Title: Circuit arrangement for evaluating an acceleration sensor using the Ferraris principle
Abstract: In order to compensate for a drop in sensitivity at high rotational speeds, an acceleration sensor having an inductive measuring head (T) which cooperates with a moving Ferraris disk (F) essentially over a main magnetic field and which supplies an acceleration-dependent variable (Vdet; V.alpha.) is expanded by an additional DC magnetic field excitation circuit (13, 14, I.sub.K, R.sub.K) with a means for driving the latter with the effect that the additional DC magnetic field acts in a compensating fashion on an eddy-current DC field, starting from a relatively high rotational speed (.omega.) of the Ferraris disk (F). This can be performed by amplifying the main magnetic field or by reducing the eddy-current DC field. A control signal (V.omega.), dependent on rotational speed, which both can be generated outside the sensor via a characteristic curve, and can be derived in the form of a control loop from the sensor signal (V.alpha.), serves as a drive.
Patent Number: 6,848,308 Issued on 02/01/2005 to Bauer, et al.
| Inventors:
|
Bauer; Franz (Herzogenaurach, DE);
Daalmans; Gabriel (Hoechstadt, DE)
|
| Assignee:
|
Siemens Aktiengesellschaft (DE)
|
| Appl. No.:
|
918653 |
| Filed:
|
July 31, 2001 |
Foreign Application Priority Data
| Dec 22, 2000[DE] | 100 64 835 |
| Current U.S. Class: |
73/514.31; 73/514.39 |
| Intern'l Class: |
G01P 015/08 |
| Field of Search: |
73/514.31,514.16,514.38,1.41
|
References Cited [Referenced By]
U.S. Patent Documents
| 5363706 | Nov., 1994 | Lew | 73/861.
|
| Foreign Patent Documents |
| 19828372 | Dec., 1999 | DE.
| |
| 10032143 | May., 2001 | DE.
| |
| 0661543 | Nov., 1994 | EP.
| |
| WO 01/23897 | Apr., 2001 | WO.
| |
Primary Examiner: Kwok; Helen
Attorney, Agent or Firm: Baker Botts L.L.P.
Claims
We claim:
1. A circuit configuration for evaluating an acceleration sensor according
to the Ferraris principle, comprising an inductive measurement head that
interacts with a movable Ferraris disk, essentially via a main
magneticizing field, and which supplies a variable that is dependent on
acceleration, further comprising a direct-current magnetic field
excitation circuit having a control loop to cause a direct-current
magnetic field to act compensatingly on an eddy-current field occurring
from a higher rotational speed of the Ferraris disk wherein the
direct-current magnetic field excitation circuit controls compensation
windings by a direct current, further comprising a magnetic field sensor
provided for measurement of a magnetic field in the sensor, said sensor
outputting a signal for regulating the direct current through the
compensation windings.
2. The circuit according to claim 1, wherein the magnetic field sensor is
configured as a Hall sensor or XMR sensor.
3. The circuit according to claim 1, wherein, by means of the measurement
of the magnetic field sensor the eddy-current field is regulable to a
preassignable value, including zero.
4. The circuit according to claim 1, further comprising a detector coil to
detect a voltage induced by the magnetic field in the acceleration sensor,
including the eddy-current field.
5. The circuit according to claim 1, wherein, a variable proportional to a
voltage induced by the magnetic field in the acceleration sensor, in
particular from the eddy-current field, is generated by a means of
differentiating the measured magnetic field.
6. The circuit according to claims 4 or 5, wherein the direct current
yields a low-frequency component of the acceleration, and the voltage
induced by the magnetic field in the acceleration sensor, in particular
from the field in the eddy, or the variable proportional to the voltage,
yields a high-frequency component of the acceleration, and the direct
current and the induced voltage or the variable proportional to the
voltage are combinable to a broad-band acceleration signal.
7. The circuit according to claim 3, wherein, by addition of a measured
value of the magnetic field sensor to the compensation current, a
broad-band value proportional to the rotational speed is determinable.
8. A digitally controlled machine tool, comprising an acceleration sensor
according to the Ferraris principle, and an evaluating circuit according
to claim 1.
