Detection device

Abstract

To provide a detection device capable of reducing the decrease in the accuracy of adjusting the amount of light emitted from a light-emitting unit.SOLUTION: A phototransistor 38 receives light emitted by a light-emitting diode 37. A controller 58 adjusts the light emission of the light-emitting diode 37 so that the light-reception adjustment voltage corresponding to the light-reception voltage of the phototransistor 38 is a value within a target adjustment range including the target adjustment value in a state where paper is between the light-emitting diode 37 and the phototransistor 38. The controller 58 sets, as the target adjustment range, a predetermined range of width equal to or greater than the light-reception adjustment change amount including the target adjustment value on the basis of the light-reception adjustment change, which is the amount of change in the light-reception adjustment voltage when the light emission of the light-emitting diode 37 is changed by the minimum unit amount in a state where paper is between the light-emitting diode 37 and the phototransistor 38.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a detection device for detecting an object to be detected, such as paper. [Background technology]

[0002] In a printing device, an optical sensor is used to detect a paper sheet being transported, and the amount of light emitted is adjusted to adjust the sensitivity of the sensor (see Patent Document 1).

[0003] Specifically, when paper is present between the light-emitting and light-receiving parts of the sensor, the controller adjusts the amount of light emitted by the light-emitting part so that the input voltage to the controller, which corresponds to the amount of light received by the light-receiving part, is a value within a target adjustment range that includes the target adjustment value.

[0004] In such sensitivity adjustment, when the amount of light emitted by the light-emitting unit is changed by one step in the adjustment resolution, the change in the input voltage to the controller may be too large, making it impossible to adjust the amount of light emitted so that the input voltage is within the target adjustment range.

[0005] On the other hand, if the target adjustment range is set to be sufficiently large, it is possible to adjust the amount of light emitted so that the input voltage to the controller is a value within the target adjustment range. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-30398 Summary of the Invention [Problem to be solved by the invention]

[0007] However, if the target adjustment range is set excessively large, even if the amount of light emitted can be adjusted so that the input voltage to the controller is within the target adjustment range, the input voltage may deviate significantly from the target adjustment value, which may reduce the accuracy of adjusting the amount of light emitted.

[0008] The present invention has been made in view of the above, and has an object to provide a detection device that can reduce a decrease in the accuracy of adjusting the amount of light emitted by a light-emitting section. [Means for solving the problem]

[0009] According to one aspect of the present invention, a detection device is provided, comprising: a light-emitting unit; a light-receiving unit that receives light emitted by the light-emitting unit; and a control unit that adjusts the amount of light emitted by the light-emitting unit so that when an object to be detected is present between the light-emitting unit and the light-receiving unit, a light-receiving adjustment voltage corresponding to the light-receiving voltage of the light-receiving unit becomes a value within a target adjustment range including a target adjustment value, wherein the control unit sets the target adjustment range to a predetermined range having a width equal to or greater than the light-receiving adjustment change amount, including the target adjustment value, based on a light-receiving adjustment change amount, which is the amount of change in the light-receiving adjustment voltage when the amount of light emitted by the light-emitting unit is changed by the smallest unit when an object to be detected is present between the light-emitting unit and the light-receiving unit.

[0010] According to another aspect of the present invention, there is provided a detection device comprising: a light-emitting unit; a light-receiving unit that receives light emitted by the light-emitting unit; a light-receiving load resistor that converts a photocurrent corresponding to the amount of light received by the light-receiving unit into a light-receiving voltage; and a control unit that adjusts the amount of light emitted by the light-emitting unit so that, when an object to be detected is present between the light-emitting unit and the light-receiving unit, a light-receiving adjustment voltage corresponding to the light-receiving voltage converted by the light-receiving load resistor becomes a value within a target adjustment range including a target adjustment value, wherein the resistance value of the light-receiving load resistor is set to a value calculated so that when the amount of light emitted by the light-emitting unit is changed by the minimum unit when an object to be detected is present between the light-emitting unit and the light-receiving unit, the amount of change in the light-receiving adjustment voltage is equal to or greater than a predetermined value within the width of the target adjustment range. Effect of the Invention

[0011] According to the detection device of the present invention, it is possible to reduce the decrease in the accuracy of adjusting the amount of light emitted by the light-emitting unit. [Brief description of the drawings]

[0012] [Figure 1] 1 is a schematic configuration diagram of a printing device provided with a detection device according to a first embodiment. [Diagram 2] 1 is a block diagram showing a configuration of a detection device according to a first embodiment. [Diagram 3] 3 is a diagram showing the circuit configurations of a paper sensor, a constant current circuit, and a current-voltage converter of the detection device shown in FIG. 2. [Figure 4] 13 is a flowchart of a sensitivity adjustment process. [Diagram 5] 11A and 11B are diagrams illustrating changes in light-emitting current and light-receiving adjustment voltage during sensitivity adjustment processing. [Figure 6] 13A and 13B are diagrams illustrating changes in light emission current and light receiving adjustment voltage during sensitivity adjustment processing when a target adjustment range is smaller than a light receiving adjustment change amount. [Figure 7] FIG. 4 is a diagram illustrating an example of photoelectric characteristics of a paper sensor. [Figure 8] 6 is a diagram showing an example of a distance characteristic between light emission and light reception of a paper sensor; [Figure 9] FIG. 13 is an explanatory diagram of a discrimination ratio and a detection threshold. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

[0014] The following embodiments are examples of devices for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not limit the material, shape, structure, arrangement, etc. of each component to those described below. The technical idea of ​​the present invention can be modified in various ways within the scope of the claims.

