JP2007050937A - Detection device and detection method for kind of sheet material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a detection device for the kind of sheet material capable of obtaining an output corresponding to an impact, small in dispersion at each measurement, and capable of correctly discriminating even a small difference in the sheet material. <P>SOLUTION: An impact sensor unit 10 is arranged at a position slightly lower than a sheet conveying surface by a sheet conveying guide 7, an impact application member 2 is dropped on and collided with the top surface of a sheet 5 and the impact through the sheet 5 is detected by the impact sensor unit 10. The impact sensor unit 10 suspends a columnar impact receiving member 11 from the ceiling of an impact sensor casing 12 and fixes it. A piezoelectric device 13 is arranged on the columnar side face thereof, and a voltage output corresponding to the shear deformation of a piezoelectric element 13 is taken out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheet material type detection device, and more particularly to a sheet material type detection device that determines the material type of a sheet by applying an impact to the sheet and detecting an impact through the sheet.

  In recent years, with the improvement in performance of image forming apparatuses such as copiers, printers, and fax machines, it has been required to deal with various types of sheets such as thick paper to thin paper, cloth, coating materials, and resin films that could not be processed conventionally. . In such various sheets, the normal image forming process for plain paper may be impossible or inappropriate, so the image forming apparatus automatically determines the sheet type and determines the sheet handling and image forming conditions. Techniques for adjustment have been proposed. Thus, it is possible to optimize the image forming process for the sheet and prevent troubles related to sheet conveyance while eliminating troublesome settings and setting mistakes by the operator.

  In electrophotographic printers, etc., the temperature and pressure for heat fixing vary depending on the thickness of the sheet, various conditions during toner image transfer vary depending on the sheet material, and the elasticity of the sheet. It has been proposed to change the sheet conveyance speed in accordance with the stiffness.

  The printing apparatus disclosed in Patent Document 1 includes a reading head that reads a sheet material type code printed on a sheet, and optimizes the printing process according to the read sheet material type code.

  The sheet material type detection device disclosed in Patent Document 2 determines the material type of a sheet by applying an impact to the sheet and detecting an impact through the sheet. Based on the determination result, the image forming process in the image forming apparatus is optimized, and troubles related to sheet conveyance are prevented. The impact is applied by the gravity drop of the impact application member or the trigger release of the impact application member biased by the spring force, and a piezoelectric element is used to detect the impact.

  The image forming apparatus disclosed in Patent Document 3 performs electrostatic photographic image formation using a photosensitive drum, and adjusts fixing conditions by identifying a sheet type.

Japanese Patent Laid-Open No. 11-314443 JP 2004-26486 A JP 2001-233500 A

  In the sheet determination method disclosed in Patent Document 1, since the sheet material type cannot be determined for a sheet on which the sheet material type code is not printed, the process cannot be optimized according to the sheet material type. .

  According to the sheet material type detection device disclosed in Patent Document 2, since the properties of the sheet necessary for setting the image forming conditions are directly measured, the image forming process and the sheet conveyance can be performed even on a sheet on which the sheet material type code is not printed. Can be optimized.

  However, since the impact through the sheet by the impact applying member directly deforms the piezoelectric element, subtle differences in the impact position and the collision process of the impact applying member greatly change the deformation state of the piezoelectric element, and particularly the output waveform. The peak value varies. In addition, when an impact that matches the natural frequency of the piezoelectric element is applied, abnormal deformation occurs in the piezoelectric element, and an impact that is greater than the actual is detected, which may result in erroneous sheet discrimination.

  In addition, since the piezoelectric element detects vibrations other than impact, the sensitivity cannot be set high, and the peak value of the output varies even with the same amount of impact, so small differences in sheet material cannot be discriminated, and the same sheet has the same collision. Even if the process is repeated, the variation for each measurement is large, and it is difficult to improve the sheet discrimination accuracy.

  An object of the present invention is to provide a sheet material type detection device that can obtain an output corresponding to an impact, has a small variation for each measurement, and can accurately determine even a small difference in sheet material.

  The sheet material type detection apparatus of the present invention includes a sensing unit that senses an impact, a moving unit that moves an impact applying member toward the sensing unit and collides with a sheet on the sensing unit, and an output of the sensing unit And a control means for identifying the impact through the sheet by the impact applying member, the sensing means includes an impact receiving member that undergoes a minute displacement upon receiving the impact, and the minute displacement. And a conversion element for converting into an electric signal.

