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US 4,053,733 AGranted
Temperature control device
AssigneeMinolta Camera Kabushiki Kaisha
InventorsTomoji Murata, Masayuki Maese
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AssigneeMinolta Camera Kabushiki Kaisha
InventorsTomoji Murata, Masayuki Maese
Estimating the term…
A temperature control device in which electric power to be supplied to a heating element is controlled correspondingly to pulse intervals applied to a switch circuit with the pulse intervals adapted to vary according to the temperature of the portion to be heated by the heating element, which temperature control device is further provided with a sensor for detecting the pulse intervals when the temperature of the portion to be heated has reached a predetermined level with the signal from the sensor being utilized as the signal for the completion of warming-up of the portion to be heated.
A temperature control device for controlling the temperature of a portion to be heated by a heating element to which electric power is supplied, the device comprising:
A temperature control device for controlling the temperature of a portion to be heated by a heating element to which electric power is supplied, the device comprising:
A temperature control device for detecting zero crossing points of an A.C. power source and for generating pulse signals at zero crossing times of the A.C. power source, for integrating a control input voltage and for producing an output of zero crossing signals after the integrated value of said control input voltage has exceeded a predetermined value, said temperature control device comprising a switching element for passing a half cycle of the A.C. power source to a heating element, a rectifier coupled to the A.C. power source, a Zener diode, an output terminal of said rectifier being connected to said Zener diode for developing trapezoidal form waves of rectified full waves across said Zener diode, a first capacitor and a diode connected to each other in series and connected to opposite sides of said Zener diode, a first transistor, the common junction of said first capacitor and said diode being connected to the base of said first transistor with said first capacitor and said first transistor forming a differential circuit so as to develop differential pulses at the base of said first transistor upon the rise of said trapezoidal form waves, series-connected resistors connected to the collector of said first transistor for developing zero crossing signals at a common junction of said series-connected resistors upon momentary conduction of said first transistor due to said differential pulses and for determining a comparison voltage, a programmable uni-junction transistor, to which said common junction of said series-connected resistors is connected, a pulse transformer to the primary winding of which the cathode of said programmable uni-junction transistor is connected for developing pulses for turning on said switch element and the secondary winding of said pulse transformer being connected to the control terminals of said switching element, a temperature sensor element disposed in the vicinity of said heating element for detecting the temperature of a heating apparatus to be heated by said heating element, one terminal of said temperature sensor element being connected to an output terminal of said rectifier, a second transistor, the other terminal of the temperature sensor element being connected to the base of said second transistor, a third transistor and a plurality of resistors connected to the collector and emitter of said second transistor and the collector of said third transistor to form with said second transistor a differential amplifier, a further plurality of resistors connected between the other terminal of said temperature sensor element and another terminal of said rectifier, series-connected resistors connected, at a common junction thereof, to the base of said third transistor for biasing said third transistor, a fourth transistor for a constant current source having the emitter thereof connected to the collector of said second transistor and the base thereof connected to the collector of said third transistor for receiving the output of said differential amplifier with the collector of said fourth transistor being connected to the anode of said programmable uni-junction transistor, a second capacitor for integration and to which the collector of said fourth capacitor is connected, and a smoothing capacitor coupled to said rectifier.
In a temperature control device in which electric power to be supplied to a heating element is controlled corresponding to pulse invervals applied to a switching element with the pulse intervals adapted to vary according to the temperature of a portion to be heated by the heating element, and in which a temperature sensor element is provided to detect the pulse intervals when the temperature of said portion to be heated has reached a predetermined level with the signal from said sensor element being utilized as signal for completion of warming-up of said portion to be heated, a temperature control circuit comprising said switching element which is coupled between an A.C. power source and said heating element, a transformer, a rectifier coupled to the A.C. power source through said transformer, a Zener diode, said rectifier having an output terminal connected to said Zener diode for developing trapezoidal form waves of rectified full waves across said Zener diode, series-connected resistors coupled to opposite sides of said Zener diode, a programmable uni-junction transistor, the common junction of said series-connected resistors being connected to the gate of said programmable uni-junction transistor for dividing the voltage of said trapezoidal form waves and for applying the same to said gate to enable phase control synchronized with the wave forms of the A.C. power source, a pulse transformer having the primary winding connected to the cathode of said programmable uni-junction transistor and the secondary winding of said pulse transformer being connected to the control terminals of said switching element, a comparison amplification control circuit connected between said output terminal of said rectifier and the anode of said programmable uni-junction transistor, said temperature sensor element being connected in parallel to said comparison amplification control circuit, a first capacitor connected to an output terminal of said comparison amplification control circuit and to the anode of said programmable uni-junction transistor for integrating output current from said comparison amplification control circuit and applying the voltage across said first capacitor to the anode of said programmable uni-junction transistor, a first transistor having the base connected to the cathode of said programmable uni-junction transistor, a charging circuit composed of a series connected resistor and a second capacitor, a second transistor, the common junction of said resistor and said second capacitor being connected to the collector of said first transistor and the base of said second transistor for rendering said first transistor conducting whenever a pulse from said programmable uni-junction transistor is applied to said first transistor so as to discharge said second capacitor, a plurality of resistors connected to said second transistor for forming a comparison and detecting circuit for comparing and detecting the potential of said second capacitor, a third transistor, to which the collector of said second transistor is connected, a warming-up completion detection relay coupled to said third transistor for being driven thereby by amplification of the output current from said second transistor, said relay having a self-holding contact and another contact for generating a signal, and a smoothing capacitor coupled to said rectifier.
