document: BACKGROUND OF THE INVENTION 
       1. Field of the Invention 
       The present invention relates to a sewing machine detector for detecting, for example, the position of a sewing needle and the speed of the sewing machine. The detector is integral with the drive and control elements of the sewing machine. 
       2. Description of the Background Art 
       FIG. 8 shows one conventional sewing machine drive system, as disclosed in Japanese Patent Disclosure Publication No. 38496 (1988), including a sewing machine 1, motor 2, belt 3 for the transmission of rotation, needle section 4, control circuit section 5 for the drive control of the motor 2, detector 6 and power indicating light 100. 
       FIG. 9 shows, in more detail, an optical fiber type needle position detector of the conventional apparatus disclosed in Japanese Patent Disclosure Publication No. 38496 (1988) which includes a detecting section 6a, an optical fiber cable 6b, a photoelectric translation processing module section 6c, and electrical connectors 6d, 7 for connecting the module section 6c and control circuit section 5. 
       FIGS. 10 and 11 show, in more detail, the detecting section 6a of the conventional needle position detector shown in FIGS. 9 and 10, including a sewing machine shaft 10, a shaft 11 of the detecting section 6a rotated in engagement with the sewing machine shaft 10, and needle UP position and needle DOWN position detecting reflective discs 12, 13 installed on the shaft 11 for reflecting light from a needle UP position detecting optical fiber 14 and a needle DOWN position detecting optical fiber 15, respectively. FIG. 11 shows a reflecting portion 13a of the reflective disc 13, an optical fiber supporter 16, a light sending optical fiber 15a provided in correspondence with the reflecting portion 13a of the needle DOWN position detecting reflective disc 13, and a light receiving optical fiber 15b provided in correspondence with the reflecting portion 13a of the needle DOWN position detecting reflective disc 13. Though not shown in FIG. 11 (See FIG. 12), a light sending optical fiber 14a and light receiving optical fiber 14b, in correspondence with the reflecting area of the needle UP position detecting reflective disc 12, are also provided and perform the same functions as described above with respect to the light sending optical fiber 15a and light receiving optical fiber 15b. 
       FIG. 12 shows a module section 6c of the needle position detector including light emitting devices 20, light receiving devices 21, a light sending optical fiber 14a for needle UP position detection, a light receiving optical fiber 14b for needle UP position detection, a light sending optical fiber 15a for needle DOWN position detection, a light receiving optical fiber 15b for needle DOWN position detection, an enclosure 22 of the module section 6c, a circuit board 23 with light emitting devices 20 mounted thereon, electronic components 24 for a signal processing circuit, a circuit board 25 on which electronic components 24 are mounted, and a connector 6d for electrical connection to a control circuit section 5. 
       The operation of the detector will be described next. First, prior to initiating operation, the positional relationships between the UP and DOWN positions of the sewing machine needle and detector reflective discs 12, 13 must be adjusted and fixed. During operation, power is supplied from the control circuit section 5 via the connectors 7, 6d, and light which has been photoelectrically-translated by the light emitting devices 20 in the module section 6c enters the light sending optical fiber 14a or 15a, reaches the light radiating portion of the detecting section 6a via the optical fiber cable 6b, is reflected by the reflecting portion 12a of the reflective disc 12 or the reflecting portion 13a of the reflective disc 13, is received by the light receiving optical fiber 14b or 15b, returns to the module section 6c  again, is photoelectrically-translated by the light receiving devices 21, is waveform-processed by the signal processing circuit 24, passes through the connectors 6d and 7 as an electrical signal, and is transmitted to the control circuit section 5 as a needle UP position or needle DOWN position signal for controlling the sewing machine. 
