JP2010058885A - Image forming device having basis weight detection means - Google Patents

Abstract

In an image forming apparatus for measuring the basis weight of a recording medium, a stable basis weight measurement result can be obtained without being affected by fluttering of the recording medium.
When a recording medium 17 is conveyed by a manual pickup roller 12 that conveys a recording medium 17 loaded on a manual feed tray 11, the manual pickup roller 12 and the recording medium 17 are in contact with each other. When carrying, it is not carried when it is separated. When the manual pickup roller 12 and the recording medium 17 are separated from each other and the recording medium is temporarily stopped, the basis weight is measured by the basis weight sensor 14 to obtain a stable basis weight measurement result. Can do.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus such as a laser printer, a copying machine, and an ink jet printer provided with a basis weight detecting means for detecting a basis weight of a recording medium using an ultrasonic sensor.

  Image forming apparatuses such as copying machines and laser printers perform printing by the following method called an electrophotographic process. A latent image is formed by exposing the surface of the uniformly charged photosensitive drum with a laser beam, and the latent image is visualized as a toner image by a developing device. Then, the toner image on the photosensitive drum is transferred to a recording medium, and the recording medium on which the toner image is mounted is fixed by heat and pressure, whereby printing is completed.

  In such an image forming apparatus, the user inputs the size and type of the recording medium to an operation panel or the like provided in the image forming apparatus, and the fixing conditions (for example, the fixing temperature and the fixing device pass through the setting). The recording medium conveyance speed) was set.

  Alternatively, an image forming apparatus has been devised that uses a sensor for discriminating a recording medium inside the image forming apparatus to variably control transfer conditions, conveyance conditions, or fixing conditions depending on the type of recording medium.

  For example, Patent Document 1 proposes an image forming apparatus including means for measuring the weight per unit area (hereinafter referred to as basis weight) of a recording medium using an ultrasonic transmitter and an ultrasonic receiver. Yes.

  A basis weight sensor using ultrasonic waves as in Patent Document 1 needs to consider an error in a measurement result due to fluttering of the recording medium when measuring the basis weight. Here, fluttering is a phenomenon in which the recording medium vibrates in a direction perpendicular to the conveying direction when the recording medium is conveyed.

Patent Document 2 proposes a method of measuring by stopping the recording medium as one of sensors for measuring the state of the surface of the recording medium by reducing the flutter. The image forming apparatus disclosed in Patent Document 2 performs registration adjustment in which a recording medium is temporarily stopped by a registration roller using a registration roller, and the recording medium is conveyed in synchronization with image formation. By this registration adjustment, the image of the recording medium is read while the recording medium is temporarily stopped, and the surface state of the recording medium is measured.
JP 2007-24837 A JP 2003-302885 A

  As in Patent Document 2, an image forming apparatus in which the printing time is shortened by changing the conveyance speed of the recording medium with the registration roller and performing the registration adjustment without stopping the recording medium with the registration roller has been put into practical use. ing. In such an image forming apparatus, since the recording medium cannot be stopped, an error may occur in the measurement of the basis weight due to the flapping of the recording medium when the basis weight is measured.

  The present invention has been made in view of the above situation, and an object of the present invention is to stably measure the basis weight even when the recording medium is not stopped by a registration roller.

  In order to achieve the above object, an image forming apparatus according to the present invention is an image forming apparatus having a paper feeding unit on which recording media are stacked, wherein the recording medium is rotated to convey the recording medium from the paper feeding unit. A member, a transmission unit that transmits an ultrasonic wave to a recording medium conveyed by the conveyance member, and a reception unit that receives an ultrasonic wave irradiated by the transmission unit. A first period in which the conveyance member and the recording medium come into contact with each other and convey the recording medium when conveyed; and a second period in which the recording medium does not come into contact with the recording medium In the second period, the basis weight is measured from the output result of the ultrasonic wave irradiated from the transmission means received by the reception means.

