JPH0379674B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a detector that is equipped with a light emitting element and a light receiving element, and detects a work cloth by introducing a work cloth between the two, and specifically relates to a detection method of the detector. The present invention relates to an adjustment device that adjusts sensitivity.

Prior Art Conventionally, a work cloth detector consisting of a light emitting element and a light receiving element detects the passing state of the work cloth based on whether or not the light receiving element receives light or the amount of light received. And if the thickness of the processed cloth changes,
Since the detection level also changed, the sensitivity had to be readjusted each time. In particular, when detecting based on the amount of received light, adjusting the sensitivity is extremely difficult and requires skill.

For example, in a sewing machine equipped with this type of detector, it is possible to detect the end of the fabric when it is desired to form a final seam along the side edge of the workpiece cloth (body) 1 shown in FIGS. 1A and B, or to detect the end of the fabric as shown in FIG. , B When the pocket cloth piece 2 is superimposed on the body part 1 and the same cloth piece 2 is sewn to the body part 1, the operator manually detects the cloth edge (step W2) of the pocket cloth piece 2 each time. I was adjusting the sensitivity. Especially when detecting the edge of the pocket cloth 2 when sewing the pocket cloth 2,
It is detected whether or not the overlapped portion W1 exists based on the amount of light transmitted between the overlapped portion W1 and the non-overlaid portion, that is, the amount of light received by the light receiving element.

Therefore, when detecting the work cloth with the above-mentioned detector, for example, if the body 1 becomes thicker than the initial setting, the amount of light transmitted will also change.
The detector would detect it as if it were the overlapped portion W1 with the pocket cloth 2, which could cause malfunction. Therefore, in the past, when the thickness of the body 1 and the pocket cloth piece 2 changed, the sensitivity of the light receiving side was adjusted one by one according to the thickness in order to avoid problems such as malfunctions as described above. However, adjusting the sensitivity requires skill and is extremely troublesome.

Purpose This invention was made to solve the above problems, and its purpose is to automatically adjust the detection sensitivity of the detector even if the amount of light transmitted varies depending on the thickness of the work cloth. To provide an automatic sensitivity adjustment device that can adjust the sensitivity to the optimum sensitivity and reduce the labor of adjustment work.

Embodiment An embodiment embodying the present invention will be described below with reference to the drawings.

In FIG. 3, the sewing machine frame 11 includes an arm portion 12 and a bed portion 13.
A needle 15 is attached to a needle bar 14 which is vertically movably mounted in the head of the needle 2. A lockstitch seam is formed on the workpiece cloth 1 by the cooperation of this needle 15 and a hook (not shown) provided in the bed portion 13. A light projector 16 constituting a detector is attached to the front surface of the head of the arm portion 12, and a case 18 containing a built-in light projecting element 17 made of a light emitting diode is fixed to the front surface of the head, as shown in FIG. It is screwed into the accommodating cylindrical portion 19a of the holder 19. A transparent protective plate 1 is attached to the lower end of the case 18.
8a is attached to prevent dust from adhering to the light projecting element 17.

A sliding plate 20 and a throat plate 21 are arranged on the bed portion 13, and a light receiver is inserted into a fitting hole 23 formed in the needle plate 21 at a predetermined distance from the needle hole 22 toward the feeding side. The upper part of 24 is fitted.
As shown in FIG. 4, the case 25 of the light receiver 24 has a base end secured to the bed part 13 with screws, and a transparent protection plate 25a is attached to the upper end. A light-receiving element 26 made of a phototransistor provided in the case 25 is arranged to face the light-emitting element 17, and directly receives the light from the light-emitting element 17. When the work cloth 1 is fed into the sewing position from the feed side and blocked by the work cloth 1, the light (transmitted light) from the light projecting element 17 that passes through the work cloth 1 is received.

Next, an electric circuit of the detector consisting of the light emitting element 17, the light receiving element 26, etc. will be explained.

In FIG. 6, a pulse signal SG2 is applied to the light projecting element 17 via a resistor R1 and an amplifier 31, which is a chopper signal SG1 (see FIG. 7) outputted from an oscillator 32, which is amplified and inverted by the same amplifier 31 and shaped. , the light is emitted based on the same signal SG2. The transistor Tr has its collector terminal connected to one end of the light emitting element 17, and the collector terminal of the transistor Tr.
A resistor R2 is connected between the emitter terminals. When the transistor Tr is in the on state, the current limiting resistor is only the resistor R1, and the light emitting element 17
As the current flowing through becomes large, the amount of light emitted from the light projecting element 17 becomes large. On the other hand, when the transistor Tr is in the off state, the current limiting resistance becomes the resistors R1 and R2,
The current flowing through the light projecting element 17 becomes small, and the amount of light emitted by the light projecting element 17 becomes small.

