US3757232A - Tion device for stopping a rotating member at a predetermined angular posi - Google Patents

Abstract

A device for stopping a rotary element accurately in a predetermined position by detecting the specific rotational position of the rotary element by a detector and actuating a relay or the like in response to a signal from said detector.

Description

United States Patent 11 1 Matsuda 1 Sept. 4, 1973 DEVICE FOR STOPPING A ROTATING [56] References Cited MEMBER AT A PREDETERMINED UNITED STATES PATENTS ANGULAR POSITION 3,241,017 3/1966 Madsen et al. 307 247 x 7 Inventor; M8580 Matsuda, Hirakata, Japan 3,367,110 2/1968 Leeson 328/155 X 3,500,375 3/1970 Klimo 328/74 X [73] Assignee: Matsushita Electric Industrial Co-, 3,482,538 12/1969 Hayashi et al. 112/219 A Ltd., Osaka, Japan 3,367,296 2/1968 Harruff 112/219 A 3,497,770 2/1970 Nellis 324/179 [221 Flled: 1970 3,230,407 1/1966 Marsh 324 174 [2 N 2,680,241 6/1954 Gridley 324/70 Related Application Data Primary Examiner.lohn S. Heyman [62] Division of Ser. No. 829,281, June 2, 1969, Attorney-Stevens, Davis, Miller & Mosher abandoned.

[57] ABSTRACT [52] US. Cl 328/74, 307/247, 307/232, A d f l l 3O7/282 318/467 1l2/2l9 A 328/l55 evlce or stopping a rotary e ement accurate y in a [51] Im Cl (505d 3/00 predetermmed pos1t1on by detecting the speclfic rota- 58] Fie'ld A 219 R tional position of the rotary element by a detector and ll2/220, 67, 87, 219 A; 307/260, 282, 247, 232; 324/70, 124, 129; 328/74; 318/467 actuating a relay or the like in response to a signal from said detector.

2 Claims, 23 Drawing Figures Pmimm i 'wn SHEET '4 UP 6 FIG. /0

DEVICE FOR STOPPING A ROTATING MEMBER AT A PREDETERMINED ANGULAR POSITION CROSS REFERENCES TO RELATED APPLICATIONS This is a divisional application of Ser. No. 829,281, filed June 2, 1969 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotational position detecting device which does not involve any mechanical contact and, therefore, is durable and which is capable of selectively detecting any two points on or a plurality of angular positions of a rotary element in a positive and stable manner.

2. Description of the Prior Art With reference, for example, to a sewing machine of the type which is driven by a clutch motor, if it is desired to stop the main shaft of the sewing machine in a prescribed angular position so as to hold the needle stationary in a desired position, there must be provided a rotational position detecting device which is adapted to detect a specific rotational position of the main shaft (rotary element) of the sewing machine and to actuate a relay or the like by a signal initiated thereby, so that a brake may be applied to said main shaft to stop it in the prescribed position precisely.

As one form of the rotational position detecting device of the character described above, a device has been employed which comprises a cylinder connected with a rotary element coaxially to be rotated thereby and having an electrically conductive portion and nonconductive portion on the peripheral surface thereof, and a plurality of brushes, said brushes being held in contact with the peripheral surface of said cylinder during rotation of the latter, so that the electrical connection between said brushes is established or interrupted incident to the rotation of said cylinder, whereby the rotational position of the rotary element, connected with said cylinder, is detected.

However, such a device which comprises brushes is disadvantageous in that satisfactory electrical connection between the conductive portion on the cylinder and the brushes cannot be maintained due to wear of said brushes and hence the device is frequently placed in a faulty condition.

Another form of the rotational position detecting device, which has been used heretofore, comprises means for generating a sine wave voltage incident to rotation of a rotary element, so that the rotational position of the rotaty element may be detected by the value of said sine wave voltage. With such device, however, it is impossible to selectively detect any two points on or a plurality of angular positions of the rotary element.

SUMMARY OF THE INVENTION The present invention is an improvement in the conventional rotational position detecting devices described above, and has for its object the provision of a novel rotational position detecting device which involves no mechanical connection and, therefore, is durable, and which is capable of selectively detecting any two points on or a plurality of angular positions of rotaty element in a positive and stable manner.

