Control apparatus for electromagnetic device having proportional

Electricity: electrical systems and devices – Control circuits for electromagnetic devices – For relays or solenoids

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Details

H01H 4732

Patent

active

051915049

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to a control apparatus for controlling an electromagnetic device, e.g., an electromagnetic proportional valve, having proportional solenoid which generates a force proportional to the value of a supplied current
2. Background Art
For example, in hydraulic circuits of construction machines, etc., electromagnetic proportional valves are widely used to control hydraulic pressure and oil flow rate. The control amount (hydraulic pressure and oil flow rate) of an electromagnetic proportional valve varies substantially in proportion to the exciting current I of a coil, as shown in the characteristic curve of FIG. 8.
In the prior art, in order to control such an electromagnetic proportional valve, a control apparatus having such circuit configuration as shown in FIG. 9 is used. That is, a controller 1, which is comprised of a microprocessor (MCU), outputs a digital signal responsive to a control target value. This digital signal is converted to an analog voltage signal by a DA converter 2. This analog voltage signal is converted to an analog current signal by a voltage/current converter (VI converter) 3. The analog current signal is applied to the coil of an electromagnetic proportional valve 4 and excited.
The voltage/current converter 3 is provided with a dither function in which a high-frequency current of 200 to 600 Hz is superposed to the coil current in the range of 10 to 20% of the rated current of the electromagnetic proportional valve 4, thus resulting in decrease of a hysteresis of the electromagnetic proportional valve 4.
In this configuration, however, there has been a problem in that the apparatus is expensive because it uses a DA converter 2 and a voltage/current converter 3. As an apparatus for controlling the electromagnetic proportional valve 4 without the above-mentioned expensive circuit parts such as the voltage/current converter or the like, a control apparatus having the configuration shown in FIG. 10 is known.
Shown in the figure are a controller 1 which is comprised of a microprocessor, an input and output control section 5 comprised of a digital output section 5a and an AD converter 5b, a driving transistor 6 for forming an exciting current for supplying electricity to the coil of the electromagnetic proportional valve 4, and a flywheel diode 7.
The controller 1 provides a duty factor value corresponding to the target value of the exciting current allowed to flow through the coil of the electromagnetic proportional valve 4 to the digital output section 5a. The digital output section 5a outputs a pulse which is at a high level for a period corresponding to the duty factor to the driving transistor 6. The high level of the pulse causes the coil of the electromagnetic proportional valve 4 to be excited for a period corresponding to the duty factor. At this time, the exciting current flowing through the coil is in the form of a sawtooth as a result of the inductance component of the coil itself and the action of the flywheel diode 7, and it is fed back to the power supply voltage side. Its average current value is proportional to the power supply voltage and the duty factor of the coil current. Hence, the power supply voltage of the coil is read out to the controller 1 via the AD converter 5b, and the duty factor value to be supplied to the digital output section 5a is corrected according to the value of the power supply voltage thus read. As a result, the exciting current is set to its target value.
Therefore, a voltage/current converter is not required in the configuration of FIG. 10, so it is inexpensive in comparison to the configuration of FIG. 9. Also, an actual exciting voltage is detected and fed back, and its duty factor is corrected so that the exciting current come close to a control target. The accuracy is therefore improved over that of the apparatus of FIG. 9.
However, in the above-mentioned configuration, a duty factor is determined from an input control target value, presupposing the direct current resistance compone

REFERENCES:
patent: 4195333 (1980-03-01), Hedel
patent: 4562548 (1985-12-01), Anderson et al.
patent: 4701588 (1987-10-01), Fukasawa
patent: 4849869 (1989-07-01), Tanuma et al.
Yasuo Tanaka, Abstract for JP 60-117604, "Controller for Electromagnetic Device With Proportional Solenoid", Jun. 25, 1985.
Rosenberg, "Dictionary of Computers, Information Processing, and Telecommunications", 1984, pp. 547 and 586.

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