Background Art In general, industrial furnaces are classified into various types according to products produced by the furnaces.

For example, the furnace types include an industrial incinerator for incinerating wastes, a melting furnace for iron mills for melting metal, a gas furnace for melting glass, a cement furnace, a pottery furnace and a calcining furnace.

One of operators'common demands relating to various furnaces is to frequently observe the inside of a furnace during the operation of the furnace using clear images.

Once a furnace is operated, the furnace is continuously operated for a certain period of time as long as a particular breakdown does not occur.

Accordingly, the inside of the furnace should be inspected by frequently observing the inside of the furnace during the operation of the furnace.

A conventional method of observing the inside of an industrial furnace is generally implemented by forming a hole having a certain size through the wall of the furnace, placing a door in front of the hole to be selectively opened and closed, and observing the inside of the furnace through the hole using the

naked eye with the door being opened.

Such a conventional method is used in about 70% of furnaces. In order to protect the eye and intercept strong visible rays when observing the inside of a furnace by the above-described method, a user should use an additional face protector to which an infrared glass is attached.

However, the conventional method is disadvantageous in that the thermal efficiency of a furnace is reduced due to the forming of a hole through the wall of the furnace, combustion mixture ratio can be changed due to the inflow of outside air, a viewing angle for observing the inside of the furnace with the naked eye is restricted due to a small-sized hole in the wall of the furnace, and an operator may be burned.

In order to solve the above problems, there was proposed another conventional method of monitoring the inside of a furnace by forming a hole through the wall of the furnace, forming a window using quartz or heat-resistant glass, placing a camera and a camera protective housing outside the window, and photographing images formed on the window using the camera and lenses.

However, this conventional method has a limitation in the monitoring of the inside of a furnace because only limited images obtained through the hole formed through the wall of the furnace can be observed.

Additionally, the glass is strongly resistant to heat, but weak to impact, abrasion and corrosion. As time passes, dirt, such as soot generated by combustion in the inside of a furnace, adheres to the inside surface of the window, so the transparency of the window is deteriorated and clear images cannot be obtained, thus the window requiring continuous maintenance.

This conventional method is more advantageous than the first conventional method, but is not appropriate for a large-sized furnace, and a furnace's temperature must be controlled precisely.

There was proposed still another conventional method of observing the inside of a furnace by inserting an image device called a lens tube into the inside

of the furnace, capturing the images of the inside of the furnace focused through a lens using a camera, and transmitting the captured images to a monitor.

As shown in Fig. 1, in accordance with this conventional method, lenses are arranged in a conventional lens tube 8 in a row, a camera protective housing 4 is connected to the back of the lens tube 8, and a general camera 5 is placed in the camera protective housing.

As illustrated in Fig. 3, the housing 4 is mounted on a cylinder rail with a housing support 9 attached to the cylinder rail. The lens tube 8 is inserted into a furnace by supplying compressed air through the compressed air supply valve 20 to the cylinder rail and therefore moving the housing support 9 so as to photograph and monitor the inside of the furnace. In the case of an abnormal situation, such as a checkup, a power failure or the interruption of compressed air, the lens tube 8 is retracted from the furnace by supplying compressed air to the compressed air supply valve 20 disposed on the front portion of the cylinder rail so as to protect the lens tube 8 from high temperature heat inside the furnace.

The image of the inside of the furnace passed through the image input hole 10 positioned in the furnace is passed through lenses 2 arranged in the lens tube 8 in a row, and transmitted in and formed in the image sensor 3.

Thereafter, the image is passed through the electric control box 30 and displayed on a control center monitor 100, so the monitoring of the inside of the furnace is enabled.

In this case, since the inside of the furnace has a high temperature, specially fabricated camera protective housing 4 and the lens tube 8 are cooled by compressed air supplied from the air control box 31 to protect them.

Thereafter, the supplied compressed air is discharged to the outside along a certain path.

However, since the system for monitoring the inside of the furnace described above employs a cylinder type retraction device and the camera

protective housing 4, additional structures are required to fixedly attach them to the system. Additionally, the entire lens tube 8 must be changed in the case where a lens is damaged, so maintenance costs and purchasing costs are high.

Disclosure of the Invention In order to overcome disadvantages occurring when a conventional lens tube, a camera and a camera protective housing are employed, an object of the present invention is to develop a vision tube 12 for monitoring the inside of a furnace, in which the inside of the furnace is sealed, the vision tube 12 is easily installed low cost, the vision tube 12 is easily maintained due to the construction of lens blocks, the structure of the vision tube 12 is simple due to the adaptation of a small-sized camera 16, and the larger area can be monitored at high picture quality.

In order to accomplish the above object, the present invention provides a vision tube 12 for monitoring the inside of a furnace, which employs lenses designed by the block as shown Fig. 2 and a small-sized camera 16 disposed behind the block type lenses instead of a conventional lens tube 8 and a camera protective housing 4.

In this case, in order to protect the vision tube 12 from high temperature heat, compressed air is supplied from a control box and discharged through and certain path and an image input hole 10 formed through the front of the front end lens block 11.