Namely, according to the present invention there is provided a rotary position detecting device which is so designed that by a relative speed of a magnetic flux and two coils arranged with a certain rotational angle relative to each other, voltage pulses are generated in the respective coils synchronously with the rotational positions of said coils and a rectangular wave voltage, appearing or disappearing only between said voltage pulses, is generated, by which the rotational position of a rotary element is detected.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation of a sewing machine control system comprising the device of the present invention;

FIG. 2 is an electric circuit diagram of the sewing machine control system;

FIG. 3 is a sewing machine braking characteristic diagram of the control system;

FIG. 4 is a vertical sectional view of the essential of one form of the rotational position detecting device according to this invention;

FIG. 5 is a sectional view taken along the line V-V' of FIG. 4;

FIG. 6 is a sectional view taken along the line VI-VI' of FIG. 4;

FIG. 7 is a block diagram of a circuit for taking out an output signal of the rotational position detecting device shown in FIG. 4;

FIGS. 8(a), (b) and (c) are a set of a voltage waveform diagram showing the relationship between the input voltage wave form and the output voltage wave form of the circuit shown in FIG. 7;

FIG. 9 is a vertical sectional view of the essential portion of a motor and associated parts in the control system shown in FIG. 1;

FIG. 10 is a side elevation, partly shown in section, of the motor and the associated parts shown in FIG. 9;

FIG. 11 is a vertical sectional view of the essential portion of another form of the rotational position detecting device according to this invention;

FIG. 12 is a sectional view taken along the line XII- -XII of FIG. 11;

FIG. 13 is a sectional view taken along the line XIII- -XIII' of FIG. 11;

FIG. 14 is an electric circuit diagram of a sewing machine control system comprising the rotational position detecting device shown in FIG. 11;

FIG. 15 is a side elevation of still another form of the rotational position detecting device according to this invention;

FIG. 16 is a vertical sectional view of a stationary portion of the rotational position detecting device shown in FIG. 15;

FIG. 17 is a plan view of the stationary portion;

FIG. 18 is a plan view of a rotational portion of the device shown in FIG. 15;

FIGS. 19(a) and (b) are a front elevation and a side elevation respectively of a conventional rotational position detecting device; and

FIG. 20 is a voltage wave-form diagram showing detection points by another form of the conventional position detecting device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 19, there is shown one form of conventional rotational position detecting device which is designed to detect the rotational position of a rotary element by the contact between said rotary element and brushes. Namely, according to this form, as shown, a rotary cylinder 191 is connected coaxially with a rotary element, the rotational position of which is to be detected, for rotation about an axis -0. The rotary cylinder 191 has an electrically conductive portion 192 and non-conductive portions 193 formed on the peripheral surface thereof for contact with brushes 194, 195, 196 respectively. As may be seen, the brush 194 is electrically connected with the brush 195 and with the brush 196 alternately through the conductive portion 192, incident to a change in rotational position of the rotary cylinder 191. Therefore, the rotational position of the rotary element, connected with the rotary cylinder 191, can be detected by a change in electrical connection between the brush 194 and the. brushes 195, 196.

However, in this type of rotational position detecting device, the brushes 194, 195, 196 are susceptible to wear and in addition the device frequently becomes faulty due to unsatisfactory electrical connection between these brushes and the conductive portion 192 of the rotary cylinder 191.

According to another form of conventional rotational position detecting device, the rotational position of a rotary element is detected by generating a voltage V of a wave form as shown in FIG. 20, corresponding to the rotational position of the rotary element, and detecting the voltage at a specific point t t, or 2 on said wave form (usually the voltage at the point 2,, is used as the voltage wave form varies depending upon the rotational speed). With such device, however, it is impossible to selectively detect any two points on or a plurality of angular positions of the rotary element. Incidentally, the axis of abscissa of the diagram shown in FIG. 20 represents time t which corresponds to the rotational angular position of the rotary element.

The present invention contemplates the elimination of the above-described drawbacks of the conventional devices, and details of the invention will be described hereinafter with reference to an embodiment thereof.

