Abstract:
A peeling device is provided and includes: a rotating body that conveys a recording material; a peeling member capable of changing from a first state in which the peeling member is away from the rotating body to a second state in which the peeling member is closer to the rotating body than the peeling member in the first state is, the peeling member in the second state peeling off the recording material from the rotating body; and a gas spraying unit that sprays a gas to the peeling member to bring the peeling member from the first state to the second state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 USC §119 from Japanese Patent Application No. 2009-001668, filed Jan. 7, 2009. 
     BACKGROUND 
     The present invention relates to a peeling device, a fixing unit, and an image forming apparatus. 
     SUMMARY 
     According to an aspect of the invention, there is provided a peeling device including: 
     a rotating body that conveys a recording material; 
     a peeling member capable of changing from a first state in which the peeling member is away from the rotating body to a second state in which the peeling member is closer to the rotating body than the peeling member in the first state is, the peeling member in the second state peeling off the recording material from the rotating body; and 
     a gas spraying unit that sprays a gas to the peeling member to bring the peeling member from the first state to the second state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual diagram showing a fixing unit according to an exemplary embodiment of the invention; 
         FIG. 2  is a bottom view showing a peeling device according to an exemplary embodiment of the invention; 
         FIG. 3  is a block diagram showing a control system of a peeling device according to an exemplary embodiment of the invention; 
         FIGS. 4A to 4D  are phase diagrams showing a positional relationship between a peeling plate and a sheet according to an exemplary embodiment of the invention; 
         FIGS. 5A to 5D  are top views showing shapes of a peeling plate according to an exemplary embodiment of the invention; 
         FIG. 6  is a conceptual diagram showing a fixing unit according to an exemplary embodiment of the invention; 
         FIG. 7  is a perspective view showing a structure for supporting a peeling plate according to an exemplary embodiment of the invention; 
         FIG. 8  is a conceptual diagram showing a fixing unit according to an exemplary embodiment; and 
         FIG. 9  is a conceptual diagram showing an image forming apparatus according to an exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     (1) First Embodiment 
     (Configuration) 
       FIG. 1  is a conceptual diagram showing a fixing unit of an exemplary embodiment of the invention.  FIG. 1  shows a fixing unit  100 . The fixing unit  100  has a heating roller  101  and an opposing roller  102 . The heating roller  101  is an embodiment of a rotating body, in which a surface layer  104  made of a resin material is provided on a surface of a base material  103  made of a cylindrical metal material. A heater  105  acting as an embodiment of a heating unit is disposed inside of the base material  103 . The heating roller  101  is rotated in a counterclockwise direction in the drawing by means of a drive mechanism which is omitted from the drawings. 
     The opposing roller  102  has a structure built from a metal cylinder, and rotates in a clockwise direction of  FIG. 1  by dint of driving force resultant from rotation of the heating roller  101  with a sheet (an embodiment of a recording material) conveyed from left to right in  FIG. 1  nipped between the opposing roller  102  and the heating roller  101 . 
     Reference numeral  106  designates a sheet that is an embodiment of a recording material. In  FIG. 1 , a toner image  107  is formed on a sheet  106 . The toner image  107  is formed by an image forming unit that is not drawn in  FIG. 1 . In  FIG. 1 , a sheet detection sensor  108  is provided for detecting arrival of the sheet  106 . The sheet detection sensor  108  is a light-receiving sensor, and detects arrival of the sheet  106  upon interruption of an optical axis linked to a light-emitting element  109 . 