  In the sheet material type detection device of the present invention, the impact receiving member receives an impact through the sheet and detects the minute displacement of the impact receiving member by the conversion element. Therefore, the impact by the impact applying member does not directly deform the conversion element. Accordingly, even if the impact location of the impact applying member relative to the impact receiving member, the collision posture, the collision process, and the like vary somewhat, the same output can be stably obtained from the conversion element as long as the minute displacement of the impact receiving member due to the collision is equal.

  Also, the mass of the impact receiving member cancels out the high frequency vibration caused by the impact applying member collision, and the minute displacement of the impact receiving member is concentrated in the collision direction. Get smaller.

  Hereinafter, a sheet material type detection device 20 which is an embodiment of the sheet material type detection device of the present invention will be described. The sheet material type detection device 20 according to the present embodiment detects the sheet type of a sheet that is mounted on the image forming apparatus 40 and formed with an image. However, the present invention may be implemented as a single measuring device that detects the sheet type, and may be installed in other image forming methods other than the image forming device 40, such as an ink jet printer, a stencil printing device, etc. You may carry out by mounting in various office machines etc. which cannot be said to be a forming apparatus.

<Image forming apparatus>
FIG. 1 is an explanatory diagram of a configuration of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a diagram of an impact measurement result by an impact sensor unit, and FIG. 3 is a flowchart of control of the image forming apparatus.

  As shown in FIG. 1, in the image forming apparatus 40 according to the present embodiment, the image forming process unit 30 forms an image of the electrophotographic system on the sheet 5. The controller 101 controls the image forming process unit 30 to execute this image formation.

  The image forming process unit 30 includes various mechanisms and devices including a photosensitive drum (not shown), a number of motors, actuators, and control sensors for driving them, as described in Patent Document 3 and the like. And connected to the controller 101. However, since the detailed configuration and control of the image forming apparatus are somewhat separated from the subject matter of the present invention, detailed description thereof is omitted.

  The sheets 5 are taken out one by one from a sheet cassette (not shown) arranged upstream of the sheet conveyance guides 6 and 7, and are guided by the sheet conveyance guides 6 and 7 and pass through the sheet material type detection device 20. The sheet material type is detected. Thereafter, the sheet 5 is conveyed to the image forming process unit 30 to form an image.

  In the sheet material type detection device 20, the impact application member 2 collides with the surface of the sheet 5, and the impact sensor unit 10 disposed at the impact position of the impact application member 2 detects the impact over the sheet, thereby detecting the sheet material type. Identify A recording mode optimized according to the identified sheet material type is set in the image forming process unit 30.

<Sheet material type detection device>
In this embodiment, the guide member of the invention is the sheet conveyance guides 6 and 7, the detection means of the invention is the impact sensor unit 10, the impact application member of the invention is the impact application member 2, the movement means of the invention is gravity and the coil 50, the invention. The control means corresponds to the impact sensor detection circuit unit 501 and the controller 101, the impact receiving member of the invention corresponds to the impact receiving member 11, and the conversion element of the invention corresponds to the piezoelectric element 13. However, these constituent members, electronic circuits, etc. The combinations thereof are merely examples of possible options, and the present invention can naturally be implemented in other modes in which some or all of these components are replaced by alternative components.

  As shown in FIG. 1, the sheet conveyance guides 6 and 7 are arranged between a sheet cassette (not shown) and an image forming process unit 30 in the image forming apparatus 40, and image formation of the sheet 5 taken out from the sheet cassette is performed. The conveyance to the process unit 30 is guided. The sheet 5 passes between the sheet conveyance guides 6 and 7 formed with a certain gap, and is conveyed and guided to the image forming process unit 30 at a predetermined speed (in the direction of the arrow in FIG. 1) by a conveyance roller (not shown). .

  The impact sensor unit 10 is attached to the housing structure 201 of the image forming apparatus 40 at the break (or opening) of the sheet conveyance guides 6 and 7, and the impact applying member 2 is disposed to face the impact sensor unit 10. ing.

  The impact sensor unit 10 holds the upper end of the impact receiving member 11 by the ceiling portion of the impact sensor housing 12 and is suspended in the internal space of the impact sensor housing 12. The upper end of the impact receiving member 11 is the impact sensor housing. It is fastened to the body 12 by caulking, press-fitting or adhesion. The impact receiving member 11 can be minutely displaced in the vertical direction by the deflection of the ceiling portion of the impact sensor housing 12 or the like.

