Heat-Fixing Device

1. Field of the Invention

This invention relates to a heat-fixing device for use in electrophotographic copying machines, and more particularly to such a device which prevents jamming of a member to be fixed during the conveyance thereof to thereby enable good conveyance and heat-fixation of the member to be achieved.

2. Description of the Prior Art

The devices for heat-fixing copy mediums by the use of radiant heat sources have heretofore been widely in use. With such devices, however, the copy medium when conveyed by conventional coveyor means such as belts or rollers has often been snagged on a projection or the like along the conveyance path due to the curling of the copy medium resulting from the heating and this has caused oblique movement of the copy medium which might possibly have resulted in jamming of the copy medium. Occurrence of such jamming could cause such an accident as burning or firing of the copy medium which has been undesirable in practice.

In view of the above-noted disadvantages, the present invention provides a device which can achieve good heat-fixation without giving rise to jamming.

The present invention also provides a heat-fixing device in which a heat source is provided on the conveyance path and conveyor means for conveying members to be fixed is provided with suction means having a plurality of openings, whereby only those of the suction openings which are covered by the member to be fixed are operable to effect the suction.

The present invention further provides a heat-fixing device in which individually controllable suction ports or suction port groups are arranged along the direction of movement on the conveyance path so that at least one of the suction ports or suction port groups covered by the member to be fixed is operable to effect the suction.

The present invention also provides a heat-fixing device in which detector means for detecting the passage of the member to be fixed are provided forwardly and rearwardly of the individually controllable suction ports or suction port groups so that the suction is controlled in accordance with the detection by each of the detector means.

The invention will become more fully apparent from the following detailed description thereof taken in conjunction with the accompanying drawings.

FIG. 1 is a perspective view illustrating an embodiment of the device according to the present invention.

FIG. 2 is a diagram showing a specific example of the control circuit.

FIG. 3 is a perspective view illustrating another embodiment of the device according to the present invention.

FIG. 3a shows a fragmentary view illustrating the duct section.

FIG. 4 is a perspective view illustrating still another embodiment of the present invention.

Details of the present invention will hereinafter be described with respect to some specific embodiments thereof shown in the drawings.

FIG. 1 illustrates an embodiment of the device according to the present invention. There is at least one set of conveyor rollers 1.sub.1, 1.sub.2, etc. over which are stretched conveyor belts 2.sub.1, 2.sub.2, etc. The conveyor belts 2.sub.1, 2.sub.2, etc. may be moved by rotation of the conveyor rollers which are driven from an unshown drive source. The conveyor belts are formed with rows of openings arranged at a predetermined interval in the direction of movement.

Sets of heat sources 3.sub.1, 3.sub.2, etc. are provided above the conveyor belts and may comprise, for example, nichrome wire heaters H.sub.1, H.sub.2, etc. and reflector shades R.sub.1, R.sub.2, etc.

Sets of suction ducts are provided on the back side of the conveyor belts which is opposite to the side which faces the heat sources. The suction ducts have slots S (indicated by broken lines) formed in parallel to the direction of movement of the belts for effecting the suction. Detector elements, such as microswitches, 5.sub.1, 5.sub.2, etc. for detecting the arrival of a member P to be fixed are provided at predetermined positions on the respective ducts to control the suction of the ducts (usually, the leading end detecting position which is concerned with activation of the ducts is located before each duct, and the trailing end detecting position which is concerned with deactivation of the ducts is located after each duct).

FIG. 2 shows an example of the control circuit in which microswitches are employed.

The microswitch MS1 disposed before the first suction duct and the microswitch MS2 disposed past the first duct are series-connected to each other on the NO side and connected to a duct fan motor M1. This is also the case with the second and subsequent suction ducts. As viewed in the arrangement shown in FIG. 1, the detector element 5.sub.0 corresponds to MS1 and the subsequent detector elements 5.sub.1 and so on correspond to MS2, MS4, etc., thus forming an arrangement of double-throw microswitches.

With such an arrangement, the microswitch MS1 is closed when the member to be fixed which may be a sheet of plain paper with electrophotographic toner particles deposited thereon comes to the first suction duct, and then the microswitch MS2 is closed by the leading end edge of the member to thereby energize the fan motor M1. Thus, the member is drawn to the belts so as to be positively conveyed. Likewise, at the second and subsequent suction ducts, their respective fan motors will be energized. Next, when the member is further conveyed and the trailing end edge thereof comes to the first suction duct, the microswitch MS1 is opened to deenergize the fan motor M1. Likewise, at the second suction duct, the microswitch MS3 is opened upon arrival of the trailing end edge of the member, thereby deenergizing the fan motor M2. In this manner, the suction fan motors are successively deenergized upon passage of the member so that the member to be fixed undergoes the fixation and is discharged out of the machine. Since the suction ducts are thus driven successively with movement of the member to be fixed and are deactivated upon passage of the trailing end edge of the member, both the fixation and the conveyance of the member to be fixed may be achieved efficiently without the necessity of reducing the fixing temperature within the fixing device.

