DE2915987A1 - NC machine tool fast reacting servo drive - uses phase signals corresp. to rotary angle of sync. machine to control current - Google Patents

Abstract

The fast reacting servo drive for e.g. a numerically controlled machine tool, uses a converter self controlled synchronous machine (1) and an angle indicator (4) which provides signals corresponding to the angle of rotation of the rotor (2). Phase signals (11) corresponding to the angle of rotation are fed to multipliers (10) for each phase, and their outputs (12) fed to equalisers (13) and current controllers (18) to the stator windings (16). A tachogenerator (5) connected to the angle indicator is followed by an equaliser (6) and a rotary speed controlled (9) interconnected with the multipliers.

Description

Responsive servo drive

PRIOR ART The invention is based on a responsive one Servo drive according to the species of the main claim. For precise, quick control of motion sequences are often, especially in numerically controlled machine tools, Servo drives are required which have sufficient streakiness at zero speed and over a wide speed range, from minimum speed values up to required maximum speed a smooth run with precisely controllable torque and have braking torque. DC motors are usually used for this, which, however, have considerable disadvantages, in particular because of the commutation required exhibit.

Via brushless DC motors with electronic commutation Although a large part of these disadvantages can be eliminated, they do occur the known drives due to electronic commutation torque fluctuations, especially at low speeds, they are suitable for the intended purpose make unsuitable.

The use of inverter-controlled AC motors is also known, however, besides a great effort, these have a difficult setting, control and regulation on.

Inverter-fed, self-controlled ones are still available for other purposes Synchronous machines known (see DBP 21 32 178 and DE-OS 26 37 178.8), the Synchronous machine has a pole wheel position encoder, whose encoder signals the generation d to change a component for a field simulation, which together with other components enables phase-corrected control of thyristors, via which both the active and the reactive component of the stator current are generated.

Such drives are, however, also because of the high torque ripple not suitable at low speeds.

Advantages of the invention & the servo drive according to the invention with the characterizing features of the main claim behaves like a similar one Drive with a DC motor, with the advantages of a synchronous machine, in particular can be fully utilized due to the collector, which is not required here.

A correspondingly high-resolution, absolute, Digital angle sensors are used via these signals from an electronic storage device Function values for the individual rotational angle positions of the rotor can be called up. It Sin or cos encoders can also be used, but in particular For synchronous machines with a large pole cover angle, corrections of the sine or Cosine function can be required to turn on even at low speeds to obtain a torque that is independent of the angular position of the rotor. These corrections can be achieved in a simple manner by a corresponding structure of the pole wheel position encoder or stored in the electronic storage device by means of appropriate modifications Perform function values.

The stator current can then be generated in a simple manner, in particular via a clocked transistor amplifier with a high switching frequency. In further training the invention can ru to keep the armature jerk effect low, a synchronous machine can be used with permanent magnet rotor.

Drawing exemplary embodiments of the invention are on two sheets of drawings and explained in more detail in the following description. It shows Fig. 1 the circuit principle with a 3-phase synchronous machine, FIG. 2 the EMF, as well a corrected phase signal from the pole wheel position encoder, Fig. 3 and 4 the construction principle a pole wheel position encoder with cams and inductive encoders.

Description of the invention In Fig. 1 the circuit principle for a three-phase synchronous machine 1 with a two-pole rotor 2 (1 pole pair) with Permanent magnet excitation shown. Directly driven by shaft 3 of the rotor 2 becomes a pole wheel position encoder 4 and a tachometer generator 5. The output signal of the tachometer generator is compared in a comparator 6 with a speed setpoint signal 7 and a Speed difference signal 8 is generated, which is fed to a PID speed controller 9. This speed control loop 5 to 9 can be used in the same way as with DC motors known to be constructed. The output voltage of the speed controller 9 is now in accordance with the invention to three multipliers lo and is there with one of the three Phase signals 11 from the pole wheel position encoder 4 are multiplied. The multiplication takes in this case not to take place linearly, but can depend on the dynamics of the synchronous machine and be adapted to the position control loop.

The phase signals 11 from the pole wheel position encoder 4, the generation of which will be described later, have a sinusoidal curve shape when the rotor is rotating, the following fixed relationship to the mechanical angle of rotation t of the three-phase synchronous machine.

where p is the number of pole pairs of the synchronous machine (in the exemplary embodiment, p = 1). In a two-phase synchronous machine, only two phase signals 11; Multiplier lo is required for two stator currents that have the following relationship: The pole wheel position encoder is constructed in such a way that it delivers instantaneous values of approximately the same size, corresponding to the angle of rotation y, at every speed as well as at standstill.

