Recording material detection device, image forming apparatus and ultrasonic transmission device

Abstract

To solve the problem in which: increasing the amplification factor of an ultrasonic wave reception level amplifies even a noise present in a circuit that receives an ultrasonic wave; and therefore, the noise may reduce the accuracy of detecting a basis weight.SOLUTION: A recording material detector comprises: an ultrasonic sensor that has sending means for sending an ultrasonic wave and receiving means for receiving an ultrasonic wave, wherein the sending means and the receiving means are provided to sandwich a conveyance path on which a recording material is conveyed; instruction means that supplies, to the sending means, a first driving input or a second driving input larger than the first driving input; and detection means that detects information on the basis weight of the recording material according to a first value at which the receiving means receives an ultrasonic wave sent from the sending means to which the first driving input is supplied, the ultrasonic wave not passing through the recording material, and a second value at which the receiving means receives an ultrasonic wave sent from the sending means to which the second driving input is supplied, the ultrasonic wave passing through the recording material.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to detection of the basis weight of a recording material using ultrasonic waves. [Background technology]

[0002] In an image forming apparatus, an image is formed on a recording material having various characteristics such as size, basis weight, and surface property. In Patent Document 1, in order to form an image according to these recording materials, a recording material detection device for determining the type of recording material (hereinafter referred to as paper type) is provided inside the image forming apparatus. In this recording material detection device, for example, a transmitting means for transmitting ultrasonic waves and a receiving means for receiving ultrasonic waves are provided on either side of a conveying path along which the recording material is conveyed. A method is proposed in which the transmitting means transmits ultrasonic waves toward the recording material and the paper type is determined using the reception level of the ultrasonic waves that pass through the recording material. In such a recording material detection device that detects the basis weight of the recording material using ultrasonic waves, the detection result may change depending on the environment in which the recording material detection device is placed. Therefore, Patent Document 2 proposes a method for detecting the basis weight according to the reception level when ultrasonic waves that do not pass through the recording material are received by the receiving means and the reception level when ultrasonic waves that pass through the recording material are received by the receiving means. In this method, the reception level when ultrasonic waves that pass through the recording material are received by the receiving means is lower than the reception level when ultrasonic waves that do not pass through the recording material are received by the receiving means. For this reason, the amplification factor of the reception level when ultrasonic waves that have passed through the recording material are received by the receiving means is made larger than the amplification factor of the reception level when ultrasonic waves that have not passed through the recording material are received by the receiving means. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2004-219856 [Patent Document 2] Patent No. 6399747 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the amplification factor of the reception level of the ultrasonic waves received by the receiving means is increased, the noise present in the circuit for receiving the ultrasonic waves is also amplified, which may result in a decrease in the detection accuracy of the information relating to the basis weight due to the noise.

[0005] An object of the present invention is to suppress a decrease in detection accuracy of information relating to the basis weight of a recording material by controlling a drive input supplied to a transmitting means. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0007] an ultrasonic sensor including a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, the transmitting means and the receiving means being disposed on opposite sides of a conveying path along which a recording material is conveyed; An instruction means for inputting, to the transmitting means, a first drive input for transmitting an ultrasonic wave having a first maximum amplitude, or a second drive input for transmitting an ultrasonic wave having a second maximum amplitude larger than the first maximum amplitude; The present invention is characterized in that it comprises a detection means for detecting information relating to the basis weight of the recording material in accordance with a first value of ultrasonic waves transmitted from the transmitting means when the first drive input is supplied, the ultrasonic waves not passing through the recording material, and received by the receiving means, and a second value of ultrasonic waves transmitted from the transmitting means when the second drive input is supplied, the ultrasonic waves passing through the recording material, and received by the receiving means. Effect of the Invention

[0008] As described above, according to the present invention, by controlling the drive voltage supplied to the transmitting means, it is possible to suppress a decrease in the detection accuracy of information relating to the basis weight of the recording material. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus 1 according to a first embodiment. [Diagram 2] 2 is a control block diagram of a recording material detection device 19 according to the first embodiment. FIG. [Diagram 3] 11 is a graph showing an approximation obtained by plotting the relationship between the position correction coefficient T and the basis weight of the recording material P. [Figure 4] 2 is a schematic diagram illustrating an example of a configuration of a transmission control unit 22 according to the first embodiment. [Diagram 5] 2 is a schematic diagram illustrating an example of a configuration of a transmission control unit 22 according to the first embodiment. [Figure 6] 2 is a schematic diagram illustrating an example of a configuration of a transmission control unit 22 according to the first embodiment. [Figure 7] 2 is a schematic diagram illustrating an example of a configuration of a transmission control unit 22 according to the first embodiment. [Figure 8] 6 is a flowchart of a process for calculating a detected value of the basis weight of a recording material P executed by the recording material detection device according to the first embodiment. [Figure 9] 5A to 5H are time charts showing signal states, voltage states, and the like related to the process of calculating a detected value of basis weight executed by the recording material detection device 19 according to the first embodiment. [Figure 10] 4 is a diagram showing an example of an output waveform of the transmitting circuit unit 28 according to the first embodiment, a waveform of a received signal, a waveform of a detection signal, and an example of a relationship between the signal-to-noise ratio. FIG. [Figure 11] FIG. 11 is a control block diagram of a recording material detection device 19 according to a fourth embodiment. [Figure 12] 13 is a flowchart of a process for calculating a detected value of the basis weight of a recording material P, which is executed by a recording material detection device according to a fourth embodiment. [Figure 13] 13A to 13H are time charts showing signal states, voltage states, and the like related to the process of calculating the detected value of basis weight executed by the recording material detection device 19 according to the fourth embodiment. [Figure 14] FIG. 13 is a control block diagram of a recording material detection device 19 according to a modified example of the fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the invention in the claims, and all of the combinations of features described in the embodiments are not necessarily essential to the solution of the present invention. EXAMPLES

[0011] [Image forming device] FIG. 1 is a schematic diagram of an image forming apparatus 1. The image forming apparatus 1 is an electrophotographic full-color printer that employs an intermediate transfer method. The image forming apparatus 1 has four image forming stations that form images of the respective colors of yellow, magenta, cyan, and black. These four image forming stations are arranged in a row at regular intervals. In the following description, the English letters Y, M, C, and K at the end of the reference symbols indicate that the corresponding members are related to the formation of toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the following description, when it is not necessary to distinguish between colors, the reference symbols without the English letters Y, M, C, and K at the end may be used.

[0012] The paper feed cassette 2 holds recording material P, which may be paper, for example. The recording material P held in the paper feed cassette 2 is fed by a paper feed roller 3. The recording material P fed by the paper feed roller 3 is conveyed by a conveying roller pair 4 and a registration roller pair 5. A registration sensor 6 for detecting the presence or absence of the recording material P is disposed near the registration roller pair 5.

[0013] The photosensitive drum 7 has a photosensitive layer on a drum-shaped aluminum substrate, and is rotated at a predetermined process speed by a drive device (not shown) in the direction of the arrow in the figure. The process speed here corresponds to the peripheral speed (surface movement speed) of the photosensitive drum 7. The charging roller 8 uniformly charges the photosensitive drum 7 to a predetermined potential. The laser scanner 9 irradiates the photosensitive drum 7 with laser light corresponding to image information, exposing the surface of the photosensitive drum 7. As a result, an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 7.

[0014] The process cartridge 10 includes a developing roller 11, which develops an electrostatic latent image formed on the photosensitive drum 7 by using toner contained in the process cartridge 10. A primary transfer roller 12 primarily transfers the image formed on the photosensitive drum 7 onto an intermediate transfer belt 13. The intermediate transfer belt 13 is driven by a drive roller 14.

[0015] The secondary transfer roller 15 performs the second transfer of the image that has been primarily transferred onto the intermediate transfer belt 13 onto the recording material P. The fixing unit 16 applies heat and pressure to fix the secondarily transferred image onto the recording material P. The components from the photosensitive drum 7 to the fixing unit 16 related to image formation described above are an example of a configuration of the image forming section 17. The paper discharge roller 18 discharges the recording material P that has been fixed by the fixing unit 16 onto a paper discharge tray.

[0016] The recording material detection device 19 as a detection means detects information related to the basis weight of the recording material P. Below, a method for determining the type of recording material P based on the basis weight of the recording material P and a method for controlling the image forming conditions (secondary transfer conditions, fixing conditions) will be described. Since the resistance value of the recording material P generally differs depending on the basis weight of the recording material P, it is necessary to change the secondary transfer conditions, such as the application of a secondary transfer bias for secondary transfer of toner, depending on the basis weight. In addition, since the heat capacity of the recording material P differs depending on the basis weight of the recording material P, it is necessary to change the fixing conditions, such as the fixing temperature and fixing time for fixing the toner, and the conveying speed of the recording material P, depending on the basis weight.

[0017] The control unit 20 is made up of storage units such as an MPU equipped with a CPU etc., a RAM used for calculations and temporary storage of data necessary for controlling the image forming apparatus 1, and a ROM for storing various data and programs for controlling the image forming apparatus 1. The control unit 20 discriminates the type of recording material P based on the detected value of information related to basis weight by the recording material detection device 19. Then, the control unit 20 determines image formation conditions according to the type of recording material P, and controls the image forming apparatus 1 to operate under the image formation conditions according to the type of recording material P.