The light receiving element 26 outputs an output voltage V1 having a level proportional to the amount of light received from the light projecting element 17, and the output voltage V1 is outputted to the variable attenuator 34 via the bandpass filter 33. The variable attenuator 34 changes the output voltage V1 from OdB to -
It is designed to be attenuated in a range of 60 dB and output to a comparator 36 as an attenuated output voltage V2 via an amplifier 35, and this amount of attenuation is output from the central processing unit 43 via an input/output interface 46 to be described later. Variable control is performed in steps (in this embodiment, in steps of 2 dB) based on the signal SG3.

The comparator 36 detects this attenuated output voltage V2.
and a reference voltage setting device 37 as a reference voltage changing means.
The attenuated output voltage V is compared with the reference voltage Vs from
When the reference voltage Vs is larger than 2, the H level (positive potential) is reached, and in the opposite case, the L level (O
outputs a detection signal SG4 (potential). The reference voltage setter 37 can change the reference voltage Vs in the range of 3V to 5V in this embodiment, and changes the reference voltage Vs in stages based on a control signal SG5 output from the central processing unit 43 via an input/output interface 46, which will be described later. It is designed to be variably controlled (in steps of ±1 dB in this embodiment).

Detection signal output from the comparator 36
The first flip-flop circuit (hereinafter referred to as the first FF circuit) 38 inputting SG4 is inverted by the fall of the L level detection signal SG4, and the output of the Q terminal of the circuit 38 changes from the H level to the L level. Become. A second flip-flop circuit (hereinafter referred to as a second FF circuit) 39 is connected to the first FF circuit 3.
In response to the falling from the H level to the L level of 8, the output SG6 of the Q terminal is inverted from the H level to the L level. Further, both the first and second FF circuits 38 and 39 receive the chopper signal SG of the oscillator 32.
Each bit is reset at the falling edge of 1.

The EXOR circuit 40 includes the first and second FF circuits 38,
39 terminals are input, and when both terminals are at the same level, the output SG7 is at L level, and when both terminals are at different levels, the output is at H level.
Output level output SG7.

The sensitivity adjustment switch 41 is a switch for operating the detector, and an on signal from the switch 41 is outputted to the central processing unit 43 via the input/output interface 46. The lighting of the monitor light emitting diode 42 is controlled based on a control signal from the central processing unit 43. The sensitivity adjustment switch 41 and the light emitting diode 42 are provided at predetermined positions on the sewing machine frame 11, for example, at a position in front of the head of the arm portion 12 where they can be operated and viewed.

A central processing unit (hereinafter referred to as CPU) 43 has a read-only memory (hereinafter referred to as ROM) 44
and readable and rewritable memory (hereinafter referred to as
RAM) 45, and the variable attenuator 34
Control signal SG for changing the attenuation amount of
3 to the attenuator 34 via the input/output interface 46, and also sets a control signal SG5 for changing the reference voltage Vs of the reference voltage setter 37 in stages via the interface 26. output to the device 37. Further, the CPU 43 controls the transistor Tr on and off, and
The Q terminal output level of the second FF circuit 39 is detected to determine whether the attenuated output voltage V2 has become larger than the reference voltage Vs, and output to the variable attenuator 34 and the reference voltage setter 37 based on the determination result. The control amount of control signals SG3 and SG5 is determined.

Next, the operation of the detector configured as described above will be explained in the ninth section.
The operation of the CPU 43 shown in the figure will be explained according to a flow chart.

Now, as shown in Figure 2 A and B, pocket cloth piece 2
In order to adjust the sensitivity of the detector when stitching the work cloth 1 to the work cloth 1, first place only the work cloth 1 on the light receiving element 26, and then turn on the sensitivity adjustment switch 41. The processing operation of step 1 is performed to turn off the transistor Tr, and the processing operation of step 2 is performed to turn on the transistor Tr. Next, the CPU 43 performs the processing operation of step 3 to output a control signal SG5 to the reference voltage setter 37 in order to minimize the reference voltage VS output from the reference voltage setter 37 (3V), and attenuates the variable attenuator 34. Step 4: Outputting the control signal SG3 to the attenuator 34 to maximize the amount (-60dB)
Performs processing operations. Meanwhile, at the same time, the oscillator 3
2 outputs a chopper signal SG1.