[0015] [First embodiment] Fig. 1 is a schematic diagram of a printing device provided with a detection device according to a first embodiment of the present invention. The path indicated by the thick line in Fig. 1 is the transport path along which paper W, which is a print medium, is transported. Of the transport paths, the path indicated by the solid line is the normal path RC, the path indicated by the dashed line is the reversing path RR, the path indicated by the broken line is the paper discharge path RD, and the paths indicated by the two-dot chain lines are the external paper feed path RS1 and the internal paper feed path RS2. In the following description, upstream and downstream refer to the upstream and downstream of the transport path.

[0016] As shown in FIG. 1, the printing device 1 includes a paper feed section 2, a transport printing section 3, an upper transport section 4, a paper discharge section 5, an inversion section 6, and a housing 7 that houses or holds each of the sections.

[0017] The paper feed unit 2 feeds paper W to the transport and print unit 3. The paper feed unit 2 includes an external paper feed tray 21, an external paper feed transport unit 22, a plurality of internal paper feed trays 23, and an internal paper feed transport unit 24.

[0018] The external paper feed tray 21 is provided on which paper sheets W to be used for printing are stacked. The external paper feed tray 21 is installed with a part thereof exposed to the outside of the housing 7.

[0019] The external paper feed conveying unit 22 takes out the paper W stacked on the external paper feed tray 21, and conveys the paper W toward the conveying printing unit 3 along the external paper feed path RS1.

[0020] The internal paper feed tray 23 is disposed inside the housing 7 and is configured to hold paper W to be used for printing.

[0021] The internal paper feed conveying unit 24 takes out the paper W stacked on the internal paper feed tray 23, and conveys the paper W toward the conveying printing unit 3 along the internal paper feed path RS2.

[0022] The transporting and printing unit 3 transports the paper W and prints on the paper W. The transporting and printing unit 3 includes a registration roller 31, a belt platen unit 32, a printing unit 33, and paper sensors 34A and 34B. The alphabetical suffixes in the reference numerals of the paper sensors 34A and 34B may be omitted to collectively indicate the sensors.

[0023] The registration rollers 31 temporarily stop the paper W conveyed by the paper feed unit 2 or the inversion unit 6, correct the skew, and then convey the paper W to the belt platen unit 32. The registration rollers 31 are disposed on the normal route RC upstream of the conveying and printing unit 3.

[0024] The belt platen unit 32 conveys the paper W conveyed by the registration rollers 31 while holding the paper W on the belt.

[0025] The printing unit 33 prints an image by ejecting ink onto the paper W transported by the belt platen unit 32. The printing unit 33 includes a plurality of inkjet heads 36 that eject ink.

[0026] The paper sensor 34 detects the conveyed paper (corresponding to the detected object) W. The paper sensor 34 is configured by a light transmission type sensor having a light emitting diode (corresponding to the light emitting portion) 37 and a phototransistor (corresponding to the light receiving portion) 38.

[0027] The paper sensor 34A is disposed upstream near the junction of the three routes, external paper feed path RS1, internal paper feed path RS2, and reverse path RR, and detects the paper W transported along each of these three routes. The light-emitting diode 37 of the paper sensor 34A is disposed below the external paper feed path RS1, internal paper feed path RS2, and reverse path RR, and emits light upward. The phototransistor 38 of the paper sensor 34A is disposed opposite the light-emitting diode 37 across the external paper feed path RS1, internal paper feed path RS2, and reverse path RR, and receives the light emitted by the light-emitting diode 37.

[0028] The paper sensor 34B detects the paper W transported from the registration rollers 31 toward the belt platen unit 32. The paper sensor 34B is disposed near the downstream side of the registration rollers 31. The light emitting diode 37 of the paper sensor 34B is disposed below the normal path RC and emits light upward. The phototransistor 38 of the paper sensor 34B is disposed opposite the light emitting diode 37 across the normal path RC and receives the light emitted by the light emitting diode 37.

[0029] The upper conveying section 4 conveys the sheet W conveyed by the belt platen section 32 to the sheet discharge section 5 or the reversing section 6 along a normal path RC.

[0030] The paper discharge unit 5 discharges the printed paper W. The paper discharge unit 5 includes a switching unit 41, a paper discharge transport unit 42, and a paper discharge tray 43.

[0031] The switching unit 41 switches the transport path of the paper W between the paper discharge path RD and the reverse path RR. The switching unit 41 is disposed at a branch point of the paper discharge path RD and the reverse path RR.

[0032] The discharge conveying section 42 conveys the paper W guided to the discharge path RD by the switching section 41 and discharges it onto the discharge tray 43 .