9. A arrangement for evaluating an acceleration according to the Ferraris
principle, comprising:
an inductive measurement head that interacts with a movable Ferraris disk,
essentially via a main magneticizing field, and which generates a first
signal that is dependent on acceleration of the Ferraris disk,
a magnetic field sensor for measuring a magnetic field in the inductive
measurement head,
an evaluation circuit coupled with the magnetic field sensor for providing
the first signal,
compensation windings arranged in the area of the inductive measurement
head for providing a compensating magnetic field which can compensate an
eddy-current field occurring from a higher rotational speed of the
Ferraris disk,
an excitation circuit receiving the first signal and generating a second
signal fed to the compensation windings for generating the compensating
magnetic field.
10. The circuit according to claim 9, wherein the magnetic field sensor is
configured as a Hall sensor or XMR sensor.
11. The circuit according to claim 9, wherein the compensating magnetic
field compensates the eddy-current field to a preassignable value,
including zero.
12. The circuit according to claim 9, further comprising a second sensor to
detect a voltage induced by the eddy-current field.
13. The circuit according to claim 12, further comprising a differentiator
for differentiating the second signal and an adder for adding the voltage
weighted by a factor to the differentiated second signal.
14. The circuit according to claim 9, further comprising a first
differentiator for differentiating the first signal and a second
differentiator for differentiating the second signal, and an adder for
adding the differentiated first and second signal.
15. The circuit according to claim 14, wherein the first signal is weighted
by a first factor before it is differentiated and the second signal is
weighted by a second factor before it is differentiated.
16. The circuit according to claim 15, further comprising a second adder
for adding the first signal weighted by the first factor and the second
signal weighted by the second factor.
Description
FIELD OF THE INVENTION
The invention relates to a circuit for evaluating an acceleration sensor
using the Ferraris principle, having an inductive measuring head which
cooperates with a moving Ferraris disk essentially over a main magnetic
field and supplies an acceleration-dependent variable.
BACKGROUND OF THE INVENTION
For the detection of changes in speed on drive shafts, the prior art
teaches the use, inter alia, of acceleration sensors which operate in
accordance with the Ferraris principle or rotary field principle. Such
sensors are based on the induction principle and are classed with
induction measuring elements.
In accordance with the Ferraris principle, a disk, for example made for
aluminum, is used as a conductor which is rotatably mounted and moves in a
magnetic field. The magnetic field may also be designated as the main
field, to be generated either by a permanent magnet or by an operating
coil. The design of such a measuring head surrounding the Ferraris disk
will be discussed in more detail below. Movement of the Ferraris disk, for
example by coupling to a drive axle, induces currents, in particular eddy
currents, in the Ferraris disk which can be evaluated by a detector coil
and provide a variable, proportional to the acceleration of the Ferraris
disk.
In practice, the solutions for evaluating such an acceleration sensor using
the Ferraris principle in accordance with the prior art exhibit
substantial drawbacks. For example, the sensitivity of the sensor drops
sharply in the case of a high rotational speed of the Ferraris disk. The
illustration according to FIG. 1 shows a diagram in this respect in which
the output signal V.alpha. of such an angular acceleration sensor
according to the prior art is plotted as a function of rotational speed
.omega.. From this it can be seen that the output signal of the sensor
drops by 3 dB as early as at a rotational speed range of approximately
3000 to 3500 rpm. This characteristic response to the rotational speed of
DC Ferraris sensors can be ascribed first to dissipation in the disk,
which leads to heating of the disk, and second, to the eddy-current field,
which acts in a compensating fashion on the applied DC magnetic field at a
relatively high rotational speed.
Based on an extrapolation of the prior art, it would seem possible to avoid
this undesired effect by using either the design of the sensor or
electronic linearization, for example, to amplify the amplitude of the
sensor signal as a function of the working point, to linearize the
sensitivity. A drop of 3 dB in the useful signal can be displaced by
higher rotational speeds by the design of the sensor, for example by
skillful selection of the material of the disk, the applied magnetic
field, and of the gap between head and disk. But these design choices
result in a loss of sensitivity.
Linearizing in an electronic way could also be performed by
post-amplification of the acceleration signal as a function of rotational
speed. However, this requires knowledge of the sensitivity characteristic
relative to rotational speed, and of the rotational speed itself.
Moreover, interference such as noise is also amplified, and this leads to
a smaller signal-to-noise ratio at higher rotational speeds.
SUMMARY OF THE INVENTION
The object of the present invention is therefore to develop a Ferraris
sensor having evaluation electronics such that the sensor is upgraded for
a substantially larger rotational speed range than has previously been
known from the prior art, and losses with regard to the sensitivity and
the signal-to-noise ratio are kept as low as possible.