Referring to FIG. 1, reference numeral 1 designates the main body of a sewing machine, 2 a main shaft of the sewing machine, 3 a pulley fixedly mounted on the main shaft 2 and 4 an angular position senser (or a rotational position detector) constituting the essential part of the present invention and connected to the main shaft 2. Reference symbol M, designates a main motor (clutch motor) for driving the sewing machine at a high speed and M designates an auxiliary motor for driving the sewing machine at a low speed. A needle bar 5 is operatively connected with the main shaft 2 to be moved up and down incident to the rotation of said main shaft. Another pulley 6 is mounted on the clutch shaft of the main motor M, and is operatively con nected with the aforesaid pulley 3 by means of a V-belt 7. A treadle 8 is providedfor pivotal movement about an axis I4 and one end of said treadle is connected to a lever 56 of the main motor M, by a connecting rod 10.

The structure of the angular position senser 4 is shown in detail inFIGS. 4 to 6 inclusive. Namely, the angular position senser comprises a pair of coils 11, 12 mounted on an end plate at an angle of a to each other and another pair of coils 13, 14 mounted on an angle adjusting plate 16 at an angle of a to each other, as best shown in FIG. 5. These coils 11, 12, 13, 14 have iron cores 11a, 12a, 13a, 14a disposed in the center thereof respectively. The angle adjusting plate 16 is slidably secured to the end plate 15 by means of a bolt 18 which extends through an arcuate slot 17 formed in said end plate. Thus, it will be seen that by displacing the angle adjusting plate 16 along the arcuate slot 17 upon loosening the bolt 18, the angle B between said pair of coils l1, l2 and said pair of coils 13, 14 can be changed. A bearing box 19 is fixed to the end plate 15 and a bearing 20 fitted in the bearing box 19 is clamped by said bearing box and the end plate 15. A rotary plate 21 carrying a magnet 22 mounted thereon is fixedly mounted on a boss 23 which is joumaled in the bearing 20 at one end and fixed to the main shaft 2 of the sewing machine at the other end by means of a bolt 24. Reference numeral 25 designates a washer, 26 a spring washer and 27 a cover. It will, therefore, be understood that the magnet 22, the rotary plate 21, the boss 23 and the bolt 24 rotate together with the main shaft 2 of the sewing machine, whilst the remaining parts are held stationarily. Now, when the main shaft 2 of the sewing machine is driven in the direction of arrow N, pulsative voltages e,, e as shown in FIGS. 8(a) and (b) appear in two coils, e.g. coils 11, 12, respectively with a time difference of (t t,). (This time difference corresponds to the angular position difference 0:.) These voltages e,, e are amplified by a wave-form shaping amplifying circuit A, and then fed to a bi-stable multivibrator circuit W as a gate pulse, as shown in FIG. 7, whereby a voltage V of rectangular wave form, as shown in FIG. 8(c) can be obtained from a power amplifier A Next, the structures of the main motor M, and the auxiliary motor M will be explained in detail with reference to FIGS. 9 and 10. I

The main motor M, is enclosed by a frame 28 and a cover 29, and comprises a stator core 30, a stator coil 31, a rotor 32 and a rotor shaft 33. The rotor shaft 33 is supported by the frame 28 and the cover 29 through bearings 34, 35. A fly-wheel 37 with a lining 36 attached thereto is fixedly mounted on one end of the rotor shaft 33 by means of a nut 38 and a key 39. A clutch bracket 40 is removably secured to the frame 28 by a fitting 41 and a bolt 42, and a sleeve 43 is fixed to said clutch bracket 40 by means of bolts 44. The sleeve 43 may be slided axially upon loosening the bolts 44. A worm wheel 45 is fixedly mounted on a metal bearing 46 which in turn is rotatably mounted on the sleeve 43. The worm wheel 45 is provided with a lining 47 and held against axial movement .by a stopper ring 48. A clutch shaft 49 is rotatably supported by a boss 50 through bearings 51, 52. A rotary disc 53 is fixedly mounted on one end of the clutch shaft 49, while a pulley 54 is fixedly mounted on the other end thereof by means of a nut 55. The boss 50 is axially slidable within the sleeve 43, so that the rotary disc 53 can be brought into engagement with either of the linings 36, 47. Furthermore, a lever 56 is pivotally mounted on the clutch bracket 40 by a pivot pin 57, with one end thereof connected to the boss 50 by a bolt 58. Namely, the bolt 58 extends through the lever 56 and further through a hole (not shown) formed in the clutch bracket 40 and a hole (not shown) formed in the sleeve 43, and is received in a groove (not shown) formed in the boss 50. Therefore, the boss 50 is slidably moved axially on revolution of the lever 56 about the pivot pin 57. A hook bolt 59 has one end secured to the lever 56 and the other end extending through a hole 40a in the clutch bracket '40, with a nut 60 threadably mounted on the end extremity thereof. Further, a coil spring 61 is mounted over the bolt 59 between the nut 60 and the clutch bracket 40. This spring 61 urges the lever 56 to revolve in a counterclockwise direction (in the direction of arrow P) about the pivot pin 57 and consequently the rotary disc 53 is urged to be brought into engagement with the lining 47. The other end of the lever 56 has a lever cover 62 pivotally connected therewith by means of a pin 63, which lever cover is urged to revolve in a clockwise direction (in the direction of arrow Q) by a spring 64. A microswitch 65 is mounted on the lever cover 62, while an operating plate 66 is fixed on the lever 56 for actuating said microswitch 65. The operating plate 66 is provided with a set screw 67 by which actuation of the microswitch 65 is adjusted. The microswitch 65 is opened or closed when the lever cover 62 makes a pivotal movement about the pin 63 under a force exerted thereon. On the other hand, another microswitch 68 is fitted to the clutch bracket 40 by means of a fitting 69, whereas a contacting member 70 to actuate the microswitch 68 is provided on the lever 56. The arrangement is such that when the lever 56 is pivoted in a direction opposite to the arrow P against the biasing force of the spring 61, the contacting member 70 is displaced in a direction to move away from the microswitch 68, whereby the contact of said microswitch is shifted.