Therefore, the light projecting element 17 starts blinking based on the oscillation operation of the oscillator 32. At this time,
Since the transistor Tr is in an on state, the only current limiting resistor is the resistor R1, so the light emitting element 17 is in a state where the amount of light emitted is large. On the other hand, the first and second FF circuits 3
8 and 39 are reset by the first fall of the chopper signal SG1 of the oscillator 32,
The output SG7 from the EXOR circuit 40 is at L level.

Based on this L level, the CPU 43 performs a processing operation in step 5 to determine whether both FF circuits 38 and 39 are not malfunctioning due to a single noise signal.
At this time, when the output SG7 of the EXOR circuit 40 is at the H level, it is determined that both FF circuits 38 and 39 are malfunctioning, and the output SG7 of the EXOR circuit 40 is at the L level. , 39 are reset.

Now, the light output from the light projecting element 17 passes through the work cloth 1 and is received by the light receiving element 26. The light receiving element 26 that received this transmitted light transmits an output voltage V1 proportional to the amount of transmitted light to the band pass filter 33.
The signal is output to the variable attenuator 34 via. The variable attenuator 34 attenuates this output voltage V1 (-60 dB) and outputs it to the comparator 36 via the amplifier 35 as an attenuated output voltage V2. At this time, the attenuated output voltage V2 is the maximum attenuated value, so initially the 8th
As shown in the figure, it is much smaller than the reference voltage Vs, and as a result, the detection signal SG4 of the comparator 36 becomes H level. Based on this H level detection signal SG4, the first and second FF circuits 38 and 39 are not inverted, and the output SG6 of the Q terminal of the second FF circuit 39 remains at the H level.

The CPU 43 performs the processing operation in step 6 based on this output. At this time, CPU43 outputs SG6
is at L level, the attenuated output voltage V
2 is smaller than the reference voltage Vs. Based on this determination result, the CPU 43 selects the variable attenuator 3.
The processing operation of step 7 is performed to determine whether the attenuation amount of step 4 is the minimum. At this time, based on the fact that the amount of attenuation is the maximum, the CPU 43 performs the processing operation of step 8 to output a control signal SG3 for reducing the amount of attenuation by one step. Therefore, at this point, the attenuation amount of the variable attenuator 34 is reduced by one step.

From this state, the next second chopper signal SG
When 1 is output, the first and second FF circuits 38,
39 is reset and the light projecting element 17 blinks again. This light emission causes the light receiving element 2 to
6 outputs an output voltage V1 at the same level as above to the variable attenuator 34 since the amount of transmitted light is the same as above. Since the amount of attenuation of the variable attenuator 34 is reduced by one step, the attenuated output voltage V2 outputted to the comparator 36 increases by the amount of attenuation reduced, as shown in FIG.

The comparator 36 compares and detects this attenuated output voltage V2 and the reference voltage Vs in the same manner as described above. At this time, as shown in FIG. 8, since the reference voltage Vs is still large, the first and second FF circuits 38 and 39 operate as before, and the CPU 43
performs the same processing operation as above and lowers the attenuation amount of the attenuator 34 by one step. Thereafter, the CPU 43 gradually decreases the amount of attenuation of the attenuator 34 until the attenuated output voltage V2 becomes larger than (exceeds) the reference voltage Vs, and gradually increases the level of the attenuated output voltage V2.

Furthermore, while repeating the above operation, when the attenuation amount of the variable attenuator 34 reaches the minimum, the CPU 43
Then, the processing operation of step 18 is performed in which the monitor light emitting diode 42 is blinked 10 times, and the operator is notified that detection is not possible. Then, the CPU 43 performs the processing operation of step 19 to turn off the light emitting diode 42, and ends the process.

Eventually, the light emitting element 17 performs the fifth blinking operation, and when the attenuated output voltage V2 output to the comparator 36 becomes larger than the reference voltage Vs as shown in FIG. 8, the detected value SG4 of the comparator 36 increases.
becomes L level and the first and second FF circuits 38,
39 is inverted, and the output SG6 of the Q output terminal of the second FF circuit 39 is set to L level. Based on this L level, the CPU 43 determines that the attenuated output voltage V2 has exceeded the reference voltage Vs, and proceeds to the processing operation of step 9.