Dependencies are inferred from the claim text.
Drawings are temporarily unavailable. Open the PDF at USPTO
No related US applications are recorded in the indexed filing history.
With sensing elements having variation of electric or magnetic properties with change of temperature: the sensing element having a resistance…
Using an analogue comparing device: delivering a series of pulses
Systems for controlling or regulating non-electric variables
Term ended 11 Oct 1994 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention relates to a temperature control device, and, more particularly, to a temperature control device for use, for example, in a heating apparatus employing an electric heating means or the like.
Conventionally, in a heating apparatus of the above described type used, for example, for fixing a developed toner powder image onto a copy paper sheet in a known electrophotographic copying machine, a temperature control device having a known zero-crossing temperature control circuit for an A.C. power source is employed, in which prior art zero crossing temperature control circuit, on-off control or proportional control is generally used. However, such a conventional temperature control device has serious disadvantages in that, the on-off control method has only rough controlling accuracy although it has a simple construction, while the proportional control method inevitably requires a complicated control device in spite of the high control accuracy thereof.
Commonly, in the heating apparatus for fixing a toner powder image of the above described type, predetermined optimum temperatures in the range of approximately 100.degree. to 200.degree. C. are required, and in bringing such a fixing device into operative condition, the fixing device must first be "warmed up", i.e., the temperature of the fixing device must be raised from room temperature level to a predetermined optimum level. Since insufficient fixing results in unclear copied images, to prevent a printing operation from being carried out before the temperature of the fixing device reaches the predetermined high level, it is necessary for the copying apparatus to be provided either with locking means for preventing a printing operation during such "warming-up time", or indication means for drawing the attention of the operator to the condition of the machine, for which purpose a temperature control device having detection means for detecting the completion of such "warming-up" is required.
These and other objects and features of the present invention will become apparent from the following description taken in conjunction with the preferred embodiment thereof with reference to the accompanying drawing, in which;
FIG. 1 is an electrical block diagram of a temperature control device according to one embodiment of the present invention,
FIGS. 2(A) through 2(E) illustrate wave forms and pulse intervals explanatory of the operation of the device of the present invention,
Before the description of the present invention proceeds, it is to be noted that like parts are designated by like numerals throughout several views of the accompanying drawings.
Referring now to FIGS. 1 to FIG. 4(C), there is shown in FIG. 1 an electrical block diagram of a temperature control device of the invention which generally comprises a zero-crossing point detection circuit 1 for detecting zero-crossing points of an A.C. power source, an integrating circuit 2 on which a control input voltage is impressed for integrating said control input voltage therein, both of which circuits 1 and 2 are coupled to a comparison circuit 3 for comparing zero-crossing signals from the zero crossing point detection circuit 1 with the integrated voltage from the integration circuit 2, and a switching circuit 4 connected between the comparison circuit 3 and a load 5, a common junction of the comparison circuit 3 and the switching circuit 4 being further connected to the integrating circuit 2. The zero crossing point detection circuit 1 produces pulses as shown in FIG. 2(B) every time the A.C. voltage as in FIG. 2(A) passes the zero crossing point. The increasing rate of the output voltage from the integrating circuit 2 is proportional to the control input voltage, i.e., the output voltage from the integrating circuit 2 reaches a predetermined voltage value Eo at speeds proportional to the magnitude of the control input voltage. The comparison circuit 3 compares the zero crossing pulses from the detection circuit 1 with the integrated voltage from the integrating circuit 2 and produces output pulses as shown in FIG. 2(D) in synchronization with the zero crossing signals generated after the integrated voltage has exceeded the predetermined value Eo. As is clear from FIG. 2(D), the intervals between the output pulses of the comparison circuit 3 become short when the control input voltage is high, while the same become long as the control input voltage decreases, and upon development of the output pulses from the comparison circuit 3, the integrated voltage of the integrating circuit 2 is reset to zero. The switching circuit 4, for example, a triac inserted between the A.C. power source and the load 5 is triggered by the output pulses from the comparison circuit 3 and supplies to the load 5 half a cycle of the A.C at the time when said output pulses are impressed thereon.
By this arrangement, when the control input voltage is high, the output voltage of the integrating circuit 2 rises in steep slopes as shown at the portion A of FIG. 2(C) and reaches the predetermined value Eo by the time when the half cycle of the A.C. power source is completed with the output voltage subsequently being impressed upon the comparison circuit 3, which comparison circuit 3 develops output pulses from a zero crossing signal Po1 after the half cycle of the A.C. power source has been completed. The output pulses thus developed turn on the switching circuit 4 which in turn supplies the load 5, for example, with a negative half cycle W.sub.N1 of the A.C. current as shown in FIG. 2(E), while the same output pulses also re-set the integrating circuit 2, which again begins to integrate the control input voltage starting from zero.