  According to the configuration of the present invention, it is possible to perform stable basis weight measurement even when the recording medium is not stopped by the registration roller.

(First embodiment)
A schematic configuration of an example of an image forming apparatus used in the first embodiment is shown in FIG. FIG. 1 is a cross-sectional view showing a schematic configuration of a color LBP which is one of image forming apparatuses.

  A color LBP 101 shown in FIG. 1 includes a manual feed tray 11, a manual pickup roller 12, a basis weight sensor 14, a paper feed cassette 102, a paper feed cassette pickup roller 103, a transfer belt drive roller 104, a transfer belt 105, and a photosensitive drum 106. -109, transfer rollers 110-113, process cartridges 114-117, optical units 118-121, fixing unit 122, and the like.

  The color LBP of this embodiment includes a basis weight sensor 14 (14a and 14b) that measures the basis weight of the recording medium 17 using ultrasonic waves immediately after the recording medium 17 is conveyed from the manual feed tray 11.

  Further, the color LBP 101 is a pick-up roller 12 for manual feed, a conveying roller 15, a pick-up roller 103 for a sheet feeding cassette, a conveying roller 132, a transfer belt driving roller 104 as a driving means, and a photosensitive drum 106 for each color ˜109 and the transfer rollers 110 to 113, a photosensitive drum drive motor (not shown), and a fixing drive motor (not shown) for driving the fixing roller included in the fixing unit 122 are provided.

  Next, as an example of printing in the color LBP 101, an operation in the case of printing by feeding from the manual feed tray 11 will be described with reference to the flowchart of FIG.

  First, print data designating the manual feed tray 11 as a paper feed port is received from a computer (not shown) connected to the color LBP 101 (S1).

  When print data is received, the manual pick-up roller 12 and the transport roller 15 which are transport members are rotationally driven to start printing (S2).

  Here, as shown in FIG. 3, the manual pick-up roller 12 of the present embodiment has a shape in which only a circular arc in a partial section is in contact with the recording medium 17 in one rotation of the roller. A roller in which 180 ° of 360 ° of rotation forms an arc is called a half moon roller. Also, a roller having a shape similar to the letter D in order to form a circular arc within 360 ° is called a D-cut roller.

  The manual pickup roller 12 of this embodiment is a half-moon roller having a diameter of 15 mm. The manual pickup roller conveys the recording medium 17 by about 23.5 mm in one rotation. The conveyance speed during conveyance of the recording medium 17 is 140 mm / sec.

  During the period in which the circular arc portion of the manual pickup roller 12 is in contact with the recording medium 17, the pressurizing means 13 moves upward, and the loaded recording medium 17 is pressed against the pickup roller 12 to carry it (S3).

  FIG. 4 shows how the recording medium 17 is conveyed. FIG. 4 shows a state where the manual pickup roller 12 is rotated 270 ° from the state shown in FIG. In FIG. 4, the recording medium 17 is transported 23.5 mm, and the recording medium 17 is in the measurement area of the basis weight sensor 14.

  Next, while the manual feed pickup roller 12 is rotated 180 °, that is, while being separated from the recording medium 17 (= 0.17 sec), the recording medium 17 is stopped in the measurement area of the basis weight sensor 14. Meanwhile, the basis weight sensor 14 measures the basis weight of the recording medium 17 (S4).

  Here, the basis weight sensor 14 will be described. As shown in FIG. 4, the basis weight sensor 14 includes an ultrasonic transmitter 14a and an ultrasonic receiver 14b. The ultrasonic transmitter 14a and the ultrasonic receiver 14b are arranged so as to sandwich the conveyance path.

  A circuit block diagram for driving the basis weight sensor 14 is shown in FIG. First, the CPU 131 sends a transmission signal 132 to the transmission circuit 133 in conjunction with the phase of the manual pickup roller 12, that is, at a timing when the manual pickup roller 12 is separated from the recording medium 17. Upon receiving the transmission signal 132, the transmission circuit 133 generates about 5 to 10 pulses of a rectangular wave 134 having a frequency of 40 kHz.