       In the conventional detector 6, the optical fibers 14, 15 act to both send and receive light to and from the detecting section 6a mounted in engagement with the sewing machine shaft 10 and including the reflective discs 12, 13 for indicating a sewing machine needle position, i.e., the optical fibers 14, 15 are employed solely for purposes of detection. The photoelectric translation processing module section 6c connected to the control circuit section 5 includes electronic parts, such as the light emitting and receiving devices 20, 21 and signal processing circuit 24, while the detecting section 6a and module section 6c are connected by optical fibers 14, 15 housed in an optical fiber cable 6b. With the conventional arrangement, as described above, the influence of static noise due to the friction of a fabric to be sewn as well as other noise is eliminated. Malfunction is thereby avoided and stable sewing machine operations can be performed. 
       In the conventional detector, as described above, light 13, sent through the light sending optical fibers 14a  or 15a, is reflected by the reflecting portion of the reflective discs 12 or 13 secured to the shaft 11 and is received through the light receiving optical fibers 14b or 15b. However, the reflective discs 12, 13 must withstand constant vibration during the operation of the sewing machine 1. Furthermore, if the bearings supporting the shaft 11 are worn, the shaft 11 vibrates to an even greater extent, causing the optical axes between the optical fibers 14, 15 and the reflecting portions of the reflective discs 12, 13 to change, resulting in an inability to receive predetermined signals. 
       Also, since the reflecting portions of the reflective discs 12, 13 are curved, they are difficult and expensive to machine. 
       Further, the rotary reflective discs 12, 13 employed as components for signal detection make the detecting section 6a relatively thick and non-compact. 
       Further, in the conventional detector, since the light sending optical fibers 14a, 15a and light receiving optical fibers 14b, 15b must be flexed, as shown in FIG. 11, in consideration of the curvatures of the reflective discs 12, 13, significant stress is imposed on the optical fibers 14, 15. 
       Due to the elasticity of the optical fibers 14, 15, and depending on the degree of curvature of the fibers, there may be a relatively large internal force directing the fibers 14, 15 to return to their original, straight line status, which internal force, as noted above, results in a significant stress in the fibers 14, 15 in the area where the fibers 14, 15 are inserted into the optical fiber supporter. Thus, in combination with the above-mentioned vibration, there is a significant possibility that the optical fiber supporter 16 may fracture. 
       Furthermore, when the curvature radius is large, the light transmitting percentage of the optical fibers 14, 15 decreases, and the efficiency deteriorates. Consequently, expensive optical fibers are necessary to prevent the above described problems. 
       The conventional apparatus as shown in FIG. 8 also includes a power indicating light 100 having a light emitting diode and lead wires run through cable 6b to turn on the light emitting diode. As noted above, the optical fibers are only employed for detection purposes. By way of contrast, power is supplied by the control circuit section 5 through regular lead wires run through cable 6b to the power indicating light 100. 
       Industrial sewing machines are often used in areas where high frequency welders are used, e.g., to seal raincoats, tents, etc. However, since high frequency welders generate high frequency electromagnetic waves of about 27 Mhz to 42 Mhz with outputs of several KW to several tens of KW, the lead wires in cable 6b for the power indicating light 100 can act as antennas thereby receiving the electromagnetic waves and generating an electromotive force. This electromotive force is highly undesirable as it affects the control device 5 and may cause the control device 5 to operate erroneously. 
       SUMMARY OF THE INVENTION 
       It is, therefore, an object of the present invention to overcome the above described disadvantages with respect to conventional apparatus by providing a low-price detector for a sewing machine which detector is durable despite the detrimental effects of vibration and which includes a thinner and more compact detecting section. 
       Another object of the present invention is to provide a detector for a sewing machine which minimizes stress imposed on the optical fibers by minimizing the curvature of the optical fibers. 
       Another object is to provide a power indicating light which does not electrically interfere with the operation of the detector and controller. 
      
      
       BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1 is a side view of a detector for a sewing machine according to a preferred embodiment of the present invention. 
       FIG. 2 is a sectional view taken along the plane A--A of FIG. 1. 
       FIG. 3 is a side view of an optical fiber supporter in the sewing machine detector according to the preferred embodiment of the present invention. 
       FIG. 4 is a front sectional view of a module section in the sewing machine detector according to the preferred embodiment of the present invention. 