To achieve this object, the invention makes use of a Ferraris sensor having
advantages over those known in the prior art, by developing the
acceleration sensor having an evaluating circuit arrangement by means of
an additional DC magnetic field excitation circuit with a means for
driving the latter to cause the additional DC magnetic field to act in a
compensating fashion on an eddy-current field, starting from a relatively
high rotational speed of the Ferraris disk. This is achieved for example,
by virtue of the fact that the additional DC magnetic field excitation
circuit comprises a means for generating a direct current which is
proportional to a control signal dependent on the rotational speed of the
Ferraris disk and which flows through an operating coil which supplies the
additional compensating DC magnetic field. It is preferred for the
operating coil to be arranged in such a way that the additional
compensating DC magnetic field can be coupled in and onto the Ferraris
disk in the region of the inductive measuring head.
The aformentioned disadvantages of the prior art are successfully avoided
as a consequence of the compensation of the drop in sensitivity by an
additional DC magnetic field excitation circuit and the means, required
therefore, for driving in accordance with the invention. The excitation
circuit includes a means for generating current which generates a direct
current which is proportional to a control signal, and an operating coil
through which the direct current flows and which generates a magnetic
field which is coupled in onto the disk in the region of the head and acts
in a compensating fashion on the DC eddy-current field.
Two types of generation of the control signal dependent on rotational speed
are proposed:
generating of the control signal outside the acceleration sensor; and
obtaining the control signal from variables of the acceleration sensor.
If the control signal is generated outside the acceleration sensor, the
excitation circuit then functions as a compensation circuit without a
regulating effect.
In a preferred embodiment of the evaluation circuit according to the
present invention, the operating coil can be used to amplify the main
magnetic field between the inductive measuring head and the Ferraris disk
in a fashion proportional to the control signal dependent on rotational
speed. In this case, it has proved to be favorable when a suitable
characteristic curve is used to relate the rotational speed of the
Ferraris disk to the control signal.
In another preferred embodiment of the present invention, the eddy-current
DC field can be reduced in a fashion proportional to the control signal,
dependent on rotational speed, by means of the operating coil. If the
control signal for driving the operating coil is not generated in the
sensor itself, but outside it, it is possible to distinguish thereby,
fundamentally, two advantageous design types. First, the operating coil
acts in the direction of the main field. For the purpose of compensating
the drop in sensitivity, the main field is additionally amplified in a
fashion proportional to the control signal with the aid of the operating
coil. The control signal is combined with a signal, for example the
rotational speed, fed from the outside. The combination is performed via a
characteristic curve. If the profile of the sensitivity against rotational
speed is known, the main field can be amplified with the aid of the
characteristic curve in a fashion inverse to the sensitivity as a function
of rotational speed. The drop in sensitivity toward higher rotational
speeds is thereby compensated. The main field can be generated in this
case by a permanent magnet or solely by the operating coil or with the aid
of a further operating coil.
Second, the operating coil acts in the direction of the eddy-current field.
The actual cause of the drop in sensitivity is the eddy-current field. In
order to counteract this the eddy-current DC field is compensated directly
with the aid of a suitably fitted winding. The control signal is combined
with the rotational speed, for example via a proportionality factor. Since
the eddy-current DC field is proportional to the rotational speed and the
compensation field is then set in a fashion proportional to the rotational
speed, this leads to compensation of the eddy-current field, and this
linearizes the sensor. The compensation need not be exact, because the
sensitivity around the rotational speed of zero is constant over a certain
range. The compensation need merely ensure that the linear range is not
left. The main field can be generated in this case as well by a permanent
magnet or with the aid of a further operating coil. The losses in the case
of higher rotational speeds are greater than without compensation, but
smaller than in the case of the previously described compensation by
increasing the main field.
If the control signal is generated from variables in the sensor, the
functional chain closes to form a control loop. In accordance with the
present invention, two types of control loop are proposed in this case:
a control loop which for the purpose of generating the control signal uses
the signal of the acceleration sensor through subsequent integration; and
a control loop which, for the purpose of generating the control signal,
uses an additional magnetic field sensor, for example a Hall sensor or an
XMR sensor.
According to a further preferred embodiment of the present invention, the
additional DC magnetic field excitation circuit forms a control loop with
the sensor by virtue of the fact that the control signal dependent on
rotational speed can be generated from the acceleration-dependent variable
of the sensor. This can be implemented particularly easily and effectively
by virtue of the fact that the control signal, dependent on rotational
speed, can be generated by an integrator by means of integrating the
acceleration-dependent variable.