[0033] The paper ejection tray 43 is a tray onto which the printed paper W ejected by the paper ejection transport section 42 is stacked. The paper ejection tray 43 is formed in the shape of a tray protruding from the housing 7.

[0034] During double-sided printing, the reversing unit 6 conveys the paper W, which has been printed on one side, along a reversing path RR, and reverses the paper W to re-feed it to the conveying and printing unit 3.

[0035] When printing is performed in the printing device 1, unprinted paper W is fed from the paper feed unit 2 to the transport printing unit 3. The fed paper W is sent to the belt platen unit 32 by the registration rollers 31, and while being transported by the belt platen unit 32, it is printed with ink ejected from the inkjet head 36. The printed paper W is transported from the belt platen unit 32 to the upper transport unit 4.

[0036] In the case of single-sided printing, the paper W that has been printed on one side and transported by the upper transport section 4 is guided by the switching section 41 from the normal route RC to the paper discharge route RD, and is discharged onto the paper discharge tray 43 by the paper discharge transport section .

[0037] In the case of double-sided printing, the paper W that has been printed on one side and transported by the upper transport unit 4 is guided by the switching unit 41 from the normal path RC to the reversing path RR, and is then reversed by the reversing unit 6 and refed to the transporting and printing unit 3. The refed paper W that has been printed on one side is sent to the belt platen unit 32 by the registration rollers 31 in the transporting and printing unit 3.

[0038] Here, the paper W that has been printed on one side has been inverted by the inversion unit 6 and is sent to the belt platen unit 32 with the unprinted side facing up. Then, while the paper W is transported by the belt platen unit 32, the unprinted side is printed with ink ejected from the inkjet head 36. The paper W that has been printed on both sides is transported by the upper transport unit 4 to the paper discharge unit 5, where it is discharged onto the paper discharge tray 43.

[0039] Next, the detection device will be described.

[0040] Fig. 2 is a block diagram showing the configuration of the detection device according to the first embodiment Fig. 3 is a diagram showing the circuit configuration of the paper sensor, constant current circuit, and current-voltage conversion unit of the detection device shown in Fig. 2.

[0041] As shown in FIG. 2, the detection device 51 includes the above-mentioned paper sensor 34, a D / A converter 52, a constant current circuit 53, a current-voltage conversion unit 54, a voltage amplification unit 55, an A / D converter 56, a comparator 57, a controller (corresponding to a control unit) 58, and a memory 59.

[0042] As described above, the paper sensor 34 includes the light emitting diode 37 and the phototransistor 38 .

[0043] The light emitting diode 37 has an anode connected to a power supply Vcc1 and a cathode connected to the collector of a transistor 61 of a constant current circuit 53, which will be described later.

[0044] The collector of the phototransistor 38 is connected to a power supply Vcc2, and the emitter is connected to ground via a resistor 65 of the current-voltage conversion unit 54 described later. The emitter of the phototransistor 38 is also connected to the voltage amplification unit 55 and the comparator 57.

[0045] The D / A converter 52 converts the digital value for indicating the light emission current IF output by the controller 58 into an analog voltage.

[0046] The constant current circuit 53 converts the analog voltage input from the D / A converter 52 into a light emitting current IF and supplies it to the light emitting diode 37. The constant current circuit 53 includes a transistor 61, an operational amplifier 62, and resistors 63 and 64.

[0047] The transistor 61 has a collector connected to the cathode of the light-emitting diode 37 , an emitter connected to ground via a resistor 63 , and a base connected to the output terminal of an operational amplifier 62 via a resistor 64 .

[0048] A non-inverting input terminal of the operational amplifier 62 is connected to the D / A converter 52. An inverting input terminal of the operational amplifier 62 is connected to the emitter of the transistor 61. An output terminal of the operational amplifier 62 is connected to the base of the transistor 61 via a resistor 64.

[0049] The resistor 63 is connected between the connection point between the emitter of the transistor 61 and the inverting input terminal of the operational amplifier 62 and ground.

[0050] The resistor 64 is connected between the output terminal of the operational amplifier 62 and the base of the transistor 61 .

[0051] The current-voltage conversion unit 54 has a resistor 65 (corresponding to a light-receiving load resistor) and converts a photocurrent Ic according to the amount of light received by the phototransistor 38 into a light-receiving voltage Ve by the resistor 65. The resistor 65 is connected between the connection point between the emitter of the phototransistor 38 and the voltage amplifier unit 55 and comparator 57 and between the ground and the connection point.

[0052] The voltage amplifier 55 amplifies the light-receiving voltage Ve of the phototransistor 38, and outputs a light-receiving adjustment voltage Vad, which is the amplified voltage.

[0053] The A / D converter 56 converts the light-receiving adjustment voltage Vad, which is an analog voltage input from the voltage amplifier 55, into a digital value.

[0054] The functions of the voltage amplifier 55 and the A / D converter 56 may be realized by the controller 58 using software.

[0055] The comparator 57 compares the light receiving voltage Ve of the phototransistor 38 with the detection threshold Vt, and outputs a comparison result indicating whether or not the light receiving voltage Ve is greater than the detection threshold Vt to the controller 58. Here, the detection threshold Vt is a threshold value of the light receiving voltage Ve for determining whether or not the paper sensor 34 is detecting the paper W (whether or not the paper W is present between the light emitting diode 37 and the phototransistor 38).

