EP1048774A2 - Method and device for detecting unbalance in a rotor driven by a brushless electric motor - Google Patents

Abstract

A measuring device registers the rotation speeed (n) and the imbalance of the rotor. When a minimum speed of the rotor is exceeded, an electrical parameter of the motor is adjusted. The electrical parameter is preferably the voltage (U) and is altered from its extent set for operation to an extent provid for a measurement in such a way that the slope of the characteristic curve of speed-torsion increases accordingly.

Description

The invention relates to a method for detecting unbalance in a by a brushless electric motor driven rotor, especially one Washing drum in a washing machine, with a measuring device the speed and the unbalance of the rotor is determined by position and size.

The invention also relates to a device for detecting unbalance.

EP 0 565 157 A1 describes a method for the detection and compensation of a Unbalance in a rotor driven by a motor is known. The rotor is for example a drum in a washing machine. It is a facility for Measurement of the unbalance according to position and size and control electronics for control of the motor based on the measured values, the torque of the Motor initially constant after accelerating the rotor to a minimum value is held so that there is a change in speed if there is an unbalance, which is evaluated to determine the position and size of the unbalance. Then will based on the determined values when the speed increases, the Attempted imbalance by appropriate control.

The minimum value to which the rotor is initially accelerated is the value at which a rotor's own imbalance is noticeable. For drum washing machines, the The drum is first accelerated to a value of about 70 rpm or 80 rpm. This is the value at which there is laundry in the drum on the inner walls creates so that there is an imbalance due to uneven distribution of the laundry noticeable. The motor drive must be controlled so that a constant drive torque results. By designing one in electronics stored engine state model, control variables are generated which are one of the Speed and independent of the load caused by any imbalance Generate engine torque. Determining the values for the size and location of the Imbalance occurs, for example, in that one of a rotary encoder of the motor delivered pulse chain evaluated by the electronics with the help of a pulse counter is that in the control program for the motor both the respective speed of the motor shaft and the respective location of a fictitious point on the motor shaft is available and that the speed of the rotor and the position and size of a possible unbalance the rotor can be detected. When the shaft rotates, the pulse counter is activated by each Flank raised in the pulse chain. However, it is not disclosed how an exact measurement of the unbalance is made.

An unbalance monitor for an automatic washing machine is known from EP 0 539 617 A1 known, the one by a speed detection device in a control device monitored, speed-controlled and fed from an AC power source Electric motor, especially a series motor, upright. For Imbalance monitoring is an imbalance sensor in the form of a when an is reached impermissible unbalance opening and thus the connection to the control device interrupting microswitch in series with the speed detection device switched. According to EP 0275862A1, imbalance-related fluctuations in the Current consumption of the drum drive motor detected.

The arrangement known from EP 0 071 308 B1 for controlling the drum speed a washing machine uses fluctuations in the control speed due to imbalance the washing drum and thus the drive motor to check for the unbalance conclude. There is a series or universal motor known to the one Tacho generator is connected. When determining the speed as a function of Torque in such a motor results in a hyperbolic drop Characteristic curve that is relatively steep. In principle, this is a relatively large one Fluctuations in the angular velocity can be expected for a defined unbalance. The Fluctuations in angular speed are at a certain average Speed measured and averaged over a period of a few seconds. The so determined Average fluctuations in the angular velocity are shown in a table with as Reference stored imbalance values assigned or calculated. These unbalance values according to the mechanical stability of the washing machine permissible values are evaluated. As a result, appropriate steps are taken Reduction of the unbalance by redistributing the laundry, limitation of the maximum Spin speed or initiated to abort the spin process.

It is the object of the invention, the method mentioned above for the detection of a Improve unbalance in such a way that even with a brushless motor a precise Determination of the unbalance is made possible.

This object is achieved according to claim 1 in that after exceeding a minimum speed of the rotor is an electrical parameter of the electric motor of its dimension intended for operation to a dimension intended for measurement is changed so that the slope of the speed-torque characteristic curve The amount increases, whereby the speed of the rotor is also above during the measurement a predetermined minimum speed, and that then the unbalance after Location and size can be measured.

Advantageous further developments result from the subclaims.

It proves to be particularly advantageous if the motor voltage is the parameter is selected and lowered during the measurement.

In an advantageous development of the method, the motor voltage can be such lower the speed-torque characteristic above the minimum speed is required for the measuring process, the speed-torque characteristic Universal motor, d. H. a serial motor, same performance.