A further preferred embodiment of the evaluation circuit in accordance with
the present invention therefore obtains the control signal, dependent on
rotational speed, through a further magnetic field sensor from the
magnetic field of the acceleration sensor, in particular from the field in
the eddy. It is thereby possible by measuring the field and using a
regulating device to regulate the field in the eddy to a specific value
(for example zero), and thus to avoid a drop in sensitivity.
Yet a further preferred embodiment makes use, (in addition to the magnetic
field sensor), of a detector coil for detecting a voltage induced by the
magnetic field of the acceleration sensor, in particular the field in the
eddy.
An alternative design of the evaluation circuit of the present invention
dispenses with the additional detector coil by virtue of the fact that a
variable which is proportional to a voltage induced by the magnetic field
of the acceleration sensor, in particular the field in the eddy, can be
generated by a means for differentiation of this magnetic field. By virtue
of the fact that a determined compensating direct current applies a
low-frequency component of the acceleration, and the voltage (Uind)
induced by the magnetic field of the acceleration sensor, in particular
the field in the eddy, (or the variable proportional thereto which
supplies a high-frequency component of the acceleration), the two signals
can be combined to form a broadband acceleration signal. By adding the
measured value of the magnetic field sensor to the compensation current,
it is also possible, however, to determine a broadband value proportional
to the rotational speed.
Such an acceleration sensor using the Ferraris principle and with an
evaluation circuit according to the invention can be used particularly
advantageously in a numerically controlled machine tool, a robot or the
like. Further advantages and details of the invention will be apparent for
the detailed description below and in conjunction with the drawing in
which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a typical sensitivity profile of a Ferraris acceleration
sensor according to the prior art;
FIG. 2 shows a side view of a known measuring head of an acceleration
sensor using the Ferraris principle;
FIG. 3 shows a front view of a known measuring head of an acceleration
sensor using the Ferraris principle;
FIG. 4 shows the principle of a control loop with the control signal being
obtained from a variable of the acceleration sensor;
FIG. 5 shows an arrangement of a magnetic field sensor with a detector coil
and a compensation winding in accordance with the invention;
FIG. 6 shows the principle of a control loop for regulating a compensation
current and evaluating the acceleration, based on an arrangement according
to FIG. 5; and
FIG. 7 shows a the principle of a control loop for regulating a
compensation current and evaluating the acceleration as in FIG. 6, but
without detector coil.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 has been explained herein above. FIG. 2 and FIG. 3 show, by way of
example, a known measuring head T of an acceleration sensor using the
Ferraris principle, in a side view (FIG. 2) and a corresponding front view
(FIG. 3).
The measuring head or probe T is constructed on an installation sheet or in
a housing 1 and has a detector-side flux-guiding structure 2 and a
flux-guiding structure 3 on the side of the Ferraris disk for the magnetic
flux, which describe a cross section in the shape of a horseshoe. The flux
guidance structure 3 has a first permanent magnet 4. Two detector coils 6
and 6' arranged in parallel and having a respective core are fitted to the
other flux guidance structure 2 at the open end of the cross section in
the shape of a horseshoe on a coil plate 9. Fitted on the latter, in turn,
in each case is a flux guidance structure 7 and 7' with respective
permanent magnets 5, this being done such that the permanent magnets 4 and
5 are situated opposite one another and remaining free therebetween is an
air gap in which the Ferraris disk F engages. The coil plate 9 has a cable
connector 10 for electric connection of, for example, an evaluation
circuit.
On the basis of such an arrangement of measuring head T, and Ferraris disk
F, FIG. 4 shows a first exemplary embodiment of the invention with a
control loop, and the acceleration sensor is used to determine the
additional DC magnetic field for compensation purposes. Obtaining a
control signal from a variable of the acceleration sensor T, 6, 6', F is
performed in this case using the principles whereby an acceleration signal
Vdet is detected via the detector coils 6 and 6' and is amplified in an
amplifier device 11, and filtered with the aid of a filter device 12 and
then released as useful signal V.alpha. for regulating, for example, drive
connected to the rotatable Ferraris disk.