The output values 12 of the three multipliers are for the subordinate Current control are each supplied to one of 3 current value comparators 13 and are compared there with current value signals 14 from current value transmitters 15, for example from three Current transformers 15 may exist, which are in the leads to each stator winding 16 of the corresponding phase. The output signals 17 from the current comparators 13 three current regulators 18 are supplied, which the currents for the three stator windings 16 of the synchronous machine. Not applicable for a two-phase synchronous machine a stator winding 16 with the associated current regulator 18, current value transmitter 15 and Current value comparator 13.

By specifying the phase signals 11 from the pole wheel position encoder 4 causes the current vectors always perpendicular to the vectors of the excitation magnetic field stand, as this is also done in the DC machine via the collector. This is how a synchronous machine that is self-controlled in this way behaves as a drive almost like a DC machine, but with the irregularities in the There is no need to jump from one commutator bar to the next. An irregularity Due to the grooving effect at low speeds, a bevel groove can almost be avoided. For synchronous machines especially medium and small power, where utilization no longer plays a major role, brings the use of a two-phase synchronous machine with approximately the same control and control dynamics a saving of almost a third of the power electronics.

The current regulator 18 should be constructed so that they accordingly the phase signals 11 from the pole wheel position encoder 4 generate currents that generate a torque cause that largely independent of the angular position of the rotor, proportionally to the output voltage of the speed controller 9 is.

For this purpose, pulsed current regulators 18 can also be used, if the clock frequency is chosen accordingly high, so that even at maximum speed no malfunctions can occur yet. Because the clock frequency, even with smaller Values of the usually required maximum speed, greater than 1 KHz, can be selected must, thyristors (as they are currently known) are ruled out. In the current regulator clocked transistors are used, the n known way a Regulation with significantly greater efficiency compared to non-clocked transistor regulators enable. While with DC motors by limiting the maximum voltages Relatively low voltages and high currents are used on the collector, which are usually stepped down before the mains voltage is rectified must, when using a synchronous machine according to the invention, the line voltage directly rectified to the current regulators via lines 19, even without a transformer are fed.

By using a higher DC voltage, the, at equal power, correspondingly smaller currents can be regulated with less effort.

In the embodiment example Fig. 1 is a permanent magnet synchronous machine 1, but a Fresderrfgung can also be used in the same way. An additional change in the external field results in additional ones Control or regulation options, especially in field weakening operation. In contrast however, permanent magnet excitation has other advantages. So be especially at Machine tools usually require fully enclosed motors to reduce their heat loss can only be released through the housing or have to be cooled separately. While the heat loss of the stator windings relatively easily through the housing dissipate leaves, the cooling of the rotor windings is difficult. As a permanent magnet rotor If this cooling is not required, external cooling can be difficult in many cases and laborious is to be dispensed with.

By using modern magnetic materials, the air gap can be chosen larger and the anchor reaction remains low. Since there is no Slip rings for power supply are required, a robutter, less susceptible to failure, maintenance-free drive possible.

Since the torque of the synchronous machine is approximately proportional to the current (J) as a function of a voltage constant (Kv) and in the ideal case, neglecting the armature reaction, the voltages induced in the stator windings 16 show the following course in a three-phase synchronous machine: the following currents are to be fed to the individual stator windings via the current regulator 18 with a subordinate current control loop: the torque independent of the angle of rotation du. '; To make rotors. One phase u1 of the induced voltage is shown in FIG. The other phases are accordingly around 2/3-t each! offset next to it. When the synchronous machine is optimally used with a large pole covering angle, the induced voltage does not show a sinusoidal curve but, as u1t shows, an approximately trapezoidal curve. In the case of stator currents with a sinusoidal profile, this can result in deviations in the torque by more than lo z. result, whereby the synchronous machine can be better utilized by more than 20 s due to the more favorable field distribution.

In a further development of the invention, the stator currents are now in their Course changed in such a way that in every angular position of the rotor there is only one of the output voltage of the speed controller 9 results in a dependent torque. This leaves can be achieved in a simple manner in that the phase signals 11 from the pole wheel position encoder 4 received a shape Ug deviating from the sinusoidal shape, whereby the den Stator windings 16 current supplied from the current regulators 18 changes accordingly. In the same way, fluctuations can also be compensated for by the grooving effect. For this purpose, the curve Ug has a further number corresponding to the number of slots, smaller To superimpose deviations (not shown). By comparing the induced Voltage with the stator currents, e.g. with an oscillograph, deviations can be determined Easily recognized in shape and size and then make corrections.