       FIG. 5 is a side sectional view of the module section in the sewing machine detector according to the preferred embodiment of the present invention. 
       FIG. 6 is a side view of a first light shielding disc in the sewing machine detector according to the preferred embodiment of the present invention. 
       FIG. 7 is a side view of a second light shielding disc in the sewing machine detector according to the preferred embodiment of the present invention. 
       FIG. 8 is an overall view showing the arrangement of a conventional sewing machine. 
       FIG. 9 is a front view of the conventional sewing machine detector shown in FIG. 8. 
       FIG. 10 is a front sectional view of the detecting section of the conventional sewing machine detector shown in FIGS. 8-9. 
       FIG. 11 is a side sectional view of the same detecting section shown in FIG. 10. 
       FIG. 12 is a sectional view of a module section of the conventional sewing machine detector shown in FIGS. 8-9. 
      
      
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       A preferred embodiment of the present invention will now be described with reference to FIGS. 1-7. Flat, sheet-shaped first, second and third light shielding discs 26a, 26b and 26c, respectively, are mounted coaxially to a shaft 11 connected to a sewing machine shaft 10. 
       The first light shielding disc 26a detects the sewing machine speed and a needle UP position, its base material being formed from a light-transmitting synthetic resin. A speed detecting light shielding area 27, needle UP position detecting light shielding area 28, angle setting scale 29 and angle indication 30 are printed, for example, in black on the surface of the base material (FIG. 6), the shaft 11 being secured at a shaft-through hole formed in the center of the disc 26a. The angle indication is provided as one tenth of the actual angle, i.e. 340° is indicated as 34°. 
       The second light shielding disc 26b is designed to detect a needle DOWN position, and its base material is also made of light-transmitting synthetic resin. A needle DOWN position detecting light shielding area 31 and an indicator arrow 32 for indicating an angle are printed on the surface of the base material, in a color different from that on the first light shielding disc 26a (e.g. red). Also, the outer circumference of the second light shielding disc 26b is provided with projections 33 such that the second light shielding disc 26b may be easily rotated with respect to the first disc 26a, the second disc 26b being free to rotate relative to the shaft 11 via a shaft-through hole formed in the center of the disc 26b. 
       Though not shown, the base material of the third light shielding disc 26c is also made of light-transmitting synthetic resin as in the first and second light shielding discs 26a and 26b. A thread trimmer timing position detecting light shielding area 34 (FIG. 1) is provided on the surface of the base material and an indicator arrow for indicating an angle is also printed on the base material in a color different from that on the first and second light shielding discs 26a and 26b (e.g. blue). The outer circumference of the third light shielding disc 26c is provided with projections such that the disc 26c may be rotated with respect to discs 26a and 26b, the third disc 26c being free to rotate via a shaft-through hole formed in the center of the disc 26c through which the shaft 11 is inserted. When the second and third discs 26b and 26c are rotated to the proper settings, they are clamped in place by a clamp (not shown). 
       An optical fiber supporter 16, as shown in FIGS. 2 and 3, includes two optical fiber supporter pieces 16a and 16b of identical shape. The optical fiber supporter piece 16a is provided with linear optical fiber fixing holes 40a (FIG. 3) for locking the ends of the light sending optical fiber for UP position detection 14a, the light sending optical fiber for DOWN position detection 15a, the light sending optical fiber for sewing machine speed detection 35a, the light sending optical fiber for thread trimmer timing position detection 36a, and the power indicating optical fiber 37. Significantly, the fibers are not flexed when inserted in the fixing holes 40a. First reflecting portions 39a are provided opposite the end faces of the light sending optical fibers 14a, 15a, 35a and 36a, respectively. The first reflecting portions 39a are provided by plating or by attaching reflective plates having a reflecting portion. 