[0056] The controller 58 determines whether the paper sensor 34 detects the paper W or not based on the above-mentioned comparison result input from the comparator 57.

[0057] Furthermore, in a sensitivity adjustment process of the paper sensor 34 described below, the controller 58 adjusts the amount of light emitted by the light-emitting diode 37 so that the light-receiving adjustment voltage Vad corresponding to the light-receiving voltage Ve of the phototransistor 38 becomes a value within a target adjustment range including the target adjustment value Vd with paper W present between the light-emitting diode 37 and the phototransistor 38. In this sensitivity adjustment process, the controller 58 sets the target adjustment range to a predetermined range equal to or greater than the light-receiving adjustment change amount ΔVg including the target adjustment value Vd, based on the light-receiving adjustment change amount ΔVg, which is the amount of change in the light-receiving adjustment voltage Vad when the amount of light emitted by the light-emitting diode 37 is changed by one step (corresponding to the smallest unit) in the adjustment resolution with paper W present between the light-emitting diode 37 and the phototransistor 38.

[0058] The controller 58 may also control the entire printing device 1. The controller 58 is configured to include a CPU and the like.

[0059] The memory 59 stores the setting value of the light emission current IF obtained by the sensitivity adjustment process of the paper sensor .

[0060] Next, the process of adjusting the sensitivity of the paper sensor 34 in the detection device 51 will be described.

[0061] Here, a binary search method is used as a method for adjusting the light emission amount of the light-emitting diode 37 for adjusting the sensitivity of the paper sensor 34. The binary search method is a method for adjusting the light emission amount so that the light receiving adjustment voltage Vad becomes a value within the target adjustment range while halving the amount of change when changing the light emission amount of the light-emitting diode 37 within the previous amount of change. Note that the method is not limited to the binary search method, and a method for increasing the light emission amount of the light-emitting diode 37 by a predetermined amount or decreasing the light emission amount by a predetermined amount may also be used.

[0062] The sensitivity adjustment process is performed with a sheet of paper W of a reference paper type between the light emitting diode 37 and the phototransistor 38 of the paper sensor 34. The sheet of paper W placed between the light emitting diode 37 and the phototransistor 38 in the sensitivity adjustment process is, for example, plain paper. By using plain paper in the sensitivity adjustment process, it is possible to detect thick paper and thin paper as well. Note that the sensitivity adjustment process may be performed for each paper type. Even in this case, the procedure of the sensitivity adjustment process is similar.

[0063] Fig. 4 is a flowchart of the process for adjusting the sensitivity of the paper sensor 34. In step S1 of Fig. 4, the controller 58 causes the light emitting diode 37 to emit light.

[0064] Specifically, the controller 58 outputs a digital value indicating the light-emitting current IF set as the light-emitting current IF at the start of the sensitivity adjustment process to the D / A converter 52. Here, the light-emitting current IF at the start of the sensitivity adjustment process is set to a value that causes the light-emitting diode 37 to emit light with an amount of light that makes the light-receiving adjustment voltage Vad sufficiently larger than the upper limit Vup of the target adjustment range.

[0065] The D / A converter 52 converts the digital value input from the controller 58 into an analog voltage. The constant current circuit 53 converts the analog voltage input from the D / A converter 52 into a light emitting current IF and supplies it to the light emitting diode 37. This causes the light emitting diode 37 to emit light with an amount of light corresponding to the light emitting current IF.

[0066] The phototransistor 38 receives the light emitted by the light-emitting diode 37. The current-voltage conversion unit 54 converts the photocurrent Ic flowing through the phototransistor 38 that has received the light into a light-receiving voltage Ve. The voltage amplification unit 55 amplifies the light-receiving voltage Ve input from the current-voltage conversion unit 54, and outputs the amplified voltage, a light-receiving adjustment voltage Vad, to the A / D converter 56. The A / D converter 56 converts the light-receiving adjustment voltage Vad input from the voltage amplification unit 55 into a digital value, and outputs this digital value to the controller 58.

[0067] Next, in step S2, the controller 58 determines, based on the digital value input from the A / D converter 56, whether the light-receiving adjustment voltage Vad is within the target adjustment range.

[0068] If it is determined that the light-receiving adjustment voltage Vad is not within the target adjustment range (step S2: NO), then in step S3, the controller 58 changes the value of the light-emitting current IF. Here, if the light-receiving adjustment voltage Vad is greater than the upper limit Vup of the target adjustment range, the controller 58 changes the light-emitting current IF to half the most recent value. If the light-receiving adjustment voltage Vad is less than the lower limit Vdn of the target adjustment range, the controller 58 changes the light-emitting current IF to twice the most recent value.

[0069] When the value of the light-emitting current IF is changed, the amount of light emitted by the light-emitting diode 37 is changed, thereby varying the light-receiving adjustment voltage Vad. After step S3, the controller 58 returns to step S2.

