The present invention relates to a device according to the preamble
of the main claim and a method according to the preamble of the independent claim.
The present invention is basic
to all actuators, in particular piezoelectric actuators
The DE 199 52 946 A1
discloses a piezoelectric drive called a piezo ring motor (PRM). This piezo ring motor has a high torque, a high positioning accuracy, a flat design and inherent sensor characteristics. This combination is particularly advantageous compared to conventional actuators. The motor principle causes a high reduction ratio between drive ring and shaft and thus provides a high positioning accuracy. In a positive variant of the engine, in which ring and shaft are subjected to a suitable toothing, the accuracy improved by missing slip again. In this way, the piezo ring motor can start each rotational angle position controlled. All that needs to be initialized is the engine control with an initial position.
Absolute positioning is only possible if the engine electronics
once an absolute position is known. After that you can join
inactive electronics no longer change the motor position. The
The last detected motor position must always be stored non-volatile
become. Are these technical requirements not available and
should be the approach of absolute angular positions after switching on
the drive must be initialized. Initializing drives
happens on conventional
Way by targeted approach an initialization position. there
The rotor of the motor is rotated until the rotor position
coincides with an outer angle mark.
This can be done automatically by using a zero position encoder
and by feedback
done on the engine control. Another possibility for a targeted start of a
Initialization position is the visual comparison, along with
a manual correction of the motor position. In both cases, essential
the relative and absolute positioning accuracy of the piezoring motor
not be used immediately.
It is advantageous if the drive without external intervention its absolute position
can also find after losing the last position. It should be one
a piezoelectric ring motor are provided with the
an online initialization and a recovery of the absolute position
executable without external position encoder
This is an initial initialization by means of a reference run
It fixes the motor and the angular position of the motor shaft
measured. The zero position is based on a measured value
approached by an external angle sensor or zero position sensor.
The engine electronics can be initialized based on the encoder
become. This conventional
disadvantageously a special setup for initialization.
Likewise, disadvantageously, a reinitialization must be performed,
Case that the engine electronics zero position, for example
due to an overload
or a memory error, loses.
It is an object of the present invention, a piezoelectric actuator, in particular a piezo ring according to the DE 199 52 946 A1
in such a way that by means of a motor control device each absolute rotational angular position is directly controllable and any shift or loss of the absolute rotational angular position is correctable by means of a simple and effective online position initialization. Position initialization means that an initial starting position is restored. Online means performing a position initialization during operation of the no-load actuator. It should be on external position sensor, such as external angle sensors or zero-position sensors are omitted.
The object is achieved by a device according to the main claim and a
Method according to the independent claim
Zero position initialization on an actuator, in particular on a piezoelectric actuator, as preferably a piezoelectric Piezoringmotor according to the DE 199 52 946 A1
is performed on the basis of a measurement of the engine's own loss torque with respect to the angular position. Each drive or motor has a unique, typical for this loss torque function, which is essentially determined by the structure of the motor or actuator. Once such a torque loss function is recorded with respect to the angle of rotation and before it is operated Way produces a calibration loss torque function. This calibration loss torque function can be used at any later time to initialize the motor position. A mathematical comparison is made of the known calibration loss torque function (calibration function) with the operating loss torque function measured during operation. In the mathematical comparison by means of correlation, the measured operating loss torque function is pushed along the rotation angle axis via the known calibration function. At the maximum of the correlation, the angular positions of the measured operating loss torque are most likely to coincide with the positions of the calibration function. The position of the maximum of the correlation function for shifting the rotation angle is used for correcting the rotation angle value stored in a motor control means. In this way, the engine control device and thus the actuator are initialized during operation.
Particularly advantageous is the loss torque function of a
piezoelectric actuator, in particular a piezoelectric
Ring motor, used for online position initialization. basis
is the comparison between a once-measured calibration loss torque function
(Calibration function) with respect to
the angle of rotation of the motor shaft and a measured operating loss torque function.
Both functions are mathematical, for example via a
Correlation, compared. The position of the maximum of the correlation over a
Displacement angle gives the displacement of the measured angular position
the angular position stored in the engine control unit again.
