JPH0239751B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature sensor disconnection detection device, and more particularly to a temperature sensor disconnection detection device that can properly detect a disconnection of a temperature sensor such as a fuser for a copying machine without wasting time. .

As a temperature sensor disconnection detection device (having a heater heating temperature control function), for example, there is one shown in FIG. A sensor 1 such as a thermistor having a resistance characteristic, a comparison resistor _R1 inserted in series with the sensor 1, a capacitor C that absorbs noise mixed in from the lead wire of the sensor 1, etc., and a control pulse connected to the base. transistors 2 and 4, which are controlled on and off by inputting
Variable resistor 3 to set heater temperature and variable resistor 3
It has a reference resistor R ₂ placed in series with the signal output point D ₁ and D ₂ and a comparison resistor.
R ₁ is set to several kiloohms and reference resistance R ₂ is set to several hundreds of ohms so that R ₁ ≫ _{R 2} is satisfied. A transistor 5 is inserted between the reference resistor R ₂ and the ground, and the output of the common signal output points D ₁ and D ₂ is sent to the microcomputer 2.
0 (A/D converter, input/output interface,
Analog input port A ₁ (contains program ROM, data storage RAM, and processing calculation CPU)
A control pulse is applied to the bases of transistors 4, 2, and 5 from output ports P ₁ , P ₂ , and P ₃ via base resistors 6 , 7 , and 8 . Further, the analog reference voltage set by the divided voltage based on the resistors 9 and 10 is input to the input port _A2 of the microcomputer 20, and the heater control signal generated based on the calculation within the microcomputer 20 is output from the output port _P4 . It is output to the heater control relay 30. A heater control relay 30 controls power supply to the heater 32 based on the AC power supply 31 . Note that A, B, C, D, and E are a charging section, an exposure section, a developing section, a transfer section, and a cleaning section arranged around the photosensitive drum 33.

In the above configuration, the heater temperature control operation will be explained as follows.

(1) Heater temperature (heater 32) determined by sensor 1
Detection mode: By program processing within the microcomputer 20, on signals are output from ports P ₂ and P ₃ and an off signal is output from port P ₁ , transistors 2 and 5 are turned on, and transistor 4 is turned off. In this state, the divided voltage V ₁ at the common connection points D ₁ and D ₂ is as follows.

That is, the combined resistance of the resistors R ₁ and R ₂ is R=R ₁ R ₂ /R ₁ +R ₂ =R ₂ /1+R ₂ /R ₁ , but since R ₁ >>R ₂ , R=R ₂ . Therefore, the divided voltage V ₁ is V ₁ =
R ₂ /R ₂ +R _D V _CC . (R _D is the resistance of sensor 1).

(2) Mode in which the set temperature set by the variable resistor 3 is detected By the program processing in the microcomputer 20, an ON signal is output from ports P ₁ and P ₃ , an OFF signal is output from port P ₂ , and the transistor 4 ,5 is turned on,
Transistor 2 is turned off. In this state, the divided voltage V ₂ at the common connection points D ₁ and D ₂ is as follows.

That is, from the above (1), the combined resistance R=R ₂ , so
The divided voltage V ₂ becomes V ₂ = R ₂ /R ₂ + R _S V _CC (R _S is the set resistance value of the variable resistor 3).

The above modes (1) and (2) are set as shown in the flowchart of FIG. 2, and the divided voltages V ₁ and V ₂ are input to the analog input port A ₁ and A/D converted,
The digital values are V _D1 and V _D2 . the digital value
V _D1 and V _D2 become V _D1 > V _D2 based on a predetermined program.
A comparison operation is performed.

(a) When V _D1 > V _D2 is yes, the control relay 30 is turned off and the heater 32 is turned off.

(b) When V _D1 > V _D2 is no, the control relay 30 is turned on and the heater 32 is turned on.

Based on the above operations, V _D1 is brought close to V _D2 and the heater temperature is controlled to reach the set temperature (in other words, the heater 32 is controlled so that the resistance value R _D of sensor 1 becomes the set resistance value R _S ).

In addition, the disconnection of sensor 1 is caused by transistors 4 and 5.
is turned off, only transistor 2 is turned on, and the voltage divided by comparison resistor R ₁ and resistor R _D of sensor 1 is V=
By reading R ₁ /R ₁ +R _D V _CC , disconnection can be detected when V=0. In this detection operation, even if the resistance R _D of the sensor 1 becomes a high resistance on the order of megohms at low temperatures, there is no risk of false detection because the comparison resistor R ₁ is set to a relatively high resistance value of several kiloohms.