[0070] In step S2, if it is determined that the light-receiving adjustment voltage Vad is within the target adjustment range (step S2: YES), in step S4, the controller 58 stores the value of the light-emitting current IF at that time as the setting value of the light-emitting current IF in the memory 59. This ends the sensitivity adjustment process.

[0071] As a result of the sensitivity adjustment process described above, as shown in FIG. 5, the light-receiving adjustment voltage Vad changes in response to changes in the light-emitting current IF, and when the light-receiving adjustment voltage Vad reaches a value within the target adjustment range from Vdn to Vup, the sensitivity adjustment (adjustment of the amount of light emitted by the light-emitting diode 37) is completed.

[0072] As described above, the target adjustment range is set to a range including the target adjustment value Vd as shown in Fig. 5. Specifically, the target adjustment range is set to a range from a lower limit Vdn expressed by the following formula (1) to an upper limit Vup expressed by the following formula (2).

[0073] Vdn = Vd - VRng ... (1) Vup = Vd + VRng … (2) The adjustment range voltage VRng in the formulas (1) and (2) indicates the voltage range that defines the target adjustment range. The width of the target adjustment range is 2×VRng.

[0074] The adjustment range voltage VRng is set so that the target adjustment range is a predetermined range that is equal to or greater than the aforementioned light-receiving adjustment change amount ΔVg and is not excessively larger than the light-receiving adjustment change amount ΔVg. Specifically, the adjustment range voltage VRng is set so that the target adjustment range is equal to or greater than the aforementioned light-receiving adjustment change amount ΔVg and the deviation of the light-receiving adjustment voltage Vad from the target adjustment value Vd when the light-receiving adjustment voltage Vad becomes a value within the target adjustment range is within an allowable range. The adjustment range voltage VRng is set, for example, based on experiments, etc.

[0075] Here, unlike the present embodiment, when the target adjustment range is smaller than the light-receiving adjustment change amount ΔVg, as shown in FIG. 6, the light-receiving adjustment voltage Vad will alternately take on values ​​greater than the upper limit Vup of the target adjustment range and values ​​less than the lower limit Vdn, and it may not be possible to adjust the light-receiving adjustment voltage Vad to a value within the target adjustment range.

[0076] On the other hand, in the present embodiment, the target adjustment range is set as described above, so that the light-receiving adjustment voltage Vad can be adjusted to a value within the target adjustment range. Also, when the light-receiving adjustment voltage Vad is a value within the target adjustment range, the deviation of the light-receiving adjustment voltage Vad from the target adjustment value Vd can be suppressed.

[0077] Next, a method for calculating the amount of change in light reception adjustment ΔVg will be described.

[0078] The factors used in calculating the light reception adjustment change amount ΔVg include the photoelectric characteristics of the paper sensor 34, the distance characteristics between the light emission and light reception of the paper sensor 34, the resolution rslDA of the D / A converter 52, the reference voltage VrfDA of the D / A converter 52, the constant current circuit constant RE, the resistance value RL of the resistor 65 of the current-voltage conversion unit 54, the amplification factor Gv of the voltage amplifier unit 55, and the discrimination ratio P.

[0079] The photoelectric characteristic of paper sensor 34 indicates the relationship between light-emitting current IF supplied to light-emitting diode 37 and photocurrent Ic flowing through phototransistor 38. The relationship between light-emitting current IF and photocurrent Ic is, for example, as shown in Figure 7. In the example of Figure 7, the photoelectric characteristic of paper sensor 34 is expressed as Ic / IF.

[0080] In the example of FIG. 7, the light emission current IF and the photocurrent Ic are in a proportional relationship, but if the light emission current IF and the photocurrent Ic are not in a proportional relationship, the photoelectric characteristic is expressed by a polynomial.

[0081] The light emitting / receiving distance characteristic of the paper sensor 34 indicates the relationship between the light emitting / receiving distance L, which is the distance between the light emitting diode 37 and the phototransistor 38 of the paper sensor 34, and the photocurrent Ic.

[0082] Fig. 8 is a diagram showing an example of the distance characteristics between the light-emitting and light-receiving elements of the paper sensor 34. The fluctuation ratio y in Fig. 8 indicates the ratio of the values ​​of the photocurrent Ic corresponding to each of a plurality of values ​​of the light-emitting and light-receiving distance L to a certain value of the photocurrent Ic. As can be seen from Fig. 8, the larger the light-emitting and light-receiving distance L, the smaller the photocurrent Ic.

[0083] In the example of FIG. 8, the fluctuation ratio y is expressed by the following formula (3), which is a cubic formula.

[0084] y=a3×L 3 +a2×L 2 +a1×L+b …(3) Here, a3, a2, a1, and b are coefficients according to the distance characteristics between the light emission and reception.

[0085] The order of the fluctuation ratio y may differ depending on the type of the paper sensor 34, etc.

[0086] The resolution rslDA and the reference voltage VrfDA of the D / A converter 52 are determined by the hardware. For example, in the case of an 8-bit D / A converter 52, the resolution rslDA is 255 steps. The reference voltage VrfDA indicates the width of the analog voltage.

[0087] The constant current circuit constant RE is the resistance value of the resistor 63 of the constant current circuit 53. As shown in the following equation (4), the light emission current IF is determined by the analog voltage Vi from the D / A converter 52 and the constant current circuit constant RE.