The CPU 43 determines whether the current attenuation amount of the variable attenuator 34 is larger than a predetermined reference attenuation amount P. The reference attenuation amount P is used to determine whether the work cloth 1 as the object to be detected is thick or thin, that is, to determine whether the work cloth 1 has poor or good transparency.
When detecting the work cloth using the attenuation amount of the attenuator 34,
This is a value that serves as a guideline for detecting cloth in the optimal condition by reducing the amount of light emitted from the light emitting element 17 if it has good transparency, and increasing the amount of light emitted if it has poor transparency. At this point, the optimum amount of light from the light projecting element 17 is determined when the work cloth 1 and the pocket cloth piece 2 are sewn together.

In the case of a thin workpiece cloth 1 that is transparent, for example, the CPU 43 turns off the transistor Tr and performs the processing operation of step 10 to reduce the amount of light emitted from the light emitting element 17, and then performs the processing operation of step 10 to reduce the amount of light emitted from the light emitting element 17. Processing operations similar to those described above are performed again under the condition of quantity.

On the other hand, in the case of thick materials with poor transparency,
The CPU 43 performs a processing operation in step 11 of outputting a control signal SG5 to the reference voltage setter 37 in order to raise the level of the reference voltage Vs by one step as shown in FIG.

When the next chopper signal G1 is output in this state, the first and second FF circuits 38 and 39 are reset and the output SG7 of the EXOR circuit 40 becomes L level. Then, the CPU 43 performs the processing operation of step 12, which is the same as step 5. on the other hand,
At the same time, when the light emitting element 17 is blinked,
The attenuated output voltage V2 at the same level as the previous time is input to the comparator 36, and the attenuated output voltage V2 and the reference voltage Vs which is one step higher are input to the comparator 36.
are compared. At this time, as shown in FIG. 8, since the attenuated output voltage V2 is larger than the reference voltage Vs,
The detection signal SG4 of the comparator 36 becomes L level, the first and second FF circuits 38 and 39 are inverted, and the output SG6 of the Q terminal of the second FF circuit 39 becomes L level.
level. Based on this L level, the CPU 43 performs the processing operation of step 13 to determine that the attenuated output voltage V2 is larger than the reference voltage Vs.
Based on this judgment signal, the CPU 43 outputs the reference voltage Vs.
The processing operation of step 11 is performed again to raise the value by one step.

Therefore, at this point, the level of the reference voltage Vs is further increased by one step. Thereafter, the CPU 43 keeps the attenuation amount of the attenuator 34 constant and gradually increases the attenuation amount of the reference voltage setter 34 until the reference voltage Vs becomes larger than the attenuation output voltage V2. go.

Eventually, the light emitting element 17 performs the ninth blinking operation, and the reference voltage Vs input to the comparator 36
As shown in FIG. 8, when the attenuated output voltage V2 becomes larger, the comparator 36 becomes H level, the first and second FF circuits 38 and 39 are not inverted, and the Q output of the second FF circuit 39 Terminal output SG6
remains at H level. Based on this level, the CPU 43 determines that the reference voltage Vs has exceeded the attenuation output V2, and proceeds to the processing operation of step 14.
Based on this determination result, the CPU 43 determines whether the transistor Tr is on or off. If the transistor Tr is on, the CPU 43 performs processing operations (steps) for setting the optimum reference voltage value Vsa for thick materials.
15), and on the other hand, if it is off, a processing operation (step 16) for setting the optimum reference voltage value Vsu for thin objects is performed.

In this case, since the transistor Tr is in the on state as described above, the CPU 43 performs the processing operation in step 15 and lowers the reference voltage Vs slightly to the thick material margin value set in advance from the current reference voltage Vs to ensure detection of the thick material. Subtract K1 (a value to provide some margin for the process) to find the optimal reference voltage setting value for thick materials.
Calculate Vsa and store it in RAM45,
The attenuation amount of the variable attenuator 34 and the on/off state of the transistor Tr at that time are stored in the RAM 45.

In addition, when the transistor Tr is off in the processing operation of step 16, the CPU 43 calculates a preset thin material margin value from the current reference voltage Vs (in order to slightly lower the reference voltage Vs to ensure detection of thin material work cloth). The optimal reference voltage setting value Vsu for thin objects is calculated by subtracting K2 (a value to provide a margin), and is stored in the RAM 45. At the same time, the attenuation amount of the variable attenuator 34 and the on/off state of the transistor Tr at that time are stored in the RAM 45. will be memorized.

