JPH048693Y2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field This invention relates to a document exposure device using an LED (light emitting diode) array.

BACKGROUND TECHNOLOGY Conventionally, in order to illuminate a document from which image information is to be read,
A document exposure device using an LED array is known, for example, in Japanese Patent Laid-Open No. 141174/1983.

In general, LEDs have low luminous efficiency, so they can be used at high densities.
When an LED array of LEDs is turned on, it generates heat, resulting in a decrease in light intensity and deterioration of the elements. Therefore, in the past, LED chips were attached to a substrate made of aluminum or other materials with good thermal conductivity.
A current of about 50% of the rated current was passed through this LED chip in the forward direction to light the LED.

Problems that the invention attempts to solve For this reason, the heat generation temperature of the substrate can be kept low as shown in curve _T1 in Figure 4, but the amount of light emitted is also
As shown in E ₁ , the reading speed was low and there were problems such as the inability to increase the document reading speed.

By the way, when the rated current is applied to the above LED chip, the light output increases as shown in curve _E2 in Figure 4, but
The substrate temperature also increases significantly, as shown by curve _T2 in the figure, which causes a decrease in the amount of light over time and deterioration of the device.

This invention attempts to improve the above-mentioned conventional problems.

Means and Effects for Solving Problems The LED array is arranged in a straight line on the top surface of the board, and a part of the heat pipe is attached to the bottom surface of the board so as to protrude along the back surface of the LED array. A document exposure device in which heat is transferred to a protrusion of a heat pipe, the cold side of a thermoelectric element is brought into close contact with the protrusion, and a heat dissipation assisting means is provided on the hot side to heat the transferred heat.

Embodiment An embodiment of this invention will be described in detail with reference to the drawings. In the figure, 1 is a substrate, and on this substrate 1, a large number of LED chips are arranged in a straight line to form an LED array 2. Above this LED array 2, for example, a cylindrical condensing lens 3 is provided parallel to the LED array 2 by means of a support member 4 protruding from the substrate 1. Further, on the lower surface of the substrate 1, a heat pipe holding member 5 made of a material with good thermal conductivity such as aluminum is attached with screws 11.
It is firmly attached. The heat pipe holding member 5 has a shape in which a prismatic body is vertically divided into two, and a recess 5c is formed on the mating surface of each member 5a, 5b so as to be located on the back side of the LED array 2. A heat pipe 6 coated with thermally conductive grease is housed so as to be in close contact with each member 5a, 5b.

On the other hand, a portion of the heat pipe 6 protrudes from the end of the heat pipe holding member 5, and a thermoelectric element 8 is attached to this hot side via a thermoelement holding member 7. The thermoelectric element 8 uses the Peltier effect to radiate the heat transferred by the heat pipe 6 on the hot side.In order to enhance the heat radiation effect, a heat sink 9 is attached to the upper surface of the thermoelectric element 8, and a heat sink 9 is attached to the upper surface of the thermoelectric element 8. A cooling fan 10 that blows cold air toward the heat sink 9 is provided near the heat sink 9 .

Note that the document exposure device configured above uses a document exposure LED array for a contact image sensor.
It can also be applied to high-density LED arrays for LED printers. In this case, it becomes possible to prevent a decrease in the amount of light emitted over time due to a rise in the temperature of the LED array, prevent deterioration of the element, and also prevent a rise in the temperature of the photoreceptor.

Effects of the invention This invention has two LED arrays as detailed above.
A heat pipe 6 is attached to the back side of the substrate 1 on which the LED array 2 is attached, and the transferred heat is dissipated by the thermoelectric element 8 attached to the protrusion of the heat pipe 6 and the heat dissipation auxiliary means. ,
Even when the rated current is passed through the LED array 2, the temperature of the substrate 1 can be kept sufficiently low as shown by curve _T3 in FIG. This makes it possible to stably obtain sufficient light output as shown by curve E ₃ in the same figure.
The reading speed of a document can be greatly improved, and it is also possible to prevent the amount of light emitted from decreasing over time and the deterioration of the elements due to heat generation of the LED array 2.
By the way, without providing a cooling means like this idea,
When the rated current was passed through the LED array 2 in the forward direction, the heat generation temperature of the substrate 1 was as shown by the curve T ₂ in FIG. 3, and the light output of the LED array 2 was as shown by the curve E ₂ in FIG. 3. In addition, a thermoelectric element and heat dissipation auxiliary means are installed at one end of the heat pipe, making it possible to dissipate heat and control the temperature of the entire LED array at one point, making the entire cooling system compact and requiring less space. It can also be easily installed.

[Brief explanation of drawings]

The drawings show one embodiment of this invention, with Fig. 1 being a perspective view, Fig. 2 being a sectional view along the line shown in Fig. 1, and Fig. 3 being a diagram showing the relationship between lighting time, relative light amount, and substrate temperature. , FIG. 4 is a conventional explanatory diagram. 1 is a board, 2 is an LED array, 6 is a heat pipe, and 8 is a thermoelectric element.

Claims (1)

[Scope of utility model registration request] An LED array 2 for illuminating a document whose image information is to be read is provided in a straight line on a substrate 1, and a heat pipe 6 is attached to the bottom surface of the substrate 1 so that a part of it protrudes along the back surface of the LED array 2.
A document exposure device in which a thermoelectric element 8 and a heat dissipation assisting means are provided on a protruding portion of a heat pipe 6.