  When the rectangular wave 134 is amplified by the amplifier circuit 135, a rectangular wave driving signal 136 as shown in FIG. 6A is generated. This drive signal 136 is applied to the ultrasonic transmitter 14a.

  The ultrasonic transmitter 14a uses piezoelectric ceramics having a peak frequency of sound pressure-frequency characteristics of 40 kHz. The ultrasonic transmitter 14 a transmits a 40 kHz ultrasonic wave 14 c according to the frequency of the drive signal 136.

  The ultrasonic wave 14c is applied to the recording medium 17, and when the recording medium 17 vibrates, the recording medium 17 vibrates the air on the ultrasonic receiver side. That is, an ultrasonic transmitted wave 14d is generated. The ultrasonic wave receiver 14b receives the transmitted wave 14d.

  The ultrasonic receiver 14b converts the vibration of the transmitted wave 14d into an electrical signal (hereinafter referred to as a received signal 137). The received signal 137 is shown in FIG.

  Received signal 137 is amplified by amplifier circuit 138. Since sufficient voltage amplitude cannot be obtained even with the amplified received signal 139, the voltage level is further increased by the integrating circuit 140. The calculation output 141 of the integration circuit is shown in FIG.

  The arithmetic output 141 is converted into a digital output 143 by the A / D conversion circuit 142 and input to the CPU 131. The CPU 131 samples the digital output 143 for one period T (= 0.025 msec) after a certain time t0 (= 0.125 msec) from the start of transmission, and sets the maximum value as the detected value.

  In order to measure the basis weight of the recording medium 17 from the obtained detection value, whether the recording medium 17 is included in any basis weight range is determined from the detection value according to the detection value → basis weight conversion table shown in FIG. . Here, the detection value → basis weight conversion table is created in advance from the detection value and basis weight measurement data shown in FIG.

  After the basis weight of the recording medium 17 is measured by the basis weight sensor 14, the conveyance speed at the time of fixing is changed according to the basis weight according to the table shown in FIG. 9 (S5).

  Similarly, the target value of the fixing temperature is variably controlled according to the basis weight according to the table shown in FIG. 9 (S6). Thereafter, as shown in FIG. 10, the recording medium 17 reaches the conveying roller 15 (S7). The recording medium 17 is conveyed to the transfer unit by the conveying roller 15 for image formation.

  Here, the distance L from the position where the basis weight sensor 14 can be measured to the conveyance roller 15 is designed to be longer than the conveyance distance (= 23.5 mm) of one rotation of the manual pickup roller 12. This is because the basis weight sensor 14 always stops temporarily at a position where the recording medium 17 can be measured.

  When the recording medium 17 is conveyed to the conveyance roller 15, the manual pickup roller 12 stops driving at a default position separated from the recording medium 17 (S8).

  Thereafter, after the recording medium leading edge sensor 124 detects the leading edge of the recording medium 17 (S9), image formation is started after a predetermined time (S10).

  Subsequently, image formation will be described. The optical units 118 to 121 for each color form a latent image by exposing and scanning the surfaces of the photosensitive drums 106 to 109 with a laser beam. The latent images on the photosensitive drums 106 to 109 are visualized as toner images by toners that are developers of the respective colors by a developing device (not shown) provided in the cartridges 114 to 117. These series of image forming operations are controlled in synchronism so that an image is transferred to a predetermined position of the recording medium 17 being conveyed.

  The recording medium 17 is transferred by superimposing yellow, magenta, cyan, and black toner images at the transfer nip. Here, the transfer bias applied at the time of transfer is corrected according to the basis weight of the recording medium 17 as shown in FIG. 11 (S11).

  The recording medium 17 on which the toner image is mounted is heated and pressed at a predetermined temperature by the fixing unit 122 to fix the toner image (S12), and is discharged to complete printing.

  When the next print data has been received when printing is completed, the process returns to S1, and when the print data has not been received, printing is terminated.