Brief Description of the Drawings The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional view showing a lens tube with lenses arranged in a row and a camera protective housing according to an embodiment of the prior art; Fig. 2 is a diagram showing a construction of a conventional system according to another embodiment of the prior art; Fig. 3 is a section view showing a vision tube of the present invention in which lenses are manufactured in a block manner and a small-sized camera is disposed therein; and Fig. 4 is a view showing the use of the vision tube in which the vision tube of the present invention is mounted on an automatic retraction apparatus to monitor the inside of a furnace.

<Description of reference numerals of principal parts> 1: object lens 2: lens 3: image sensor 4: camera protective housing 5: camera 6: inner tube 7: outer tube 8: lens tube 9: housing support 10: image input hole 11: front end lens 12: vision tube 13: relay lens block 14: protrusion 15: focus adjusting spring 16: small-sized camera 17: focus adjusting handle 18: focus adjusting bolt 19: input/output connector 20: compressed air supply valve 21: control box 22: compressed air supply tube 30: electric controller 31: air controller 100: monitor Best Mode for Carrying Out the Invention With reference to the accompanying drawings, a vision tube for monitoring the inside of a furnace according to the present invention is described.

Fig. 4 is a diagram showing the use of a vision tube according to an embodiment of the present invention, in which the vision tube is mounted on an automatic retraction apparatus to monitor the inside of a furnace. A hole having a certain size is formed through the wall of a furnace to monitor the inside of the furnace, a vision tube 12 is connected with a carriage plate and a rail though a coupling bracket 23, a wall sleeve 24 and a flange 25 of the vision tube 12 are brought into contact with each other to prevent supplied compressed air from leaking, an electric locking device 22 mounted on a frame and a latch mounted on the coupling bracket 23 are interlocked with each other, and the vision tube 12 is inserted into the inside of the furnace.

In the vision tube 12 inserted into the furnace, as shown in Fig. 3, an image of the inside of a furnace input through an image input hole 10 formed in the front of a first vision tube 16 passes through a front end lens block 11 and an image formation lens block 12, a relay lens block 13 and an optical attenuation filter, and forms in an image sensor of a small-sized camera 16.

In that case, block type lenses, in which protrusions 14 are formed on the lens blocks to position the lens blocks at the center of the vision tube, are employed, so only a damaged lens block can be replaced at the time of maintenance. Accordingly, the present invention overcomes a disadvantage of a conventional lens tube in which costs and time are required to replace an entire lens tube with a new one when a lens of the lens tube is damaged.

Additionally, a focus adjusting spring 15 is positioned in front of the small-sized camera 16, and a focus adjusting handle 17 and a focus adjusting bolt 18 are employed. As a result, at the time of initial setting or in the case where the focus of a camera is changed due to internal or external impact and an image is not clear, the focus of the camera can be adjusted by rotating the focus adjusting handle 17 and thus reciprocating the focus adjusting bolt 18.

Additionally, when impact is exerted on the lens tube, the impact is buffered by the elasticity of the focus adjusting spring 15, so damage to the lenses can be

prevented.

As shown in Fig. 3, a cable extending from an input/output connector 19 at the rear end of the vision tube to a control box supplies power to the small- sized camera 16 disposed in the vision tube, and transmits the images of the inside of a furnace to the control box 21 to be displayed on a monitor.

In addition, the present invention cools the vision tube with compressed air to protect the vision tube inserted into the furnace from high temperature heat.

In this case, the compressed air supplied at a site and used to protect the vision tube is sent to the control box 21, purified by a filter to remove dirt and supplied at constant pressure through a pressure switch.

The supplied compressed air is sent to a compressed air supply valve 20 connected to the rear end of the vision tube 12 through a compressed air supply pipe 22, passes through a space between an inner tube 6 for protecting block type lenses and the small-sized camera 16 and an outer tube 7 made of special material for protecting the inner tube from external heat, and discharged through the image input hole 10 formed in the front end of the vision tube.

In addition, the compressed air is supplied to the compressed air supply valve 20 attached to the wall sleeve mounted on the wall of the furnace, passes through a space between the vision tube 12 and the hole of the furnace, passes the vision tube, and is discharged into the inside of the furnace.

The vision tube 12 inserted into the furnace through the above- described method can endure high temperature heat because the vision tube 12 employs the outer tube 7 made of high temperature heat-resistant material and there is used a cooling effect generated by discharging compressed air, which is supplied to and passed through a space between the inner and outer tubes 6 and 7, through the image input hole 10 formed in the front end of the vision tube, and compressed air, which is supplied to and passed through a space between the outer surface of the vision tube 12 and the wall sleeve, to the inside of the

furnace.

Industrial Applicability A system for monitoring the inside of a furnace with a vision tube 12 comprised of a block type lenses and a small-sized camera 16 and inserted into the inside of the furnace includes the small-sized camera 16 instead of a conventional lens tube 8 and a camera protective housing 4 and employs a vision tube 12 in which lenses are designed by the block to easily assemble and dissemble the vision tube 12. Accordingly, the system of the present invention can be easily installed, and can monitor the larger region of the inside of the furnace using the vision tube integrated with the small-sized and low cost camera that is modularized and therefore is easily repaired.

In addition, the present invention allows high performance products to be manufactured and provided at low costs, so the inside of a furnace used in an iron mill, a cement factory, an incinerator and a power plant can be continuously monitored and the reliability and quality of products are improved, thus significantly developing industrial furnace industry.