Presses – Automatic or material triggered control
Reexamination Certificate
1999-09-27
2001-05-29
Gerrity, Stephen F. (Department: 3721)
Presses
Automatic or material triggered control
C100S048000
Reexamination Certificate
active
06237479
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a controller for a press in which a slide is rectilinearly driven by an electric servo motor, that is, a so-called servo press.
BACKGROUND ART
In recent years, a rectilinear motion-type press (hereinafter referred to as a servo press) in which a slide is rectilinearly driven by an electric servo motor such as an AC servo motor or the like is used in many fields. The reason for the above is that compared with conventional mechanical presses, the servo press has advantages of being able to operate with freer slide motion at higher speed and to easily control pressure, thus enabling a higher degree of forming and improving productivity. Further, as compared with oil hydraulic presses, the servo press has advantages of providing lower noise, lower vibration, and higher energy saving, being clean without oil leakage, and being able to start and stop a slide extremely in a short time, thus improving working environment, productivity, and the like.
Known as a controller for such a servo press is a servo press controller disclosed in Japanese Patent Publication No. 3-33439 which shows a controller which operates predetermined servo calculation processing with one computer unit (hereinafter called CPU) as a core, outputs the servo command to a servo pack (a so-called servo amplifier) to control the position and speed of a servo motor, and rectilinearly drives a ram (a slide) with the stroke thereof being within a previously set range.
In the aforesaid conventional servo press controller, however, there occur disadvantages regarding safety described below.
1) When a CPU chip malfunctions, for example, due to thermal runaway, abnormalities in power supply voltage, or electrical noise, the maximum value of speed command or position command is sometimes outputted. Thereby, there is the possibility that so-called servo runway occurs, whereby the ram abruptly operates at high speed in an unexpected direction.
2) Further, when a ram position sensor breaks down, some electrical noise is intermingled with a signal line of the position sensor, or a contact failure in a input connector of position signals and the like occurs, there is the possibility that the position control of the ram becomes impossible, thereby producing servo runaway.
3) Furthermore, when the control software of the CPU malfunctions due to some program error and the like and so-called software runaway occurs, there is also the possibility that servo runaway occurs.
DISCLOSURE OF THE INVENTION
The present invention is made in view of the aforesaid disadvantages, and its object is to provide a servo press controller which can prevent servo runaway caused by the malfunction of CPUs for controlling a servo, the fault of a position detector, and the like and has a higher level of safety.
A servo press controller according to the present invention is a servo press controller which drives a slide supported on a frame to be rectilinearly movable by a servo motor to thereby conduct press working characterized by including
an operation input element which inputs press operation signals including an operation mode and an operation starting signal for a press by means of manipulation of an operation switch by an operator or communication from the outside, and outputs the inputted press operation signals,
a first CPU which previously stores set data including motion data of the slide and starting conditions of the press, outputs the stored set data at the time of press starting, and decides whether press starting is possible or not based on the stored set data and the press operation signals inputted from the operation input element to thereby output a press starting signal,
a second CPU which decides that press starting is possible based on the set data inputted from the first CPU and the press operation signals inputted from the operation input element, and calculates and outputs a position command of the servo motor based on the motion data in the set data at least when the press starting signal shows that press starting is possible,
a first position sensor for detecting the position of the slide, a second position sensor for detecting the rotational position of the servo motor,
a third CPU which inputs position signals from at least either of the first position sensor or the second position sensor, and calculates and outputs a speed command with at least one of the inputted position signals as a position feedback signal, based on a position deviation between the position command from the second CPU and the position feedback signal, and
a servo amplifier for controlling a driving current of the servo motor in such a manner that a speed deviation between the speed command inputted from the third CPU and a speed feedback value of the servo motor calculated based on the position signal inputted from the second position sensor decreases,
the first to third CPUs having the function of sending and receiving watch dog signals at least either of between the first CPU and the second CPU, or between the second CPU and the third CPU to thereby check whether the partner CPU is in normal operation, and having the function that when one CPU is judged to be abnormal by the check, the partner CPU stops the press for emergency.
According to the above configuration, a plurality of (for example, three) CPUs provided in the controller respectively conduct different processing related to servo press control (the input of set data, the calculation of a servo position command, the calculation of a servo speed command, and the like) and monitor an abnormality in each other's computer. Specifically, two CPUs mutually send and receive watch dog signals to thereby check whether the watch dog signal sent from the partner CPU is normal or not, and thus it is confirmed whether the partner CPU is in normal operation or not. In this case, when it is decided that the partner CPU has a computer abnormality, the press is stopped for emergency, thus preventing the abnormal operation of the slide caused by servo runaway. The decision whether press starting is possible or not is performed by two CPUs (for example, for the input of set data and for the calculation of a servo position command), and only when both CPUs decide that the starting is possible, the press can be started, thereby eliminating the possibility that the press is wrongly started due to the braking of a signal line, a contact failure, noise, the fault of an input circuit, or the like. Accordingly the safety of the servo press can be further improved.
Further, respective software languages for the first CPU and the second CPU may be different.
According to the aforesaid configuration, the software for the first CPU (for the input of the set data) and the second CPU (for the calculation of a servo position command) is described in different languages, for example, a Programming Language C and a ladder sequence language, which eliminates the possibility that the similar bugs (troubles such as a program error and the like) occur in the software of both CPUs. Accordingly, it is prevented that both the CPUs have computer abnormalities at the same time, and either one normal CPU can surely detect the computer abnormality of the other CPU to thereby stop the press for emergency by the monitoring function by means of the aforesaid watch dog signals. As a result, servo runaway and the like are prevented, thereby greatly improving safety.
Furthermore, respective computers of the first CPU and the second CPU may be different in at least either of CPU chip model number or CPU chip manufacturer.
According to the aforesaid configuration, the respective computers of the first CPU (for the input of the set data) and the second CPU (for the calculation of a servo position command) are different in CPU chip model number or manufacturer, which eliminates the possibility that both CPU chips simultaneously get in thermal runaway or software runaway. Accordingly, both the CPUs can be prevented from having computer abnormalities at the same time, and either one normal CPU ca
Gerrity Stephen F.
Komatsu Ltd.
Sidley & Austin
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