  As described above, since the manual pickup roller 12 is a half-moon roller, the recording medium 17 is repeatedly conveyed and stopped at regular intervals by continuously rotating the manual pickup roller 12. Therefore, the basis weight can be measured by the basis weight sensor 14 while the recording medium 17 protruding from the paper feed tray 11 is stopped in the measurement area of the basis weight sensor 14. As a result, the basis weight can be measured while the recording medium 17 is stopped, and the stable basis weight can be measured without being affected by the fluttering of the recording medium 17.

  The stop time of the recording medium 17 in the first embodiment is 0.17 sec. The stop time of the recording medium in an image forming apparatus that stops the recording medium with a conventional registration roller is about 1 second. In other words, by using the pickup roller rather than the image forming apparatus in which the recording medium 17 is stopped by the registration roller, the printing time of less than 1 second can be shortened.

  In this embodiment, the stop time of the recording medium 17 is 0.17 sec. However, since the measurement time of the basis weight sensor 14 is 0.150 msec, the time for actually stopping the recording medium 17 is designed to be shorter. May be.

  In the present embodiment, a half-moon roller is used as the manual pickup roller 12. However, a barrel shape as shown in FIG. 12A or a shape as shown in FIG. In FIG. 12A, two sets of conveyance and stop can be performed by one rotation of the roller. In FIG. 12B, four sets of conveyance and stop can be performed by one rotation of the roller.

  By the way, since the intensity of the ultrasonic sensor is easily affected by temperature and atmospheric pressure, there is a measurement method for correcting the detection value of the ultrasonic sensor using the intensity measurement result of the ultrasonic sensor when there is no recording medium 17. . Even in such a case, the present embodiment can be applied.

  In the description of the present embodiment, the color LBP has been described as an example. However, the present invention is not limited to the color LBP, and can be applied not only to the monochrome LBP but also to all image forming apparatuses that change printing conditions according to the recording medium.

(Second Embodiment)
In the first embodiment, the recording medium 17 has moved to the measurement area of the basis weight sensor 14 when the manual pick-up roller 12 rotates once. However, in practice, the recording medium 17 is set in front of the paper feed tray 11, the manual pickup roller 12 is deteriorated, or the recording medium 17 is fed out while sliding with respect to the recording medium 17. A situation occurs where the sensor 14 does not reach the measurement area. A case where the recording medium 17 does not reach the measurement area of the basis weight sensor 14 will be described in this embodiment.

  Since the schematic configuration of the color LBP 101 of the present embodiment is the same as that of the first embodiment, description thereof is omitted.

  Next, a retry operation when the color LBP 101 measures the basis weight of the recording medium 17 will be described with reference to the flowchart shown in FIG.

  First, the color LBP 101 receives print data from a connected host computer or the like (S21).

  The color LBP 101 which has received the print data rotates the manual pickup roller 12 and the transport roller 15 (S22).

  The recording medium 17 is separated by the manual pick-up roller 12 and conveyed to the conveyance path (S23).

  At this time, a case where the recording medium 17 stops before the basis weight sensor 14 will be described. The grammage sensor 14 starts measuring the grammage when the manual pickup roller 12 and the recording medium 17 are separated and the recording medium 17 is not conveyed (S24).

  At this time, since the recording medium 17 has not yet been transported to the measurement area of the basis weight sensor 14, the ultrasonic wave transmitted from the ultrasonic transmitter 14a directly reaches the ultrasonic receiver 14b. It can be seen that this directly received ultrasonic wave has a faster arrival time and a large amplitude of the ultrasonic wave as compared with the case where it is received through the recording medium 17 as shown in FIG.

  Considering this, the CPU 131 takes in the digital output 143 as an output result after 0.050 msec from the transmission (S25). It is determined whether the digital output 143 is within a certain threshold range. Here, if the digital output 143 is 100 or more, it is determined that there is no recording medium 17 (No in S26), and the process returns to S24 and the basis weight measurement is repeated again until the basis weight of the recording medium 17 is measured.