[0018] [Recording material detection device 19] FIG. 2 is a block diagram relating to the recording material detection device 19. As shown in FIG.

[0019] The recording material detection device 19 is composed of an ultrasonic sensor 21 which is a basis weight detection means, a transmission control unit 22 , and a reception detection unit 23 , and is controlled by a control unit 20 .

[0020] The ultrasonic sensor 21 is a sensor that detects the basis weight of the recording material P by ultrasonic waves, and is composed of a transmitting means 21a that transmits ultrasonic waves and a receiving means 21b that receives ultrasonic waves. The ultrasonic sensor 21 is also called an ultrasonic transmitting device.

[0021] The control unit 20 has the functions of a switching instruction unit 20a, a transmission instruction unit 20b, and a reception level detection unit 20c for controlling the recording material detection device 19. The switching instruction unit 20a outputs a switching signal for switching the driving voltage supplied to the recording material detection device 19. The transmission instruction unit 20b outputs a driving signal for instructing the transmission means 21a to transmit ultrasonic waves. At this time, the waveform of the driving signal generated by the transmission instruction unit 20b becomes as shown in (d) and (e) of FIG. 9, and the second driving signal becomes a signal in which the High signal and the Low signal are reversed from the first driving signal by the operational amplifier 34. In other words, when the first driving signal is a High signal, the second driving signal becomes a Low signal. Also, when the first driving signal is a Low signal, the second driving signal becomes a High signal. The reception level detection unit 20c detects the reception level (voltage value) of the ultrasonic waves received by the reception means 21b. The first drive signal and the second drive signal when the receiving means 21b receives ultrasonic waves that do not pass through the recording material P are also referred to as a first drive input. The first drive signal and the second drive signal when the receiving means 21b receives ultrasonic waves that pass through the recording material P are also referred to as a second drive input.

[0022] In this embodiment, in order to measure the received signal once, a pulse wave is output as a drive signal, and then the output of the pulse wave is stopped for a predetermined time, and after the ultrasonic wave has attenuated, the pulse wave is output again to perform the next measurement. This reduces the influence of reflected waves from the recording material P and surrounding members, and the direct wave transmitted by the transmitting means 21a can be received by the receiving means 21b. Such a signal is called a burst wave. In this embodiment, as an example, two pulse waves with a frequency of 40 kHz are used in one measurement, and the period of the burst wave is 10 msec.

[0023] The transmission control unit 22 is a circuit unit having a function of driving the transmitting means 21a in response to the first drive signal, the second drive signal, and the switching signal from the control unit 20. The transmission control unit 22 is composed of a transmitting circuit unit 28 consisting of a first output circuit unit 24, a second output circuit unit 25, a third output circuit unit 26, and a switching unit 27, and a voltage conversion unit 29 (also called a voltage supply unit). The output end from the first output circuit unit 24 is connected to the USS-H terminal of the transmitting means 21a. The output end of the second output circuit unit 25 and the output end of the third output circuit unit 26 are each connected to the switching unit 27, and the output end from the switching unit 27 is connected to the USS-L terminal of the transmitting means 21a. In this embodiment, the USS-H terminal is also called the first terminal, and the USS-L terminal is also called the second terminal. The switching unit 27 is a switch element having a function of switching between the output from the second output circuit unit 25 and the output from the third output circuit unit 26 by a switching signal from the switching instruction unit 20a, and outputting the output to the USS-L terminal of the transmitting means 21a. The switching unit 27 is also referred to as a first switching means. In this embodiment, when the switching signal is a High signal, a drive signal is output from the second output circuit unit 25, and when the switching signal is a Low signal, a drive signal is output from the third output circuit unit 26.

[0024] The transmitting means 21a transmits ultrasonic waves at a frequency of 40 kHz in response to the output from the transmitting circuit section 28. The receiving means 21b receives the ultrasonic waves transmitted from the transmitting means 21a, and outputs a reception signal corresponding to the amplitude of the received ultrasonic waves to the reception detection section 23. Note that although the frequency of the ultrasonic waves is set to 40 kHz in this embodiment, any frequency can be used as long as it can detect the characteristic value of the basis weight of the recording material P, and the frequency can be set in accordance with the characteristics of the element. Also, the transmitting means 21a and the receiving means 21b are disposed near the transport path that transports the recording material P, with the transport path between them, so that they can receive ultrasonic waves via the recording material P.

[0025] The maximum amplitude of the ultrasonic waves transmitted by the transmitting means 21a when the receiving means 21b receives ultrasonic waves not passing through the recording material P is also referred to as the first maximum amplitude, and the input to the transmitting means 21a for transmitting ultrasonic waves of the first maximum amplitude is also referred to as the first drive input. The maximum amplitude of the ultrasonic waves transmitted by the transmitting means 21a when the receiving means 21b receives ultrasonic waves passing through the recording material P is also referred to as the second maximum amplitude, and the input to the transmitting means 21a for transmitting ultrasonic waves of the second maximum amplitude is also referred to as the second drive input.

[0026] The receiving detection unit 23 is a circuit unit having a function of amplifying the amplitude of a reception signal received by the receiving means 21b of ultrasonic waves passing through the recording material P as shown in FIG. 10(a) and performing half-wave rectification. The detection signal generated by the receiving detection unit 23 is input to the AD port of the control unit 20 and converted from an analog signal to a digital signal by the reception level detection unit 20c. The control unit 20 detects the waveform of the detection signal based on the digital signal converted by the reception level detection unit 20c, calculates its peak value (maximum value), and calculates it as the reception level of the ultrasonic waves. In this embodiment, the peak value of the detection signal output by the receiving detection unit 23 is used to calculate the reception level, but any characteristic value that can determine the level of the reception signal, such as an effective value or an average value, may be used. The receiving detection unit 23 is also referred to as a receiving detection means.

[0027] Here, the reason why in this embodiment, when the receiving means 21b receives ultrasonic waves not passing through the recording material P, the switching signal is set to a Low signal and the voltage Vc supplied to the transmitting means 21a is set to 2 V will be described.

[0028] In this embodiment, as shown in FIG. 10, the reception signal received by the receiving means 21b becomes a detection signal that is half-rectified by the receiving detection unit 23. At this time, if the amplification factor of the reception signal is not adjusted in the receiving detection unit 23, there is an upper limit to the value of the detection signal that the receiving detection unit 23 can generate. If the detection signal is equal to or lower than the upper limit, the peak value (maximum value) calculated based on the digital signal converted from the analog signal by the receiving level detection unit 20c can be calculated as the reception level of the ultrasonic wave. However, if the amplitude of the reception signal is large and the detection signal is equal to or higher than the upper limit of the detection signal that the receiving detection unit 23 can generate, the peak value (maximum value) calculated by the receiving level detection unit 20c will be equal to the upper limit of the detection signal that the detection signal can generate. For this reason, even when the receiving means 21b receives ultrasonic waves that are not transmitted through the recording material P, if 10V is supplied to the transmitting means 21a, the amplitude of the reception signal will be too large, and the detection signal will exceed the upper limit of the detection signal that the receiving detection unit 23 can generate. Therefore, when the receiving means 21b receives ultrasonic waves that have not passed through the recording material P, the switching signal is set to a Low signal, and the voltage Vc supplied to the transmitting means 21a is set to 2V.

[0029] In this embodiment, when the receiving means 21b receives ultrasonic waves not passing through the recording material P, the voltage Vc supplied to the transmitting means 21a is set to 2 V, but it may be 2 V or more. If the value of a reception level Va, which will be described later, is equal to or less than the value of a detection signal that the reception detection unit 23 can generate, the voltage Vc supplied to the transmitting means 21a may be 2 V or more.

[0030] <Correction of positional variation between the receiving means 21b and the transmitting means 21a> Next, a description will be given of correction of positional variations between the receiving means 21b and the transmitting means 21a, which is necessary for discriminating the paper type.

[0031] In the manufacturing process of the image forming apparatus 1, when the ultrasonic sensor 21 is attached to the image forming apparatus 1, the positions of the receiving means 21b and the transmitting means 21a relative to the recording material P to be detected may vary. This variation in position may change the time at which the ultrasonic waves reach the receiving means 21b, and may also change the time at which the reception level detected by the reception level detection unit 20c reaches its peak value. For this reason, by calculating the correction coefficient as described below, it is possible to detect the basis weight by correcting the variation in position.