       FIG. 1  shows a peeling device  110  that is an embodiment of the invention.  FIG. 2  shows the peeling device  110  when viewed from below in  FIG. 1 . The peeling device  110  has a peeling plate  111  that is an embodiment of a peeling member and gas spraying devices  112   a  to  112   d  that each is an embodiment of the gas spraying unit. The peeling plate  111  is made of plate-shaped resin plate that is wide in an axial direction of the heating roller  101 . The peeling plate  111  is fastened to a support member  115  fixed to a member that supports the fixing unit  100 , and extends from the support member toward a location where the heating roller  101  contacts the opposing roller  102 . The peeling plate  111  is made of a material and in a configuration such that, when an edge (hereinafter called a “front edge”) of the peeling plate achieved in an upstream direction designated by reference numeral  116  is pressed toward the heating roller  101 , the edge becomes elastically deformed while a portion of the peeling plate  111  fixed to the support member  115  is taken as a fulcrum, whereupon the front edge  116  comes into contact with the heating roller  101 . 
     The gas spraying devices  112   a  to  112   d  for spraying compressed air to a surface A are disposed on the same side as that of the surface A that is opposite to a surface of the peeling plate  111  opposing the heating roller  101 . The gas spraying device  112   a  has a nozzle  113   a  and an electromagnetic valve  114   a ; the gas spraying device  112   b  has a nozzle  113   b  and an electromagnetic valve  114   b ; the gas spraying device  112   c  has a nozzle  113   c  and an electromagnetic valve  114   c ; and the gas spraying device  112   d  has a nozzle  113   d  and an electromagnetic valve  114   d.    
     The nozzles  113   a  to  113   d  are cylindrical, and compressed air is squired in a left direction of the drawing from circular orifices provided at respective extremities of the nozzles. The electromagnetic valves  114   a  to  114   d  are supplied with compressed air from a compressed gas supply system omitted from  FIG. 1 . The electromagnetic valves  114   a  to  114   d  control timing at which compressed air is supplied to the nozzles  113   a  to  113   d.    
     (Configuration of the Control System and Configuration of the Compressed Air Supply System) 
       FIG. 3  is a block diagram showing a control system and a compressed gas supply system of the fixing unit shown in  FIG. 1 . Since the fixing unit is identical with an ordinary fixing unit in terms of a configuration for controlling fixing operation, descriptions of the fixing unit are omitted. 
     In  FIG. 3  a sheet detection circuit  131  generates a signal showing presence and absence of a sheet in accordance with an output from a sheet detection sensor  108  shown in  FIG. 1 . An arithmetic operation circuit  132  computes a time (a position on a time axis) at which a front edge of the sheet  106  approaches closest to a front edge  116  of the peeling plate  111  from an output from the sheet detection circuit  131 ; namely, information about the position of the sheet detected by the sheet detection sensor  108 . 
     An electromagnetic valve control circuit  134  controls timing at which the electromagnetic valve  114  is opened and closed, from a result of computation performed by the arithmetic operation circuit  132 . In the embodiment, the electromagnetic valve control circuit  134  performs control operation for opening the electromagnetic valves  114   a  to  114   d  at a point in time 20 msec before the time when the front edge of the sheet  106  approaches closest to the front edge  116  of the peeling plate  111 ; and maintaining the open state for 40 to 100 msec and subsequently closing the electromagnetic valves  114   a  to  114   d.    
     A compressor pump  135  is a pump that compresses air to pressure which is higher than ordinary pressure. A regulator  136  stabilizes the compressed air pressure from the compressor pump  135 . The air (compressed air) compressed by the compressor pump  135  is stored in an air tank  137 . The compressed air stored in the air tank  137  is squirted toward the surface A of the peeling plate  111  from the nozzles  113   a  to  113   d  by way of the electromagnetic valves  114   a  to  114   d.    
     In the embodiment, settings are made, as calculated values disregarding a loss, in such a way that compressed air is squirted at a flow rate of about 600 m/sec from the nozzles  113   a  to  113   d . When compared with compressed air generated under a method for storing in a tank air whose pressure is made higher than ordinary pressure, air flow generated by use of a fan has been assumed to be insufficient for operation to be described later. Further, a gas to be used can also be a nitrogen gas, or the like, rather than air. 