According to the invention, it is possible to use a universal motor in a household appliance, for example in a washing machine, against a brushless motor, in particular an asynchronous motor. Because of the different speed-torque characteristics brushless drive motors can be one Universal motor method used for measuring unbalance does not immediately affect transfer a brushless motor. There are therefore procedural steps required, for example, to adjust the speed-torque characteristic of an asynchronous motor to achieve that of a universal motor. This is the only way to replace it the drive with a speed-controlled universal motor in connection with a Triac or chopper actuator possible using an asynchronous motor, for example is supplied with a supply voltage by an inverter. It is According to the invention not required that the program control on the has to react to measured unbalance values, knowledge of the design of the drum drive, d. H. of the engine used. The unbalance values determined are comparable regardless of the drive system.

According to the invention, the fixed electrical parameters occurring speed-torque characteristic changed so that their position unbalanced and size much easier to grasp.

Fig. 1

ein Prinzip-Schaltbild eines durch einen Umrichter geregelten Asynchronmotors zum Antrieb einer Wäschetrommel und

Fig. 2

ein Drehzahl-Drehmoment-Diagramm des Asynchronmotors gemäß Fig. 1.

The invention will now be explained in more detail in an exemplary embodiment with reference to the drawing. Show it:

Fig. 1

a schematic diagram of a controlled by an inverter asynchronous motor for driving a laundry drum and

Fig. 2

a speed-torque diagram of the asynchronous motor according to FIG. 1.

A laundry drum 1 (FIG. 1) is a rotor which is mounted horizontally for a while. Via a pulley 2 attached to the shaft, it is driven via a V-belt 3 by an asynchronous motor 4, the drive shaft of which also has a pulley over which the V-belt 3 runs. A rotary encoder 6 connected to the motor shaft of the asynchronous motor 4, for example mounted on the motor shaft, preferably generates pulse-shaped signals which are supplied to a motor controller 7 as actual values n _actual .

The motor controller 7 is part of a converter 8. The motor controller 7 is preferably part a microcontroller in which the functions of the motor controller 7, namely the Generation of the generation of the voltage provided with the reference numerals 13 and 14 and the rotating field frequency are integrated. The microcontroller also contains the Summation point 16 and multiplication point 17. On the microcontroller is preferably also the control scheme is stored. The microcontroller contains preferably a memory, for example a ROM. The converter 8 includes one the voltage 9 of an AC voltage-applied filter 10, the Line voltage superimposed harmonics and high-frequency electromagnetic interference filtered out. An intermediate circuit 11 is arranged downstream of the filter 10, in which one is not here Rectifier bridge shown serves to rectify the mains voltage 9, the Rectifier bridge is preferably connected downstream of a smoothing capacitor. The of the DC link 10 generated DC voltage is used on the one hand for Power supply to a multi-phase electronic commutator, d. H. one Inverter 12, three out of phase with each other from the DC voltage AC voltages R, S, T generated for the asynchronous motor 4. The inverter 12 also includes controllable power transistors, not shown, e.g. IGBT's. Inverters of the type described above mainly work with sinus-weighted pulse width modulation according to the so-called Undershoot method, i.e. by means of the higher frequency pulse width modulation frequency becomes a lower AC voltage or 3 phase AC voltage (motor voltage) shown.

The inverter 12 is regulated by the motor controller 7, the regulation of the Speed of the asynchronous motor 4 via the manipulated variables formed in the motor controller 7 for the Motor voltage or the rotating field frequency of the inverter 12 takes place, which in Fig. 1, reference numerals 13 and 14 are assigned for illustration. For Power supply to the motor controller 7 and the inverter 12 is used Power supply 15, which in turn z. B. from the intermediate circuit 11 with DC voltage becomes.

The laundry drum 1 is initially used to initiate the spinning process Distribution ramp accelerated to a speed at which the laundry due to the centrifugal forces rests on the inner surface of the drum 1. The measuring speed is Avoidance of mechanical resonances above 70 rpm, preferably between 80 and 100 rpm of the laundry drum 1. The shape of the distribution ramp is determined by the speed-controlled operation of the asynchronous motor 4 by the inverter 12 certainly. The speed behavior of the asynchronous motor 4 can thereby Inverters 12 can be influenced according to the following method:

A voltage-frequency characteristic for the is in a memory, not shown here Asynchronous motor 4 stored, which is supplied to the inverter 12 as a reference variable is, so that the inverter 12 from it the motor voltage U, consisting of the three partial voltages R, S, T, which are out of phase with one another, and the motor speed wins.