[0032] When the receiving means 21b receives ultrasonic waves that have not passed through the recording material P, the receiving level output by the receiving level detection unit 20c is designated as Va. When the receiving means 21b receives ultrasonic waves that have passed through the recording material P, the receiving level output by the receiving level detection unit 20c is designated as Vp. The position correction coefficient T is calculated using the receiving levels Va and Vp. In this embodiment, the receiving level Va is also referred to as a first value, and the receiving level Vp is also referred to as a second value. T = Vp / Va (Eq. 1)

[0033] The control unit 20 calculates the basis weight using a graph showing an approximation formula obtained by plotting the relationship between the position correction coefficient T and the basis weight value of the recording material P, as shown in Fig. 3. Then, the paper type of the recording material P is determined based on the calculated basis weight, image formation conditions are determined according to the type of recording material P, and the operation of the image forming apparatus 1 is controlled. The approximation formula here is obtained in advance from the actual basis weight and the correction coefficient T, and is stored in the non-volatile memory of the control unit 20. In this embodiment, the approximation formula is used, but a conversion table showing the relationship between the position correction coefficient T and the basis weight value of the recording material P may also be used.

[0034] <Ultrasonic attenuation by recording material P and method for identifying paper type> The attenuation of ultrasonic waves by the recording material P will be described below. The amount of attenuation of ultrasonic waves passing through the recording material P increases in proportion to the basis weight of the recording material P. In other words, the greater the basis weight of the recording material P, the greater the amount of ultrasonic attenuation, and therefore the smaller the value of the reception level Vp. If the recording material P is thin paper with a small basis weight, the amount of ultrasonic attenuation is less than that of plain paper, and therefore the value of the reception level Vp is greater than that of plain paper. On the other hand, if the recording material P is thick paper with a large basis weight, the amount of ultrasonic attenuation is greater than that of plain paper, and therefore the value of the reception level Vp is smaller than that of plain paper. In other words, if the value of the reception level Vp increases, the value of the position correction coefficient T also increases.

[0035] For example, the control unit 20 uses the approximation line shown in Fig. 3 to determine the basis weight corresponding to the value of the position correction coefficient T. If the basis weight determined by the control unit 20 is smaller than an arbitrary threshold, the paper type of the recording material P is determined to be thin paper. If the basis weight determined by the control unit 20 is larger than the arbitrary threshold, the paper type of the recording material P is determined to be thick paper. The arbitrary threshold in this case is, for example, a basis weight of 59 g / m2 as shown in Fig. 3. 2 The following cases are thin paper with a basis weight of 60 g / m 2 ~90g / m 2 For plain paper, the basis weight is 90 g / m 2 In addition, the method of determining the paper type is not limited to this, and the relationship between the basis weight and the paper type may be stored in a non-volatile memory in advance, and that information may be used.

[0036] <Overview of Operation of the Outgoing Call Control Unit 22> An outline of the operation of the outgoing call control unit 22 will be described with reference to Fig. 4. Fig. 4 is an example of a schematic configuration diagram of the outgoing call control unit 22.

[0037] The transmission control unit 22 is supplied with a voltage Vb from a power supply unit (not shown) in the image forming apparatus 1. The voltage conversion unit 29 is a step-down converter that converts the voltage Vb supplied from the power supply unit (not shown) into an arbitrary voltage Vc. The voltage Vc supplied by the voltage conversion unit 29 is supplied to the transmission circuit unit 28. In this embodiment, the voltage conversion unit 29 switches the voltage Vc between 2V and 10V according to a switching signal output by the switching instruction unit 20a. When the switching signal is a High signal, the voltage Vc becomes 10V, and when the switching signal is a Low signal, the voltage Vc becomes 2V. In this embodiment, the voltage Vc when the switching signal is a Low signal is also referred to as a first drive voltage, and the voltage Vc when the switching signal is a High signal is also referred to as a second drive voltage. In this embodiment, a step-down converter is used as the voltage conversion unit 29, but it is sufficient if it is possible to switch the voltage required when driving the transmission circuit unit 28. For example, a boost converter that boosts a voltage of 3.3V may be used. The voltage Vc may be set appropriately depending on the voltage range (also referred to as the operable voltage range) within which the transmitting means 21a can transmit ultrasonic waves. It is preferable that the voltage Vc be switchable between the upper limit voltage and the lower limit voltage of the voltage range within which the transmitting means 21a can transmit ultrasonic waves. In this embodiment, the operable voltage range of the transmitting means 21a is from 2V to 10V, so the switchable voltage Vc is set to 2V and 10V.

[0038] The transmission circuit section 28 is composed of a first output circuit section 24, a second output circuit section 25, and a third output circuit section 26. The first output circuit section 24 is composed of a gate drive circuit section 30 and a half-bridge circuit section 31. The second output circuit section 25 is composed of a gate drive circuit section 32 and a half-bridge circuit section 33. The third output circuit section 25 is connected to GND (also called ground) and is composed of a circuit capable of outputting a fixed voltage of 0V.

[0039] The half-bridge circuit section 31 includes a switching element Q1 connected to a voltage Vc and a switching element Q2 connected in series to the switching element Q1. Both the switching element Q1 and the switching element Q2 are configured by MOSFETs. The switching element Q1 is supplied with the voltage Vc, and the switching element Q2 is supplied with a voltage corresponding to the ground.

[0040] The gate drive circuit section 30 is composed of a gate drive circuit section 30a that drives the switching element Q1, and a gate drive circuit section 30b that drives the switching element Q2. The gate drive circuit section 30a includes an NPN transistor Tr1, a PNP transistor Tr2, an NPN transistor Tr3, and a resistor R1. Tr3 is connected to the ground, and the resistor R1 is connected to the power supply voltage Vb. The gate drive circuit section 30b includes an NPN transistor Tr4, a PNP transistor Tr5, an NPN transistor Tr6, a resistor R2, and a resistor R3. Tr6 is connected to the ground, and the resistor R2 is connected to the voltage Vb.

[0041] The first drive signal output by the output instruction unit 20b is input to resistor R3 and Tr6 of the gate drive circuit unit 30b. When the first drive signal is a High signal, Tr6 is connected to ground, so 0V is input to the base terminals of Tr4 and Tr5. When 0V is input to the base terminals of Tr4 and Tr5, 0V is output as a drive signal for the switching element Q2 from the connection point between the emitter terminal of Tr4 and the collector terminal of Tr5. Also, when the first drive signal is a High signal, 0V is input from the collector terminal of Tr6 to Tr3 of the gate drive circuit unit 30a for the reasons described above.

[0042] When the first drive signal is a low signal, the voltage Vb is input to the base terminals of Tr4 and Tr5 via resistor R2. When the voltage Vb is input to the base terminals of Tr4 and Tr5, the voltage Vb is output from the connection point between the emitter terminal of Tr4 and the collector terminal of Tr5 as the drive signal for the switching element Q2. When the first drive signal is a low signal, the voltage Vb is input from the collector terminal of Tr6 to Tr3 of the gate drive circuit unit 30a for the reasons described above.

[0043] When a voltage Vb is input to Tr3 of the gate drive circuit section 30a, 0V is input to the base terminals of Tr1 and Tr2 because Tr3 is connected to ground. When 0V is input to the base terminals of Tr1 and Tr2, 0V is output as a drive signal for switching element Q1 from the connection point between the emitter terminal of Tr1 and the collector terminal of Tr2.

[0044] When 0V is input to Tr3 of the gate drive circuit section 30a, a voltage Vb is input to the base terminals of Tr1 and Tr2 via resistor R1. When a voltage Vb is input to the base terminals of Tr1 and Tr2, the voltage Vb is output as a drive signal for switching element Q1 from the connection point between the emitter terminal of Tr1 and the collector terminal of Tr2.

[0045] In this way, when the first drive signal is a High signal, the output from the gate drive circuit unit 30b is 0V, and the output from the gate drive circuit unit 30a is voltage Vb. Also, when the first drive signal is a Low signal, the output from the gate drive circuit unit 30b is voltage Vb, and the output from the gate drive circuit unit 30a is 0V. Therefore, the relationship between the outputs of the gate drive circuit unit 30b and the gate drive circuit unit 30a is reversed when the first drive signal is a High signal and when it is a Low signal. That is, when the first drive signal is a High signal, the switching element Q1 is in the ON state because the voltage Vb is input, and the switching element Q2 is in the OFF state because 0V is input. Therefore, no voltage is supplied from the switching element Q2, and the voltage Vc is output from the switching element Q1 as the output voltage of the half-bridge circuit unit 31. Also, when the first drive signal is a Low signal, the switching element Q1 is in the OFF state because 0V is input, and the switching element Q2 is in the ON state because the voltage Vb is input. For this reason, no voltage is supplied from switching element Q1, and 0 V is output from switching element Q2 as the output voltage of half-bridge circuit section 31. In this way, in response to the change in the first drive signal, the voltages Vc and 0 V are alternately input to the USS-H terminal of transmitting means 21a as the output of half-bridge circuit section 31 by the switching operations of switching element Q1 and switching element Q2.

[0046] The second drive signal input to the second output circuit section 25 is different from the first drive signal in that the High signal and the Low signal are reversed, but has the same circuit configuration as the first output circuit section 24. Therefore, an overview of the operation of the second output circuit section 25 will not be described.

[0047] The circuit connected to the USS-L terminal of the transmitting means 21a is switched between the second output circuit section 25 and the third output circuit section 26 by the switching section 27 in response to a signal output from the switching instruction section 20a. This switching switches the drive mode of the transmitting means 21a between a half-bridge drive mode and a full-bridge drive mode. Each mode will be described below.