The auxiliary motor M is enclosed by a frame 71 and a cover 72, and comprises a stator core 73 having a stator coil 74, a rotor 75 and a rotor shaft 76. The rotor shaft 76 is supported by the frame 71 and the cover 72 through bearings 77, 78. A worm gear 79 is tighly mounted on one end of the rotor shaft 76 by means of a sleeve 80 and a nut 81, and is held against rotation by a key 82 which is fitted in between the rotor shaft 76 and said worm gear 79. On the other end of the rotor shaft 76 is mounted a brake disc 83 which is held against rotation by keys 84, 85 but is slidable axially on said rotor shaft 76. The brake disc 83 is urged upwardly by a spring 86. An iron core 87 provided with an electromagnetic brakecoil 88 and a lining 89 is secured to the cover 72 by means of a screw 90. Reference numeral 91 designates an end plate fitted to the cover 72 and 92 designates a bolt supported by the end plate 91 with the inner end thereof screw-threaded into the iron core 87.

The space interval between the lining 89 and the brake disc 83 can be adjusted by moving the iron core 87 in a vertical direction by turning the bolt 92 after loosening the screw 90. The auxiliary motor M is mounted on the clutch bracket 40 of the main motor M I by a bolt 93, with the worm gear 79 in meshing engagement with the worm wheel 45. Thus, it will be seen that the rotation of the auxiliary motor M, can be transmitted to the rotary disc 53 and the pulley 54 through the worm gear 79 and the worm wheel 45.

Referring now to FIG. 2, there is shown anelectric circuit of the sewing machine control system shown in FIG. I.

The circuit comprises a powersourceswitch 94, a coil 1., of an electromagnetic relay having contacts S S S S,, S,, 5,, S and S a coil L, of an electromagnetic relay having contacts S S S S S S S and S a change-over switch 95 having contacts 8,, and S a microswitch 65 having contacts S and S a microswitch 68 having contacts S and S resistors r r,, r,,

r r r r r r r r r r r r and r diodes D D D D D D D-,, D D and D condensers C and C transistors T,, T T T, and T of which the transistors T and T form a bi-stable multivibrator circuit, a thyristor SCR and a transformer H. Terminals B and B are connected with each other. The condenser c and the resistor r are connected in series to constitute a charged circuit which is connected across the transistor T by the medium of a relay contact S and across which a switch contact S is connected. The transistor T acts as a switching element.