     (Example of Operation) 
       FIG. 1  shows the general structure and provides descriptions of an operation of the fixing unit  100  whose control system is shown in  FIG. 3 . When the sheet  106  with the toner image  107  formed thereon approaches the heating roller  101  and reaches an imaginary line (an optical axis) between the sheet detection sensor  108  and the light-emitting element  109 , an output from the sheet detection sensor  108  changes. The sheet detection circuit  131  detects the change and outputs a detection signal to the arithmetic operation circuit  132 . The arithmetic operation circuit  132  received the detection signal calculates a time at which the leading edge of the sheet  106  will arrive at the front edge  116  of the peeling plate  111 . 
     On the basis of a computation result, the electromagnetic valve control circuit  134  performs control operation for opening the electromagnetic valves  114   a  to  114   d  at a point in time 20 msec before the time when the front edge of the sheet  106  comes closest to the front edge  116  of the peeling plate  111  and holding the open state for 40 to 100 msec and subsequently closing the electromagnetic valves  114   a  to  114   d . At this time, the compressed air is squirted from the electromagnetic valves  114   a  to  114   d  in a pulsing manner at a time interval of 40 to 100 msec. 
     The control parameters are determined so as to fulfill conditions under which the nozzle  113   a  squirts a compressed gas before the front edge of the sheet  106  arrives at the front edge  116  of the peeling plate  111  and under which, after the front edge of the sheet  106  has passed by the front edge  116  of the peeling plate  111 , a squirt of the compressed air from the nozzle  113   a  is completed. 
       FIGS. 4A to 4D  are phase diagrams showing a positional relationship between the peeling plate  111  and the sheet  106 .  FIG. 4A  shows a state in which the front edge of the sheet  106  (a front edge achieved in the traveling direction) approaches closest to the front edge  116  of the peeling plate  111  after elapse of 30 msec. The position of the sheet  106  achieved at this time varies according to the conveyance speed of the sheet; however, in the present embodiment, the sheet has not yet reached a position that can be illustrated. In a state shown in  FIG. 4A , the peeling plate  111  does not remain in contact with the heating roller  101 , and the front edge  116  of the peeling plate  111  is spaced apart from the heating roller  101 . The state shown in  FIG. 4A  is an example of the first state. 
       FIG. 4B  shows a state in which the front edge of the sheet  106  approaches closest to the front edge  116  of the peeling plate  111  after elapse of 20 msec. The electromagnetic valve  114   a  is opened at this timing, and the nozzle  113   a  squirts compressed air. Although unillustrated in  FIGS. 4A to 4D , the other electromagnetic valves and the other nozzles also perform similar operations. 
     When the nozzle  113   a  squirts compressed air, the flow of the thus-squirted air collides against the surface A of the peeling plate  111 , whereupon the peeling plate  111  becomes elastically deformed in such a way that the edge  116  of the peeling plate  111  moves toward the heating roller  101 .  FIG. 4B  shows a deformed state of the peeling plate  111 . In a period during which a squirt of compressed air from the nozzle  113   a  continues, the front edge  116  is pushed against the heating roller  101  by pressure of the compressed air, so that the peeling plate  111  holds a state shown in  FIG. 4B . The state shown in  FIG. 4B  is an example of the second state. In the embodiment, in the state shown in  FIG. 4A  that is an example of the first state, the peeling plate  111  is spaced apart from the heating roller  101  and is not in contact with the heating roller  101 . When the state shown in  FIG. 4B  that is an example of the second state is achieved, the front edge  116  of the peeling plate  111  approaches the heating roller  101 , and the peeling plate  111  comes into contact with the heating roller  101 . 
     In the meantime, the sheet  106  undergoes heat from the heating roller  101  and pressurization as a result of being nipped between the heating roller  101  and the opposing roller  102 . Toner forming the toner image  107  becomes fused by heating and pressurizing actions, whereupon the toner image is fixed on the sheet  106 . At this time, when the toner image is a color image or a high pixel density image (e.g., an image, such as a photographed landscape), a phenomenon of an image-generated surface of the sheet  106  affixing to the heating roller  101  arises as illustrated. 