[0048] [Half-bridge drive mode] When the switching signal is a Low signal, the USS-L terminal is connected to the ground of the third output circuit section 26. Therefore, the transmitting means 21a is driven at 2V only by the first output circuit section 24. That is, when a burst wave of 2V is input from the USS-H terminal by the switching element Q1 of the first output circuit section 24, the transmitting means 21a receives 0V from the USS-L terminal by the third output circuit section 26. In this embodiment, this state is also referred to as the first state. Moreover, when 0V is input from the USS-H terminal by the switching element Q2 of the first output circuit section 24, the transmitting means 21a receives 0V from the USS-L terminal by the third output circuit section 26. In this embodiment, this state is also referred to as the second state.

[0049] In this way, ultrasonic waves are emitted by alternately inputting 0V and 2V burst waves from the USS-H terminal by switching element Q1 and switching element Q2. The operating mode of the bridge circuit when the switching signal is a Low signal is also called the half-bridge drive mode.

[0050] [Full-bridge drive mode] When the switching signal is a High signal, the USS-L terminal is connected to the second output circuit section 25. Therefore, the transmitting means 21a is driven at 10V by being connected to both the first output circuit section and the second output circuit section. That is, when a burst wave of 10V is input from the USS-H terminal by the switching element Q1, 0V is input from the USS-L terminal by the switching element Q4 to the transmitting means 21a. In this embodiment, this state is also referred to as the third state. Also, when 0V is input from the USS-H terminal by the switching element Q2, a burst wave of 10V is input from the USS-L terminal by the switching element Q3 to the transmitting means 21a. In this embodiment, this state is also referred to as the fourth state. In this way, a burst wave of 10V is input alternately from the USS-H terminal and the USS-L terminal, so that an ultrasonic wave with a larger amplitude than that in the half-bridge driving mode can be transmitted. The operation mode of the bridge circuit when the switching signal is a High signal is also referred to as the full-bridge driving mode. For this reason, in this embodiment, when the receiving means 21b receives ultrasonic waves via the recording material P, the transmitting means 21a is driven in the full-bridge drive mode.

[0051] In this embodiment, as a method of switching from the full-bridge driving mode to the half-bridge driving mode, the output of the second output circuit unit 25 is switched to the output of the third output circuit unit 26 by the switch element of the switching unit 27. However, it is sufficient if a fixed voltage can be input to the USS-L terminal of the transmitting means 21a. For example, as shown in FIG. 5, the switching unit 40 may switch between inputting the second drive signal from the transmission instruction unit 20b to the second output circuit unit 25 or inputting a fixed voltage (0V) according to the ground to the second output circuit unit 25. The switching unit 40 is also referred to as the second switching means. At this time, when the switching signal from the switching instruction unit 20a is a High signal, the second drive signal is input from the transmission instruction unit 20b to the second output circuit unit 25. The transmission instruction unit 20b that outputs the second drive signal input to the second output circuit unit 25 is also referred to as the fourth output circuit unit. Furthermore, when the switching signal from the switching instruction unit 20a is a Low signal, a fixed voltage (0V) corresponding to the ground is input to the second output circuit unit 25. The circuit that is connected to the ground and can output the fixed voltage of 0V is also referred to as a fifth output circuit unit. Even in this case, if the switching signal is a Low signal, 0V is input from the ground to the second output circuit unit 25 regardless of the drive signal from the transmission instruction unit 20b. This makes it possible to maintain the state in which 0V is supplied to the USS-L terminal. Therefore, the circuit operates in a half-bridge drive mode.

[0052] Hereinafter, an operation will be described in a case where the switching signal from the switching instruction unit 20a is a Low signal and a fixed voltage (0V) corresponding to the ground is input to the second output circuit unit 25 by the switching unit 40. When a burst wave of 2V is input from the USS-H terminal by the switching element Q1 of the first output circuit unit 24, the transmitting means 21a receives 0V from the second output circuit unit 25. This state is also referred to as a fifth state. In addition, when 0V is input from the USS-H terminal by the switching element Q2 of the first output circuit unit 24, the transmitting means 21a also receives 0V from the second output circuit unit 25. This state is also referred to as a sixth state.

[0053] Hereinafter, an operation will be described in a case where the switching signal from the switching instruction unit 20a is a High signal and the second drive signal is input from the transmission instruction unit 20b to the second output circuit unit 25 by the switching unit 40. When a burst wave of 10V is input from the USS-H terminal by the switching element Q1 of the first output circuit unit 24, 0V is input to the transmitting means 21a by the switching element Q4 of the second output circuit unit 25. This state is also referred to as the seventh state. Moreover, when a burst wave of 10V is input from the USS-H terminal by the switching element Q2 of the first output circuit unit 24, a burst wave of 10V is input to the transmitting means 21a by the switching element Q3 of the second output circuit unit 25. This state is also referred to as the eighth state.

[0054] Note that it is only necessary to be able to switch between the half-bridge drive mode and the full-bridge drive mode, and the type of elements in the half drive circuit and the configuration of the gate drive circuit can be changed as appropriate.

[0055] [Switching of voltage Vc depending on the presence or absence of recording material P] 8 and 9, a method for reducing the signal-to-noise ratio of the reception level Vp output by the reception level detection unit 20c when the receiving means 21b receives ultrasonic waves via the recording material P by controlling the voltage conversion unit 29. Fig. 8 is a flowchart of the process for calculating the basis weight of the recording material P, and Figs. 9(a) to (h) are time charts showing the states of signals and voltages related to the process for calculating the basis weight.

[0056] In S100, the control unit 20 starts a paper feed operation upon receiving a print instruction.

[0057] 9B, the switching instruction unit 20a outputs a Low signal as a switching signal to the voltage conversion unit 29, thereby causing the voltage conversion unit 29 to output a voltage Vc of 2 V to the first output circuit unit 24. This drives the transmitting means 21a in the half-bridge drive mode.

[0058] In S102, the control unit 20 executes the following process at a timing when the recording material P has not yet reached the ultrasonic sensor 21 after the start of the paper feed operation. That is, the control unit 20 starts measuring the reception level of ultrasonic waves by the receiving unit 21b when the receiving unit 21b receives ultrasonic waves not passing through the recording material P, as shown in FIG. 9(a). At this time, the transmitting circuit unit 28 drives the transmitting unit 21a in the half-bridge drive mode. That is, as shown in FIG. 9(f), voltages of 2V and 0V are alternately input from the first output circuit unit 24 to the USS-H terminal, and as shown in FIG. 9(g), 0V is input from the third output circuit unit 26 to the USS-L terminal.

[0059] In S103, the reception detection unit 23 generates a detection signal as shown in FIG. 9(h) based on the reception signal by the receiving means 21b during a predetermined time from the start of measurement of the reception level of the reception signal, and calculates the reception level Va. At this time, the detection signal generated by the reception detection unit 23 is converted by the reception detection unit 23 into a waveform having a peak value for each half wave of 40 kHz, which is the same frequency as the ultrasonic wave transmitted from the transmitting means 21a. Also, at this time, even if the number of pulses of the first drive signal is two pulses as shown in FIG. 9(d), the number of waveforms of the detection signal as shown in FIG. 9(h) exceeds two. This is because there is reverberation of the transmitting means 21a or the receiving means 21b. The control unit 20 detects the second waveform of the detection signal converted by the reception level detection unit 20c, and calculates its peak value. At this time, the peak value of the second waveform is calculated by detecting the detection signal during any predetermined time synchronized with the first drive signal. The predetermined time here is calculated and set in advance based on the relationship between the distance between the transmitting means 21a and the receiving means 21b and the sound speed of the ultrasonic waves. In this embodiment, the control unit starts the paper feed operation in S100, but the paper feed operation may be started after the reception level Va is calculated by the reception detection unit 23.

[0060] In S104, the switching instruction unit 20a outputs a High signal as a switching signal to the voltage conversion unit 29 as shown in Fig. 9(b) to cause the first output circuit unit 24 to output a voltage Vc of 10 V as shown in Fig. 9(c), thereby driving the transmitting means 21a in the full-bridge drive mode.

[0061] In S105, when the leading edge of the recording material P reaches the registration sensor 6 and the output of the registration sensor 6 changes, the control unit 20 advances the process to S106 if the output indicates that the recording material P has been detected.

[0062] In S106, the control unit 20 starts counting the number of steps S of the pulse motor (not shown) in order to detect the timing at which the leading edge of the recording material P reaches the ultrasonic sensor 21 after reaching the registration sensor 6.

[0063] In S107, the control unit 20 determines whether the count value of the number of steps S has reached a predetermined value (100) and advances the process to S108 when the count value of the number of steps S has reached the predetermined value (100).