If, unlike the above-described control circuit, not all of the fan motors need be energized during the passage of the member to be fixed, it will be apparent that suitable modifications may be made, including a design for changing over the suction fans in succession.

FIG. 3 illustrates a further embodiment of the device according to the present invention.

In the embodiment described just above, the suction of the suction ducts is controlled by ON-OFF of the suction fan motors, whereas in the present embodiment, valves are provided to the openings formed in ducts and either the microswitches as will be described or photocells PC1 and PC2 are provided to detect the member to be fixed, whereby the valves are opened and closed. As in the previous embodiment, conveyor belts 33 and 34 are stretched over and between conveyor rollers 31 and 32 and formed with a number of openings and duct 35 is formed with suction ports corresponding to those openings, but valves 36 are provided which can block the suction ports of the suction duct (these valves are shown as comprising a movable plate formed with openings).

The heat source is provided by a parallel arrangement of tungsten lamps H.sub.11, H.sub.12, etc. which are temperature-controlled under a reflection factor R.sub.1, and photocells PC1 and PC2 are disposed at the positions as between the conveyor belts 33 and 34 whereat the light from the lamps may be intercepted by the image transfer medium as it arrives there. These photocells may advantageously have a sensitivity to the infrared range, since no particular light source is then required.

With this arrangement, the suction duct is activated upon interception of light at PC2 and deactivated upon detection of light at PC1. If such a design is made that an ON signal is produced when both PC1 and PC2 are shielded against light and that an OFF signal is produced when PC1 has detected light, then the control of the suction port will be more reliable. The driving of the valves may be effected as by operation of a solenoid energizable in response to the detection signal.

On the other hand, it will be apparent that a good relationship between the member to be fixed and the operation of the valves may be provided by activating the valves in plural suction ducts successively upon detection of the leading edge of the member and deactivating them successively upon detection of the trailing end edge of the member, in a manner similar to that described in connection with the previous embodiment.

Where discharge rollers 6 are provided as shown, the operation may be continued until the leading end edge of the member to be fixed is nipped between these rollers, whereupon the operation may be stopped. This holds true of the device of the previous embodiment.

FIG. 4 illustrates still a further embodiment of the device. Suction duct 45 is disposed on the underside of the heat source so as to occupy a sufficient area and the duct is formed with suction ports 45.sub.1, 45.sub.2, etc. arranged in parallel rows along an axis perpendicular to the direction of movement of the member to be fixed, and individually controllable valves 46.sub.1, 46.sub.2, etc. are provided for each of the rows.

A detector element such as ultrasonic oscillator 47.sub.1 disposed at the entrance to the heat-fixing device and an associated reception element 47.sub.2 are cooperable with each other to detect the entry of the member to be fixed and produce a detection signal, in response to which a program control mechanism is energized to produce a program control signal, which in turn energizes selenoids SL1 and SL2 to move arms A1, A2, etc., thus opening and closing the valves in succession.

As an example, the program control may sufficiently effectively be designed such that energization is caused to take place in succession with a predetermined retardation by time limit means from entry of the detection signal till the actuation of the valves and that the hold means for each valve releases in a predetermined time after the actuation of the valves.

The release signal may of course be produced by the time limit means in response to the detection signal.

On the other hand, it will also be effective if it is arranged that the holding time of the hold means may be changed in accordance with the variable length of the member to be fixed.

As described above with respect to some specific embodiments, the member to be fixed is conveyed beneath the heat source while being drawn into intimate contact with the conveyor means and this eliminates irregular movement of the member on the path of conveyance and also reduces the possibility of snagging the member. Even if there is a slight possibility of snapping the irregular movement is eliminated and thus, the possibility of jamming may be sufficiently eliminated in either event.

Moreover, the suction takes place only in the area where the member to be fixed is present and this leads to the elimination of wasteful discharge of the heat from without the heat-fixing device which might possibly reduce the temperature within the device and accordingly the efficiency thereof, and good fixation may thus be ensured.

From what has been disclosed hereinabove, it will be readily apparent to those skilled in the art that many other modifications and/or additions may be made to the device described above, and it is intended that these be covered by the present invention as disclosed herein and as defined in the appended claims.