     Descriptions are hereunder provided on the premise that the sheet  106  remains in close contact with and affixed to the heating roller  101 . In the present embodiment, before arrival of the sheet  106  at the front edge  116  of the peeling plate  111 , the peeling plate  111  is pressed toward the heating roller  101  by compressed air as shown in  FIG. 4B , so that the front edge  116  remains in contact with the heating roller  101 . Therefore, as shown in  FIGS. 4C and 4D , the peeling plate  111  pushes its way between the sheet  106  and the heating roller  101 . The sheet  106  affixed to the heating roller  101  is peeled off from the heating roller  101  by the peeling plate  111  in association with rotation of the heating roller  101 . 
     When the heating roller  101  further rotates from a state shown in  FIG. 4D , the sheet  106  moves along a lower surface of the peeling plate  111  in a rightward direction of the drawing. The heating roller  101  is thereby prevented from continually rotating while the sheet  106  remains affixed to and wrapped around the heating roller  101 . 
     When the nozzle  113   a  stops squirting compressed air, the elastically-deformed peeling plate  111  returns to the position shown in  FIG. 4A . Since the front edge of the sheet  106  has already passed by the front edge  116  of the peeling plate  111  in this stage, the sheet  106  advances in a rightward direction of the drawing and at a position beneath the peeling plate  111 . Thus, the effect of the peeling plate  111  peeling the sheet  106  off from the heating roller  101  is achieved. 
     In addition to the working-effect, an effect of peeling of the sheet  106  being promoted by the compressed air flow squirted from the nozzle  113   a  and an effect of prevention of affixing of the sheet  106  to the peeling plate  111  are also achieved. Specifically, the air flows from the nozzle  113   a  toward the front edge  116  along a back surface of the peeling plate  111 ; hence, an effect of the sheet  106  peeled off from the heating roller  101  being peeled further off from the heating roller  101 ; namely, an effect of peeling of the sheet  106  from the heating roller  101  being further promoted, is achieved. Moreover, the air flow from the nozzle  113   a  flowing toward the front edge  116  enters between the sheet  106  and the peeling plate  111 , thereby preventing affixing of the sheet  106  to the peeling plate  111 . 
     During operation, the peeling plate  111  contacts the heating roller  101  in a period of 40 to 100 msec. Since the contact time is limited, infliction of damage on the surface of the heating roller  101 , which would otherwise be caused by contact of the peeling plate  111 , is prevented. 
     (Modifications) 
     The peeling plate  111  can also be split into a plurality of pieces. The peeling plate can also assume any of shapes, such as those shown in  FIGS. 5A to 5D . The direction of the nozzles  113   a  to  113   d  is not limited to the illustrated direction. The requirement is that the nozzles be adjusted to, in agreement with a working mode of the invention, a direction in which a sheet is reliably peeled off from a heating roller most efficiently. Further, the number of nozzles is not limited to the number of the illustrated nozzles. 
     The peeling member is not limited to a plate member like the peeling plate  111  and can also be a line-shaped member such as an extended pawl. In this case, it is preferable to achieve a configuration in which a plurality of peeling members are positioned and in which a sheet is peeled off from a rotating body at a plurality of positions. In the case in order to efficiently receive wind pressure of a compressed gas, it is preferable to provide each of the peeling members with a surface which undergoes wind pressure. 
     In order to efficiently deform the peeling plate  111  by means of wind pressure of the compressed air, a scale-like member is provided on the surface A of the peeling plate  111 , to thus realize a configuration that does not hinder movement of the sheet traveling from a left direction of the drawing and that is susceptible to wind pressure of the compressed air squirted from the nozzle  113   a.    
