Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
1999-03-16
2001-12-04
Metjahic, Safet (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S166000, C324S207200, C318S254100
Reexamination Certificate
active
06326778
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method and apparatus for transmission of data and more particularly to a method and apparatus for transmitting speed information and other information detected by a sensing device.
2. Description of Related Art
Sensing devices that detect the speed of a moving object (rotary movement or linear movements) and transmit the information about the detected speed as well as additional information such as temperature, switching behavior, and direction of movement, to a control device, can transmit this information in various ways, which all tend to have certain problems associated therewith.
All of the information, i.e., the detected speed and the additional information detected, can be transmitted in parallel. This approach, however, requires additional lines and connections to the sensing device. The additional lines and terminals add to the cost and affect the reliability both during manufacture and operation. The additional lines and contact terminals on the sensing device and the internal wiring required inside a semiconductor chip in which such sensing devices are integrated, can result in EMI or EMV interference.
Another approach for transmitting the afore-mentioned information uses a very fast serial data protocol. In this approach, the speed information and the additional information are transmitted sequentially. In comparison to parallel transmission, no additional lines or contact terminals on the sensing device are required. The data protocol, however, must be transmitted relatively fast so that all the information is transmitted within an acceptable time.
Yet another approach for overcoming the disadvantages uses a so-called multilevel analog transmission. This transmission of the information, however, requires an extremely accurate calibration of the sensing device and/or an extremely accurate measurement. Problems with this transmission technology can arise, particularly if the sensing device is subjected to severe temperature fluctuations.
It is therefore desirable to provide a method of the type described above which is much simpler and much less susceptible to errors than the conventionally employed transmission methods. The method may also allow a relatively low-frequency serial data transmission over two-wire lines. It would also be desirable to provide a sensing device for carrying out such a transmission method.
SUMMARY OF THE INVENTION
According to the present invention, a transmission clock cycle is selected as a function of speed detected by a sensing device and additional information is transmitted as a modulation of the transmission clock cycle.
In order to be able to select the transmission clock cycle as a function of the speed detected by the sensing device, code information may advantageously be applied to the movable object that is monitored by the sensor, at regular intervals on the side that is scanned by the sensing device. This code information may be scanned and evaluated by the sensing device used to measure the speed. In the simplest case, the code information may be in the form of colored bars arranged at regular intervals on the object to be moved. Other forms of code information are also possible. For example, the teeth and gaps of gears or racks may be used to provide code information. Depending on how fast the moving object moves or turns, the code elements of the code information move faster or slower past the sensor of the sensing device, which may be detected by the sensor device to evaluate the speed.
The detection signal that is produced when the code elements move past the sensor of the sensing device may advantageously be supplied to a threshold value discriminator to derive from the detection signal an unambiguous square-wave signal. This square-wave signal may then provide the transmission clock cycle for the additional information. For example, the additional information could be the temperature or the switching behavior of the sensor. The direction of movement may also be transmitted to a control device as additional information. According to the invention, this additional information may be transmitted as modulation of the transmission clock cycle.
Advantageously, the modulation may be performed by binary data bits, with one data bit being transmitted between the individual edges of the transmission clock pulses.
Optical, inductive, and magnetic sensors may be used as sensors of the sensing device. The code information, or the code elements applied as code information to the object to be moved, may depend on the type of the selected sensor.
According to another advantageous feature of the invention, the sensing device may have one or more Hall sensors which detect the movement of teeth and gaps as they pass during the movement of the rack or gear. The consecutive tooth edges may be detected and the resultant cycle signal may be transmitted almost without any time delay to a control device which generates a transmission clock pulse that corresponds to the passing edges. If the teeth move quickly past the sensor, then the transmission clock frequency may be higher than when the teeth move more slowly past the sensor. The code elements, in this case the teeth and alternate gaps, may correspond exactly to the transmission clock pulses.
The method of the invention may advantageously employ a two-wire line as the transmission channel; in other words, no additional wire connections or terminals may be needed at the output of the sensing device for data transmission. In addition, data may be easily transmitted, using only two signal levels (in voltage or current mode).
The sensing device according to the invention for carrying out the above method may produce a data signal at the output terminals of the sensing device, wherein the transmission clock cycle of this signal may be a measure of the speed of the movable object that is detected by the sensor. The transmission clock cycle may be modulated with additional information.
A sensing device of this type may be produced, for example, as a monolithic integrated circuit. A sensing device of this type may be advantageously employed in automobiles for controlling an ABS (anti-lock braking system).
The method and the sensing device of the invention will now be described in greater detail with reference to embodiments shown in the figures.
REFERENCES:
patent: 5319291 (1994-06-01), Ramirez
patent: 5459405 (1995-10-01), Wolf et al.
patent: 5723957 (1998-03-01), Ishikawa
patent: 5859510 (1999-01-01), Dolan et al.
patent: 26 04 599 A1 (1977-11-01), None
patent: 0 766 088 A1 (1997-02-01), None
patent: WO 97/08674 (1997-06-01), None
patent: WO 98/09173 (1998-05-01), None
Foley Hoag & Eliot LLP
Metjahic Safet
Micronas GmbH
Zaveri Subhash
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