Thick material optimum reference voltage value Vsa mentioned above for RAM45
When the attenuation amount and the like of the variable attenuator 34 are stored,
After the CPU 43 carries out the processing operation in step 17 to turn on the monitor light emitting diode 42 and informs the operator that the sensitivity adjustment of the detector is completed,
A series of sensitivity adjustment operations for the work cloth 1 are completed.

When the adjustment work is completed and the operator guides the work cloth 1 and the pocket cloth piece 2 to the overlapping sewing position and starts sewing, the CPU 43 changes from the sensitivity adjustment mode to the work cloth detection mode. The CPU 43 reads out the optimal reference voltage value Vsa stored in the RAM 45 and data on the amount of attenuation of the attenuator 34 when the transistor Tr is turned on. Then, based on this data, the CPU 43 outputs a control signal SG5 for causing the reference voltage setter 37 to output the thick material optimum reference voltage setting value Vsa, turns on the transistor Tr, and turns on the attenuation amount of the attenuator 34. The control signal SG3 is outputted so that the above-mentioned attenuation amount is achieved.

When the detector detects the overlapped portion W1 shown in FIG. , the light emitting element 17 is larger than the sensitivity adjustment processing operation performed using only the work cloth 1.
The amount of light received will decrease. Therefore, since the attenuated output voltage V2 is much smaller than the optimum reference voltage setting value Vsa, the detection signal SG of the comparator 36
4 becomes H level, and based on this H level
The CPU 43 determines that the two overlapping portions W1 are now passing over the light receiving element 26.

When the sewing progresses and the edge of the pocket cloth piece 2 reaches the light-receiving element 26, that is, when the step W2 comes, the light from the light-emitting element 17 reaches the light-receiving element 26 through only the workpiece cloth 1. , the light receiving element 26 receives the same amount of light as in the sensitivity adjustment processing operation performed only with the work cloth 1. Therefore, since the attenuated output voltage V2 becomes larger than the optimum reference voltage setting value Vsa, the detection signal SG4 of the comparator 36 becomes L.
level, and based on this L level, CPU4
3 determines that the stepped portion W2 is now passing over the light receiving element 26.

In this way, in this embodiment, the optimal sensitivity of the detector is determined when the two pieces of work cloth 1 are overlapped and sewn together depending on the thickness and material of the work cloth 1 by simply placing the work cloth 1 on the light receiving element 26 in advance. In other words, the optimum amount of light to be projected according to the thickness of the work cloth 1 is determined, and the reference value for the amount of received light corresponding to the optimum amount of light to be projected is automatically set.

In addition, as shown in FIG. 1A and B, one piece of work cloth 1
When forming seams along the side edges of the processed fabric 1
directly onto the light emitting element 1 without placing it on the light receiving element 26.
Sensitivity adjustment processing is performed by irradiating the light receiving element 26 with the light No. 7. Then, a sensitivity processing operation similar to that described above is performed, and the optimal sensitivity of the detector when forming a seam along the side edge of the work cloth 1 is set.

Then, when the adjustment work in this case is completed and the operator guides the work cloth 1 to the sewing position and starts sewing, the CPU 43 changes from the sensitivity adjustment mode to the work cloth detection mode. The CPU 43 is the RAM 4
Optimal reference voltage value Vsa or Vsu stored in 5
Then, data on the amount of attenuation of the attenuator 34 when the transistor Tr is turned on and off is read out. Based on this data, the CPU 43 outputs the optimum reference voltage setting value Vsa from the reference voltage setter 37.
Or control signal SG5 for outputting Vsu
At the same time, it turns on or off the transistor Tr and outputs a control signal SG3 so that the attenuation amount of the attenuator 34 becomes the attenuation amount in this case.

When the detector is detecting the work cloth 1 shown in FIG. 1B, the light from the light emitting element 17 passes through the work cloth 1 and reaches the light receiving element 26. The amount of light received by the light projecting element 17 is smaller than when the sensitivity adjustment processing operation is performed by receiving light from the light source. Therefore, the attenuated output voltage V
2 is much smaller than the optimum reference voltage setting value Vsa or Vsu, the detection signal SG4 of the comparator 36 becomes H level, and based on this H level, the CPU 43 determines that the work cloth 1 is currently passing over the light receiving element 26. judge things.