[0088] IF = Vi ÷ RE … (4) The resistance value RL of the resistor 65 of the current-voltage conversion unit 54 determines the light-receiving voltage Ve. The light-receiving voltage Ve is expressed by the following equation (5).

[0089] Ve = Ic × RL … (5) The amplification factor Gv of the voltage amplifier 55 is the ratio between the light receiving voltage Ve and the light receiving adjustment voltage Vad. The light receiving adjustment voltage Vad is expressed by the following formula (6).

[0090] Vad = Ve × Gv … (6) The discrimination ratio P is the ratio of the light receiving voltage Ve when there is paper W between the light emitting diode 37 and the phototransistor 38 to the light receiving voltage Ve when there is no paper W between the light emitting diode 37 and the phototransistor 38. The discrimination ratio P differs depending on the type of paper W. The discrimination ratio P also differs depending on the structure of the paper sensor 34 and the size of the opening for passing light that is formed in the guide plate that guides the paper W between the light emitting diode 37 and the phototransistor 38. The discrimination ratio P is found by experiment.

[0091] From the resolution rslDA of the D / A converter 52, the reference voltage VrfDA, and the constant current circuit constant RE described above, the light emitting current ΔIF for one step in the adjustment resolution of the light emission amount of the light emitting diode 37 is calculated by the following formula (7).

[0092] ΔIF = VrfDA / RE / rslDA … (7) Using the photoelectric characteristic (Ic / IF) of the paper sensor 34 described above, the distance characteristic between the light emitter and receiver expressed by equation (3), and ΔIF calculated by equation (7), the photocurrent ΔIc corresponding to ΔIF is calculated by the following equation (8).

[0093] ΔIc=(Ic / IF)×(VrfDA / RE / rslDA) ×(a3×L 3 +a2×L 2 +a1×L+b) …(8) By multiplying ΔIc by the resistance value RL of resistor 65 and the amplification factor Gv, the light receiving voltage ΔVe corresponding to ΔIF when there is no paper W between the light emitting diode 37 and the phototransistor 38 is calculated using the following equation (9).

[0094] ΔVe=(Ic / IF)×(VrfDA / RE / rslDA) ×(a3×L 3 +a2×L 2 +a1×L+b)×RL×Gv …(9) By dividing ΔVe by the discrimination ratio P corresponding to the paper W used in the sensitivity adjustment process, the light reception adjustment change amount ΔVg is calculated by the following formula (10).

[0095] ΔVg=(Ic / IF)×(VrfDA / RE / rslDA) ×(a3×L 3 +a2×L 2 +a1×L+b)×RL×Gv / P …(10) By rearranging the above equation (10), the following equation (11) is obtained.

[0096] ΔVg=(Ic / IF)×VrfDA×(a3×L 3 +a2×L 2 +a1×L+b) ×RL×Gv÷(RE×rslDA×P) …(11) Based on the amount of change in light-receiving adjustment ΔVg calculated by the above formula (11), the controller 58 sets the target adjustment range described above.

[0097] In addition, the A / D converter 56 has a high resolution and has a small effect on the amount of change in light-receiving adjustment ΔVg. Therefore, in this embodiment, the resolution of the A / D converter 56 is not used to calculate the amount of change in light-receiving adjustment ΔVg.

[0098] Next, a method for setting the target adjustment value Vd will be described.

[0099] The target adjustment value Vd is set so that the light receiving voltage Ve of the phototransistor 38 when the paper W is between the light emitting diode 37 and the phototransistor 38 becomes a value obtained by dividing the detection threshold Vt by the square root of the discrimination ratio P. In other words, the target adjustment value Vd is a value obtained by multiplying the value obtained by dividing the detection threshold Vt by the square root of the discrimination ratio P by the amplification factor Gv, and is expressed by the following formula (12).

[0100] Vd = (Vt / √P) × Gv … (12) Here, the detection threshold value Vt is set in advance for each paper type.

[0101] As described above, the discrimination ratio P is determined by an experiment. The diagram on the left side of Fig. 9 shows the transition of the light receiving voltage Ve of the phototransistor 38 in this experiment. In this experiment, the ratio of the light receiving voltage Ve when there is a sheet of paper W between the light emitting diode 37 and the phototransistor 38 to the light receiving voltage Ve when there is no sheet of paper W between the light emitting diode 37 and the phototransistor 38 is calculated as the discrimination ratio P. In this experiment, the same type of paper W as the paper W used in the sensitivity adjustment process is used.

[0102] The diagram on the right side of Fig. 9 shows the transition of the light receiving voltage Ve when the paper sensor 34 detects paper W after the sensitivity adjustment process. If the amount of light emitted by the light emitting diode 37 is adjusted in the sensitivity adjustment process so that the light receiving adjustment voltage Vad becomes equal to the target adjustment value Vd, the target adjustment value Vd is set as described above, and therefore, as shown in the diagram on the right side of Fig. 9, the light receiving voltage Ve when paper W is present between the light emitting diode 37 and the phototransistor 38 is the detection threshold value Vt divided by √P.