The generation of the phase signals 11 from the encoder signals of the pole wheel position encoder 4 is possible in many ways. The easiest seems to be to use Sine-cosine potentiometers e.g. for a two-phase synchronous machine, however Due to signs of wear and tear, these should rarely be considered. Low-wear Pole wheel position encoders, on the other hand, can be built with inductive or capacitive encoders, which at the same time allow a simple change in the course of the curve. In Fig. 3 and 4 are parts for such a pole wheel position encoder for a four-pole synchronous machine (2 pole pairs) shown. There are two disks on the shaft 30 of the synchronous machine 31 wedged from magnetically non-conductive, but electrically conductive material and held at a parallel distance by an intermediate ring 32. The edge areas 33 of the disks 31 engage in the slots 34 of three E cores 35 without contact made of ferromagnetic material. The E-cores are about adjustable Fastenings 36 at a rotation angle distance of 120 on the inner wall of the housing 37, attached to the synchronous machine or a correspondingly mounted housing part. A high-frequency coil 39 is fastened on each of the middle limbs 38 of the E cores. The high-frequency coils 39 are parts of oscillating or feedback circuits in a known manner of three inductive encoders, which depending on the depth of engagement of the disc edge areas 33 emit a proportional, rectified high frequency signal.

The outer edges 40 of the two disks 31 point to the middle disk radius 41 a constantly changing distance along the circumference, this distance selected according to the desired output signal of the respective pole wheel encoder phase is. For example, by superimposing a direct voltage, it can be achieved that the output signals correspond to the respective distance from the mean disk radius also change their polarity according to the direction of the distance. The DC voltage can in turn by adding a third of the output voltages of all three Output signals are generated. If the distances change, as with solid Line 42 shown, sinusoidal to the mean disk radius 41 over the angle of rotation, With inductive encoders of the same size, a constant mean value voltage results. Is done by changing the circumference of the discs, e.g. according to the dashed line Line 43 is a correction for a large pole cover angle, this fluctuates Total voltage, but these fluctuations are caused by a corresponding change the curve shape of the outer edge can be taken into account.

Instead of inductive encoders, appropriately constructed Encoders with Hall probes, capacitors or optical encoders are used. Particularly The use of a high-resolution absolute digital tanner can be advantageous, which supplies a coded signal corresponding to the angle of rotation θ of the rotor. Upper This signal can then be used, for example, via an electronic read-only memory are retrieved, from which then the corresponding phase signals 11 for the multiplier lo can be derived. By selecting the digital encoder, code, memory logic, Storage methods, memories, evaluation logic, digital-to-analog converters, etc., can be with modern electronic components the necessary phase signals 11 for the Generate multiplier lo with little effort.

So it is possible to only use the function values for a sub-area to save all angles of rotation e.g. 0 to gate or only up to ç / 2 and the other function values for the other angles of rotation can be derived from these function values. By using of memories with fast access times is also multiplexed, even possible at high maximum speeds. The resolution of the signal curves into individual ones Function values should be chosen so large that even the smallest Speeds there are no more disruptive torque fluctuations can. If one uses programmable memories, there is the advantage of a simple one Correction and adaptation to different synchronous machines without use other building blocks.

The phase signals 11 or the stored function values can also contain additional correction values in the same way that Compensate for torque fluctuations caused by the grooving effect. Through this an inclined groove can be dispensed with, which means that the production of the synchronous machine can be simplified.

In certain applications, especially machine tools with high-resolution encoders that are sufficiently rigidly connected to the drive, You can also use the output signals of these position encoders instead of the pole wheel position encoder Find. The prerequisite for this, however, is that it is an absolute encoder acts, i.e. the position value signals follow a defined path even at standstill or specify angle. It is also possible for various applications the signals of the pole wheel position encoder 4, especially when using an absolute digital pole wheel position encoder, at the same time for path control (positioning or path control) to use and thereby save other donors. Especially if a very A fine-resolution digital encoder is used, can also be made from the encoder signals a speed signal is derived and the tachometer generator is saved as a result will.

The arrangement according to the invention enables a responsive Servo drive, which at standstill is an externally acting in every rotor angle position Torque is opposed to an equal moment without this being an essential one The angle of rotation of the rotor is changed. He behaves like a responsive one DC motor, however, avoids all the main disadvantages of this motor, which caused by the commutation. It can be used up to very high speeds Full control in all four quadrants and can withstand very high, short power surges. With DC motors, both are restricted to prevent the destructive firing of the To avoid the collector.

