JPS62296314A - Motor driving circuit for laser printer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a motor drive circuit for a radar printer, and particularly to a safety circuit thereof.

(Prior Art) Conventionally, as this type of drive circuit, there is one shown in FIG. 2.

In the figure, 1 is a Ti source, 2 is a motor drive circuit, and 3 is a single motor for driving a polygon mirror or for sub-scanning. A control circuit 4 receives the power supply 1 via a power supply line 5, supplies current to the motor 3, and controls its rotation speed. A current detection resistor 6 supplies current from the power supply 1 to the control circuit 4 via the resistor 6, and also takes out the voltage across the resistor 6 to the control circuit 4 in order to detect the current. Reference numeral 7 is a current detection fuse, and generally speaking, the rotational drive load in a laser printer 43 is dynamic during steady rotation. , there is only a frictional load, resulting in a small current, but at startup, it becomes a large current due to the inertia of the motor 3, etc. and static frictional load, so the current detection level is higher than the normal electromotive current. It is set to be disconnected by the circulating current.

(Problem to be Solved by the Invention) However, with the above-mentioned current detection fuse, it is possible to detect an abnormality in the motor, etc., where the current exceeds the starting current, but it is possible to detect an abnormality in the motor, etc., where the current exceeds the starting current. No small current abnormalities could be detected. Therefore, there was a problem that the current capacity of the power supply had to be made larger than necessary for the load.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides a 1iv111 circuit that supplies current to the motor and controls the rotational speed of the motor, and a power supply between the power supply and the control circuit. A resistor that is connected in series to the line and detects the motor current, and the upper temperature of the resistor during the motor startup period is sufficiently lower than the temperature at which it is saturated due to the continuation of the current during the startup period. The set current detection resistor is connected in series with and adjacent to the N flow detection resistor, and its cutting temperature increases due to the rise in temperature due to the startup period and the steady rotation of the motor. A temperature fuse is provided between the hot water temperature and the saturated temperature.

(Function) According to the present invention, the temperature rise during normal startup of the current detection resistor is set sufficiently lower than the saturation temperature, so that it approaches or lowers the upper limit temperature due to the current during normal steady rotation. The detected temperature of the temperature fuse is set between the rising temperature during normal startup and steady rotation, and the saturation temperature, so the detected temperature is determined by the current during steady rotation. By setting the temperature close to the temperature rise due to BL, the temperature fuse will be disconnected if this continues even if an abnormal current is considerably smaller than the starting current.

(Embodiment) FIG. 1 is a drive circuit diagram showing an embodiment of the present invention. Parts common to those in FIG. 1 are denoted by the same reference numerals, and different parts will be mainly explained.

In the figure, 2A is a drive circuit. 6A is a current detection resistor which, like the current detection resistor 6 in FIG. 2, supplies current from the power supply 1 to the control circuit 4 and detects the current.

The heat capacity and heat dissipation coefficient are set so that the temperature rise of the resistor 6A due to the normal startup of the motor 3 is sufficiently lower than the temperature at which it is saturated due to the continuation of the current during the startup period. . 8 is the temperature fuse,
It is connected in series with the current detecting resistor 6A, and as shown in FIG. 3(A) or (B), it is placed adjacent to the current detecting resistor 6A and fixed therebetween with adhesive 9, tape 10, or the like.

Next, the temperature rise of the current detection resistor 6A will be explained. The temperature of the resistor 6A is T ('C), and the ambient temperature is 8 <"C.
), the thermal resistance between the surface of the resistor 6A and its surroundings (atmosphere) is A ('C/W), and the power consumption by the resistor 6A is C (W).
), the relationship between power consumption and saturation temperature rise is expressed by (T-8)=A-C...Equation (1). And the relationship between the current and the saturation temperature rise is the resistance 6A.
When the resistance value of is R (Ω) and the ffi current is I (A), equation (1) is as follows: (T-B) = A -R-1...Equation (2)
), and therefore the rise in hot stones is proportional to the square of the current.