[0064] In S108, the control unit 20 drives the ultrasonic sensor 21 by the transmission circuit unit 28, and starts measuring the reception level of the reception signal by the reception detection unit 23 when the receiving means 21b receives ultrasonic waves through the recording material P. At this time, the transmission circuit unit 28 drives the transmitting means 21a in full-bridge drive mode. Therefore, a voltage of 10 V is alternately input from the first output circuit unit 24 to the USS-H terminal as shown in Fig. 9(f) and a voltage of 10 V is alternately input from the second output circuit unit 25 to the USS-L terminal as shown in Fig. 9(g).

[0065] In S109, the receiving detection unit 23 executes the following process in the same manner as the measurement method in which the receiving means 21b receives ultrasonic waves that do not pass through the recording material P. That is, the receiving detection unit 23 detects the detection signal during a predetermined time period from the start of measurement, and calculates the reception level Vp in which the receiving means 21b receives ultrasonic waves that pass through the recording material P.

[0066] In S110, the control unit 20 substitutes the reception levels Va and Vp into equation (1) to calculate a position correction coefficient T. In S111, the basis weight of the recording material P is calculated using the calculated position correction coefficient T and the approximation equation stored in the storage unit. In S112, the image forming conditions are determined according to the calculated basis weight, and the process ends. Note that in this embodiment, the basis weight may be calculated based on the position correction coefficient T, or the image forming conditions may be changed based on the position correction coefficient T. Also, in this embodiment, the paper type may be determined based on the position correction coefficient T.

[0067] In this way, when the receiving means 21b receives ultrasonic waves not passing through the recording material P, the transmitting circuit section 28 inputs 2V to the USS-H terminal and 0V to the USS-L terminal, causing the transmitting means 21a to transmit ultrasonic waves with an amplitude corresponding to when 2V is supplied. On the other hand, when the receiving means 21b receives ultrasonic waves passing through the recording material P, the transmitting circuit section 28 inputs 10V alternately to the USS-H terminal and the USS-L terminal, causing the transmitting means 21a to transmit ultrasonic waves with an amplitude corresponding to when 20V is supplied. Therefore, when the receiving means 21b receives ultrasonic waves passing through the recording material P, the amplification factor of the received ultrasonic signal can be reduced, and the effect of noise present in the circuit receiving the ultrasonic waves on the detection result of the basis weight can be reduced.

[0068] <Comparison of the method in Example 1 with the conventional method> In the following, a method for suppressing the deterioration of the detection accuracy of the basis weight in this embodiment will be described in comparison with the conventional method. Fig. 10 is a diagram showing an example of the output waveform of the transmitting circuit section 28, the waveform of the received signal, an example of the waveform of the detection signal, and an example of the relationship between the signal-to-noise ratio. Fig. 10(a) shows the conventional method, and Fig. 10(b) shows the present embodiment.

[0069] In the conventional method, as shown in FIG. 10(a), the reception signal when the receiving means 21b receives ultrasonic waves through the recording material P is attenuated more than the reception signal when the receiving means 21b receives ultrasonic waves not through the recording material P. Therefore, when the receiving means 21b receives ultrasonic waves through the recording material P, regardless of the type of the recording material P, the reception level Vp is calculated using the detection signal obtained by amplifying the reception signal at a preset constant amplification factor, and the basis weight is detected. (In this example, the amplification factor is increased from 1 to 20 times). However, at this time, when the reception signal when the receiving means 21b receives ultrasonic waves through the recording material P is amplified, the noise signal (not shown) present in the circuit receiving the ultrasonic waves is also amplified. Therefore, the signal-to-noise ratio, which is the ratio of the noise signal to the ultrasonic reception signal, is large.

[0070] On the other hand, in this embodiment, as shown in Fig. 10(b), when the receiving means 21b receives ultrasonic waves through the recording material P, the output voltage of the transmitting circuit section 28 is increased instead of amplifying the received signal. In this way, by increasing the driving voltage supplied to the transmitting means 20a, a received signal with a large amplitude can be obtained. Therefore, the amplification factor of the ultrasonic wave reception level can be reduced, and the signal-to-noise ratio can be prevented from increasing.

[0071] As described above, this embodiment has the following effects. When ultrasonic waves that do not pass through the recording material P are received, the transmitting means 21a is driven in half-bridge drive mode using a voltage on the lower limit side of the operable range voltage of the transmitting means 21a, and the reception level Va is calculated by the reception level detection unit 20c. When the receiving means 21b receives ultrasonic waves that pass through the recording material P, the transmitting means 21a is driven in full-bridge drive mode using a voltage on the upper limit side of the operable range voltage of the transmitting means 21a, and the reception level Vp is calculated by the reception level detection unit 20c. By switching the voltage and the operation mode of the bridge circuit, the amplitude of the ultrasonic waves transmitted by the transmitting means 21a can be increased, and the amplitude of the ultrasonic waves that pass through the recording material P and reach the receiving means 21b can also be increased. Therefore, it is possible to suppress an increase in the signal-to-noise ratio of the received signal. Therefore, it is possible to detect the basis weight of the recording material P with higher accuracy than before.

[0072] In this embodiment, not only is the voltage supplied to the bridge circuit switched depending on the presence or absence of the recording material P, but the operation mode of the bridge circuit is also switched by a switching signal output by the switching instruction unit 20a. However, it is only necessary to change the amplitude of the ultrasonic waves transmitted to the recording material P depending on the presence or absence of the recording material P, and for example, a method of switching either the voltage of the bridge circuit or the operation mode of the bridge circuit may be used. EXAMPLES

[0073] 6, the present embodiment does not have the third output circuit unit 26, and does not require switching from the full-bridge driving mode to the half-bridge driving mode. In other words, the first output circuit unit 24 and the second output circuit unit 25 may be used to drive the transmitting means 21a in the full-bridge driving mode at all times.

[0074] When the switching signal is a Low signal, the transmitting means 21a receives 0V from the switching element Q4 of the second output circuit section 25 when a burst wave of 2V is input from the USS-H terminal by the switching element Q1 of the first output circuit section 24. This state is also referred to as the ninth state. Moreover, the transmitting means 21a receives a burst wave of 2V from the switching element Q3 of the second output circuit section 25 when 0V is input from the USS-H terminal by the switching element Q2 of the first output circuit section 24. This state is also referred to as the tenth state.

[0075] Furthermore, when the switching signal is a High signal, when a burst wave of 10V is input from the USS-H terminal by the switching element Q1 of the first output circuit section 24, the transmitting means 21a receives an input of 0V from the switching element Q4 of the second output circuit section 25. This state is also referred to as the eleventh state. Furthermore, when a burst wave of 10V is input from the USS-H terminal by the switching element Q2 of the first output circuit section 24, the transmitting means 21a receives an input of a burst wave of 10V from the switching element Q3 of the second output circuit section 25. This state is also referred to as the twelfth state.

[0076] At this time, the lower limit of the ultrasound transmitted by the transmitting means 21a is an ultrasound with an amplitude equivalent to that when 4 V is supplied, but the transmitting means 21a can transmit ultrasound up to an amplitude equivalent to that when 20 V is supplied, as in Example 1.

[0077] As described above, the ultrasonic waves emitted by the transmitting means 21a have an amplitude equivalent to that when 2V to 20V is supplied in the first embodiment, whereas the ultrasonic waves have an amplitude equivalent to that when 4V to 20V is supplied in the second embodiment. In this case, in this embodiment, even if the lower limit of the amplitude of the ultrasonic waves emitted by the transmitting means 21a is increased by 2V, the value of the reception level Va is equal to or less than the value of the detection signal that the reception detection unit 23 can generate. In this way, when the detection accuracy of the value related to the basis weight is satisfied, even if the lower limit of the amplitude of the ultrasonic waves emitted by the transmitting means 21a is increased, the same effect as in the first embodiment can be obtained. Furthermore, in the second embodiment, it is possible to transmit ultrasonic waves having an amplitude equivalent to that when 20V is supplied from the transmitting means 21a without using the switching unit 27 or the switching unit 40. This allows the number of parts to be reduced, and the manufacturing costs to be reduced. EXAMPLES

[0078] Furthermore, in this embodiment, as shown in FIG. 7, the second output circuit section 25 and the third output circuit section 26 may not be provided, and the transmitting means 21a may be driven in the half-bridge drive mode by always using the first output circuit section 24.

[0079] When the switching signal from the switching instruction unit 20a is a Low signal, the transmitting means 21a receives 0V from the second output circuit unit 25 when a burst wave of 2V is input from the USS-H terminal by the switching element Q1 of the first output circuit unit 24. This state is also referred to as a thirteenth state. In addition, the transmitting means 21a also receives 0V from the second output circuit unit 25 when 0V is input from the USS-H terminal by the switching element Q2 of the first output circuit unit 24. This state is also referred to as a fourteenth state.

[0080] Furthermore, when the switching signal from the switching instruction unit 20a is a High signal, when a burst wave of 10V is input from the USS-H terminal by the switching element Q1 of the first output circuit unit 24, the transmitting means 21a receives 0V as an input from the second output circuit unit 25. This state is also referred to as the fifteenth state. Furthermore, when 0V is input from the USS-H terminal by the switching element Q2 of the first output circuit unit 24, the transmitting means 21a also receives 0V as an input from the second output circuit unit 25. This state is also referred to as the sixteenth state.