Summary It becomes a responsive servo drive with a Synchronous machine (1) proposed, which one over the full speed range continuous four-quadrant control enables. Powered by a self-commutated converter Current regulation of the phase currents for the stator windings (16) via appropriately shaped Phase signals (11) from a pole wheel position encoder (4), control is enabled, which regardless of the angular position (t) of the rotor (2) from standstill to maximum Speed causes a torque output of the synchronous machine (1), which only from Output signal of a speed controller (9) depends. This is done by the angular position (9,) of the rotor (2) dependent individual values of the phase signals (11) are selected such that that with a constant output signal of the speed controller (9) in current controllers (18) for the stator windings (16) currents are generated at each angular position (y) Generate largely constant torque.

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Claims (12)

Claims cl Fast-reacting servo drive with an approximate Continuous four-quadrant control over the full speed range via a speed control loop at which the speed is proportional to the size and polarity of an input DC voltage is adjustable, characterized by the combination of the following features: a) one Converter-fed, self-controlled synchronous machine (1), b) a pole wheel position encoder (4) of the encoder signals according to the mechanical angle of rotation () of the rotor (2) supplies, c) devices for generating angle-of-rotation-dependent phase signals (11) from these encoder signals, the voltages of which are a constant sine-like Function of an angle of rotation (f of the rotor (2) correspond to the synchronous machine (1), d) one of the number of phases of the synchronous machine (1) corresponding number of self-guided Power amplifier (18) high switching frequency for generating this sine-like Functions corresponding currents for the stator windings (16) of the synchronous machine, and e) Preamplifiers for these power amplifiers (18) with one each Multiplier (lo) in which the angle of rotation dependent phase signals (11) with the DC voltage of the speed controller (9) can be multiplied1 and the output voltages (12) the multiplier the currents for the stator windings (16) of the synchronous machine (1) determine. 2. Servo drive according to claim 1, characterized in that when using a two-phase synchronous machine, the angle of rotation-dependent phase signals (11) similar to the functions where p is the number of pole pairs of the synchronous machine and y is the mechanical angle of rotation of the rotor (2). 3. Servo drive according to claim 1, characterized in that when using a three-phase synchronous machine (1) the rotation angle-dependent phase signals (11) of the functions where p is the number of pole pairs of the synchronous machine (1) and / or the mechanical angle of rotation of the rotor (2). 4. Servo drive according to one of claims 1 to 3, characterized in that that the pole wheel position encoder (4) is a high-resolution, absolute, digital position encoder is, an electronic storage device is provided in the function values stored for individual angular positions of the rotor (2) of the synchronous machine (1) and the corresponding function values via the digital signals of the position encoder can be called up to create the phase signals (11) that are dependent on the angle of rotation. 5. Servo drive according to claim 4, characterized in that the storage device contains a pre-programmable read-only memory for the function values. 6. Servo drive according to one of claims 1 to 3, characterized in that that the pole wheel position encoder (4) is an inductive or capacitive encoder, the one Contains cam (31) which is fixed to the shaft of the rotor (2) of the synchronous machine (1) is connected and the curve area of the cam (31) in a field of several The number of encoder probes corresponding to the number of phases of the synchronous machine intervenes, which are fixedly mounted distributed over the outer circumference of the cam disk. 7. Servo drive according to one of claims to 6, characterized in that that the pole wheel position encoder is also part of the measuring system for the travel of the Servo drive is. 8. Servo drive according to one of claims 1 to 8, characterized by a pole wheel position encoder which is designed in such a way that the phase signals which are dependent on the angle of rotation (11) have a curve, which through the power amplifier (18) currents for a torque of the synchronous machine generate that largely independently of the Angular position (<p) of the rotor (2) proportional to the DC output voltage of the speed controller (9) is. 9. Servo drive according to claim 9, characterized in that the synchronous machine (1) a permanent magnet rotor (2) with a large pole wheel cover angle while remaining the same has a small air gap and the resulting torque fluctuations if the angular position changes, they are compensated for by correction values which the Function values that change over the angle of rotation according to a sine function are superimposed. lo. Servo drive according to claim lo, characterized in that over additional correction values for fluctuations in the torque due to the grooving effect are balanced. 11. Servo drive according to one of claims 1 to lo, characterized in that that to generate the currents for the stator windings (16) of the synchronous machine (1) clocked transistor amplifiers (18) are provided. 12. Servo drive according to one of claims 1 to 11, characterized in that that a signal generator (5) is provided, which one of the rotary movement of the rotor (2) the synchronous machine (1) emits a dependent output signal, a speed setpoint comparator is provided in which a speed difference signal (8) from the comparison of the output signal is generated with a predetermined setpoint signal (7), this speed difference signal a speed controller (9) is supplied, which is designed as a PID controller and a DC voltage signal for the multiplier Uo) generated.