Subsequently, the useful signal V.alpha. is integrated by a downstream
integrator circuit 13, the result being a voltage V.omega. which is
proportional to the rotational speed .omega.. The voltage V.omega. is
subsequently applied to a series circuit composed of a resistive component
R.sub.K and an inductive component, and an operating coil or compensation
coil 14 preferably arranged in the region of the measuring head T, which
thus leads to a current I.sub.K which is proportional to the rotational
speed .omega.. In this way, the current I.sub.K generates in the region of
the measuring head T an additional magnetic field which is proportional to
the rotational speed .omega. and counteracts the undesired DC eddy-current
field. A precondition for this is that it is ensured by the winding of the
compensation coil 14 or by the polarity of the voltage V.alpha. (for
example via an inverter) that the polarity of the compensation field is
opposite to that of the eddy-current field.
Another preferred embodiment of the present invention, which is illustrated
in FIG. 5, detects the magnetic field in accordance with the invention
with the aid of an additional measuring device 15 in the acceleration
sensor T, F. This can be, for example, the field Bmess in the eddy. Via a
suitably fitted winding 14 for compensating the eddy-current DC field, the
compensation current I.sub.K is set such that the field at the measuring
point Bmess of the measuring instrument 15 assumes a prescribable value
such as, for example, zero. The compensation current I.sub.K required
therefor is determined in this case by a regulation explained in more
detail below.
FIG. 5 illustrates a corresponding arrangement having a measuring
instrument for the field +Bmess and -Bmess, specifically magnetic field
sensors 15, 15', and compensation windings 14, 14', as well as detector
coils 16, 16' for detecting an induced voltage Uind. The profile of the
eddy current I.sub.W in the Ferraris disk F, which rotates with a speed v,
is shown, as is the magnetic field B produced by the eddy current. The
respective magnetic flux .PHI..sub.W induced by the eddy current I.sub.W
is now detected at the two measuring points +Bmess and -Bmess with the aid
of the magnetic field sensors 15 and 15', which are provided in twofold
fashion by analogy with the coils 6 and 6' of the measuring head T. The
appropriately assigned compensation windings 14, 14' and the two detector
coils 16, 16' are now arranged in the direction of flux on the respective
axis of the induced magnetic flux .PHI..sub.W such that the eddy-current
DC field can be influenced by the compensation windings 14, 14' to which
the compensation current I.sub.K or -I.sub.K is applied, and an induced
voltage Uind can be detected by the detector coils 16, 16', being
dimensioned in accordance with the equation:
Uind=k*N*(d.PHI..sub.W /dt) (1)
The regulating device can be configured in this case in various forms. In a
first variant, which is shown in FIG. 6, the measuring instrument 15, 15'
is for the field Bmess (magnetic field sensor) and the detector coils (16
or 16' ) is for detecting the induced voltage Uind are used to generate
the sensor signal dv/dt. In the second variant, shown in FIG. 7, it is
even possible to dispense with detector coils 16, 16' for detecting the
induced voltage Uind.
In accordance with the first variant (FIG. 6), it holds that the
magnetomotor force is:
.PHI..sub.W =k.sub.W *L.sub.W *I.sub.W -k.sub.K *L.sub.K *I.sub.K, (2)
where L.sub.K is the inductance of the compensation coil 14, and L.sub.W is
the eddy-current inductance.
It holds for the measured field that:
Bmess=k.sub.m *.PHI..sub.W (3)
The calculating rule (1) set forth above holds for the induced voltage. It
holds for the relationship between the speed v of the Ferraris disk F and
the eddy current I.sub.W that:
I.sub.W =v*B*W/R.sub.w, (4)
with R.sub.W as the eddy-current resistance.
The equation (4) can now be used to derive by differentiation:
d/dtv=R.sub.W /(B*W)d/dt I.sub.W
With the aid of equation (2), this becomes:
d/dtv=R.sub.W /(B*W)*(d/dt.PHI..sub.W +k.sub.K *L.sub.K
ddtI.sub.K)/(k.sub.W *L.sub.W) (5)
With the aid of equation (1), equation (5) yields:
d/dtv=R.sub.W /(B*W*k.sub.W *L.sub.W)*(Uind/(k*N)+k.sub.K d/dtI.sub.K)
or in a simplified version:
d/dtv=k.sub.1 *Uind+k.sub.2 d/dtI.sub.K (6).
According to the present invention, the arrangement shown in FIG. 6, which
is explained below, serves in accordance with this variant for the purpose
of regulating the field Bmess and evaluating equation (6).