By means of the correction of the stored in the engine control unit
Angle of rotation with the displacement angle may be the motor or actuator
to be initialized during operation.
The detection of the loss torque functions takes place with no-load actuator or motor. The displacement angle Δφ determines the displacement Δφ max of the detected angular position φ with respect to the angular position φ G stored as an initial starting position in a motor control device. By means of the correction, the operating loss torque function M (φ) is again approximated to the original calibration loss torque function (calibration function) M (φ).
the proposed solution
Angle sensors are avoided.
advantageous embodiments can be found in the subclaims.
According to one
advantageous embodiment converts the device for detection
the loss torque functions, that is, the calibration loss torque function
and the operating loss torque function, this in torque
per proportional voltage functions. In this way, the loss torque functions
Can be further processed in an electronic way. For example, you can
This way the loss torque functions are stored and mathematical
or physically compared.
According to a further advantageous embodiment, the mathematical comparison is carried out by means of a cross-correlation (see equation 1). An alternative comparison function can be used, which assumes that the mean values of functions remain unchanged over longer periods of time. This alternative comparison function is, for example, that with Equation 2
certain. Thus, it is advantageous to use a comparison function which is different from the cross-correlation and which retains the scaling and mean value of the loss torque functions.
According to a further advantageous embodiment, the actuator is a piezo ring motor, the at least two electromechanical drive elements, at least one drive ring which can be excited by the stroke of the electromechanical drive elements to a circumferential displacement movement, and a shaft which can be placed on the drive ring, so that through the Displacement movement of the drive ring, the shaft is rotatable, has, and the at least one drive ring is mechanically stiffened connected to the drive elements. This piezo ring motor can also do all in the DE 199 52 946 A1
have disclosed features. The disclosure of this document is the entire content of this patent application.
According to a further advantageous embodiment in the form of a form-fitting variant of the engine, while ring and shaft are acted upon with suitable teeth, has at least one tooth tip on the drive ring and at least one associated tooth valley on the shaft and / or at least one tooth valley on the drive ring and at least one associated Denture head on the shaft one of an ideal form ing shaping for generating at least one characteristic pulse in the loss torque function. This is particularly advantageous for improving the noise immunity of the device. This targeted change in the tooth shape improves the immunity to interference of the correlation measurement, in particular the cross-correlation measurement.
According to one
Further advantageous embodiment, the calibration loss torque function (calibration function)
stored in a memory device.
According to one
further advantageous embodiment performs a switching device,
in a first mode, operating loss torque functions of the device
for mathematical comparison and in a second operating mode calibration functions
the storage device to.
According to one
Another advantageous embodiment is a multi-channel piezo driver
for adjusting the output signals of the engine control unit
Piezoelectric actuators of the actuator provided.
According to one embodiment of a method according to the invention, the mathematical comparison is carried out by means of a correlation, in particular a cross-correlation (see equation 1). Likewise, an alternative compare function may be used which preserves the scaling and mean of loss torque functions. This can in particular the function
According to one
further advantageous embodiment of the method according to the invention
is determined by means of a shape deviating from an ideal shape of
Drive ring and / or shaft of the actuator at least one characteristic
Pulse generated in the loss torque function. On
In this way, a characteristic mark can be generated.
The present invention will be described in conjunction with the figures
of exemplary embodiments
described in more detail.
1 a representation of an embodiment of a device according to the invention;
2 an illustration of a calibration loss torque function and an operation loss torque function according to the embodiment; and
3 a representation of the mathematical comparison based on a cross-correlation.
