Electricity: measuring and testing – Electrical speed measuring – Including speed-related frequency generator
Reexamination Certificate
1998-11-05
2001-03-20
Oda, Christine (Department: 2862)
Electricity: measuring and testing
Electrical speed measuring
Including speed-related frequency generator
C324S173000
Reexamination Certificate
active
06204658
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method for evaluating an output signal of a device which senses cyclical motion, in particular, a method applicable to evaluation of an output of a sensing device for determination of rotational speed.
A system employing an evaluation method of this type is disclosed, for example, in EP 0 684 480 A1 (U.S. Pat. No. 5,606,252). The known system evaluates a signal which is emitted by a sensing device used for the determination of the rotational speed of a rotating part. When such devices are used in a vehicle, the rotating parts monitored are generally the wheels, the rotational speeds of which are used, for example, as input signals for an anti-lock brake system (ABS).
In a sensing device upon which the known evaluation method is based, a pulse wheel having a series of teeth is mounted on the rotating part. The pulse wheel, referred to also as a pole wheel particularly in connection with sensing devices employing inductive action, is actively coupled with an inductive sensor attached on a fixed part which inductively produces a periodic signal during rotation of the pole wheel. When the rotational speed remains constant, the signal produced by the sensor has a,constant frequency due to an equidistant placement of the teeth on the pole wheel. The actual rotational speed of the rotating part is directly related to the frequency of the inducted signal, which may be determined following suitable conversion.
The above signal is normally transmitted to an electronic control device for evaluation. The evaluation process is then carried out in the form of a program sequence in a microprocessor located in the control device.
In sensor systems of the type described above, damage to the pole wheel may result in generation of irregular signals despite a constant rotational speed of the measured part. A pole wheel may be damaged, for example, as a result of an accident, such that one or more teeth,may be missing. Consequently, signal cycles in the output signal of the sensor or in the signal received by the control device will be missing. In accordance with conventional evaluation methods, an undesirable alteration in the rotational speed derived from the received signal may result.
It is therefore an object of the invention to provide a method for evaluating an output signal of a device sensing cyclical motion, in accordance with which abnormal signal evolutions occurring as a consequence of damage to the sensor device are recognized and displayed in a reliable manner.
SUMMARY OF THE INVENTION
In accordance with these and other objects of the invention, there is provided an evaluation method for evaluating an output signal of a sensing device for detection of rotational speed in which the output signal has a periodic time cycle with a predetermined target number of signal periods for each movement cycle. A cycle time value is determined by timely evaluation of signal cycles following each other and a change is noted in the cycle time value or in the speed value derived therefrom. The signal cycles are counted until at least the predetermined target number is reached in order to define a complete movement cycle, and an error signal is produced only when a change in the cycle time value or in the speed value derived therefrom which exceeds a predetermined measure occurring in a complete movement cycle occurs again in a subsequent movement cycle in approximately the same manner.
Contrary to known methods in which an evaluation of an output signal for purposes of recognizing signal abnormalities is carried out for only a relatively short time span comprising few signal cycles, the evaluation method according to the invention takes place over an extended period of sufficient duration to permit at least two complete movement cycles by the rotating part, wherein the completion of an entire movement cycle is effected by counting the signal cycles. Thus, for example, when the invention is used in vehicle technology to determine the rotational speeds of the wheels, the output signal is observed during at least two complete wheel revolutions.
The invention has the advantage that it can be readily implemented in the form of a program sequence in any currently available type of microprocessor. Moreover, since only a minimal amount of memory is required, the invention may be used with inexpensive microprocessors of very simple design.
The evaluation method in accordance with the invention provides the further advantage that damage of a diverse nature, or other kinds of defects present in the sensing device, can be recognized in a reliable manner. Thus, in addition to recognizing the presence of a single defect in the form, for example, of a missing tooth on a pole wheel, the method is equally effective in identifying any cyclically repeated signal abnormalities as malfunctions. However, in accordance with the invention, sporadic interferences with signals which occur in practice, and which can therefore be tolerated, do not lead to error detection.
In an advantageous further embodiment of the invention, the number of signal cycles is determined during an observation cycle in order to allow proper evaluation. The observation cycle (which, as explained below, differs from the evaluation method) is selected so that it is long enough to comprise several signal cycles, but at the same time being substantially shorter than a complete movement cycle. Using the number of signal cycles thus obtained, and taking into account the length of the observation cycle, a short-term mean value of the cycle time of the signal cycles can then be determined. This mean value can then be used advantageously for the recognition of damages to the sensing device resulting in relatively considerable interference, in particular with signal sequences with frequent, small errors.
The applicability of the invention to the most varied types of sensing systems is yet another of its advantages. Thus, in addition to use of the method in conjunction with the already described inductively functioning sensing systems, the method in accordance with the invention could also be used to evaluate an optical sensing system, for example operating with a reflected-light barrier or a forked light barrier and a pulse wheel, instead of a pole wheel. In such optical sensing devices, dirt, or other form of optical obscurement, may result in undesirable, cyclically recurring signal interferences.
In an advantageous further embodiment of the invention, the movement cycle described above, which comprises a target number of signal cycles determined by the design of a particular sensing device, is replaced by a monitoring cycle (defined below) for the production of the error signal. In accordance with the embodiment, the error signal is generated only when changes in the cycle time value, or the speed value derived therefrom during a complete monitoring cycle, which exceed a predetermined measure, and which have already occurred during at least one preceding complete monitoring cycle, occur again in the same or nearly same manner. Such a monitoring cycle comprises a multiple of the target number of signal cycles of a movement cycle. By virtue of the longer monitoring cycle, the embodiment provides the advantage that reliable generation of the error signal is ensured even for signal interferences in the sensor signal which are close to the trigger threshold of the sensing device and therefore occur only sporadically.
In a particularly advantageous embodiment, the monitoring cycle comprises an integral multiple of the target number of signal cycles of a movement cycle, i.e. the monitoring cycle comprises several complete movement cycles.
When the invention is applied in practice to vehicle technology, for example in combination with sensing systems of the type described above for the determination of the rotational speed of vehicle wheels, pole wheels with different numbers of teeth are used depending on vehicle model or tire size. The number of different pole wheels that can possibly be used in this regard
Holst Hans
Stanusch Gerald
Andersen Henry S.
Oda Christine
Proskauer Rose LLP
WABCO GmbH
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