     (2) Second Embodiment 
     (Configuration) 
     There is hereunder described a configuration in connection with the configuration shown in  FIG. 1 , wherein the peeling plate  111  contacts the heating roller by the action of the spring during squirting of compressed air and recedes from the heating roller during the period of a non-squirt of compressed air.  FIG. 6  is a conceptual diagram showing a fixing unit utilizing an exemplary embodiment of the present invention.  FIG. 6  shows a peeling device  210  differing from its counterpart shown in  FIG. 1  in terms of the structure of the peeling plate. In  FIG. 6 , the reference numerals that are the same as those shown in  FIG. 1  designate the same elements described in connection with  FIG. 1 . Further, a control system of the second embodiment is structurally identical with that shown in  FIG. 2 . 
     The peeling device  210  shown in  FIG. 6  has a peeling plate  201 . The peeling plate  201  is a resin or metal plate. 
       FIG. 7  is a perspective view showing the g peeling plate  201  shown in  FIG. 6  and a supporting structure therefor. The peeling plate  201  has flanges  202   a  and  202   b  that stand upright on a surface of the peeling plate. A shaft member  203  penetrates through the flanges  202   a  and  202   b  in a relatively-rotatable manner. Both ends of the shaft member  203  are fixed to a housing of an apparatus omitted from the drawings. Torsion coil springs  205  are wrapped around a periphery of the shaft member  203 . One end of each of the torsion coil springs  205  is fastened to the shaft member  203 , and the other end of the same remains in contact with an upper surface of the peeling plate  201 . 
     Force is exerted on the front edge  216  of the peeling plate  201  (corresponding to reference numeral  116  shown in  FIG. 1 ) in a direction designated by arrow  204  shown in  FIG. 7 . When the force is greater than repulsive force of the torsion coil springs  205 , the front edge  216  of the peeling plate  201  rotates around the shaft member  203 , while taking the shaft member as an axis, in the direction of arrow  204 . When the force is eliminated, the front edge  216  of the peeling plate  201  returns to its original position by dint of repulsive force of the coil springs  205 . A configuration of a returning unit for returning the peeling member to its original state before movement is constructed from the foregoing structure. 
     (Example of Operation) 
     When the nozzle  113   a  (and the unillustrated nozzles  113   b  to  113   d ) squirts compressed air in the leftward direction of the drawing in the state shown in  FIG. 6 , a surface B undergoes wind pressure. By means of the wind pressure, the front edge  216  moves upwardly while taking the shaft member  203  as an axis, to thus contact the heating roller  101 . When squirts of the compressed air are stopped, the front edge  216  is brought out of contact with the heating roller  101  by dint of repulsive force of the torsion coil springs  205  shown in  FIG. 7 , to thus return to its original position. A positional relationship between the peeling plate  201  and the sheet  106  achieved as a result of operation is the same as that achieved in the case shown in  FIG. 4 . The action of the compressed air squirted from the nozzle  113   a  is also the same as that achieved in the first embodiment. 
     (3) Third Embodiment 
       FIG. 8  is a conceptual diagram showing a fixing unit utilizing a third embodiment of the present invention.  FIG. 8  shows a fixing unit  308 . The fixing unit  308  has a fixing roller  309  and a pressure roller  310 . The fixing roller  309  has a heater  351 . The fixing roller  309  is rotated by means of an unillustrated drive mechanism. A fixing belt  353 , which is an embodiment of a rotating body, is passed between the fixing roller  309  and the tension roller  352 . The tension roller  352  exerts tensile force to the fixing belt  353 . A heating roller  355  having a built-in heater  354  remains in contact with the fixing belt  353 . The pressure roller  310  is disposed opposite the fixing roller  309 . 
     The peeling device  110  similar to that shown in  FIG. 1  is disposed on a sheet-output side of the fixing unit  308 . Details of the peeling device  110  are the same as those described in connection with  FIG. 1 . The sheet detection sensor  108  for detecting the sheet  106  is disposed upstream of the fixing roller  309 . The fixing unit is the same as that described in connection with the first embodiment with regard to another configuration and the control system of the peeling device  110 . The operation of the peeling mechanism is also identical with that described in connection with the first embodiment. In the configuration shown in  FIG. 8 , the peeling device  210  shown in  FIG. 6  can also be adopted. 