Alternatively, as shown in FIG. 1, the actual speed n _{actual of} the asynchronous motor 4 is compared at a summation point 16 with the target speed n _target . The control difference obtained from this is fed to the motor controller 7, which uses this to obtain signal variables for the voltage control element 13 and the speed control element 14. Instead of the feedback of the actual speed n _{actual of} the asynchronous motor 4 or in addition to this feedback, the motor current or the motor voltage dropping in the motor windings can also be measured and compared with corresponding target values for the current or the voltage and a corresponding control circuit as reference variables be fed. In particular, a slip control, a flow-oriented current control, a control based on the rotating field vector can be provided for the asynchronous motor 4 using mathematical motor models or the like. In all cases, the voltage and the speed or the rotating field frequency for the asynchronous motor 4 are formed as manipulated variables.

The assignment between motor voltage and rotating field frequency is either at Control based on characteristics stored in a memory, or it is determined by a control algorithm such as that shown in FIG. 1 Control loop. Due to the usual design of the engine operation for an optimal Engine utilization and good efficiency with good dynamics at the same time does not meet the requirements for the unbalance detection task. Therefore at Reaching the speed of more than 70 rpm regulating the speed for that Speed actuator 14 or its control turned off, and the fixed value, the Measuring speed corresponds to the speed frequency of the asynchronous motor 4 is maintained.

The value for the motor voltage U is reduced according to the following criterion. In the speed range of the unbalance measurement after the laundry has been applied to the inner surface of the drum 1, the load moment caused by the weight of laundry and water drops to approximately one tenth of the torque required in normal washing operation. Therefore, the electric power supplied to the electric motor and, accordingly, the torque of the motor generated therefrom can be considerably reduced. The following relationship applies to the maximum achievable torque m _k :

In the case of an asynchronous motor, the maximum achievable torque, the so-called overturning moment m _k , depends on the square of the motor voltage U, on the square of the magnetic reversal frequency and on a motor-specific constant c ₁ . The overturning moment m _k occurring in the course of the torque (m) -speed (n) characteristic curve is associated with the overturning slip s _k as the relative difference between the stator and rotor rotational frequency. The tilt slip s _k is a second motor-specific variable. The dependence of the quantities c ₁ and s _k on the magnetic reversal frequency of the winding and stator-rotor iron circuit, the heating of the winding and on non-linearities of the magnetization curve is not taken into account here. In the operating range of the motor, there is an increase in the speed-torque characteristic curve, which also depends on the square of the motor voltage, at a constant rotating field frequency (stator rotating frequency). For the mathematical illustration of this dependency, the following greatly simplified approximation equations can be drawn up for the area of interest here: The following relationship exists between the magnetic reversal frequency f _u and the rotating field frequency f with the number of pole pairs p of the asynchronous motor 4: f = f u p and between the relative torque m _d / m _k and the operating slip s and the tilt slip s _k : m d m k = 2nd s / s k + s k / s

With the consideration that the operating slip s is small compared to the tilt slip s _k , the term s / s _k can be neglected, and the slip s results approximately to: s ≈ m d m k * s k 2nd

The influence of the motor voltage U follows from (1) and (4): s ≈ m d * f U 2nd c 1 * U 2nd * s k 2nd

By combining the motor-specific quantities c ₁ and s _k / 2 into a factor c, (4) can be simplified to: s ≈ c * m d * f U 2nd U 2nd

Furthermore, the angular velocity ω on the motor shaft with the magnetic reversal frequency f _u , the number of pole pairs p of the asynchronous motor 4 and the slip s results in: ω = f u * 2 * π p * (1-s)

If (5) is used in (6), the following applies for a constant magnetic reversal frequency f _u : ω ≈ f u * 2 * π p * (1-c * m d * f U 2nd U 2nd )

From equation (8) it can be seen that with the same load torque m _d, the angular velocity ω of the rotor and thus of the driven washing drum 1 also decreases by reducing the motor voltage U. It follows that, for example, load fluctuations caused by imbalance by reducing the motor voltage U result in greater variations in this angular velocity ω.

According to equation (8), the relationships in FIG. 2 are shown as curves. The relationships of the angular velocity differences Δω for two motor voltages U1, U2 as a function of torque differences Δm during operation without speed control are shown, the relationship between the angular velocity ω and the speed per minute n being: n = 60 2 * π * ω

It shows that with the same torque difference Δm, the difference in angular velocities Δω ₂ at voltage U2 is much larger than the difference in angular velocities Δω ₁ with voltage U1.

The limit of the voltage drop results from the maximum torque occurring at the measuring point, ie the breakdown torque m _k , must always be greater than the load torque m _d by a safety factor for the overload capability. A start-up with the lowered voltage is usually not possible.