FIG. 4 is a temperature rise characteristic diagram of the resistor 6A, and the time t
In the stop period DO, the temperature rise (T-8) is 0, and in the start period D1, the starting current is 11.
(assumed to be constant), the power consumption (1) rises exponentially toward the saturation value (1-[3) due to R, and transitions to a steady rotation period D2. Therefore, the temperature upper limit value of O1 during startup 11 is the temperature upper limit 1 (T2-8>
, a peak value X occurs as shown in FIG.

Note that TI and T2 are the saturation temperatures of 11.R and I2.R when the ambient temperature is 8, respectively.

In this way, when the peak value X is present, X<('H-B)< (TI-13)...・
...by setting the value close to the peak value X under the conditions of formula (3)! Saturation value according to III flow 11 (
The cutting operation is performed at a sufficiently lower temperature than TI-8). In addition, considering the temperature change of the ambient temperature [3] in equation (3), assuming that the minimum hot water temperature is 81 and the maximum temperature is 82, the cutting temperature Tf of the temperature fuse 8 is calculated as follows:
(X+81><Tf<(A-R-11+81))
......Formula (4) %Formula%) ...Formula (5) It is necessary to satisfy the following two equations, so Equations (4) and (5
) to (X+82)<Tf<(A-R-11+81)
. . . It should be set so as to satisfy equation (6).

In addition, when there is no peak Vi×, instead of formula (3), (T2-8)<(Tf-8>< (TI -8>)
......Equation (7) becomes, and instead of Equation (6), (A-R-[2+82) <Tr < (A-R・f
1+81) ・・・・・・・・・
- Equation (8) may be set to a satisfactory value.

For example, R...0.5Ω, Δ-35℃/W, B1 =
Assuming 0℃, B2=40℃, 11=4△, I2...1△, and when calculating the peak value of X=40℃ after starting motor 3, according to formula (3), 40+40<Tf< 35X 0.5×42+0゜80
<Tf <280. If there is no beak 1iilliX, formula (1)
Therefore, 35x 0.5x12+40<Tf <35x
O, 5x42+0°57.5<Tf<280.

Therefore, when there is a beak [X, the cutting temperature Tf of the temperature fuse 8 should be between 80°C and 280°C, and when there is no peak value X, the cutting temperature Tf should be between 57.5°C and 280°C. is set at a lower position, taking into consideration the safety of operation and the like.

(Effects of the Invention) As explained above, according to the present invention, even if the current is relatively small below the starting current, if this continues abnormally,
It is safe because the current supply circuit is disconnected by the temperature fuse, so the current capacity of the power supply does not need to be larger than necessary for the load.

[Brief explanation of the drawing]

Fig. 1 is a drive circuit diagram showing an embodiment of the present invention, Fig. 2 is a drive circuit diagram showing a conventional example, Fig. 3 (^) (B) is an assembly diagram of the current detection resistor and temperature fuse, respectively, and Fig. 4 The figure is an explanatory diagram of the temperature rise of the current detection resistor. 1...Power source 3...Motor 4...Control circuit 6A...Current detection resistor 8...Temperature fuse Part I of the present invention. Drive circuit diagram from Shiba! V 〇 Circuit diagram Figure 2

Claims (1)

[Scope of Claims] A control circuit that supplies current to the motor and controls the rotational speed of the motor; and a resistor that is connected in series to a power line between a power source and the control circuit and that detects the current of the motor. a current detection resistor that is set to a value sufficiently lower than the temperature at which the temperature rise of the resistor due to the motor startup period is saturated due to the continuation of the current during the startup period; and a current detection resistor connected in series with the current detection resistor. and a thermal fuse installed adjacent to the laser printer, the cutting temperature of which is set between the increased temperature due to the startup period and the increased humidity due to steady rotation of the motor, and the saturated temperature. Motor drive circuit.