  The impact receiving member 11 has a cylindrical shape, and an annular piezoelectric element 13 is bonded to the side surface of the impact receiving member 11 on the cylinder. The piezoelectric element 13 has a pair of cylindrical electrodes 14 and 15 attached to the inner side surface and the outer side surface, and generates a shear deformation according to the acceleration acting on the impact receiving member 11 to change the dielectric constant. The electric capacity between the pair of electrodes 14 and 15 is changed.

  That is, the impact receiving member 11 having the piezoelectric element 13 bonded to the center at the center is in a state of being supported by the impact sensor housing 12 and suspended. When the impact applying member 2 applies acceleration to the impact receiving member 11 via the sheet 5, stress is generated between the impact receiving member 11 and the piezoelectric element 13. At this time, the adhesive surface between the impact receiving member 11 and the piezoelectric element 13 is displaced in the same vertical direction as the direction of impact application, so that shear stress is generated in the piezoelectric element 13.

  A change in electric capacity between the pair of electrodes 14 and 15 due to the shear deformation of the piezoelectric element 13 is converted into an electric signal by the impact sensor detection circuit unit 501. The conversion circuit (charge amplifier) 103 of the impact sensor detection circuit unit 501 generates a voltage signal that follows the change in the capacitance between the pair of electrodes 14 and 15. The peak detection circuit 102 converts the voltage signal of the conversion circuit 103 into a digital signal and samples it, and outputs a digital value of the peak voltage excluding the noise component.

  The impact applying member 2 is formed of a material such as metal. The impact applying member 2 is normally held at a standby position indicated by a solid line by causing a current to flow from the power source 51 to the coil 50 to generate a magnetic force in the coil 50. When the current of the power supply 51 is cut, the magnetic force of the coil 50 is lost, and the impact applying member 2 falls freely by gravity and collides with the sheet 5 as indicated by a broken line.

  Due to the collision of the impact applying member 2, the sheet 5 held in the cut (or opening) of the sheet conveying guides 6 and 7 is bent downward as shown by a broken line and comes into contact with the upper end surface of the impact receiving member 11, The impact applying member 2 presses the impact receiving member 11 over the sheet 5 with a surplus momentum.

  Therefore, the momentum of the impact applying member 2 is transmitted to the impact receiving member 11 after the bending resistance of the sheet 5 is subtracted, and the acceleration of the impact receiving member 11 due to this attenuated impact force is detected by the piezoelectric element 13.

  As shown in FIG. 2, the output voltage of the conversion circuit 103 changes according to the acceleration acting on the impact receiving member 11 after the impact applying member 2 collides with the sheet 5. However, since the acceleration of the impact receiving member 11 is obtained by subtracting the bending resistance of the sheet 5, the peak of the output voltage is lower in the sheet having a large bending rigidity in FIG. 2 than in the sheet having a small bending rigidity. In FIG. 2, for simplification, the output voltage is shown excluding the noise component, the vertical axis is the output voltage, and the horizontal axis is the time.

As a result of an experiment using the sheet material type detection device 20 shown in FIG. 1, the maximum voltage is Va in the case of a sheet material of type A sheet material (paper having a basis weight of 120 g / m ^{2 and} a thickness of 150 μm). In the case of the sheet material B (paper having a basis weight of 80 g / m ^{2 and} a thickness of 100 μm), the maximum voltage is Vb. In the case of the sheet material C type (paper having a basis weight of 60 g / m ^{2 and} a thickness of 80 μm), the maximum voltage is Vc. And the relationship of Vc>Vb> Va was confirmed.

  That is, the sheet material A, which is thick paper and has high bending rigidity, has a large amount of energy absorption of the paper. Therefore, the stress generated between the impact receiving member 11 and the piezoelectric element 13 is small, and the maximum voltage is small. On the other hand, the sheet material C, which is thin paper and has a small bending rigidity, has a small energy absorption amount of the paper, so that the stress generated between the impact receiving member 11 and the piezoelectric element 13 is large and the maximum voltage is large.

