Data processing: measuring – calibrating – or testing – Measurement system – Dimensional determination
Reexamination Certificate
2000-11-20
2003-07-08
Barlow, John (Department: 2863)
Data processing: measuring, calibrating, or testing
Measurement system
Dimensional determination
Reexamination Certificate
active
06591220
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method and an apparatus for measuring angles and/or distances.
Conventional angle/distance measuring systems have either been configured to output incremental signals or to output absolute-value signals and are therefore predominantly used, for example, for specific industrial applications.
Inexpensive incremental transmitters have the disadvantage that during very slow movements/revolutions there is no adequate signal resolution, and that during very rapid movements/revolutions and at high resolution the signal transmission is limited by the frequency.
A resolution of, for example, 18 bits, that is to say 256000 pulses/revolution—which means a resolution of about 4 &mgr;m for a 1 m circumference in the case of precise machines—results in signal transmission frequencies of approximately 30 MHz at 6000 rev/min. This is much too high for most control systems and causes problems for an interference-free signal transmission over long distances.
The complicated and expensive absolute transmitters are on the other hand restricted in terms of their internal signal processing by complicated electronics for high resolution and rapid measurement sequences, so that the absolute systems are used only for relatively low rotational speeds.
In recent times, combinations of incremental and absolute transmitters have increasingly been used, for example for servodrives which, at a standstill, transmit the absolute value and during movement sequences transmit the incremental information through the use of sine/cosine signals to be evaluated in a peripheral electronic/control system, which then determines the current value by computation on the basis of the absolute value originally measured at a standstill (see, for example, European Patent No. EP 0 575 843). Therefore, during operation, the measured value is only formed by the extensive peripheral electronics, which is equipped with sample-and-hold components and complex A/D converter components and needs computers or processors both in the transmitter (transducer) electronics and in the peripheral electronics. In addition to the loss of the correct absolute position (interference), which is always a problem in this case, the interference-free transmission of the analog signals in accordance with phase and magnitude is also very critical over long cable lengths and comes up against physical limits in the case of highly dynamic drives (although the bandwidth of the transmission has been reduced through the use of SIN/COS voltages). In addition, it is very difficult to transmit analog signals via optical fibers, so that for the required EMC (electromagnetic compatibility), special and enhanced screening measures have to be taken and complicated line drivers have to be used in the case of copper cables.
These above-described solutions are either inadequate or else very complicated, expensive and unreliable at high resolutions and in the case of rapid movements. For example in the case of the above-mentioned combination of the incremental measurement transmitter and the absolute measurement transmitter, it is therefore necessary to bring the drive or machine to a stop if one wants to check the absolute value or if the latter has to be redetermined in the event of a fault being established. This is already a problem in the case of machines and drives under the current safety standard, and is unsatisfactory for many operational procedures. In addition, the divided measured-value processing results in totally unsatisfactory reliability and responsibility in the case of erroneous measured values, and to similarly erroneous signal processing in service and guarantee work at the user's or customer's premises.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method and an apparatus for measuring angles and/or distances which overcome the above-mentioned disadvantages of the heretofore-known methods and apparatuses of this general type.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for measuring angles and/or distances, including:
a sensing head having a first sensor and a second sensor;
the first sensor determining an absolute value of an angle and/or a distance;
the second sensor determining an incremental value of the angle and/or the distance, the incremental value lying between two successive absolute values; and
a circuit for forming a total absolute value from the absolute value and the incremental value and for providing the total absolute value as a binary/digital value, the circuit for forming the total absolute value being provided in the sensing head.
In other words, the apparatus according to the invention for measuring angles and/or distances includes a sensing head having at least one sensor for detecting absolute values of angles and/or distances and at least one sensor for determining incremental values of angles and/or distances lying between two successive absolute values. In the sensing head there is a device for forming 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 for providing this total absolute value in binary/digital form.
With the objects of the invention in view there is also provided, a method for measuring angles and/or distances, the method includes the steps of:
determining an absolute value with a first sensor of a sensing head of a measuring apparatus;
determining an incremental value with a second sensor of the sensing head;
forming a total absolute value from the absolute value and the incremental value; and
providing the total absolute value as a binary/digital value.
In other words, in the method according to the invention for measuring angles and/or distances with the above-defined measuring apparatus, a total absolute value is formed from an absolute value determined by at least one sensor and an incremental value determined by at least one sensor. This total absolute value is provided in binary/digital form.
According to the invention, the absolute value, which is determined by the measuring system, and the fine value, which is determined separately between two values of the determined absolute value, are processed directly in the transmitter electronics (transducer electronics). The absolute value and the fine value are combined and are provided as a total absolute value in binary/digital form to the transmitter output (transducer output) over the entire operating range. The entire signal processing is therefore carried out in the sensing head, so that the complicated signal transmission (cable, screening and so on) is significantly simplified and, above all, the complicated peripheral electronics (A/D converter, sample-and-hold components, computer and so on) can be dispensed with.
In addition, the signal processing, which is provided in the transmitter and has the shortest-possible path connections, not only offers the lowest susceptibility to interference and the highest processing speed, but also allows to control signal delays and allows the most precise fine-value interpolation. The signal delays between the true angle/distance position and the signal output are therefore to be attributed only to the configuration of the transmitter and not to additional factors such as different cable lengths and/or a peripheral-signal processing device. It is therefore possible to compensate for the lagging measured value, also referred to as a slip error, simply by including the signal delays in the signal processing and therefore it is possible to always output the true actual angle/distance position.
In accordance with another feature of the invention, a synchronization device is connected to the circuit for forming the total absolute value, the synchronization device controlling a synchronous combining of incremental values determined by the second sensor for forming the total absolute value.
In accordance with yet another feature of the in
Greenberg Laurence A.
Herra Rotterdam B.V.
Lau Tung S
Locher Ralph E.
Stemer Werner H.
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