1 shows a representation of an embodiment of a device according to the invention. 1 schematically shows a structure of a motor controller 9 . 6 and 7 for a piezo ring motor 1 with which a method according to the invention for online position initialization can be carried out. The facilities 9 . 6 and 7 are part of the engine control. Facility 9 denotes a user interface, which may be, for example, a digital data bus, a serial interface, and the like. Facility 6 includes a controller for generating the control signals of the actuators, in particular sine and / or cosine functions of the piezo ring motor 1 , In normal operation, ie there is no overload on the piezo ring motor 1 on, this slip-free follows the control signals. By counting the periods, with a known initial rotation angle, the just current rotation angle of the motor shaft can be determined with sufficient accuracy. Facility 7 is a multi-channel piezo driver 7 , which controls the output signals 6 to the piezoelectric actuators of the piezo ring motor 1 adapts. Facility 2 is a converter that evaluates the feedback signals of the actuators and generates a torque-proportional voltage U (φ). Facility 3 is a switching device 3 , which are only used to record the calibration function, ie before the operation of the actuator 1 recorded calibration loss torque function M (φ), is switched to a position a. In operation, the switching device 3 switched to position b. The device 5 is a storage device 5 in which the calibration loss torque function (calibration function) is stored. Is the switching device 3 Switched to position b, the measured operating loss torque function U (φ) to a cross-correlator 4 pass the measured operating loss torque function with that in the memory device 5 stored calibration function u c (φ) compares. The cross-correlation function r (Δφ) represents the value for the similarity of two input functions. This is done by measuring the measured operating loss torque ment function along the X-axis, or the φ-axis, relative to the calibration function. For each position, a correlation coefficient is calculated. If the magnitude of the correlation coefficient r = 1, then both input functions are identical. That is, the output function on the device 4 for mathematically comparing the calibration function u c (φ) with the operating loss torque function u (φ), is a function whose global maximum is found at a displacement angle Δφ at which the calibration function and the measured operating loss torque function are most similar. An institution 8th searches the shift angle Δφ associated with the global maximum of the cross-correlation function r (Δφ) and sends it to the controller 6 out. The control 6 adds the displacement angle Δφ to the instantaneous value of the angle of rotation φ G which the controller controls 6 has saved and thereby compensates for the error in the stored angle of rotation value. In normal operation, the shift should be Δφ = 0, ie ei ne correction by means of an online initialization leads to no change of the moment in the controller 6 stored value for the motor rotation angle. In the case of an overload, ie a too high torque, there may be a change in the motor rotation angle, which in the control 6 currently stored motor rotation angle φ G deviates from the real motor rotation angle value. In this case, a shift Δφ ≠ 0 by the cross-correlator 4 detected. By adding Δφ to the currently stored motor rotation angle φ G , it is corrected and the system is initialized online.
The cross-correlation can be calculated according to the following equation:
The disadvantage is the compensation of displacements of the input function u c
(φ) and u (φ) to each other by subtracting the average values of both functions according to equation 1. This is only necessary if due to the change of the boundary conditions, the mean values of the functions over large Change periods, as is the case with aging, for example. If the boundary conditions are stable, a following Equation 2 leads to better results, since in addition the mean values are included in the similarity analysis:
In an experiment, the most important steps using an appropriate software were an online initialization to a piezo ring motor 1 traced. For this purpose, a calibration loss torque function or calibration function was first recorded in 2 is shown. Significantly, a characteristic course can be seen, the fingerprint of the piezo ring motor 1 is comparable. After a few turns of the piezo ring motor 1 The operating loss torque function M (φ) has been measured over an angular range of α = 206 ° 2 dotted is shown. The associated rotation angle was set to start with φ G = 0 ° and should be corrected by an initialization. The aim was to calculate the function of the correlation to the displacement angle Δφ by cross-correlation of the calibration function and the operating loss torque curve.
A result of the calculation of the correlation function is according to 3 shown. The position of the maximum of the function with respect to the X-axis gives the shift of the measured operating loss torque function to the calibration function. In the experiment, a shift of Δφ = 241.4 ° was determined. For the correction, ie for the initialization, the shift angle Δφ must be added to the angle φ G originally defining 0 °. As a check, a conventional measurement with a rotary encoder coupled to the motor shaft was carried out in parallel to the described test procedure. The measurement showed a shift of Δφ = 239.9 °. The comparison between the measurement results of the measurement based on the cross correlation and an external rotation angle sensor shows a good agreement with ei ner deviation of only 1.5 °.
use of Equation 2 for similarity comparison becomes
a same data set, a deviation between the rotational angle measured value
based on the similarity comparison
and the measured value of an external rotary encoder of only 0.5 °.