[0081] In this case, the lower limit of the ultrasound transmitted by the transmitting means 21a is an ultrasound with an amplitude equivalent to that when 2V is supplied, and the upper limit of the ultrasound transmitted by the transmitting means 21a is an ultrasound with an amplitude equivalent to that when 10V is supplied.

[0082] As described above, the ultrasonic waves emitted by the transmitting means 21a have an amplitude equivalent to that when 2V to 20V is supplied in the first embodiment, whereas the ultrasonic waves have an amplitude equivalent to that when 2V to 10V is supplied in the third embodiment. In this case, even if the upper limit of the amplitude of the ultrasonic waves emitted by the transmitting means 21a is reduced by 10V, the same effect as in the first embodiment can be obtained if the detection accuracy of the value related to the basis weight is satisfied. Furthermore, in the third embodiment, it is possible to transmit ultrasonic waves having an amplitude equivalent to that when 10V is supplied from the transmitting means 21a without using the second output circuit section 25 and the third output circuit section 26, the switching section 27, or the switching section 40. This allows the number of parts to be reduced, and the manufacturing costs to be reduced.

[0083] In the first to third embodiments, the transmitting means 21a transmits ultrasonic waves having a frequency of 40 kHz in response to the output from the transmitting circuit section 28, and the driving voltage supplied to the transmitting means 20a is switched in response to the presence or absence of the recording material P. However, in order to prevent the signal-to-noise ratio of the received signal from increasing, the driving voltage may be constant regardless of the presence or absence of the recording material P, and the frequency of the driving signal output by the transmission instruction section 20b may be switched in response to the presence or absence of the recording material P. For example, the frequency of the driving signal when the amplitude of the ultrasonic waves is maximum may be set as the first frequency, and the frequency of the driving signal when the amplitude of the driving signal is smaller than that of the ultrasonic waves when the driving signal is at the first frequency may be set as the second frequency. In this case, when the receiving means 21b receives ultrasonic waves through the recording material P, the transmission instruction section 20b outputs a pulse wave having the first frequency as the driving signal. Also, when the receiving means 21b receives ultrasonic waves not through the recording material P, the transmission instruction section 20b outputs a pulse wave having the second frequency as the driving signal. As a result, when the receiving means 21b receives ultrasonic waves that have passed through the recording material P, the transmitting means 21a can output ultrasonic waves with a larger amplitude than when the receiving means 21b receives ultrasonic waves that have not passed through the recording material P. This makes it possible to suppress an increase in the signal-to-noise ratio that occurs when the receiving means 21b receives ultrasonic waves that have passed through the recording material P, due to the amplification of the received signal. This makes it possible to detect the basis weight of the recording material P with higher accuracy than before.

[0084] Also, the driving voltage and the frequency of the driving signal output by the transmission instruction unit 20b may be constant regardless of the presence or absence of the recording material P, and the duty ratio of the High signal and the Low signal of the driving signal may be switched depending on the presence or absence of the recording material P. This allows the transmitting unit 21a to output ultrasonic waves having a larger amplitude when the receiving unit 21b receives ultrasonic waves via the recording material P than when the receiving unit 21b receives ultrasonic waves not via the recording material P. This makes it possible to suppress an increase in the signal-to-noise ratio caused by amplifying the received signal when the receiving unit 21b receives ultrasonic waves via the recording material P. EXAMPLES

[0085] In the first to third embodiments, when the reception detection unit 23 does not adjust the amplification factor of the received signal, the driving voltage supplied to the transmitting means 20a is switched depending on the presence or absence of the recording material P. That is, when the receiving means 21b receives ultrasonic waves through the recording material P, a larger driving signal is supplied to the transmitting means 20a than when the receiving means 21b receives ultrasonic waves not through the recording material P, thereby obtaining a received signal with a larger amplitude. In this way, when the receiving means 21b receives ultrasonic waves through the recording material P, an increase in the signal-to-noise ratio caused by increasing the amplification factor of the received signal of ultrasonic waves attenuated by the recording material P is suppressed. In this embodiment, there is no switching instruction unit 20a, and a driving voltage of 10V is supplied to the transmitting means 20a regardless of the presence or absence of the recording material. Then, the transmitting means 21a is always driven in the full-bridge drive mode using the first output circuit unit 24 and the second output circuit unit 25 as in the second embodiment, and ultrasonic waves with an amplitude equivalent to that when 20V is supplied can be transmitted regardless of the presence or absence of the recording material. In the reception detection unit 23, when the receiving means 21b receives ultrasonic waves that have not passed through the recording material P, the amplitude of the reception signal generated by the receiving means 20b is reduced to obtain a reception level that can be detected by the reception level detection unit 20c.

[0086] [Switching of the amplification rate of ultrasonic waves according to the presence or absence of the recording material P in the receiving detection unit 23] Fig. 11 is a block diagram of the recording material detection device 19 in this embodiment. In the following description, the same components as those in Fig. 2 are given the same reference numbers and the description thereof will be omitted.

[0087] The control unit 20 has a gain instruction unit 20d for controlling the amplification factor of the reception detection unit 23. As described above, the reception detection unit 23 is a circuit unit having a function of amplifying and half-wave rectifying the reception signal from the receiving means 21b. The reception detection unit 23 switches the amplification factor of the reception signal from the receiving means 21b according to the gain instruction signal from the gain instruction unit 20d. Hereinafter, the switching of the amplification factor of the reception signal from the receiving means 21b by the reception detection unit 23 will be described using an inverting amplifier circuit using an operational amplifier. Note that, although an inverting amplifier circuit is used in this embodiment, any circuit capable of amplifying a signal, such as an amplifier circuit using a transistor, can be used instead.

[0088] The inverting amplifier circuit is a circuit in which the amplification factor is determined by the ratio between the resistance value of the input section connected to the negative terminal and the resistance value of the feedback section between the negative input terminal and the output terminal. Therefore, the amplification factor can be changed by switching the resistance value of the input section or the resistance value of the feedback section with a switch. In this embodiment, the reception detection section 23 switches the amplification factor between, for example, 1 / 10 and 1 according to the gain instruction signal output by the gain instruction section 21d. The reception detection section 23 sets the amplification factor to 1 / 10 when the gain instruction signal is a Low signal, and sets the amplification factor to 1 when the gain instruction signal is a High signal. In this embodiment, the reception signal of the ultrasonic wave not passing through the recording material received by the receiving means is also referred to as the first reception value, and the reception signal of the ultrasonic wave passing through the recording material received by the receiving means is also referred to as the second reception value. The gain instruction section 20d is also referred to as the amplification factor switching instruction section, and the gain instruction signal output by the gain instruction section 20d is also referred to as the amplification factor switching signal. Further, the Low signal of the gain instruction signal is also referred to as a first amplification factor switching signal, the amplification factor of 1 / 10 is also referred to as a first amplification factor, and the detection signal obtained by amplifying the received signal by the first amplification factor is also referred to as a first conversion value. Further, the High signal of the gain instruction signal is also referred to as a second amplification factor switching signal, the amplification factor of 1 is also referred to as a second amplification factor, and the detection signal obtained by amplifying the received signal by the second amplification factor is also referred to as a second conversion value. Note that in this embodiment, the amplification factor is switched between, for example, 1 / 10 and 1, but is not limited to this magnification. The amplification factor when the ultrasonic wave not passing through the recording material is received by the receiving means may be, for example, 1 / 20, and may be any amplification factor that can reduce the received signal. Further, the amplification factor when the ultrasonic wave passing through the recording material is received by the receiving means may be any magnification that satisfies the accuracy of the value used for basis weight detection.

[0089] Next, the setting of the amplification factor in the reception detection unit 23 will be described below. When the receiving means receives ultrasonic waves through a recording material, the amplitude of the reception signal input to the reception detection unit 23 is small. Therefore, in order to set the amplification factor by the reception detection unit 23 to 1, the gain instruction unit 20d outputs a High signal as a gain instruction signal. Also, when the receiving means receives ultrasonic waves not through a recording material, the amplitude of the reception signal input to the reception detection unit 23 is large. Therefore, when the reception signal is amplified and half-wave rectified by the reception detection unit 23, it is desired to prevent the reception signal from exceeding the amplitude range of the half-wave rectification by the reception detection unit 23 (hereinafter also referred to as saturation). Therefore, the gain instruction unit 20d outputs a Low signal as a gain instruction signal, and sets the amplification factor to 1 / 10, which is a magnification smaller than when the gain instruction signal is a High signal.

[0090] As described above, in this embodiment, the gain indication unit 21d outputs a Low signal when the receiving means receives ultrasonic waves that do not pass through the recording material, and outputs a High signal when the receiving means receives ultrasonic waves that pass through the recording material.