  On the other hand, when the recording medium 17 stops within the measurement area of the basis weight sensor 14, the CPU 131 captures the digital output 143 and measures the basis weight of the recording medium 17 after 0.125 msec from the transmission (S27).

  Hereinafter, S28 to S36 are the same as S5 to S13 in the flowchart described with reference to FIG. 2 of the first embodiment, and a description thereof will be omitted.

  As described above, the basis weight sensor 14 using ultrasonic waves can detect whether the recording medium 17 is within the measurement area of the basis weight sensor 14. Therefore, when the recording medium 17 is not in the measurement area of the basis weight sensor 14, the basis weight may be measured again after the recording medium 17 is conveyed into the measurement area by the manual pickup roller 12. At this time, the manual pickup roller 12 may remain continuously rotated.

  By doing so, it is possible to prevent erroneous basis weight measurement when the recording medium 17 is not within the measurement region, and it is possible to perform stable basis weight measurement.

  In this embodiment, when there is a recording medium, the presence / absence of the recording medium is detected at the timing when the digital output 143 is 0, that is, after 0.050 msec from the transmission. However, the measurement timing is not limited to 0.050 msec after the ultrasonic transmission, and may be performed simultaneously with the basis weight measurement, for example. When the basis weight measurement and the recording medium presence / absence detection are performed at the same time, the threshold can be detected by setting the threshold for the presence / absence of the recording medium to 255 (decimal notation) with the digital output 143.

(Third embodiment)
In the first and second embodiments, an example in which the present invention is applied to a manual paper feed tray has been described. In the third embodiment, an example applied to a cassette paper feeder will be described.

  FIG. 15 shows a schematic configuration of a cassette paper feeding device in the third embodiment.

  In FIG. 15, reference numeral 302 denotes a cassette paper feeder, 303 denotes a cassette pickup roller, 325 denotes a recording medium, 331 denotes a separation claw, 334 (334a and 334b) denotes a basis weight sensor, and 335 denotes a transport roller. The cassette pickup roller 303 is a half-moon roller as in the first embodiment, but may have a shape as shown in FIG. 12 as in the first embodiment.

  Next, the paper feeding operation will be described. When the cassette pickup roller 303 rotates 90 °, the cassette pickup roller 303 comes into contact with the recording medium 325 and conveyance is started.

  The recording medium 325 that has been transported passes over the separation claw 331 and is transported by only one sheet. The recording medium 325 is conveyed to the support roller 332. The support roller 332 is a driven roller that is not connected to a power source.

  The recording medium 325 sandwiched between the support rollers 332 is conveyed to the cassette pickup roller 303 and guided in the traveling direction by the conveyance guide 333.

  When the cassette pickup roller 303 rotates 270 °, the cassette pickup roller 303 is separated from the recording medium 325. At this time, the recording medium 325 is nipped by the support roller 332 and stopped. Since the support roller 332 has a high static frictional force due to the pressing force between the rollers of the support roller 332, the recording medium 325 on the conveyance path can be prevented from returning backward due to its own weight.

  When the cassette pickup roller 303 rotates 630 ° (= 360 ° + 270 °), the recording medium 325 is conveyed into the measurement area of the basis weight sensor 334.

  While the recording medium 325 is stopped, the basis weight sensor 334 measures the basis weight. When the basis weight has been measured, the conveyance speed during fixing and the target temperature of the fixing device are determined as in the first embodiment. Subsequently, the recording medium 325 is conveyed to the conveying roller 335 by the cassette pickup roller 303. Thereafter, the cassette pickup roller 303 is stopped.

  As described above, even in the cassette paper feeding device, the recording medium 325 can be stopped by a mechanism for supporting the recording medium 325 conveyed against the gravity, that is, by holding the roller. Therefore, also in this embodiment, since the basis weight can be measured in a state where the recording medium 325 is stopped, it is possible to obtain a stable basis weight measurement result.