     (4) Fourth Embodiment 
     (Image Forming Apparatus) 
     An image forming apparatus having the fixing unit described in connection with the first embodiment is described.  FIG. 9  is a conceptual diagram showing an embodiment of an image forming apparatus utilizing the present invention.  FIG. 9  shows an image forming apparatus  30 . The image forming apparatus  30  has a sheet feeding unit  20  that feeds a sheet; an image forming unit  300  that is an embodiment of an image forming unit; and the fixing unit  100  of the drawing. 
     (Sheet Feeding Unit) 
     The sheet feeding unit  20  has a storage device  21  storing a plurality of sheets; a delivery mechanism that delivers a sheet from the storage device  21  in a rightward direction of the drawing and that is omitted from the drawings; and a conveyance roller  22  that conveys the sheet delivered form the delivery mechanism in the rightward direction. 
     (Image Forming Unit)] 
     An image forming unit  300  has conveyance rollers  301  that convey a sheet delivered from the sheet feeding unit  20  into the image forming unit  300 . Conveyance rollers  302  are disposed downstream of the conveyance rollers  301 . The conveyance rollers  302  convey the sheet delivered from the conveyance rollers  301  or a sheet delivered from conveyance rollers  315  to be described later over a conveyance path  304  toward a secondary transfer section  303 . The secondary transfer section  303  has a transfer roller  306  and an opposing roller  307 . By nipping a transfer belt  305  and the sheet between the transfer roller  306  and the opposing roller  307 , the secondary transfer section  303  transfers the toner image on the transfer belt  305  onto the sheet. 
     The fixing unit  100  is disposed downstream of the secondary transfer section  303 . The fixing unit  100  has the configuration and functions described in connection with  FIGS. 1 to 4 . 
     The conveyance rollers  311  are disposed downstream of the fixing unit  100 . The conveyance rollers  311  deliver the sheet delivered from the fixing unit  100  to the outside of the image forming unit or to conveyance rollers  312 . The conveyance rollers  312  delivers the sheet delivered from the conveyance rollers  311  toward an inverter  313  and delivers the sheet output from the inverter  313  to the conveyance path  314 . The conveyance rollers  315  for delivering the sheet conveyed in a leftward direction of the drawing to the conveyance rollers  302  is placed in the conveyance path  314 . The conveyance path  314  is a conveyance path for turning the sheet inside out. 
     The image forming unit  300  has primary transfer units  317 ,  318 ,  319 , and  320 . Each of the primary transfer units has a photosensitive drum, a cleaner, an electrifier, an exposure unit, a development unit, and a transfer roller. The primary transfer units  317 ,  318 ,  319 , and  320  generate Y (yellow), M (magenta), C (cyan), and K (black) toner images and transfer the thus-formed images on the rotating transfer belt  305 . The YMCK toner images are thereby superimposed one on top of the other, whereupon a color toner image is produced on the transfer belt  305 . 
     (Example of Operation) 
     An example of an operation for forming an image on the sheet housed in the storage device  21  is hereunder described. First, the sheet housed in the storage device  21  is conveyed in a rightward direction of the drawing by the conveyance rollers  22  and then delivered from the sheet feeding unit  200  to the image forming unit  300 . The sheet taken into the image forming unit  300  is conveyed in the rightward direction of the drawing over the conveyance path  304 , to thus be delivered to the secondary transfer section  303 . 
     The respective YMCK toner images are superimposed, at the timing, one on top of the other on the transfer belt  305  by actions of the primary transfer units  317  to  320 , whereby a color toner image is produced. The color toner image on the transfer belt  305  is transferred to the sheet in the secondary transfer section  303 . The fixing unit  100  fixes the color toner image on the sheet to the sheet. At this time, peeling of the sheet from the heating roller is promoted by the principle descried in connection with  FIG. 4 . The sheet subjected to image fixing processing is output to the outside of the apparatus by the actions of the conveyance rollers  311  (or delivered toward inverter  313 ). 