What is shown in FIG. 6 is the principle of the electric regulation with
the aid of which the components 14 to 16 are driven or evaluated in order
to regulate the compensation current and evaluate the acceleration. The
compensation current I.sub.K is determined from the difference, -, of the
value .PHI..sub.W, determined by the magnetic field sensor 15, in Bmess,
and the value zero by an PI controller 17, which is fed into the
compensation winding 14. Furthermore, the value I.sub.K is weighted with a
factor k.sub.2 and differentiated in a means 18. Subsequently, an
acceleration-dependent variable d/dt v (acceleration value as derivative
of speed v with respect to time t) is determined in accordance with
equation (6) from the value obtained in the process by its addition "+" to
the induced voltage Uind weighted with the factor k.sub.1, and determined
by the detector coil 16.
The objective is to obtain an acceleration signal at the Ferraris sensor
with as broad a band as possible. Particularly in case of slow
compensation regulation, the desired broadband nature is not provided
simply by evaluating the compensation current. In the arrangements
according to FIG. 6 and FIG. 7, which are explained below, the signal
I.sub.K includes the low-frequency component and Bmess includes the
high-frequency component of the acceleration d/dt, v or the rotational
speed v or .omega. itself. The desired broadband signal for the
acceleration is then obtained by combining these two variables.
If the regulation is slow, then, Bmess is regulated to zero in a stationary
fashion, and a field which induces a voltage Uind is produced dynamically.
The compensation current I.sub.K is built up with the dynamics of the
regulation and can be effectively differentiated. The dynamic component is
included in Uind. Taken together, these two produce the acceleration
signal (which is correct in stationary and dynamic terms).
If, by contrast, the regulation is very fast, Bmess also vanishes
identically in a dynamic fashion. According to the calculation rule (3),
it is also the case that .PHI..sub.W =0 dynamically, and thus that the
induced voltage Uind=0. In that case, the branch with Uind and k.sub.1,
can be eliminated. The input of the differentiator 18 then also
corresponds to the speed .omega. in stationary and dynamic terms.
The foregoing holds correspondingly for the negative regulation branch with
the elements 14', 15' and 16' as shown in FIG. 5, but taking into account
the corresponding change in sign. Furthermore, using equation (3) the
following may be determined from the calculation rule (5):
d/dtv=R.sub.W /(B*W)*(d/dt Bmess/k.sub.m +k.sub.K *L.sub.K
d/dtI.sub.K)/(k.sub.W *L.sub.W),
or in simplified terms:
d/dtv=k.sub.3 d/dt Bmess+k.sub.2 d/dtI.sub.K (7)
In accordance with equation (7), it is therefore possible according to the
present invention, to eliminate even the detector coil 16 used in the
variant according to FIG. 6. Instead of this, Bmess is differentiated in a
further means 19 and, weighted with k.sub.3, further processed to form a
signal 20 proportional to the induced voltage Uind.
The illustration according to FIG. 7 shows such an arrangement, similar to
FIG. 6, for regulating the compensation current I.sub.K and evaluating the
acceleration. Exactly as described in the case of FIG. 6, the compensation
current I.sub.K is regulated via the PI controller 17 and further
processed via the factor k.sub.2 and the differentiator 18. Adding "+"
this signal to signal 20 produces the acceleration-dependent variable d/dt
v (acceleration value as derivative of the speed v with respect to time t)
in accordance with equation (7).
In addition, a broadband speed value v can be determined by adding "+"
Bmess weighted with k.sub.3 and the compensation current I.sub.K weighted
with k.sub.2.
If the regulation is, in turn, slow, the branch via I.sub.K supplies the
stationary component, and that via Bmess the dynamic component of the
acceleration value.
Of course, as an alternative to the embodiment shown in FIG. 7 it is also
possible first to add and then differentiate (only once). One of the
differentiators 18 or 19 thereby becomes dispensable. The rotational speed
signal v or .omega. (correct in stationary and dynamic terms) is present
before the differentiation. If, in turn, the regulation is very fast,
Bmess also vanishes identically in a dynamic fashion. The corresponding
branch supplies zero, and can then be eliminated.
The losses in the case of relatively high rotational speeds are certainly
greater according to this principle than without compensation according to
the invention, but smaller than in the case of compensation by increasing
the main field. They are identical to the case of the controlled
compensation.
Of course, with knowledge of the above the person skilled in the art can
design further advantageous embodiments depending on requirements, but
these are all based on the principle of compensating the eddy-current DC
field according to the invention.
*