As the sewing progresses and the end of the work cloth 1 reaches the light receiving element 26, the light from the light emitting element 17 reaches the light receiving element 26 directly. The light receiving element 26 receives the same amount of light as before. Therefore, the attenuated output voltage V2 is equal to the optimum reference voltage setting value Vsa or Vsu.
Since it becomes larger, the detection signal SG4 of the comparator 36 becomes L level, and based on this L level, the CPU 43 determines whether the end of the currently processed cloth is the light receiving element 2.
6. Judge that it has passed above 6.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above-described embodiment, after the attenuation amount of the attenuator 34 is reduced in the processing operation of step 8, the reference voltage setter 37 is reduced in the processing operation of step 11. Sensitivity was adjusted by lowering the reference voltage Vs output from the sensor, but as shown in Figure 10, the reference voltage Vs is always kept constant, and the processing operations in steps 5 to 8 lower the reference voltage. The attenuated output voltage V2, which has become larger than Vs, is then applied to the reference voltage Vs.
The optimum reference voltage setting value Vsa or Vsu and the attenuation amount may be set by increasing the attenuation amount of the variable attenuator 34 until it becomes smaller.
In this case, step 11 of the CPU 43 shown in FIG.
The processing operation is performed by the variable attenuator 3 as shown in FIG.
The processing operation of step 11 is to increase the attenuation amount of step 4 by one step.

Effects of the Invention As described in detail above, the present invention has a detection means that detects the amount of light transmitted through a work cloth, and a detection means that detects the thickness of the work cloth based on a detection signal from the detection means. an optimum light emitting amount determining means for determining an optimum amount of light emitted from the light emitting element to the work cloth based on a detection signal from the detecting means; A light projection amount adjusting means for adjusting the light amount, and a light reception amount reference value setting means for setting a light reception amount reference value of the light receiving element according to the optimum light projection amount to the work cloth based on the determination signal from the determination means. Therefore, even if the thickness of the work cloth changes, the optimum detection sensitivity according to the thickness, that is, the optimum light emission amount for the thickness is determined each time, and the light emission amount is adjusted to that value. It is possible to automatically set a light reception reference value corresponding to the amount of light, and it is possible to reduce the labor required for adjusting work for changes in cloth thickness.

[Brief explanation of drawings]

Figures 1A and B are a partially cutaway front view and a side sectional view of the work cloth, Figures 2A and B are a partially cutaway front view and side sectional view of the workpiece cloth and pocket cloth, and Figure 3 is a view of the sewing machine. 4 is a front view showing how the light emitting element and light receiving element are attached; FIG. 5 is a partial plan view of the sewing machine bed; FIG. 6 is an electric block circuit diagram of the detector; and FIG. 7 is a side view. 8 is a diagram showing the output waveforms of the chopper signal and pulse signal, FIG. 8 is a diagram showing the relationship between the attenuated output voltage and the reference voltage, FIG. 9 is a flowchart showing the processing operation of the CPU, and FIG. 10 is another example of the present invention. FIG. 11 is a flowchart showing the processing operation of the CPU. Processing cloth 1, pocket cloth piece 2, sewing machine frame 1
1, arm part 12, bed part 13, light emitting element 1
7, light receiving element 26, variable attenuator 34, comparator 36, reference voltage setter 37, sensitivity adjustment switch 41, central processing unit (CPU) 43.

Claims (1)

[Scope of Claims] 1. A detection means 26 which is composed of a light projecting element 17 and a light receiving element 26 and detects the amount of light transmitted through the work cloth 1 introduced between the two 17 and 26, and a detection signal from the detection means. Detection means 43 for detecting the thickness of the work cloth 1 based on the thickness of the work cloth 1; step 9), the optimum projection from the light emitting element 17 to the work cloth 1 is determined based on the detection signal from the detection means 43. Optimal light projection amount determining means (Tr, R1,
R2, 43; Step 2, Step 10); and a light emitting amount adjusting means (Tr, R1, R2, 43; Step 2, Step 10) that adjusts the amount of light emitted from the light emitting element 17 based on the determination signal from the determining means 43.
10), and a light receiving element 2 according to the optimum amount of light projected onto the work cloth 1 based on the determination signal from the determination means 43.
6. An automatic sensitivity adjustment device for a detector, comprising: a received light amount reference value setting means 43 for setting the received light amount reference value of step 6; step 15, step 16.