[0091] <Method of switching the amplification factor of the signal received by the reception detector 23 depending on the presence or absence of a recording material> A method for switching the amplification factor of the signal received by the reception detection unit 23 by the gain instruction unit 20d switching the gain instruction signal depending on the presence or absence of recording material will be described below with reference to Figs. 11 and 12. Fig. 11 is a flowchart of the process for calculating the detected value of the basis weight of the recording material P in this embodiment. Fig. 12 is a time chart showing the states of signals and voltages involved in the process for calculating the detected value of the basis weight executed by the recording material detection device 19 in this embodiment. Note that the same components as those in Figs. 8 and 9 are given the same numbers and their explanations will be omitted. The same reference numerals are used to denote the same functions and operations, and explanations will be omitted.

[0092] In S100, the control unit 20 starts a paper feed operation upon receiving a print instruction.

[0093] In S301, the gain switching instruction unit 20d outputs a Low signal as a gain switching signal to the reception detection unit 23 as shown in Fig. 13(b). The voltage conversion unit 29 causes the first output circuit unit 24 to output a voltage Vc of 10 V, and the transmitting means 21a is driven in the full-bridge drive mode. Therefore, the gain switching instruction unit 20d outputs a Low signal as a gain switching signal to the reception detection unit 23, whereby the amplification factor of the received signal is set to 1 / 10 by the reception detection unit 23.

[0094] In S302, the control unit 20 executes the following process at a timing when the recording material P has not yet reached the ultrasonic sensor 21 after the start of the paper feed operation. That is, the control unit 20 starts measuring the reception level of ultrasonic waves by the receiving unit 21b when the receiving unit 21b receives ultrasonic waves not passing through the recording material P, as shown in FIG. 13(a). At this time, the transmitting circuit unit 28 drives the transmitting unit 21a in the full-bridge drive mode. That is, as shown in FIG. 13(f), voltages of 10V and 0V are alternately input from the first output circuit unit 24 to the USS-H terminal, and as shown in FIG. 13(g), voltages of 10V and 0V are alternately input from the second output circuit unit 26 to the USS-L terminal.

[0095] In S103, the reception detection unit 23 generates a detection signal as shown in FIG. 13(h) based on the reception signal by the receiving means 21b during a predetermined time from the start of measurement of the reception level of the reception signal, and calculates the reception level Va. At this time, the detection signal generated by the reception detection unit 23 is converted by the reception detection unit 23 into a waveform having a peak value for each half wave of 40 kHz, which is the same frequency as the ultrasonic wave transmitted from the transmitting means 21a. Also, at this time, even if the number of pulses of the first drive signal is two pulses as shown in FIG. 13(d), the number of waveforms of the detection signal as shown in FIG. 13(h) exceeds two. This is because there is reverberation of the transmitting means 21a or the receiving means 21b. The control unit 20 detects the second waveform of the detection signal converted by the reception level detection unit 20c, and calculates its peak value. At this time, the peak value of the second waveform is calculated by detecting the detection signal during any predetermined time synchronized with the first drive signal. The predetermined time here is calculated and set in advance based on the relationship between the distance between the transmitting means 21a and the receiving means 21b and the sound speed of the ultrasonic waves. In this embodiment, the control unit starts the paper feed operation in S100, but the paper feed operation may be started after the reception level Va is calculated by the reception detection unit 23.

[0096] In S303, the gain switching instruction unit 20d outputs a High signal as a gain switching signal to the reception detection unit 23 as shown in FIG. 13(b), thereby causing the reception detection unit 23 to set the amplification factor of the received signal to 1.

[0097] The subsequent processing is the same as that in FIG. 8, and therefore the description will be omitted.

[0098] As described above, according to this embodiment, the switching instruction unit 20a is not provided, and a driving voltage of 10V is supplied to the transmitting means 20a regardless of the presence or absence of a recording material. Then, the transmitting means 21a is always driven in full-bridge driving mode using the first output circuit unit 24 and the second output circuit unit 25 in the same manner as in the second embodiment, and ultrasonic waves with an amplitude equivalent to that when 20V is supplied can be transmitted regardless of the presence or absence of a recording material. Then, in the reception detection unit 23, when the receiving means 21b receives ultrasonic waves not passing through the recording material P, the amplitude of the receiving signal generated by the receiving means 20b is reduced to obtain a receiving level that can be detected by the receiving level detection unit 20c. In this way, the amplification factor of the receiving signal is switched by the receiving detection unit 23 depending on the presence or absence of the recording material P, and the magnitude of the amplitude of the receiving signal is adjusted, so that the signal-to-noise ratio of the receiving signal can be prevented from increasing. In this embodiment, in addition to the operation of the second embodiment, a configuration for improving the signal-to-noise ratio of the receiving signal by optimizing the amplification factor of the receiving detection unit 23 has been described. However, in the case where the switching instruction unit 20a is not provided and a drive voltage of 10V is supplied to the transmitting means 20a regardless of the presence or absence of a recording material, it is also possible to apply the combination with the first or third embodiment.

[0099] [Modification of Example 4] In the fourth embodiment, the following method has been described. First, the switching instruction unit 20a is not provided, and a drive voltage of 10V is supplied to the transmitting means 20a regardless of the presence or absence of a recording material. Then, as in the second embodiment, the first output circuit unit 24 and the second output circuit unit 25 are used to always drive the transmitting means 21a in full-bridge drive mode, and ultrasonic waves with an amplitude equivalent to that when 20V is supplied can be emitted regardless of the presence or absence of a recording material. Then, in the reception detection unit 23, when the receiving means 21b receives ultrasonic waves that have not passed through the recording material P, the amplitude of the reception signal generated by the receiving means 20b is reduced, thereby obtaining a reception level that can be detected by the reception level detection unit 20c.

[0100] In this embodiment, as in the fourth embodiment, the switching instruction unit 20a is not provided, and a driving voltage of 10V is supplied to the transmitting circuit unit 28 regardless of the presence or absence of a recording material. Then, as in the second embodiment, the first output circuit unit 24 and the second output circuit unit 25 are used to drive the transmitting means 21a in a full-bridge driving mode at all times, and ultrasonic waves of an amplitude equivalent to that when 20V is supplied can be transmitted regardless of the presence or absence of a recording material. Then, in this embodiment, the control unit 20 has a gain instruction unit 20e, and the transmitting circuit unit 28 has a first amplification factor switching unit (not shown) and a second amplification factor switching unit (not shown). Then, when the receiving means 21b receives ultrasonic waves not passing through the recording material P, the first amplification factor switching unit and the second amplification factor switching unit increase the amplification factor of the voltage input to the transmitting circuit unit 28 to, for example, 1 / 5, thereby reducing the driving voltage input to the transmitting means 21a.

[0101] [Switching of the amplification factor of the driving voltage in the transmission control unit 22 according to the presence or absence of the recording material P] Fig. 14 is a block diagram of the recording material detection device 19 in this embodiment. In the following description, the same components as those in Fig. 13 are given the same reference numbers and the description thereof will be omitted.

[0102] The control unit 20 has a gain instruction unit 20e for controlling the amplification factor of the voltage input to the transmission circuit unit 28. The first amplification factor switching unit and the second amplification factor switching unit of the transmission circuit unit 28 switch the amplification factor of the voltage input to the transmission circuit unit 28 in response to a gain instruction signal from the gain instruction unit 20e. In this embodiment, the voltage values ​​converted by the first amplification factor switching unit and the second amplification factor switching unit are the same voltage value. In this embodiment, an inverting amplifier circuit using an operational amplifier is used to switch the amplification factor, and since this has the same configuration as in the fourth embodiment, a description thereof will be omitted. In this embodiment, an inverting amplifier circuit is used, but any circuit capable of amplifying a signal, such as an amplifier circuit using a transistor, can be used instead.

[0103] Next, the setting of the amplification factor in the first amplification factor switching unit and the second amplification factor switching unit will be described below. When the ultrasonic wave passing through the recording material is received by the receiving means, the amplitude of the reception signal input to the reception detection unit 23 is small. Therefore, it is desirable that the amplitude of the ultrasonic wave transmitted by the transmitting means 21a is large. Therefore, in order to set the amplification factor in the first amplification factor switching unit and the second amplification factor switching unit to 1, the gain instruction unit 20e outputs a High signal as the gain instruction signal. Also, when the ultrasonic wave not passing through the recording material is received by the receiving means, the amplitude of the reception signal input to the reception detection unit 23 is large. It is desirable that the amplitude of the ultrasonic wave transmitted by the transmitting means 21a is small. Therefore, the gain instruction unit 20e outputs a Low signal as the gain instruction signal, and sets the amplification factor in the first amplification factor switching unit and the second amplification factor switching unit to 1 / 5, which is a magnification smaller than when the gain instruction signal is a High signal.

[0104] As described above, in this embodiment, the gain indication unit 21e outputs a Low signal when the receiving means receives ultrasonic waves that do not pass through the recording material, and outputs a High signal when the receiving means receives ultrasonic waves that pass through the recording material.

[0105] In this way, the first amplification factor switching unit and the second amplification factor switching unit switch the amplification factor of the voltage input to the transmitting circuit unit 28 depending on whether or not recording material P is present, thereby preventing the signal-to-noise ratio of the received signal from increasing.

