Source: http://patents.com/us-7746064.html
Timestamp: 2018-12-17 15:14:47
Document Index: 651002314

Matched Legal Cases: ['art 15', 'art 11', 'art 11', 'art 11', 'art 15', 'art 11']

US Patent # 7,746,064. Speed measurement for an electrical permanent-magnet synchronous machine - Patents.com
United States Patent 7,746,064
Knorr , et al. June 29, 2010
Speed measurement for an electrical permanent-magnet synchronous machine
Inventors: Knorr; Markus (Augsburg, DE), Jajtic; Zeljko (Munchen, DE)
Appl. No.: 11/576,025
PCT Filed: September 19, 2005
PCT No.: PCT/EP2005/054644
PCT Pub. No.: WO2006/072472
PCT Pub. Date: July 13, 2006
Sep 27, 2004 [DE] 10 2004 046 824
Current U.S. Class: 324/174 ; 324/161; 324/207.15; 324/207.2
Current International Class: G01P 3/48 (20060101); G01R 33/06 (20060101)
Field of Search: 324/207.2,207.15,207.16,207.22,207.24,207.25,161,173,174 73/514.39,514.31 310/68R,68B,254,12,216,184
4581553 April 1986 Moczala
4710683 December 1987 Bahn et al.
5091665 February 1992 Kelly
690 21 156 Dec., 1995 DE
101 35 540 Feb., 2003 DE
2 273 166 Jun., 1994 GB
03155362 Jul., 1991 JP
1. A speed measurement device for an electrical machine, which has a primary part, a secondary part, and permanent magnets said speed measurement device comprising: a first sensor having a sensor coil which generates a first signal value having a position-dependent component and a speed-dependent component; a second sensor constructed as a Hall sensor to generate a position-dependent second signal value to eliminate the position-dependent component of the sensor coil; a flux guidance device for guidance of a magnetic flux, wherein at least one of the first and second sensors is arranged in an area of the flux guidance device and configured to measure the magnetic flux in the flux guidance device; and an evaluation device relating the first signal value to the second signal value, wherein a ratio between the first signal value and the second signal value is proportional to the speed of the machine.
12. A primary part of a permanent-magnet electrical synchronous machine, comprising: a first sensor having a sensor coil which generates a first signal value having a position-dependent component and a speed-dependent component; a second sensor constructed as a Hall sensor to generate a position-dependent second signal value to eliminate the position-dependent component of the sensor coil, wherein the first and second sensors are configured for measurement of a speed; a flux guidance device for guidance of a motor flux of the permanent-magnet electrical synchronous machine, with at least one of the first and second sensors being constructed for attachment to or adjacent to the flux guidance device, wherein the flux guidance device has teeth; and an evaluation device relating the first signal value to the second signal value, wherein a ratio between the first signal value and the second signal value is proportional to the speed of the machine.
20. A method for measurement of a speed of a machine, said method comprising the steps of: guiding a magnetic field produced by permanent magnets of the machine by a flux guidance device to a first sensor which measures a magnetic field to generate a first signal value having a position-dependent component and a speed-dependent component; guiding the magnetic field by means a further flux guidance device to a second sensor, which measures the magnetic field to generate a position-dependent second signal value to eliminate the position-dependent component of the first signal value; and relating the first signal value to the second signal value, wherein a ratio between the first signal value and the second signal value is proportional to the speed of the machine.
22. The method of claim 20, wherein signal disturbances of the first signal value and of the second signal value, caused by a current flowing in a primary part, and further comprising the step of compensating the signal disturbances by a compensation device.
One or more sensors is or are therefore advantageously arranged directly in the magnetic circuit of the primary part of the electrical machine. In consequence, a component of the useful flux of the electrical machine is detected by one or more sensors of the speed measurement device. Thus, according to the invention, no free-space field is used or detected for speed measurement, with this being intended to relate either to a linear movement or a rotary movement. That magnetic flux which is also used to form the power of the electrical machine, or else the power of a motor, is detected as a sensor flux. The use of a useful flux of the electrical machine, that is to say of a magnetic flux which is used for power generation, means that the sensor flux resulting from this is not so heavily dependent on geometric and magnetic tolerances and/or faults of individual permanent magnets in a permanent-magnet electrical machine, as would be the case, for example, with point detection of the free-space field of permanent magnets. One reason for this is that the useful flux, that is to say in particular the motor flux of a motor, is collected by a magnetic circuit of the electrical machine, and thus represents a type of integral variable. In particular, the effects of local errors or faults in the field distribution are very greatly reduced by "integration" in this integral variable. The integration effect is achieved in particular by the flux guidance of a laminated core. The integrating effect in the case of useful flux may have various advantages: the use of the useful flux (in the case of a motor, this is the motor flux) as an integral variable improves the signal quality factor for at least one of the sensors that are also used for speed measurement (sensor with a coil (sensor coil) or Hall sensor); in addition to a generally improved signal form, the signal form can also be optimized by variation of the magnetic circuit geometry; for example, this makes it possible to achieve better position detection (in this context, it should be noted that at least one sensor of the speed measurement device can also be used for position detection); position detection errors can be minimized by the achievement of less sensitivity to at least one local error or fault of a permanent magnet; examples of a local error or fault are: a discrepancy from the required magnetization strength and/or magnetization direction, a discrepancy of a permanent magnet from the required geometry (in particular of the thickness which, for example, influences the distance between a primary part and a secondary part of an electrical machine), etc.