     When an elaborate image is produced at high speed, the amount of toner to be used must be increased, and rotation of the heating roller (or the fixing belt) in the fixing unit must be made faster. As a consequence, the adhesion of the heating roller or the fixing belt to the sheet becomes high, and affixing of the sheet to the heating roller or the fixing belt becomes more obvious. Since the sheet is forcefully peeled off from the heating roller or the fixing belt by adoption of the configuration shown in  FIG. 1 ,  6 , or  8 . Hence, even when affixing of the sheet to the heating roller or the fixing belt becomes evident, occurrence of a problem, such as sheet jamming or deformation of a sheet, attributable to affixing of a sheet can be prevented. 
     (5) Fifth Embodiment 
     In the state shown in  FIG. 4B , the front edge  116  of the peeling plate  111  contacts the rotating heating roller  101 . However, there is also possible a case where the sheet  106  is peeled off from the rotating heating roller  101  by the peeling plate  111  in a state where the front edge  116  of the peeling plate  111  approaches the surface of the heating roller  101  by air pressure of the compressed air but remains out of contact with the heating roller. 
     For instance, when the rigidity of the sheet  106  is high and when the front edge of the sheet  106  achieved in the direction of conveyance is slightly levitated (spaced away) from the heating roller  101  after passed through a nip area between the heating roller  101  and the opposing roller  102 , the front edge  116  of the peeling plate  111  may also be out of contact with the surface of the rotating heating roller  101  in a state where the air pressure of the compressed air acts on the sheet. 
     Even in such a case, an eccentricity of the heating roller (a deviation of a distance between the periphery of the heating roller  101  and the center of rotation) and runout of the shaft may increase through repeated operation for reasons of deterioration, abrasion, and the like, of various members. In such a case, the front edge  116  may intermittently (an intermittent manner) contact the rotating heating roller when the nozzle  112   a  squirts a compressed gas, or the front edge  116  may contact the rotating heating roller  101  at all times when the nozzle  112   a  squirts a compressed gas. 
     Even when such a situation has actually developed, a time during which the peeling plate  111  contacts the heating roller  101  can be limited by utilization of the present invention. Hence, infliction of damage to the surface of the heating roller  101 , which would otherwise be caused by a contact of the peeling plate  111  with the heating roller  101 , can be prevented. 
     From the beginning of operation, the front edge  116  may also intermittently (or an intermittent manner) contact the rotating heating roller  101  at the time of squirting of a compressed gas from the nozzle  112   a  for reasons of an eccentricity of the heating roller  101 , rattling or deformation of a structure for supporting the shaft of the heating roller  101 , the deflection of the heating roller  101  itself, and the like. Even in such a case, even when such a possibility has come to true, the time during which the peeling plate  111  contacts the heating roller  101  can be limited by utilization of the present invention; hence, infliction of damage to the surface of the heating roller  101 , which would otherwise be caused by contact of the peeling plate  111  with the heating roller  101 , can be prevented. 
     (Application to Another Device) 
     In the above exemplification, embodiments of the present invention have been described by means of taking the fixing unit as an embodiment. However, a peeling device of the present invention can also be applied to a device other than the fixing unit. For instance, a glossing device to be disposed downstream of the fixing unit has been known. The glossing device performs operation for heating an image fixed on a sheet again and cooling the image while pressing a glossing surface with assured flatness against an image-produced surface of the sheet, to thus enhance flatness of an image surface, whereby there is performed processing for enhancing the feeling of gloss. Even in such a device, the sheet is brought into contact with a rotating body (e.g., a belt member), and hence peeling of the sheet from the rotating body is required. The peeling mechanism shown in  FIG. 1  or  6  can be adopted for a section where the sheet is peeled off from the rotating body. 
     A peeling device of the present invention can be used for peeling off a document from a blanket in offset printing. 
     An embodiment of the invention can be utilized for a peeling device, a fixing unit, and an image forming apparatus.