(Fourth embodiment)
In the fourth embodiment, means for making the first printout time earlier than those in the first to third embodiments will be described.

  FIG. 16 shows a schematic cross-sectional view of a color LBP 401 provided with a basis weight sensor 44.

  In FIG. 16, 44, 434 and 454 are basis weight sensors. Reference numeral 42 denotes a manual pickup roller, and reference numerals 403 and 443 denote cassette pickup rollers. Similar to the first to third embodiments, each pickup roller is a half-moon roller, but may have a shape as shown in FIG. 12 as in the first to third embodiments.

  46 is a recording medium presence sensor of the manual feed tray 41, 423 is a recording medium presence sensor of the paper feed cassette 402, and 453 is a recording medium presence sensor of the paper feed cassette 442.

  Taking the operation of the color LBP 401 as an example, the fourth embodiment will be described with reference to the flowchart of FIG. In the following description, the manual feed tray 41 will be described, but the same control can be applied to the paper feed cassettes 402 and 442.

  The color LBP 401 detects the presence or absence of a recording medium during standby (S41).

  When the recording medium 47 is set on the manual feed tray 41 during standby and the recording medium presence sensor 46 detects that the recording medium 47 is present, the manual pickup roller 42 starts rotating (S42).

  After the recording medium 47 is conveyed by a certain distance by the manual pickup roller 42, the recording medium 47 is repeatedly stopped for a certain time (S43).

  While the recording medium 47 is temporarily stopped, the basis weight of the recording medium 47 is measured by the basis weight sensor 44 (S44).

  When the basis weight is measured, the manual pickup roller 42 is stopped and waited (S45).

  The above is the control for the manual feed tray 41, but the control for the paper feed cassette 402 is also described.

  It is detected whether or not the recording medium 425 is present in the paper feed cassette 402 (S41). When the recording medium 425 is set in the paper feed cassette 402, the cassette pickup roller 403 starts to rotate.

  The recording medium 425 is conveyed by a certain distance by the cassette pickup roller 403, and then repeatedly stopped for a certain time (S43).

  While the recording medium 47 is temporarily stopped, the basis weight of the recording medium 425 is measured by the basis weight sensor 434 (S44).

  When the basis weight is measured, the cassette pickup roller 403 is stopped and stands by (S45).

  This control is the same for the cassette 442 as well.

  By the control so far, the color LBP 401 waits until print data is sent in a state where the recording medium is conveyed to each basis weight sensor as shown in FIG. 18 (S46).

When the color LBP 401 receives the print data, the conveyance speed and fixing temperature at the time of fixing are determined in accordance with the basis weight of the recording medium at the designated paper feed port (S47, S48).
Then, the rotation of the pickup roller and the conveyance roller is started (S49).

  When the recording medium is conveyed to the conveyance roller, it is conveyed to the transfer unit for image formation by the conveyance roller (S50).

  When the recording medium is conveyed to the conveying roller, the pickup roller stops (S51).

  Thereafter, when the recording medium leading edge sensor 424 detects the recording medium (S52), image formation is started after a predetermined time since the leading edge of the recording medium is detected (S53).

  Then, the image is transferred with a bias corresponding to the basis weight (S54) and fixed at a fixing temperature determined according to the basis weight of the recording medium and the ambient temperature (S55).

  As described above, in this embodiment, the basis weight of a recording medium that has not yet received print data and is set in advance in a manual feed tray or a paper feed cassette during standby is measured. As a result, the basis weight can be measured in a state where the recording medium is stopped, so that a stable basis weight measurement result can be obtained and the first print can be performed rather than the control for measuring the basis weight after receiving print data. Outtime can be shortened.