According to the invention, these advantages can be achieved not only by the use of the useful flux. In order to achieve the described advantages, it is also possible to achieve the integrating effect described above by, for example, a means for magnetic flux guidance (for example a laminated core) for example, which is not used to carry a useful flux. In this case, it would then also be less problematic to choose as the means for magnetic flux guidance not only a laminated core but also a design in which Eddy currents are completely excluded, in comparison to the laminated core. This design is, for example, a soft-magnetic block composed of ferrite or some other soft-magnetic material (for example powder pressed cores), which has teeth or else a plastic block in which soft-magnetic material is integrated.
According to the invention, the strong influence of local errors or faults in the field distribution of individual permanent magnets is reduced, since the free-space field (stray field) is no longer detected for signal detection. Until now, with the prior art, it has been necessary for accurate measurement for: the stray field to have a sinusoidal distribution, the geometry of the sensor coil to be very accurate, and/or the distance between the Hall sensor (that is to say the Hall element) and a magnet surface to be maintained exactly.
Until now, compliance with these requirements has resulted in high costs. According to the invention, requirements such as these can now be reduced. This is a result in particular of the fact that the measurement signal of the Hall sensor is based on a point variable and, until now, the induction distribution has been measured in the stray field of the permanent magnets. According to the invention, the Hall sensor measures the useful flux, so that induction distributions in the permanent magnets have a negligible effect on the measurement result. The measurement signal in the sensor coil is based on an integral variable, in which case, according to the prior art, the area integral of the magnetic stray field was measured over the coil area. Maintenance of an exact coil geometry was therefore elementary. According to the invention, the sensor coil surrounds a flux guidance piece, with this flux guidance piece being used to guide a portion of the magnetic useful flux. This therefore also advantageously reduces the requirements for an exact coil geometry.
A portion of the main machine flux can be detected by means of the first sensor and by means of the second sensor. In this case, the first sensor and the second sensor are located, for example, adjacent to and/or in the primary part of the electrical machine. In a further possible embodiment, the two sensors--the first sensor and the second sensor--or else only one of the sensors are or is arranged outside the laminated core area of the primary part. In this case, the two sensors are arranged in such a manner that they detect the magnetic flux of the permanent magnets of the secondary part, which are not covered by the laminated core of the primary part. These permanent magnets which are not covered by the laminated core of the primary part are free-standing. With this arrangement of the sensors, these sensors are arranged outside a magnetic circuit of the primary part. In particular, the magnetic circuit of the primary part is governed essentially by the laminated core of the primary part. If a sensor detects a magnetic field or a magnetic flux outside the magnetic circuit of the primary part, then the sensor can either be fitted to the primary part such that the sensor is integrated in the primary part, or such that the sensor is fitted to the primary part by means of a holding device. If a holding device is used, the sensor is located, for example, in a separate sensor box which is fitted to the primary part, with the sensor box being separated from permanent magnets of the primary part via an air gap.
The signals detected by the sensors are in general sinusoidal. For example, a voltage U.sub.s can be determined as a signal from the sensor coil. In this case, this voltage U.sub.s has a proportionality which can be represented as follows: U.sub.s.about.K1.phi.(.alpha.)d.alpha./dt (the coil signal U.sub.s is dependent on position and rotation speed) where: K1 is a proportionality constant, .phi.(.alpha.) is a magnetic flux (dependent on angle and position), d.alpha./dt is an angular velocity and .alpha. is an angle position in the case of a rotating machine, or a position in the case of a linear motor.
The signal from the Hall sensor U.sub.h is dependent only on position. The voltage U.sub.h is proportional to the magnetic flux .phi.. This proportionality can be described, for example, as follows: U.sub.h.about.K2.phi.(.alpha.) where:
.phi.(.alpha.) is a magnetic flux (dependent on angle and position).
