Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Reexamination Certificate
2000-07-24
2001-12-25
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
C318S603000, C318S687000
Reexamination Certificate
active
06333614
ABSTRACT:
Applicant claims, under 35 U.S.C. §119, the benefit of priority of the filing date of Oct. 15, 1997 of a German patent application, copy attached, Serial Number 197 45 490.9, filed on the aforementioned date, the entire contents of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for monitoring the operational state of electric motors, and a circuit arrangement for executing the method.
2. Description of the Related Art
It is known that safety functions are increasingly provided for the most varied types of machine tools and processing centers, which as a rule assures a limited operation, a safe stop or safe operating stop of the respective machines even if one or several components fail, or in case of wrong operation. By means of this it is intended to dependably prevent accidents in which the workpiece, the tool or the machine could be damaged or the user could even be injured. To avoid expensive additional arrangements, these safety functions are integrated into the control unit of the machine.
So that the control unit of the machine can dependably detect at what time it is necessary to perform a safety function, the functions and parameters relevant for safety are also positively monitored. To this end, it is necessary that two independent processors perform the monitoring actions simultaneously.
It is disadvantageous here that up to now only the safe processing and the safe forwarding of the signals received from an electric motor or transmitted to an electric motor were monitored. If operational states should occur inside the electric motor itself which might lead to an unsafe operational state of the entire machine, this cannot be detected by the control unit, since in this case there is no erroneous processing or transmission.
SUMMARY OF THE INVENTION
An object and advantage of the present invention therefore is to disclose a method and a circuit arrangement, by means of which a control unit of a machine tool or of a robotic device can assuredly detect whether the electric motors regulated by the control unit are in a safe operating state.
This object and advantage is attained by a first aspect of the present invention that regards a method for monitoring the operational state of an electric motor that includes changing a torque current of an electric motor and performing a first evaluation of an output signal of an angle encoder during a testing interval, wherein the angle encoder is connected to the electric motor, and the output signal is representative of the number of revolutions of the angle encoder. Simultaneously and independently performing a second evaluation of the output signal a second time during the testing interval. Determining first and second changes in number of revolutions of the angle encoder during the testing interval based on the first and second evaluations, respectively. Detecting a safe operational state for the electric motor if the magnitude of each of the first and second changes in number of revolutions lies above a minimum value and performing steps for producing a safe operational state for the electric motor if either of the first and second changes in number of revolutions lies below a predetermined value.
A second aspect of present invention that attains the object and advantage regards a circuit arrangement for monitoring the operational state of an electric motor that includes an angle encoder mechanically connected with an electric motor. A first processor electrically connected to the angle encoder, wherein the first processor includes a first comparator that receives an output signal from the angle encoder. A second processor electrically connected to the angle encoder, wherein the second processor includes a second comparator that receives the output signal from the angle encoder. A shutoff component connected to the first and second processors to receive output signals from the first comparator and the second comparator, wherein the shutoff component shuts off the electric motor should an error be detected in either one of the output signals of the first and second comparators during a testing interval.
The method and circuit arrangement in accordance with the invention has the advantage that, in addition to monitoring the transmission and detection of the control signal, the output signal of the angle encoder of the electric motor is also monitored. Because of this, no danger can arise for the user or the machine, even if a malfunction occurs in an angle encoder or an electric motor which, for example, causes a stoppage of the electric motor or prevents the evaluation of the output signal from the angle encoder.
The present invention will be explained in greater detail in what follows by means of the embodiments represented in the drawings. Shown are in:
REFERENCES:
patent: 3794899 (1974-02-01), Breslow
patent: 4463300 (1984-07-01), Mayne et al.
patent: 4594538 (1986-06-01), Schmitt
patent: 5689170 (1997-11-01), Ishikawa
patent: 42 24 620 (1964-03-01), None
patent: 40 16 836 (1991-11-01), None
patent: 195 22 447 (1997-01-01), None
patent: 0 247 994A2 (1987-12-01), None
patent: 0 247 994A3 (1988-11-01), None
patent: 0 443 384 (1991-08-01), None
patent: 0 450 834 (1991-10-01), None
patent: 0 658 832A2 (1995-06-01), None
patent: 0 658 832A3 (1998-05-01), None
patent: 2 063 595 (1981-06-01), None
“Controleur de rotation minimale” Tout L'Electronique, No. 406, Jan., 1976, p. 65.
D. Dietrich et al., “Prozesssicherheit mit parallelen Systemen,” Elektronik, vol. 66, No. 5, Mar. 19, 1984, pp. 20-22 and 25.
Brinks Hofer Gilson & Lione
Dang Khanh
Johannas Heidenhain GmbH
LandOfFree
Method and circuit for monitoring the operating condition of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and circuit for monitoring the operating condition of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and circuit for monitoring the operating condition of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2560176