The rotational position detecting device of the invention, constructed as described above, operates in the following manner: Namely, when the power source switch 94 is switched on, the main motor M is placed -in operation and the fly-wheel 37 is rotated at a high speed. Then, the treadle 8 is stepped to pull the lever cover 62 in the direction of arrow F whereupon the lever 56 is pivoted about the pivot pin 57 in a direction opposite to the direction of arrow P, so that the boss 50 is moved to the right bringing the rotary disc 53 into engagement with the lining 36 on the fly-wheel 37. There fore, the rotation of the fly-wheel 37 is transmitted to the main shaft 2 of the sewing machine through the clutch shaft 49, the pulley 54 and the V-belt 7, and thus the main shaft 2 is driven at a high speed of n. By the pivotal movement of the lever 56, the contacting member is also displaced, allowing the contact S of the microswitch 68 to be closed, so that the coil L of the electromagnetic relay is energized. As a result, the contact S is opened and the contacts 8 S and S, are closed to place the auxiliary motor M in operation, whereby the worm-wheel 45 is rotated at a low speed. Upon rotation of the main shaft 2, the pulse voltages as shown in FIGS. 8(a) and (b) are developed in the coils ll, 13 and 12, 14. However, since the contacts S S are closed, the pulse voltage developed in the coils 11, 12 is impressed on the bi-stable circuit, composed of the transistors T and T through the closed contacts S S to energize the same and the base current of the transistor T is interrupted only for a t t (corresponding to the anglea). In this case, the contact S of the microswitch 65 and the contact S of the change-over switch 95 are open, so that the coil L is not energized and the contacts S S are maintained in an open position. Then, the treadle 8 is returned to the original position, whereupon the lever 56 is pivoted in the direction of arrow P under the biasing force of the spring 61 and returns to its original position, with the result that the rotary disc 53 is engaged with the lining 47 rotating at a low speed. Therefore, the rotating speed of the rotary disc 53 is rapidly reduced and the rotating speed of the main shaft 2 is reduced accordingly. Finally, the main shaft 2 comes to be driven by the auxiliary motor M at a low rotational speed of n as shown in FIG. 3. On the other hand, the contact S of the microswitch 68 is opened and the contact S,, is closed incident to the return movement of the lever 56. Therefore, the current supplied to the coil L, of the electromagnetic relay is controlled by the state of the transistor T When the rotating speed of the main shaft 2 is higher than n, the duration of deenergization of the transistor T (that is, the duration of interruption of the base current of the transistor T represented by the time t, t,)

is short, so that the contacts S S and S, are maintained closed by the charging current for the condenser C, (passing through the coil L,) and the contact S, is maintained in an open position. As the rotating speed of the main shaft 2 approaches the value of n', the deenergization time of the transistor T or the time t, t, becomes longer and the charging current for the condenser C, is no longer able to sufficiently energize the electromagnetic relay coil L,, so that the contacts S,,, S, and S,, are opened and the contact S, is closed. Consequently, the current supply to the auxiliary motor M is interrupted and the electromagnetic brake coil 88 is energized. The brake disc 83 is attracted by the coil to be in engagement with the lining 89 and thus the auxiliary motor M stops rotating. Therefore, the worm wheel 45 stops rotating and the rotary disc 53, the clutch shaft 49 and the pulley 54 also stop rotating, whereby the main shaft 2 of the sewing machine is stopped at a prescribed angular position. In this case, the needle bar 5 which is reciprocated vertically incident to the rotation of the main shaft 2 is held stationarily in its lowest position (with the needle stabbing into a cloth). At the same time, the transistor T is energized, upon closure of the contact S,,, by a current flowing through a circuit of "the coil L, the resistor R, the base of the transistor T and thereby the transistor T, is deenergized. The current is supplied to the base of the transistor T through the resistors r and r,,, but will not be supplied again to the coil L, as the contact S,,, is opened.

Then, the treadle 8 is stepped to pivot it in an opposite direction, whereupon the lever cover 62 is pivoted in a direction opposite to the direction of arrow about the pivot pin 63 against the biasing force of the spring 64, under a force imposed thereon in the direction of arrow F so that the button of the microswitch 65 is disengaged from the set screw 67 and thus the contact S,,, is closed. Therefore, a current flows through a circuit of the electromagnetic coil L, the contact S,, the contact S,,, the contact S,, the resistor r the gate of the thyristor SCR the diode D the transistor T (this transistor T is in the energized state as .the current is supplied to the base thereof), to energize said thyristor SCR. Consequently, a circuit of the coil L, the diode D, the thyristor SCR the diode D the transistor T and a circuit of the electromagnetic relay coil L the diode D the thyristor SCR the diode D the transistor T are energized, with the result that the contacts S,,, S,,

S,,, S,,, S,, and S,, are closed and the contacts S,, S,,, S

and S,,, are opened. In this case, the thyristor SCR becomes deenergized at the point when the contact S,,, is closed, with the anode and cathode thereof shorted. However, the coil L is maintained energized as the contact S,, is closed.