[0103] In the example of Fig. 9, when there is no paper W between the light-emitting diode 37 and the phototransistor 38, the phototransistor 38 is saturated. The virtual voltage in Fig. 9 indicates the light-receiving voltage Ve when the phototransistor 38 is not saturated. As shown in Fig. 9, when there is no paper W between the light-emitting diode 37 and the phototransistor 38 and the phototransistor 38 is not saturated, the light-receiving voltage Ve is a value obtained by multiplying the detection threshold Vt by √P. In other words, the detection threshold Vt is located in the middle of the discrimination ratio P. As a result, a sufficient detection margin and non-detection margin are ensured for the detection threshold Vt, thereby reducing erroneous detection of the paper W.

[0104] Here, the paper sensor 34 has hysteresis, and when the light receiving voltage Ve falls below the detection threshold Vt by the negative side of the hysteresis, the leading edge of the paper W is detected. Also, when the light receiving voltage Ve rises above the detection threshold Vt by the positive side of the hysteresis, the trailing edge of the paper W is detected. The detection margin is from the light receiving voltage Ve when there is no paper W between the light emitting diode 37 and the phototransistor 38 to the positive side of the hysteresis. The non-detection margin is from the positive side of the hysteresis to the light receiving voltage Ve when there is no paper W between the light emitting diode 37 and the phototransistor 38, assuming that the phototransistor 38 is not saturated.

[0105] As described above, in the detection device 51, the controller 58 sets the target adjustment range to a predetermined range including the target adjustment value Vd based on the light receiving adjustment change amount ΔVg in the sensitivity adjustment process. This makes it possible to adjust the light receiving adjustment voltage Vad to a value within the target adjustment range, while preventing the target adjustment range from becoming excessively large for the light receiving adjustment voltage Vad, and suppresses the deviation of the light receiving adjustment voltage Vad from the target adjustment value Vd when the light receiving adjustment voltage Vad becomes a value within the target adjustment range. Therefore, it is possible to reduce the decrease in the adjustment accuracy of the light emission amount of the light emitting diode 37.

[0106] Furthermore, in the detection device 51, the controller 58 sets the target adjustment value Vd so that the light receiving voltage Ve of the phototransistor 38 when the paper W is between the light emitting diode 37 and the phototransistor 38 is a value obtained by dividing the detection threshold Vt by the square root of the discrimination ratio P. In other words, the controller 58 sets the target adjustment value Vd so that the detection threshold Vt is the median value in the discrimination ratio P. This ensures a sufficient detection margin and non-detection margin for the detection threshold Vt, thereby reducing erroneous detection of the paper W.

[0107] [Second embodiment] Next, a second embodiment, which is a partial modification of the first embodiment described above, will be described.

[0108] In the above-described first embodiment, the target adjustment range is set based on the light-receiving adjustment change amount ΔVg calculated by equation (11). In contrast, in the second embodiment, the resistance value RL of the resistor 65 (light-receiving load resistor) of the current-voltage converter 54 is calculated so that the light-receiving adjustment change amount ΔVg is equal to or greater than a predetermined value within the width of the target adjustment range, and the resistance value RL is set to this calculated value.

[0109] In this case, the light receiving adjustment change amount ΔVg is set to a value equal to or greater than a predetermined value within a preset target adjustment range. The light receiving adjustment change amount ΔVg is set so that the deviation of the light receiving adjustment voltage Vad from the target adjustment value Vd when the light receiving adjustment voltage Vad becomes a value within the target adjustment range in the sensitivity adjustment process is within an allowable range. The light receiving adjustment change amount ΔVg in this case is set based on, for example, an experiment.

[0110] Using this amount of change in light reception adjustment ΔVg as a calculation input value, the resistance value RL of the resistor 65 is calculated by the following equation (13) obtained by modifying equation (11).

[0111] RL = ΔVg × (RE × rslDA × P) ÷((Ic / IF)×VrfDA ×(a3×L 3 +a2×L 2 +a1×L+b)×Gv) …(13) The resistor 65 of the current-voltage conversion unit 54 has the resistance value RL calculated as described above.

[0112] In this way, similarly to the first embodiment, the light-receiving adjustment voltage Vad can be adjusted to a value within the target adjustment range, the target adjustment range can be prevented from becoming excessively large with respect to the light-receiving adjustment voltage Vad, and the deviation of the light-receiving adjustment voltage Vad from the target adjustment value Vd when the light-receiving adjustment voltage Vad reaches a value within the target adjustment range can be suppressed. Therefore, the deterioration of the adjustment accuracy of the light emission amount of the light-emitting diode 37 can be reduced.

[0113] The procedure for adjusting the sensitivity of the paper sensor 34 in the second embodiment is the same as that in the first embodiment. Also in the second embodiment, as in the first embodiment, the target adjustment value Vd is set so that the detection threshold value Vt is the median value in the discrimination ratio P.

[0114] [Other embodiments] As described above, the present invention has been described by the first and second embodiments, but the descriptions and drawings forming part of this disclosure should not be understood as limiting the present invention. Various alternative embodiments, examples and operating techniques will become apparent to those skilled in the art from this disclosure.