FIG. 3 is a cross-sectional view illustrating a schematic configuration of a color LBP according to the first embodiment. 6 is a flowchart showing an image forming operation of a color LBP in the first embodiment. FIG. 3 is a diagram illustrating a manual sheet feeding unit before a sheet feeding operation according to the first embodiment. FIG. 4 is a diagram illustrating a manual sheet feeding unit when a manual pickup roller rotates 270 degrees from the state of FIG. 3 in the first embodiment. The circuit block diagram of the basic weight sensor using the ultrasonic wave in 1st Embodiment. The figure which showed the signal waveform of each part of the basic weight sensor using the ultrasonic wave in 1st Embodiment. The conversion table which derives the basic weight of a recording medium from the detected value of the basic weight sensor using the ultrasonic wave in 1st Embodiment. The graph showing the relationship between a basic weight and a detected value when a recording medium is measured with the basic weight sensor using the ultrasonic wave in 1st Embodiment. 6 is a table showing image forming conditions (conveying speed, fixing temperature) according to the basis weight of the recording medium in the first embodiment. FIG. 3 is a diagram illustrating a manual sheet feeding unit in a state where a recording medium according to the first embodiment is conveyed to a conveyance roller. 6 is a table showing image forming conditions (transfer bias) according to the basis weight of the recording medium in the first embodiment. The figure which showed the various shape of the pick-up roller in 1st Embodiment. 9 is a flowchart showing an image forming operation of a color LBP in the second embodiment. The figure which showed the signal waveform of each part of the basic weight sensor when there is no recording medium in the measurement area | region of the basic weight sensor in 2nd Embodiment. The figure which showed the cassette paper supply part of the color LBP in 3rd Embodiment. Sectional drawing which showed schematic structure of color LBP in 4th Embodiment. 10 is a flowchart showing an image forming operation of a color LBP in the fourth embodiment. FIG. 10 is a diagram illustrating a state in which printing is waiting with a color LBP according to a fourth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Tray for manual feed 12 Pickup roller for manual feed 14 Basis weight sensor 14a Ultrasonic transmitter of basis weight sensor 14b Ultrasonic receiver of basis weight sensor 14c Ultrasonic 14d Transmitted wave 15 Conveyance roller 17 Recording medium loaded on manual feed tray 101 color LBP
131 CPU
132 Transmission Signal 133 Transmission Circuit 134 Square Wave 135 Amplification Circuit 136 Rectangular Wave Drive Signal 137 Reception Signal 138 Amplification Circuit 139 Amplified Reception Signal 140 Integration Circuit 141 Operation Output of Integration Circuit 142 A / D Conversion Circuit 143 Digital Output

Claims (5)

An image forming apparatus having a paper feed unit for loading a recording medium,
A conveying member that is rotationally driven to convey the recording medium from a paper feeding unit;
Transmitting means for transmitting ultrasonic waves to the recording medium conveyed by the conveying member;
Receiving means for receiving the ultrasonic wave irradiated by the transmitting means,
When the recording medium is conveyed by the conveying member, a first period in which the conveying member and the recording medium come into contact with each other and convey the recording medium, and the recording medium is conveyed without contacting the recording medium. And a second period not to
In the second period, the basis weight is measured from the output result of the ultrasonic wave emitted from the transmission unit received by the reception unit.   The image forming apparatus according to claim 1, wherein the conveying member has a shape that generates the first period and the second period at least once during one rotation.   When the measurement result of the basis weight measurement is a measurement result that is not within a predetermined threshold range, it is determined that the recording medium is in a position where the ultrasonic wave from the transmission unit is not irradiated, The image forming apparatus according to claim 1, wherein the rotation of the conveying member is continued and the basis weight is measured again.   Before printing data for image formation is transmitted, the basis weight of the recording medium is measured, and after the basis weight is measured, the recording medium is measured at the position where the basis weight is measured. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus is on standby until print data is received. Forming means for forming an image on the recording medium;
Fixing means for fixing the image formed on the recording medium by the forming means;
5. The image forming apparatus according to claim 1, wherein the fixing temperature and the conveyance speed of the fixing unit are variably controlled according to the measurement result of the basis weight.

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