[0106] In this embodiment, the reception signal of the ultrasonic wave not passing through the recording material received by the receiving means is also referred to as the first reception value, and the reception signal of the ultrasonic wave passing through the recording material received by the receiving means is also referred to as the second reception value. The gain instruction unit 20e is also referred to as the amplification factor switching instruction unit, and the gain instruction signal output by the gain instruction unit 20e is also referred to as the amplification factor switching signal. The Low signal of the gain instruction signal is also referred to as the first amplification factor switching signal, the amplification factor of 1 / 5 is also referred to as the first amplification factor, and the voltage obtained by converting the voltage input to the transmission circuit unit 28 by the first amplification factor is also referred to as the first conversion input value. The first amplification factor switching unit and the second amplification factor switching unit are also referred to as the amplification factor switching unit. The High signal of the gain instruction signal is also referred to as the second amplification factor switching signal, the amplification factor of 1 is also referred to as the second amplification factor, and the voltage obtained by converting the voltage input to the transmission circuit unit 28 by the second amplification factor is also referred to as the second conversion input value. [Explanation of symbols]

[0107] 1. Image forming device 19 Recording material detection device 20 Control section 20a Switching instruction section 20b Call instruction section 20c Reception level detector 20d Gain indicator 20e Gain indicator 21 Ultrasonic Sensor 21a Means of transmission 21b Receiving means 22 Outgoing call control section 24 First output circuit section 25 Second output circuit section 26 Third output circuit section 27 Switching section 28 Transmitting circuit section 29 Voltage conversion section

Claims

1. an ultrasonic sensor including a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, the transmitting means and the receiving means being disposed on either side of a conveying path along which a recording material is conveyed; an instruction means for inputting to the transmitting means a first drive input for transmitting an ultrasonic wave having a first maximum amplitude, or a second drive input for transmitting an ultrasonic wave having a second maximum amplitude larger than the first maximum amplitude; a detection means for detecting information relating to the basis weight of the recording material in accordance with a first value of ultrasonic waves transmitted from the transmitting means when the first drive input is supplied, the ultrasonic waves not passing through the recording material, and received by the receiving means, and a second value of ultrasonic waves transmitted from the transmitting means when the second drive input is supplied, the ultrasonic waves passing through the recording material, and received by the receiving means; A recording material detection device comprising:

2. 2. The recording material detection device according to claim 1, wherein the instruction means includes a first output circuit portion connected to a first terminal of the transmitting means, and a second output circuit portion connected to a second terminal of the transmitting means.

3. the indicating means includes a third output circuit portion connected to the second terminal of the transmitting means, 3. The recording material detection device according to claim 2, further comprising a first switching means for switching between connecting the second output circuit unit to the second terminal of the transmitting means and connecting the third output circuit unit to the second terminal of the transmitting means.

4. When the first drive input is input from the instruction means to the transmission means, the first switching means connects the third output circuit unit to the second terminal; The recording material detection device according to claim 3, characterized in that the instruction means switches between a first state in which the first output circuit unit outputs the first drive input and the third output circuit unit outputs an input corresponding to ground, and a second state in which the first output circuit unit outputs an input corresponding to ground and the third output circuit unit outputs an input corresponding to ground.

5. When the second drive input is input from the instruction means to the transmission means, the first switching means connects the second output circuit unit to the second terminal; The recording material detection device according to claim 3 or 4, characterized in that the instruction means switches between a third state in which the first output circuit unit outputs the second drive input and the second output circuit unit outputs an input corresponding to ground, and a fourth state in which the first output circuit unit outputs an input corresponding to ground and the second output circuit unit outputs the second drive input.

6. a fourth output circuit section connected to the second output circuit section and configured to output a drive signal to the second output circuit section; a fifth output circuit section connected to the second output circuit section and outputting an input corresponding to a ground to the second output circuit section; 3. The recording material detection device according to claim 2, further comprising a second switching means for switching between connecting the fourth output circuit portion to the second output circuit portion and connecting the fifth output circuit portion to the second output circuit portion.

7. When the first drive input is supplied from the indicating means to the transmitting means, the second switching means connects the fifth output circuit unit to the second output circuit unit; The recording material detection device according to claim 6, characterized in that the instruction means switches between a fifth state in which the first output circuit unit outputs the first drive input and the second output circuit unit outputs an input corresponding to ground, and a sixth state in which the first output circuit unit outputs an input corresponding to ground and the second output circuit unit outputs an input corresponding to ground.

8. When the second drive input is supplied from the indicating means to the transmitting means, the second switching means connects the second output circuit unit to the fourth output circuit unit; The recording material detection device according to claim 6 or 7, characterized in that the instruction means switches between a seventh state in which the second drive input is output from the first output circuit unit and an input corresponding to ground is output from the second output circuit unit, and an eighth state in which an input corresponding to ground is output from the first output circuit unit and the second drive input is output from the second output circuit unit.

9. When the first drive input is supplied from the indicating means to the transmitting means, The recording material detection device according to claim 2, characterized in that the instruction means switches between a ninth state in which the first output circuit unit outputs the first drive input and the second output circuit unit outputs an input corresponding to ground, and a tenth state in which the first output circuit unit outputs an input corresponding to ground and the second output circuit unit outputs the first drive input.

10. When the second drive input is supplied from the indicating means to the transmitting means, The recording material detection device according to claim 2 or 9, characterized in that the instruction means switches between an eleventh state in which the second drive input is output from the first output circuit unit and an input corresponding to ground is output from the second output circuit unit, and a twelfth state in which the first output circuit unit outputs an input corresponding to ground and the second drive input is output from the second output circuit unit.

11. When the first drive input is supplied from the indicating means to the transmitting means, The recording material detection device according to claim 2, characterized in that the instruction means switches between a thirteenth state in which the first output circuit unit outputs the first drive input and the second output circuit unit outputs an input corresponding to ground, and a fourteenth state in which the first output circuit unit outputs an input corresponding to ground and the second output circuit unit outputs an input corresponding to ground.

12. When the second drive input is supplied from the indicating means to the transmitting means, The recording material detection device according to claim 2 or 11, characterized in that the instruction means switches between a 15th state in which the first output circuit unit outputs the second drive input and the second output circuit unit outputs an input corresponding to ground, and a 16th state in which the first output circuit unit outputs an input corresponding to ground and the second output circuit unit outputs an input corresponding to ground.

13. an ultrasonic sensor including a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, the transmitting means and the receiving means being disposed on either side of a conveying path along which a recording material is conveyed; and an instruction means for inputting a drive input to the transmission means, the indicating means includes a first output circuit section connected to a first terminal of the transmitting means, and a second output circuit section connected to a second terminal of the transmitting means; An ultrasonic emitting device characterized by switching between a state in which the drive input is output from the first output circuit unit and an input corresponding to ground is output from the second output circuit unit, and a state in which an input corresponding to ground is output from the first output circuit unit and the drive input is output from the second output circuit unit.

14. an ultrasonic sensor including a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, the transmitting means and the receiving means being disposed on either side of a conveying path along which a recording material is conveyed; an instruction means for inputting a drive input to the transmission means; an amplification factor switching means for converting a drive input input to the transmitting means into a first converted input value smaller than the drive input using a first amplification factor when the receiving means receives ultrasonic waves not passing through a recording material, and for converting the drive input input to the transmitting means into a second converted input value using a second amplification factor when the receiving means receives ultrasonic waves passing through a recording material; a detection means for detecting information regarding the basis weight of the recording material in accordance with a first value obtained by receiving, by the receiving means, ultrasonic waves transmitted from the transmitting means when the first converted input value is input to the transmitting means, and a second value obtained by receiving, by the receiving means, ultrasonic waves transmitted from the transmitting means when the second converted input value is input to the transmitting means.

15. an amplification factor switching instruction means for outputting an amplification factor switching signal for switching the amplification factor of the drive input input to the transmitting means to the amplification factor switching means; The recording material detection device according to claim 14, characterized in that the amplification ratio switching instruction means outputs a signal instructing the use of the first amplification ratio when the receiving means receives ultrasonic waves that have not passed through a recording material, and outputs a signal instructing the use of the second amplification ratio when the receiving means receives ultrasonic waves that have passed through a recording material.

16. an image forming means for forming an image on a recording material; 16. An image forming apparatus, comprising: an image forming unit that changes conditions for forming an image based on a detection result obtained by the recording material detection device according to claim 1.

17. an ultrasonic sensor including a transmitting means for transmitting ultrasonic waves and a receiving means for receiving the ultrasonic waves, the transmitting means and the receiving means being disposed on either side of a conveying path along which a recording material is conveyed; an instruction means for inputting to the transmitting means a first drive input for transmitting an ultrasonic wave having a first maximum amplitude, or a second drive input for transmitting an ultrasonic wave having a second maximum amplitude larger than the first maximum amplitude; a control means for controlling image forming conditions in response to a first value of ultrasonic waves transmitted from the transmitting means when the first drive input is supplied, the ultrasonic waves not passing through a recording material, and received by the receiving means, and a second value of ultrasonic waves transmitted from the transmitting means when the second drive input is supplied, the ultrasonic waves passing through the recording material, and received by the receiving means; An image forming apparatus comprising:

Images