[0115] In the first embodiment, some of the elements used to calculate the light receiving adjustment change amount ΔVg may be omitted. Also, other elements may be used to calculate the light receiving adjustment change amount ΔVg. Also, in the second embodiment, some of the elements used to calculate the resistance value RL of the resistor 65 may be omitted. Also, other elements may be used to calculate the resistance value RL of the resistor 65.

[0116] In the second embodiment, the current-voltage conversion unit 54 may have a plurality of switchable resistors 65 each having a different resistance value, and the controller 58 may select from the plurality of resistors 65 the resistor 65 having the resistance value RL calculated as described above.

[0117] Thus, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention-specifying matters related to the scope of the claims appropriate from the above description.

[0118] [Note] This application discloses the following inventions.

[0119] (Appendix 1) A light emitting portion; a light receiving unit that receives light emitted by the light emitting unit; a control unit that adjusts the amount of light emitted by the light emitter so that a light-receiving adjustment voltage corresponding to a light-receiving voltage of the light-receiving unit is within a target adjustment range including a target adjustment value when an object to be detected is present between the light emitter and the light-receiving unit, The control unit sets the target adjustment range to a predetermined range that is equal to or greater than the light receiving adjustment change amount and includes the target adjustment value, based on the light receiving adjustment change amount, which is the change in the light receiving adjustment voltage when the amount of light emitted by the light emitting unit is changed by the smallest unit when an object to be detected is present between the light emitting unit and the light receiving unit.

[0120] (Appendix 2) A light emitting portion; a light receiving unit that receives light emitted by the light emitting unit; a light-receiving load resistor for converting a photocurrent corresponding to an amount of light received by the light-receiving section into a light-receiving voltage; a control unit that adjusts the amount of light emitted by the light emitting unit so that a light receiving adjustment voltage corresponding to a light receiving voltage converted by the light receiving load resistor is within a target adjustment range including a target adjustment value when an object to be detected is present between the light emitting unit and the light receiving unit, A detection device characterized in that the resistance value of the light-receiving load resistor is set to a value calculated so that the change in the light-receiving adjustment voltage when the amount of light emitted by the light-emitting unit is changed by the minimum unit when an object to be detected is present between the light-emitting unit and the light-receiving unit is greater than or equal to a predetermined value within the width of the target adjustment range.

[0121] (Appendix 3) The control unit is The detection device described in Appendix 1 or 2, characterized in that the target adjustment value is set so that a threshold value of the light receiving voltage of the light receiving unit for determining whether or not an object to be detected is present between the light emitter and the light receiving unit is the median value of the ratio between the light receiving voltage of the light receiving unit when an object to be detected is present between the light emitter and the light receiving unit and the light receiving voltage of the light receiving unit when no object to be detected is present between the light emitter and the light receiving unit. [Explanation of symbols]

[0122] 1 Printing device 34, 34A, 34B Paper sensor 37 Light Emitting Diode 38 Phototransistor 51 Detection Device 52 D / A converter 53 Constant current circuit 54 Current-to-voltage conversion section 55 Voltage amplifier 56 A / D Converter 57 Comparator 58 Controller 59 Memory 61 Transistor 62 Operational Amplifier 63~65 Resistance

Claims

1. A light emitting portion; a light receiving unit that receives light emitted by the light emitting unit; a control unit that adjusts the amount of light emitted by the light emitter so that a light-receiving adjustment voltage corresponding to a light-receiving voltage of the light-receiving unit is within a target adjustment range including a target adjustment value when an object to be detected is present between the light emitter and the light-receiving unit, The control unit sets the target adjustment range to a predetermined range that is equal to or greater than the light receiving adjustment change amount and includes the target adjustment value, based on the light receiving adjustment change amount, which is the change in the light receiving adjustment voltage when the amount of light emitted by the light emitting unit is changed by the smallest unit when an object to be detected is present between the light emitting unit and the light receiving unit.

2. A light emitting portion; a light receiving unit that receives light emitted by the light emitting unit; a light-receiving load resistor for converting a photocurrent corresponding to an amount of light received by the light-receiving section into a light-receiving voltage; a control unit that adjusts the amount of light emitted by the light emitting unit so that a light receiving adjustment voltage corresponding to a light receiving voltage converted by the light receiving load resistor is within a target adjustment range including a target adjustment value when an object to be detected is present between the light emitting unit and the light receiving unit, A detection device characterized in that the resistance value of the light-receiving load resistor is set to a value calculated so that when the amount of light emitted by the light-emitting unit is changed by the smallest unit when an object to be detected is present between the light-emitting unit and the light-receiving unit, the change in the light-receiving adjustment voltage is greater than or equal to a predetermined value within the width of the target adjustment range.

3. The control unit is The detection device described in claim 1 or 2, characterized in that the target adjustment value is set so that the threshold value of the light receiving voltage of the light receiving unit for determining whether or not there is an object to be detected between the light emitter and the light receiving unit is the median value of the ratio between the light receiving voltage of the light receiving unit when there is an object to be detected between the light emitter and the light receiving unit and the light receiving voltage of the light receiving unit when there is no object to be detected between the light emitter and the light receiving unit.

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