current of the signal S1 is smoothed by the
`[0066]
`FIG. 17 shows a diagram of the upper step loss
`inductance L,, of the motor coil 3 so that it exhibits an
`threshold of the period duration of the PWMsignal depend-
`approximated sinusoidal form, as will be explained in further
`ing on the current through the motorcoil;
`detail below. Per phase (coil 3) of the stepper motor, one
`[0067]
`FIG. 18 shows a block diagram ofa further embodi-
`motor control 1 each is required, i.e., two in the present
`mentof a stepper motor loss detection circuit accordingto the
`example of a two-phase motor, wherein the drive currents are
`invention;
`offset relative to each other by a phase of 90° (generally 180°
`[0068]
`FIG. 19 shows a signal diagram of the essential
`divided by the numberofphases), i.e., in case of a two-phase
`signals of the embodimentof the invention according to FIG.
`motor, one motorcoilis activated with sinusoidal current and
`the other one with cosinusoidal current.
`18;
`FIG. 20 showsa block diagram of a third embodi-
`[0069]
`mentof a stepper motor loss detection circuit accordingto the
`invention;
`[0070]
`FIG. 21 shows a signal diagram which schemati-
`cally illustrates the gradient analysis according to the
`embodimentofthe invention of FIG. 20; and
`[0071]
`FIG. 22 shows an enlarged section of the signal
`diagram of FIG. 21.
`[0072]
`Skilled artisans appreciate that elements in the fig-
`ures have not necessarily been drawnto scale. For example,
`
`In order to minimize losses, each of the motorcoils
`[0078]
`3 is activated via one driver 2 each of which comprises an
`H-bridge (illustrated in the circuit diagram of FIG. 4) by
`meansof a so-called “Locked-Antiphase-PWM”in such a
`way(see signal S1, illustrated in FIG. 6) that a sinusoidal or
`cosinusoidal current, respectively, will flow through the two
`motorcoils 3. The driver 2 receives a PWM signal S7, which
`will be explained in furtherdetail, on its input. Furthermore,
`the driver 2 comprises an H-bridge consisting of two half
`bridges which, in each case, are composed of two NMOS
`
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`US 2011/01336