Furthermore, it can be seen from (7) and from Fig. 2 that by lowering the Motor voltage U from the voltage U1 to the voltage U2 the average speed or Angular velocity ω decreases. At a certain angular velocity ω must be reached during the unbalance measurement before the control is switched off and the motor voltage U is reduced, a correspondingly higher one beforehand Angular velocity ω have been reached.

By specifying the motor voltage to adapt the speed-torque characteristic of the motor, the resolution of the unbalance detection can be compared to Improve measurement errors considerably. As can be seen from Fig. 2, namely lead the same Torque fluctuations or changes at the lower voltage U2 a change in angular velocity Δω2 that is much greater than the change in Angular velocity Δω1 at voltage U1; d. H. Unbalance, such Torque fluctuations can be caused at the lower voltage U2 much better, d. H. measure with much higher resolution than at voltage U1.

As an alternative, instead of reducing the motor voltage as described U the rotating field frequency can be increased. Here, the motor voltage U decreases Reaching the application of the laundry on the outer surface of the laundry drum 1 constant held and the rotating field frequency increased until the measuring speed is reached. The Explanation of this possibility follows from the fact that at constant Motor voltage U with increasing magnetic or rotating field frequency inductive reactances of the motor 4 also increase and thus the motor current and thus reduce the engine stall torque. The engine stall torque is reversed proportional to the square of the magnetic reversal frequency.

These options can now be used to drive the drive in the measuring range Adjust unbalance so that comparable conditions with regard to the characteristic of the Universal motor can be adjusted.

In order to increase the reproducibility, the motor voltage U depending on the grid voltage currently applied to the inverter 12 and of the winding temperature can be made.

The winding temperature of the asynchronous motor 4 is determined, for example, by a Detected temperature sensor, which converts them into an electrical signal and via a Signal line feeds the engine controller 7. In the controller 7 there is, for example, a table stored with temperature values from which by comparison with that by the sensor measured temperature the motor voltage in the unbalance measuring range accordingly can be corrected. If the load torque after exceeding the landing speed has decreased, the controller 7 reduces the voltage via the voltage manipulated variable 13. On A comparable effect is achieved by increasing the frequency manipulated variable 14.

The signals generated by the rotary encoder 6 are preferably pulse-shaped and are in counted a counter contained in the controller 7, the number of the rotary encoder 6 delivered pulse chain is evaluated so that both the respective speed of the Motor shaft as well as the respective position of a fictitious point on the motor shaft is available and thus the speed of the rotor, d. H. the drum 1, available is. Thus, the position and size of a possible one can also be controlled by the controller 7 Detect unbalance on the rotor.

It can be provided that the motor controller 7 to be regulated by him Parameters, in particular the motor voltage U or the motor current I either already lowered or increased before the measurement or only during the measurement. Instead of one single parameters such as the motor voltage can also have a plurality of parameters, especially the motor voltage U in connection with the winding temperature of the Motors, 4 are taken into account. Differences between the maximum and minimum angular velocity of the drum 1 for dimensioning the size of the Unbalance used. In addition, the position of the unbalance is determined using the Speed curve detected and always tracked by the encoder 6 so that the The position of the unbalance is always available in the motor controller 7. The location of the imbalance to determine the change in the meter reading over a certain Period examined. The change in the meter reading per time period, divided by the number of possible pulses per rotor rotation corresponds to the change in the position of one fictitious point on the rotor, which results if this is from the mean value deviates, an imbalance results. With an indirect drive in which the motor, As shown in Fig. 1, the laundry drum 1 drives a drive belt 3, the mechanical transmission ratio to be taken into account.

The detection of the position of the unbalance is necessary for drive systems that have a enable active unbalance compensation. Here, e.g. through one of the unbalance counteracting modulation of the angular velocity of the drum the effects the unbalance reduced.

If an imbalance has been determined, appropriate measures can be taken to reduce it, for example by redistributing the laundry, by Limitation of the maximum spin speed or by aborting the Spinning process. As an alternative to the motor controller 7, a control device can be used be provided, the corresponding parameters such as the speed of the engine, the Motor current, the motor voltage and / or the temperature of the motor windings supplied be so that the control device corresponding to those stored in a memory Characteristic curves that take these parameters into account, the motor voltage accordingly adjusts. It goes without saying that another parameter is selected as the manipulated variable can be.