  As described above, even if the impact energy applied to the sheet 5 by the impact applying member 2 is the same, the rigidity in the bending direction of the sheet depends on the basis weight of the sheet material (basis weight = weight per unit area) and the sheet material type. Therefore, the maximum voltage is output differently depending on the sheet type.

<Control of image forming apparatus>
As shown in FIG. 1, the controller 101 which is a microcomputer control device forms an image on the sheet 5 by program-controlling the image forming process unit 30. Prior to image formation, the sheet material type detection device 20 distinguishes the sheet material type of the sheet 5 into three types and optimizes the processing conditions in the image forming process unit 30.

  As shown in FIG. 2, in the sheet material type detection device 20, if the maximum voltage is in the range A, the sheet 5 is determined as the sheet material A type, and if the maximum voltage is in the range B, the sheet 5 is determined as the sheet material B type. If the maximum voltage is in the range C, the sheet 5 is determined as the sheet material C type.

  As shown in FIG. 3, when the sheet 5 is conveyed by a conveyance roller (not shown) and passes near the impact sensor unit 10 (YES in S11), the controller 101 controls the power source 51 to release the magnetic force (S12). ).

  At the next moment, the impact applying member 2 starts to fall freely and collides with the sheet 5. Thereafter, the impact force is transmitted as vibration to the impact receiving member 11 through the sheet 5, and the piezoelectric element 13 starts to vibrate in the vertical direction at the same time. At this time, a shear stress is generated in the piezoelectric element 13, and the generated shear stress causes a capacitance change between the pair of electrodes of the piezoelectric element 13 and is converted into a voltage signal by the impact sensor detection circuit unit 501, and the maximum. The output voltage value is detected. Here, the sheet 5 with high bending rigidity exhibits a low maximum voltage, and the sheet 5 with low bending rigidity exhibits a high maximum voltage.

  When the peak detection circuit 102 outputs the maximum voltage to the controller 101 (YES in S13), the controller 101 reads the maximum voltage (S14) and compares it with the result of the maximum voltage to determine the sheet material type (S15). .

  As shown in FIG. 2, the controller 101 stores a data table in which each sheet material corresponds to the maximum voltage. The controller 101 determines whether the maximum voltage matches the range A: sheet material A type voltage range, B: sheet material B type voltage range, or C: sheet material C type voltage range. For example, if the maximum voltage is Va, the sheet material is in the class A voltage range, so the sheet material is determined to be class A, and if the maximum output is Vc, it is determined to be class C.

  When the determination of the type of sheet material is completed, the controller 101 sets a recording mode (S16). For example, in the case of the sheet material A, the sheet conveyance speed, the developing condition, the developing material fixing condition (temperature and temperature distribution), etc., which are adapted to the conditions of the sheet material A are determined. Then, the image forming process unit 30 is controlled to perform image formation such as printing and printing on the sheet 5 in the recording mode optimal for the sheet material A type.

<Another embodiment>
FIG. 4 is an explanatory diagram of a sheet material type detection device according to another embodiment. The sheet material type detection device 120 according to another embodiment is arranged by replacing the sheet material type detection device 20 of FIG. 1 and is controlled by the controller 101 according to the flowchart of FIG.

  As shown in FIG. 4, the impact sensor unit 110 includes an impact receiving member 111, an impact sensor housing 112, a piezoelectric element 113, and a stress amplification member 114. The impact receiving member 111 has a cylindrical shape, and an upper end is bonded to the impact sensor housing 112. A cylindrical piezoelectric element 113 is surface bonded to the outer periphery of the center of the column of the impact receiving member 111. The piezoelectric element 113 has a pair of electrodes formed on the outer and inner side surfaces, and when a force is applied from the outside to generate a stress / impact, a capacitance change between the pair of electrodes can be generated to extract a voltage signal. It is.

  A cylindrical stress amplifying member 114 having a large specific gravity such as metal is bonded to the outer periphery of the piezoelectric element 113. That is, the impact receiving member 111 in which the stress amplifying member 114 is bonded to the outer periphery of the piezoelectric element 113 is in a state of being supported by the impact sensor housing 112 and suspended. Thus, when the impact applying member 2 collides from the upper direction, the impact receiving member 111 vibrates up and down and the piezoelectric element 113 also vibrates. At this time, the stress amplification adhered to the outer periphery of the piezoelectric element 113 The inertial force of the member 114 works to promote vertical vibration.