Suitable arrangement of the two sensors allows the two sinusoidal signals to have an identical phase angle. The ratio of the voltages of the sensor signals U.sub.s/U.sub.h is directly proportional to the rotation speed or to the speed. By way of example, the speed relates to the speed of a primary part of a linear motor. The position dependency of the signal from the sensor coil can be eliminated by means of the Hall sensor. For example, the rotation speed then becomes: n=K*(U.sub.s/U.sub.h).
In one advantageous refinement of the speed measurement device, the first sensor and second sensor have an electrical phase offset as already mentioned. One particularly advantageous electrical phase offset results from an offset angle of 90.degree. electrical.
The invention is also achieved by means of a speed measurement device for a permanent-magnet electrical synchronous machine, which has a primary part and a secondary part and also has at least two speed measurement devices of the type described above. This upgraded speed measurement device thus has a first speed measurement device and a second speed measurement device, in which case the first and the second speed measurement devices can be fitted or are fitted to the primary part with an electrical phase offset. In one advantageous refinement, the phase offset is 90.degree. or 270.degree.. This makes it possible to achieve a rotation-speed actual-value signal which can be evaluated, at the zero crossings of the sinusoidal function.
In a further advantageous refinement, the first sensor and the second sensor have an electrical phase offset. The phase offset makes it possible to simplify the computational processing of the sensor signals. By way of example, a phase lead of 90.degree. electrical is chosen for one advantageous refinement.
At least one of the sensors used for the speed measurement device is advantageously also used for generation of a position signal for the secondary part or the primary part. This makes it possible, for example, to operate an electrical machine on a position-controlled basis, without any additional, that is to say external, position transmitter. Signals from the Hall sensor can be used as a position transmitter for position-controlled operation of the electrical machine. The method includes evaluation, suitable interpolation of the Hall signals and subsequent referencing to an absolute position. A "teach-in process" can also be carried out. This process can be used for position-controlled operation of the motor.
The nominal position is "learnt" directly using a "teach-in process", and is related to a Hall position signal. The Hall position signal may then have absolute position inaccuracies. Once the nominal position has been "learnt", it can nevertheless be reproduced exactly and repeatedly by means of the "motor's-own" Hall signals (for example for a controlled point-to-point movement process).
In one method for measurement of a speed of a permanent-magnet electrical machine, a position-dependent first signal value for a magnetic field is measured by means of a first sensor, and a position-dependent and speed-dependent second signal value for a magnetic field is measured by means of a second sensor. After measurement, the first signal value is related to the second signal value. This has already been described further above. In this case, advantageously: a) a magnetic field which has been produced by means of permanent magnets is guided by means of a flux guidance device to a first sensor, with a position-dependent first signal value for a magnetic field being measured by means of the first sensor, and b) the magnetic field which has been produced by means of the permanent magnets is guided by means of a further flux guidance device to a second sensor, with a position-dependent and speed-dependent second signal value for a magnetic field being measured by means of the second sensor, after which the first signal value is related to the second signal value.
In one refinement of the method, a flux guidance device is used which has teeth, with the teeth being positioned opposite the permanent magnets.
The secondary part 15 and/or the primary part 11 can move linearly. The movement direction is indicated by an arrow 41, in which case the direction may be both positive and negative. The movement direction runs, for example, along an axis x. A magnetic field 33 can be produced by means of the permanent magnets 19. The magnetic field 33 runs, inter alia, within the primary part 11. Since the magnetic field can be differentiated only with difficulty from the magnetic flux in the drawing, the same reference signal 33 is used for both. Different magnetic fluxes .phi. occur, depending on the position of the primary part 11 with respect to the secondary part 15. By way of example, the flux .phi..sub.0=.phi. sin x is illustrated in the area of the first sensor 25. The magnetic flux .phi..sub.90=.phi. cos x is illustrated in the area of the Hall sensor 31. A magnetic sensor flux 40 is tapped off from this magnetic field 31. The primary part 11 is designed such that it has a laminated core 43.
The signal values determined by the sensors can be transmitted by means of connections 35 and 36 to an evaluation device 37. For example, the sensor coil signal can thus be transmitted as a voltage U.sub.s proportional to .phi.(x)*v (v is the speed), and the Hall voltage U.sub.h proportional to .phi.(x) for the Hall sensor 31.
The illustration in FIG. 4 shows two curves U.sub.s and U.sub.h. One curve U.sub.s represents the profile of the voltage U across the sensor coil. Curve U.sub.h represents the voltage U across the Hall sensor as a function of the position on the x axis. Both curve profiles are sinusoidal. The voltages U.sub.s and U.sub.h are plotted with respect to the position x.
Previous Patent US 7,746,063 | Next Patent US 7,746,065