Coded data generation or conversion – Digital pattern reading type converter – Incremental
Reexamination Certificate
2002-04-04
2003-12-23
Tokar, Michael (Department: 2819)
Coded data generation or conversion
Digital pattern reading type converter
Incremental
C341S015000, C341S017000, C701S220000, C303S186000, C303S187000, C033S707000
Reexamination Certificate
active
06667696
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a sensor system which is to be used for angular and position measurements.
How the digital absolute value is determined in the encoder is to be left open here. For example, it may be determined using the method described in the Swiss Patent Application No. 02105/99. In that example the angular and/or position measuring device contains a scanning head with at least one sensor for determining absolute angular and/or position values and at least one sensor for determining angular and/or position incremental values lying between two consecutive absolute values. The scanning head contains the means of creating a total absolute value from an absolute value determined by at least one sensor and an incremental value determined by at least one sensor and of making this total absolute value available in binary/digital form.
Therefore, the absolute value recorded by the measuring system and the fine value determined separately between two values of the recorded absolute value are brought together instantly in the electronics of the encoder, combined as a total absolute value in binary/digital form and provided for encoder output across the whole operating range. Thus, all of the signal processing occurs in the scanning head, so that complicated signal transfer (cable, shielding etc.) is considerably simplified and costly electronic peripherals (AD converters, sample and hold components, processors etc.) may be dispensed with.
The said patent application describes relationships between greatest measurement speed and resolution, which show that encoder resolutions above the 18 bits required for the field of application (e.g. motors with 0 to 6000 rpm or positioning speeds of up to 10 m/sec.) are approaching the limits of the system. In cases requiring resolutions of, for example, 20 bits and greater, it is recommended to transfer the 12-bit SIN/COS signals (analog values) from the encoder to the evaluation unit in addition, in order to carry out external finest resolutions of, for example, 10 bits. A resolution of the angular/path sections approaching 22 bits can be achieved with all of the additional features associated with this such as wiring measures, components, susceptibilities and above all problematic encoder accuracy.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a measuring system which overcomes the above-mentioned disadvantages of the heretofore-known measuring systems of this general type and which allows an increase in encoder accuracy without the need to accept the above-mentioned disadvantages.
With the foregoing and other objects in view there is provided, in accordance with the invention, a sensor system, wherein a digital absolute value of the particular position of a stationary part (stator) of an encoder (
1
) with respect to a part moving relative to it (rotor) is created, and which is transferred in serial transmission to an evaluation circuitry (
3
), whereby the transfer of the absolute value is induced by an external signal, wherein the change in absolute value is recorded each time by the sensor, finest interpolation with selectable absolute resolution takes place beginning each time from the time of said change, and the absolute value is amended by the accumulated result of finest interpolation when interrogated by the external signal.
According to another feature of the invention, the speed derived from the change in the absolute value is taken into consideration during finest interpolation.
According to another feature of the invention, the time of the change is transmitted to the evaluation circuitry (
3
) via a separate line (
5
) or old signal output, and finest interpolation occurs in the evaluation circuitry (
3
).
According to another feature of the invention, transmission of the time takes places via the line (
4
′) for serial transmission of the absolute value.
According to another feature of the invention, finest interpolation takes place in the sensor (FIG.
3
).
According to another feature of the invention, the absolute value is amended by the result of finest interpolation before transfer.
According to another feature of the invention, the absolute value and result of finest interpolation are transferred consecutively and the absolute value is amended subsequently.
According to another feature of the invention, the absolute value is created from a scanned absolute track of the rotor and interpolation of the distance/angle in between.
According to another feature of the invention, when using a register (
11
) to give the absolute value, the change in a certain selectable register position determines the time of the change.
According to another feature of the invention, the edge of the signal changing the register position determines the time.
According to another feature of the invention, a counter (
13
) counts the pulses of a generator (
14
) from the time of the change.
According to another feature of the invention, the direction of movement of the rotor of the encoder (
1
) is determined in the sensor and output via a separate line (L/R).
High position resolution is required, where precise adjustments need to be brought into position as rapidly as possible and the position must be strictly maintained even when there are variations in load or where there is interference. Demanding servo control systems operate at cycle times (time between two control/positioning actions on the drive) of down to approximately 50 &mgr;sec. If we take as an example a shaft of approximately 40
Ø
mm and an absolute encoder resolution of 17 bits, this corresponds to a resolution increment of approximately 1 &mgr;m.
This means that at most the 1 &mgr;m step is recorded in the cycle time of 50 &mgr;sec., corresponding to an acceleration of
a
=2
s/t
2
=2 &mgr;m/(50
2
*&mgr;m
2
)=(2*10
6
)/2500
a
=(2/2.5)*10
3
=800 m/sec
2
≈80 g
However, the aim is to get down to ranges of g=10 m/sec
2
, which means that resolutions of over 22 bits are required. What is particularly difficult with such resolutions is that with the current state of the art the existing and faded analog signal (SIN/COS signal) with noise for the path must first be differentiated, in order to get the required speed for the controller. The extent of the problem becomes clear when the normal 1V
ss
−SIN/COS signals with a 12-bit AD conversion (e.g. in order to get from a 10-bit incremental base resolution to the 22-bit total resolution) are to be used and need to process voltages of several {fraction (1/10)}mV in harsh industrial conditions.
The underlying invention avoids analog signal processing via cable prone to interference, and costly as well as problematic analog conversions in the evaluation circuitry. Instead only digital signals are used which can be processed precisely and without interference in the computer control systems which function on a digital basis in any case.
This method benefits from, for example, the well known and obvious fact about incremental encoders that division accuracy is much greater than the resolution predetermined by the increment. In addition, the repeatability of the sensor values is many times greater. In practice 30 to 100 times more accurate values are obtained in precision encoders than the resolution, let alone the achievable absolute value accuracy, would predict. This is because the scale disks—for example in optical encoders—are produced using highly accurate lithographic processes. These devices are used in the production of masks for semi-conductors and achieve a precision of up to a few nanometers. This means that synchronized sensor systems—as recited, for example, in Swiss Patent No. 02 105/99—which function on an incremental basis, are predestined to achieve much greater resolutions.
Evaluation systems which record the position of increments on the basis of mean-value generation of several increments, are particularly suitable in this respect. Even the zero crossings of the SI
Greenberg Laurence A.
Locher Ralph E.
Mai Lam T.
Stemer Werner H.
Tokar Michael
LandOfFree
Sensor system for measuring angles and positions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Sensor system for measuring angles and positions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Sensor system for measuring angles and positions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3160883