  That is, even with slight vibrations, the adhesive surface portion of the impact receiving member 111 and the piezoelectric element 113 is displaced in the vertical direction, and the structure is easy to generate shear stress, so that a highly sensitive voltage signal can be output. I can do it.

<Correspondence with Invention>
The sheet material type detection device 20 of the present embodiment includes an impact sensor unit 10 that senses an impact, and a coil 50 that moves the impact applying member 2 toward the impact sensor unit 10 and collides with the sheet 5 on the impact sensor unit 10. And a controller 101 that discriminates the impact of the impact applying member 2 through the sheet based on the output of the impact sensor unit 10. The impact sensor unit 10 includes an impact receiving member 11 that undergoes a minute displacement upon receiving an impact through the sheet by the impact applying member 2, and a piezoelectric element 13 that converts the minute displacement into an electrical signal. Therefore, since the impact receiving member 11 receives an impact through the sheet and the minute displacement of the impact receiving member 11 is detected by the piezoelectric element 13, the impact applied by the impact applying member 2 is directly applied as in the device disclosed in Patent Document 2. The piezoelectric element 13 is not deformed. Therefore, even if the impact location, the collision posture, and the collision process of the impact applying member 2 with respect to the impact receiving member 11 vary somewhat, the same output from the piezoelectric element 13 is stable as long as the impact amount of the impact receiving member 11 due to the collision is equal. Obtained.

  Further, since the mass of the impact receiving member 11 integrates and cancels the high-frequency vibration caused by the collision of the impact applying member 2 and the minute displacements of the impact receiving member 11 are concentrated in the collision direction, the output of the piezoelectric element 13 based on the minute displacements. Peak variation is reduced.

  That is, since the impact through the sheet by the impact applying member 2 does not directly deform the piezoelectric element 13, a subtle difference in the collision position and the collision process of the impact applying member 2 hardly affects the deformation state of the piezoelectric element 13, and the output voltage The waveform, especially its peak value, is stable. In addition, even if an impact that matches the natural frequency of the piezoelectric element 13 is applied, the deformation is suppressed by the impact receiving member 11, so that the piezoelectric element 13 may be deformed abnormally and an impact exceeding the actual level may be detected. There is no.

  In addition, since the piezoelectric element 13 is difficult to detect vibrations other than the impact from above, the sensitivity can be set high. If the impact amount is the same, the output peak values are almost equal, and even a small difference in sheet material can be determined. Therefore, the variation in each measurement when the same collision is repeated on the same sheet is reduced, and the sheet discrimination accuracy can be increased.

  The shock sensor housing 12 has a bottom side supported and a ceiling side facing the impact applying member 2, and the impact receiving member 11 is formed in a column shape and has one end on the ceiling of the shock sensor housing 12. The other end side is freely protruded into the internal space of the impact sensor housing 12. Therefore, the impact through the sheet 5 due to the collision of the impact applying member 2 efficiently accelerates the impact receiving member 11 and slightly displaces it.

  In addition, sheet conveyance guides 6 and 7 for guiding the sheet 5 to be conveyed are provided, and the impact receiving member 11 is retracted from the guide surface of the sheet 5 by the sheet conveyance guides 6 and 7 and is not connected to the sheet conveyance guides 6 and 7. Arranged in contact. Therefore, when the impact applying member 2 collides, the acceleration obtained by subtracting the bending resistance of the sheet supported by the sheet conveyance guides 6 and 7 can be detected by the piezoelectric element 13. That is, the bending resistance of the sheet can be more accurately evaluated than when the impact applying member 2 is caused to collide with the sheet 5 and the impact receiving member 11 in close contact with each other. Acceleration measurement with a high S / N ratio is possible by being isolated from vibrations of the sheet conveyance guides 6 and 7 and the conveyance rollers.

  The impact receiving member 11 is formed in a cylindrical shape, and the piezoelectric element 13 is fixed to the cylindrical surface of the impact receiving member 11, and electrodes are arranged on annular inner and outer surfaces surrounding the cylindrical surface. Therefore, even if the piezoelectric element 13 is locally deformed by sound wave vibration generated in the impact receiving member 11 when the impact applying member 2 collides, the influence of the deformation is integrated and canceled along the cylindrical surface, and the SN ratio is high. Acceleration measurement is possible. There is little influence (pyroelectric effect) due to local temperature changes.