       The optical fiber supporter piece 16b is provided with linear optical fiber fixing holes 40b for locking the ends of the light receiving optical fiber for UP position detection 14b, the light receiving optical fiber for DOWN position detection 15b, the light receiving optical fiber for sewing machine speed detection 35b and the light receiving optical fiber for thread trimmer timing position detection 36b. Again, significantly, the fibers are not flexed when inserted in the fiber fixing holes 40b. Furthermore, second reflecting portions 39b are provided opposite to the end faces of the light receiving optical fibers 14b, 15b, 35b and 36b. The second reflecting portions 39b may be provided in an identical manner as described above with respect to the first reflecting portions 39a. 
       The optical fiber supporter 16 is fastened, as by a screw or the like, to the enclosure of the detecting section 6a such that the first reflecting portions 39a and second reflecting portions 39b are in opposition and such that the light shielding areas 27, 28, 31, 34 of the first to third light shielding discs 26a, 26b, 26c are disposed between the first and second reflecting portions 39a and 39b (see FIG. 2). Consequently, light transmitted from the light sending optical fibers 14a, 15a, 35a, 36a, and reflected by the first reflecting portions 39a, passes through the first to third light shielding discs 26a, 26b, 26c, is reflected by the second reflecting portions 39b, and enters the light receiving optical fibers 14b, 15b, 35b, 36b. 
       A power indicating window 38 is provided along a wall of the detecting section 6a so as to receive one end of the power indicating optical fiber 37. Also, a fixing block 41 is provided within the module section 6c for securing the light sending optical fibers 14a, 15a, 35a, 36a, 37 and the light receiving optical fibers 14b, 15b, 35b, 36b. A circuit board 23 (FIG. 5) is fixedly secured within the module section 6c to the light emitting devices 20 and the light receiving devices 21. 
       In the above described detector of the preferred embodiment, light is radiated from the light emitting devices 20 in the module section 6c (FIGS. 4, 5), passes through the light sending optical fibers 14a, 15a, 35a, 36a, 37 and is sent to the detecting section 6a. Light transmitted through the light sending optical fibers 14a, 15a, 35a, 36a is projected on the first reflecting portions 39a from the ends of the light sending optical fibers 14a, 15a, 35a, 36a and is reflected by the first reflecting portions 39a toward the first to third light shielding discs 26a, 26b, 26c. When the light shielding areas 27, 28, 31, 34 of the first to third light shielding discs 26a, 26b, 26c are in transmitting positions, light is transmitted through the first to third light shielding discs 26a, 26b, 26c and directed to the second reflecting portions 39b, then reflected by the second reflecting portions 39b to the light receiving optical fibers 14b, 15b, 35b, 36b. The light directed to the light receiving optical fibers 14b, 15b, 35b, 36b enters the light receiving devices 21 (FIG. 5), is photoelectrically-translated therein, and is output as an electrical signal (e.g., a low level signal) in a conventional manner. 
       By way of contrast, when the light shielding areas 27, 28, 31, 34 of the first to third light shielding discs 26a, 26b, 26c are in shielding positions, light is not transmitted through the first to third light shielding discs 26a, 26b, 26c, i.e., light does not reach the second reflecting portions 39b and is not directed to the light receiving optical fibers 14b, 15b, 35b, 36b. In this situation, the light (or its absence) is converted to an electrical signal (e.g., a high signal) by the light receiving devices 21. 
       Thus, a speed signal for detecting the speed of a sewing machine 1 can be detected by the speed detecting light shielding area 27; a sewing machine needle UP position by the needle UP position detecting light shielding area 28; a sewing machine needle DOWN position by the needle DOWN position detecting light shielding area 31; and a thread trimmer timing position by the thread trimmer timing position detecting light shielding area 34. 
       When the optical axes of the light sending optical fibers 14a, 15a, 35a, 36a and the light receiving optical fibers 14b, 15b, 35b, 36b are not precisely aligned, light does not reach the light receiving optical fibers 14b, 15b, 35b, 36b, even if the light shielding areas 27, 28, 31, 34 of the first to third light shielding discs 26a, 26b, 26c  are in the transmitting positions. Consequently, only high level electrical signals are provided. In the preferred embodiment, however, the light sending optical fibers 14a, 15a, 35a, 36a, first reflecting portions 39a, second reflecting portions 39b and light receiving optical fibers 14b, 15b, 35b, 36b are integrally secured and fixed in position by the optical fiber supporter 16, thereby providing accurate optical axes and a constant and stable operation. 