Upon opening of the contact S,, the electromagnetic brake coil 88 is deenergized to place the auxiliary motor M, in motion and the main shaft 2 of the sewing machine is driven at a low speed in the same way as described before. However, since the contacts S-, and 8, are open and the contacts S,, and S,, are closed, the transistor T, is energized by a pulse voltage e, generated when the flux of the magnet 22 moves the across the coil 13, and consequently the base current of the transistor T, is interrupted. As a result, the coil L, is deenergized, and the contacts S,,, S, and S,, are opened and the contacts S, and S,, are closed. Therefore, the current supply to the auxiliary motor M is interrupted and the electromagnetic brake coil 88 is energized to apply a brake force to the auxiliary motor M Thus, the main shaft 2 of the sewing machine is stopped in a prescribed angular position. In this case, the needle bar 5 is immovably located in its lifted position (with the needle lifted). The coil 14 is not needed in this case. The lifted position of the needle bar 5 may be adjusted by the position of the angle adjusting plate 16. The thyristor SCR Will not be energized again because the contact S,, is open at the point when the contact S,, is closed.

When the contact S,,, is closed by operating the change-over switch 95, the electromagnetic relay coil L is energized through the diode D and the contact S,,, or through the contacts S,, and S and the coil L, is energized through the diode D, and the contact S,,,so that the contacts S,,, S and S,, are closed and the contact S, is opened and the main shaft 2 is driven at a low speed from the auxiliary motor M The main shaft 2 continues rotating at the low speed as long as the contact S,,, of the change-over switch is held closed. Now, when the contact S,,, of the change-over switch 95 is opened, the transistor T is deenergized, in the same manner as described above, by the pulse voltage e, generated when the coil 13 moves across the flux of the magnet 22 and the needle bar 5 of the sewing machine is held immovably in its lifted position. In this case, the coil L is energized through the contacts S,, and S As'may be apparent from the embodiment described above, the rotational position detecting device according to the present invention is entirely free of troubles resulting from unsatisfactory contact, which becomes a cause of malfunction, since the structure of the rotational angular position sensing portion involves no mechanical contact. Therefore, the device is highly durableand serviceablealmost semi-permanently and enables the rotational position of a rotary element to be detected in a positive and stable manner.

Another embodiment of a;the rotational position detecting device according to the present invention will be describedwith reference to FIGS. 11 to 14 inclusive, which is adapted for use in a sewing machine of the type which is driven by a clutch motor and provided with thread cutting means.

According to this embodiment, as shown in FIGS. 11 to 13, a pair of coils ll, 12 are mounted on an end plate 15 at an angle of a to each other and another pair of coils 13, 14 are mounted on angle adjusting plates l6, 16 respectively. The coils ll, 12, 13 and 14 have iron cores 11a, 12a, 13a and 14adisposed in the center thereof respectively. The angle adjusting plates 16, 16' are respectively secured to the end plate 15 by means of bolts 18, 18' extending through an elongate arcuate slot 17 formed in said end plate, in such a manner that the positions of said respective plates l6, 16' may be adjusted by a sliding movement of said bolts in said slot. Therefore, by displacing the angle adjusting plate 16 along the slot 17 upon loosening the bolt 18, the angle B between the coils 11 and 14 can be changed. Likewise, by displacing the angle adjusting plate 16 along the slot 17 upon loosening the bolt 18', the angle 7 between the pair of coils l3 and 14, and the angle 8 between the coils l2 and 13 can be changed. A bearing box 19 is fixed to the end plate 15 and a bearing 20 fitted in the bearing box 19 is clamped by said bearing box and the end plate 15. A rotary plate 21 carrying a magnet 22 mounted thereon is fixedly mounted on a boss 23 which is journaled in the bearing 20 at one end and fixed to the main shaft 2 of the sewing machine at the other end by means of a bolt 24. Reference numeral 25 designates a washer, 26 a spring washer anf 27 a cover. It will, therefore, be understood that the magnet 22, the rotaty plate 21, the boss 23 and the bolt 24 rotate together with the main shaft 2 of the sewing machine, whilst the remaining parts are held stationarily. Now, when the main shaft 2 of the sewing machine is driven in the direction of arrow N, pulsative voltages e,, e as shown in FIGS. 8(a) and (b) appear in two coils, e.g. coils 1 1, 12, respectively with a time difference of l, t,. (This time difference corresponds to the angular position difference a.) These voltages e,, e, are amplitied by a wave-fonn shaping amplifying circuit A, and then fed to a bistable multivibrator circuit W as a gate pulse, as shown in FIG. 7, whereby a voltage V of rectangular wave form, as shown in FIG. 8(a) can be obtained from a power amplifier A The detailed structures of a main motor M, and an auxiliary motor M, are the same as those shown in FIGS. 9 and respectively.