However, in the sensor disconnection detection device described above, when the sensor 1 becomes high in resistance due to low temperature during the disconnection detection operation, the divided voltage V becomes V=R ₁ /R ₁ +R _D V _CC [1-exp {−1/C(1/R ₁ +1/R _D )t}] Take the transient value. Note that the above formula is derived as follows.

The equivalent circuit at the time of wire breakage detection is shown in FIG.

In this circuit, the circuit equation is V _CC = R _D i ₁ + R ₁ i ₂ 0 = -R ₁ i ₂ + 1/C∫i ₃ dt i ₁ = i ₂ + i ₃ From the above three equations, i ₁ and i ₂ are When erased, R _D i ₃ + R _D + R ₁ /CR ₁ ∫i ₃ dt=V If the charge of _{the CC} capacitor is q, then i ₃ = dq/dt, so the above equation becomes R _D dq/dt+R _D +R ₁ /CR ₁ q=V _CC ...(1) If the initial conditions are t=0, q=0, the general solution to equation (1) is q=CR ₁ /R _D +R ₁ V _CC (1- exp-t/T) However, T=CR _D R ₂ /R _D +R _1Here , since q=CV, V=q/C=R ₁ /R _D +R ₁ V _CC (1-exp-t /T) = R ₁ /R _D +R ₁ V _CC {1-exp[-1/C(1/R ₁ +1/R _D )t]}. Therefore, since it takes a long time to reach the final value of V=R ₁ /R ₁ +R _D V _CC (proportional to the time constant R ₁ R _D /R ₁ +R _D C), it is necessary to Temperature detection operation may be delayed.

The present invention has been made in view of the above, and in order to eliminate wasted sensor disconnection detection time and prevent delays in temperature detection operations for heater temperature control, a disconnection is determined according to the level of a disconnection detection signal. The present invention provides a sensor disconnection detection device that increases or decreases the time.

The sensor disconnection detection device according to the present invention will be described in detail below.

FIG. 3 shows an embodiment of the present invention. When the number of checks is m=0, the first check (m=1) is performed, transistors 4 and 5 in FIG. 1 are turned off, and transistor 2 is turned on. do. When the predetermined time T has elapsed, the voltage V at the common connection point D ₁ and D ₂ = R ₁ /R ₁ +R _D V _CC {1-exp[-1/C (1/R ₁ +1/R _D )T ]} is input to the analog input port _A1 of the microcomputer 20, A/D converted, and stored in RAM (not shown). When the A/D conversion value exceeds a predetermined level, the sensor 1 determines that there is no disconnection and completes the disconnection check. On the other hand, when the A/D conversion value is smaller than a predetermined level, the voltage V when the time nT, which is the time T multiplied by n (n>1), has elapsed = R ₁ /R ₁ + R _D V _CC [1 -exp{-1/C(1/R ₁ +1/R _D )tT}] is input and processed to check for disconnection. Such a disconnection check is performed l times (l>1) (from m=1 to m=l), and when a disconnection is detected l times in succession, it is determined that the disconnection has occurred and the disconnection check is completed.

In the above embodiment, the time for determining disconnection is divided into two stages, but the invention is not limited to this.

As explained above, according to the sensor disconnection detection device according to the present invention, the time required to determine a disconnection is increased or decreased depending on the level of the disconnection detection signal, thereby eliminating wasted time for detecting a disconnection of the sensor and controlling the heater temperature. This can prevent delays in temperature detection operations.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing a sensor disconnection detection device having a heating temperature control function, Fig. 2 is a flowchart for controlling the heating temperature, Fig. 3 is a flowchart showing an embodiment of the present invention, and Fig. 4 2 is a circuit diagram showing an equivalent circuit when detecting a wire breakage in the sensor wire breakage detection device of FIG. 1; FIG. Explanation of symbols, 1...Sensor, 3...Variable resistance for set temperature, 20...Microcomputer, 30...Heater control relay, 32...Heater, 33...Photoconductor, 3
4... Fixing heating roll, R ₁ ... Comparative resistance, R ₂ ...
...Reference resistance.

Claims (1)

[Claims] 1. A sensor section having a resistance value that changes depending on the temperature of the heating section, and a comparison resistor provided in series with the sensor section, and a connection point between the sensor section and the comparison resistor. What is claimed is: 1. A sensor disconnection detection device for detecting a disconnection in a sensor unit based on a voltage level, comprising: a control unit that increases or decreases a determination time for a disconnection according to the voltage level.