       Also, in the preferred embodiment, light is radiated from the light emitting device 20 in the module section 6c in FIG. 5, through an additional power indicating optical fiber 37, to the power indicating window 38 for power indication. Since the power indicating optical fiber runs from the module section 6c all the way to the detecting section 6a, there is no interference or &#34;noise&#34; problem, as is the case in the conventional detector assembly including a regular lead wire. 
       First to third light shielding discs 26a, 26b, 26c are disposed coaxially, as shown in FIG. 2, the first light shielding disc 26a being unrotatably secured to the shaft 11, and the second and third light shielding discs 26b, 26c being rotatably mounted to the shaft 11 when clamps (not shown) are loosened. The second and third light shielding discs 26b, 26c are unclamped from the shaft 11 only during angle adjustment. In addition, the second and third light shielding discs 26b, 26c have indicator arrows printed thereon for indicating an angle of rotation. The indicator arrows are printed in different colors so that the discs 26a, 26b and 26c may be differentiated. Further, the outer circumferences of the second and third light shielding discs 26b, 26c are provided with projections for manually rotating the second and third light shielding discs 26b, 26c relative to the shaft 11 and the first disc 26a. 
       As noted above, the indicator arrows of the second and third light shielding discs 26b, 26c are printed in different colors to facilitate the reading of an angle as determined with reference to the angle setting scale 29 of the first light shielding disc 26a. Thus, by reading the angle indication 30 (one-tenth of the actual angle) printed on the first disc 26a, the angles of the needle UP signal, needle DOWN signal and thread trimmer timing are easily determined. 
       It should be noted that the light-transmitting base materials of the first to third light shielding discs 26a, 26b, 26c may, alternatively, be non-light-transmitting and include drilled portions where light is to be transmitted. 
       It should be noted that signals other than the four signals detected, i.e. needle UP position signal, needle DOWN position signal, speed detection signal and thread trimmer position detection signal, may also be detected, and that at least two or more of the signals may be detected simultaneously. 
       It should also be noted that the reflecting portions 39a, 39b, provided in two places in the first embodiment, may, alternatively, be provided in one place if the positions and reflecting angles of the reflecting portions are such that the ends of the optical fibers are supported linearly so as to reduce stress in the optical fibers. 
       The present invention, unlike the conventional apparatus having rotary reflective discs, is capable of stably detecting sewing machine control signals despite shaft vibration due to the excessive wear. 
       Also, since there is no need for curved reflecting portions on the reflective discs, the present invention is less expensive to manufacture and results in a thinner, more compact detecting section. 
       It should also be noted that the present detector significantly reduces stress imposed on the optical fibers since the fibers are supported linearly. Also, stationary reflecting portions enable optional and additional optical axes to be generated. 
       Also, the present invention provides for the easy generation, during assembly, of accurate optical axes, which accuracy is maintained for long periods of time. 
       The present invention also includes an optical fiber power indicating cable which does not interfere or adversely affect sewing machine control circuitry. Furthermore, the power indicating cable can be run simultaneously with the optical fibers for detection, thereby simplifying the construction.
summary: A detector is provided for a sewing machine wherein light transmitting/shielding discs are mounted coaxially on a shaft of the sewing machine and sandwiched between light receiving and light transmitting optical fibers positioned along opposite side portions of the disc assembly and leading to a processing module section. The detector is able to detect a plurality of positional settings of the sewing machine as well as additional settings without imposing undue stress on the light transmitting optical fibers since the optical fibers remain linear. A power indicating light, connected to the processing module section via an optical fiber, ensures that there is minimal electrical interference with the operation of the detector.