  In the sheet material type detection device 120 of another embodiment, an annular stress amplifying member 114 is fixed to the outer side surface of the annular piezoelectric element 113. Therefore, due to the inertia of the stress amplifying member 114, the shear deformation of the piezoelectric element 13 when acceleration is generated in the impact receiving member 111 increases, and a large output voltage change can be extracted with a high SN ratio even with a small acceleration.

  As described above, the sheet material type detection device 20 according to the present embodiment basically uses the output signal of the impact sensor unit 10 that causes the impact applying member 2 to collide with the sheet 5 and senses the impact level of the sheet 5. It is configured. The impact sensor unit 10 for sensing the impact level of the sheet 5 includes an impact receiving member 11 with which the impact applying member 2 collides, and a piezoelectric element 13 for obtaining an electric signal corresponding to the acceleration of the impact receiving member 11. Then, the impact receiving member 11 generates shear stress in the piezoelectric element 13 by being displaced in the impact direction.

  Therefore, it is possible to extract only the stress having the same component as that in the impact application direction, and a highly accurate impact sensor with less noise can be realized. By using this impact sensor, the physical properties of each sheet material can be read finely, and accurate and accurate sheet discrimination can be realized.

  As a result, printing and printing are performed in an image forming process mode of an optimum condition corresponding to each sheet material type, so that a high-quality image forming apparatus can be provided.

  As for the impact application configuration, in the present invention, the impact energy is given to the sheet 5 by the magnetic force holding using the coil 50 and the method of free fall. Various methods using a spring, a cam, or the like as shown in Patent Document 2 may be used.

  In the present embodiment, the impact receiving member 11 has a columnar or cylindrical shape, but may be any configuration that can convert the impact force into stress, and is not limited to the columnar or cylindrical shape.

1 is an explanatory diagram of a configuration of an image forming apparatus according to an embodiment of the present invention. It is a diagram of the impact measurement result by an impact sensor unit. 3 is a flowchart of control of the image forming apparatus. It is explanatory drawing of the sheet material classification detection apparatus of another embodiment.

Explanation of symbols

2 Impact application member (impact application member)
5 Sheet 6, 7 Guide member (sheet conveyance guide)
10 Sensing means (impact sensor unit)
11 Shock receiving member 12 Housing structure (shock sensor housing)
13 Conversion element (piezoelectric element)
20, 120 Sheet material type detection device 30 Image forming process unit 50, 51 Moving means (coil, power supply)
101, 501 Control means (impact sensor detection circuit unit, controller)

Claims (7)

Sensing means for sensing impact;
Moving means for moving the impact applying member toward the sensing means to collide with a sheet on the sensing means;
In the sheet material type detection device, comprising: a control unit that identifies an impact through the sheet by the impact applying member based on an output of the sensing unit.
The sensing means includes an impact receiving member that undergoes minute displacement upon receiving the impact;
A sheet material type detection device comprising: a conversion element that converts the minute displacement into an electrical signal. A housing structure in which the bottom side is supported and the ceiling side is arranged facing the impact applying member,
2. The impact receiving member is formed in a columnar shape, the one end side is fixed to the ceiling of the housing structure, and the other end side is freely protruded into the internal space of the housing structure. The sheet material type detection device described. A guide member for guiding the conveyed sheet;
The sheet material type detection device according to claim 1, wherein the impact receiving member is retracted from a guide surface of the sheet by the guide member and is disposed in non-contact with the guide member. The impact receiving member is formed in a cylindrical shape,
The said conversion element is a piezoelectric element which is fixed to the cylindrical surface of the said impact receiving member, and has arrange | positioned the electrode in the cyclic | annular inner-outer surface surrounding the said cylindrical surface. Sheet material type detection device.   The sheet material type detection device according to claim 4, wherein an annular weight member is fixed to the outer side surface. In the type detection method of the sheet material for identifying the sheet by detecting the impact through the sheet when the impact applying member collides with the sheet,
A sheet material type detection method comprising: attaching a piezoelectric element to an impact receiving member disposed at a collision position of the impact applying member; and detecting an output corresponding to a shear strain of the piezoelectric element after the impact applying member collides. . 7. The sheet material type detection method according to claim 6, wherein the impact receiving member is arranged away from the sheet, and the acceleration of the impact receiving member obtained by subtracting the bending resistance of the sheet is detected by the piezoelectric element.

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