There is an electrical connection between the intermediate circuit 11 and the motor controller 7 18, via which the motor controller controls the voltage of the intermediate circuit 11 monitored, so that especially when braking the asynchronous motor 4 and thus accompanying voltage feedback in the intermediate circuit 11, this a certain does not exceed the specified height; on the other hand, if the tension in the DC link 11 a different from the target voltage due to the power supply Has voltage, this by appropriate control of the inverter 12th by the motor controller 7 by changing the pulse widths of the voltages R, S, T be balanced.

Claims (18)

Method for detecting unbalance in a rotor driven by a brushless electric motor (4), in particular a washing drum in a washing machine, a measuring device determining the speed (s) and the unbalance of the rotor by size or by size and position, characterized in that after a minimum speed of the rotor has been exceeded, at least one electrical parameter of the electric motor (4) is changed from its dimension intended for operation to a dimension intended for a measurement such that the slope (dn / dm) of the speed (n) torque ( m) characteristic curve increased in amount, the speed (n) of the rotor also being above a predetermined minimum speed (n _M ) during the measurement, and then the unbalance being measured according to position and size. Method according to Claim 1, characterized in that the Motor voltage (U) is selected before or during the measurement is lowered. Method according to Claim 1, characterized in that the The rotating field frequency of the motor is selected before or during the measurement is increased. A method according to claim 1 to 3, characterized in that to increase the Accuracy of the measuring method, the voltage as an additional parameter of the intermediate circuit (11) and / or the temperature of the motor windings Electric motor (4) is selected. Method according to one of claims 1 to 4, characterized in that the parameter is changed such that the speed (n) -torque (m) characteristic curve above the minimum speed (n _M ) of the electric motor, in particular of the asynchronous motor (4), the Speed (n) -torque (m) curve of a universal motor with the same power. Method according to one of claims 1 to 5, characterized in that the actual speed (n _actual ) of the electric motor (4) is measured by a rotary encoder (6) as the current angular velocity (ω) and a control circuit (7, 13, 14, 12) to regulate the motor voltage (U) and that the control circuit lowers the motor voltage (U) after exceeding the minimum speed (n _M ) or changes another parameter of the electric motor (4) in such a way that its output torque decreases. Method according to one of claims 1 to 6, characterized in that the motor current, in particular in connection with a measurement of the actual speed (n _actual ) of the electric motor (4), is measured and serves as a controlled variable. Method according to claim 5 or 6, characterized in that the slip (s) of the electric motor (4), the motor current, in particular depending on magnetic flux, or the rotating field of the voltages (R, S, T) or the associated currents of the electric motor (4), in particular using a mathematical engine model, is regulated. A method according to claim 6, characterized in that a controller (7) in the Control circuit (7, 13, 14, 12) signal variables for setting the motor voltage and / or the rotating field frequency, which in turn generates manipulated variables for an inverter (12) of the electric motor (4). A method according to claim 9, characterized in that the control signal for Position of the motor voltage and the control signal for the rotating field frequency Generation of the speed fed to a multiplication point (17) and from this can be fed to the inverter (12). Method according to one of claims 1 to 10, characterized in that the actual speed (n _actual ) of the electric motor (4) is measured by a rotary encoder (6) as the current angular velocity (ω) and is fed to a control device for controlling the motor voltage (U) , in which control variables for the motor voltage and the motor speed for controlling the inverter (12) are generated on the basis of stored characteristic curves. Method according to one of claims 1 to 11, characterized in that the control or regulation of the speed of the electric motor (4) is switched off above the minimum speed (n _M ) and the speed reached of the electric motor (4) is used as the measuring speed and then that Slope (dn / dm) of the torque (m) -speed (n) characteristic is increased in amount. Method according to Claim 12, characterized in that the minimum speed (n _M ) is the speed (n) at which the laundry lies against the inner circumferential surface of the laundry drum (1). Device for carrying out a method according to claim 1, characterized in that the electric motor (4) can be regulated by means of the measured actual speed (n _actual ) via a motor controller (7) by means of a voltage control variable and a speed control variable or can be controlled via a control circuit. Apparatus according to claim 14, characterized in that the Voltage control variable and the speed control variable via an inverter (12) can be fed to the electric motor (4). Device according to claim 15, characterized in that the inverter (12) voltage signals fed from an intermediate circuit (11) can be fed and that this in the inverter (12) according to the values of Voltage control variable and the speed control variable are changeable. Device according to one of claims 14 to 16, characterized in that the intermediate circuit (11) a filter (10) for filtering out high-frequency is upstream of electromagnetic interference. Device according to one of claims 14 to 17, characterized in that the motor controller (7) and the inverter (12) through a power supply unit (15) together can be supplied with voltage.

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