The electric circuit of the sewing machine control system using the above-described rotational position detecting device is shown in FIG. 14. Namely, the circuit comprises a power source switch 94, a coil L, of an electromagnetic relay having contacts 8,, S S S S S 5,, and S,,,, a coil L of an electromagnetic relay having contacts 8,, S 8,, S,,,, S,,, 8, 8, and S a relay L, of an electromagnetic coil for cutting a sewing thread, a microswitch 65 having contacts 8,, and S a microswitch 68 having contacts 8,, and S resistors r,,

'22 a '4 5: 8 '1 s 's '10 '11 '12 '13 '14 '15 m '11: 1s: '10 '20 21 '22 and '23 diodes 1 2 3 41 5 6, D,, D D,,, D,,,, D,, and D condensers C,, C, and C transistors T,, T T,,, T,, T T,,, T, and T of which the transistors T and T form a bistable multivibrator circuit, thyristors SCR, and SCR,, and a transformer H. The terminals 8,, B, and B B are respectively connected with each other.

The rotational position detecting device according to this embodiment operates in the following manner: Namely, when the power source switch 94 is switched on, the main motor M, is placed in operation and-the fly-wheel 37 is rotated at a high speed. Then, the treadle 8 is stepped to pull the lever cover 62 in the direction of arrow F,, whereupon the lever 56 is pivoted about the pivot pin 57 in a direction opposite to the direction of arrow P, so that the boss 50 is moved to the right, bringing the rotary disc 53 into engagement with the lining 36 on the fly-wheel 37. Therefore, the rotation of the fly-wheel 37 is transmitted to the main shaft 2 of the sewing machine through the clutch shaft 49, the pulley 54 and the V-belt 7, and thus the main shaft 2 is driven at a high speed of n. By the pivotal movement of the lever 56, the contacting member 70 is also displaced, allowing the contact 8,, of the microswitch 68 to be closed, so that the coil L, of the electromagnetic relay is energized. As a result, the contact S, is opened and the contacts S,,,, S and S, are closed to place the auxiliary motor M, in operation, whereby the worm wheel 45 is rotated at a low speed. Upon rotation of the main shaft 2, the pulse voltages as shown in FIGS. 8(a and (b) are developed in the coils ll, 13 and l2, 14. However, since the contacts 8,, S are closed, the pulse voltage developed in the coils ll, 12 is impressed on the bi-stable multivibrator circuit, composed of the transistors T, and T through the contacts 8,, 8, to energize the same and the base current of the transistor T, is interrupted only for a time t, (corresponding to the angle a). In this case, the contact 8 of the microswitch 65 is open, so that the coil L, is not energized and the contacts S 8,, are maintained in an open position. Then, the treadle 8 is returned to the original position, whereupon the lever 56 is pivoted in the direction of arrow P under the biasing force of the spring 61 and returns to its original position, with the result that the rotary disc 53 is engaged with the lining 47 rotating at a low speed. Therefore, the rotating speed of the rotary disc 53 is rapidly reduced and the rotating speed of the main shaft 2 is reduced accordingly. Finally, the main shaft 2 comes to be driven by the auxiliary motor M at a low rotational speed of n as shown in FIG. 3. On the other hand, the contact 8,, of the microswitch 68 is opened and the contact 8,, is closed incident to the return movement of the lever 56. Therefore, current supplied to the coil L, of the electromagnetic relay is controlled by the state of the transistor T,. approaches When the rotating speed of the main shaft 2 is higher than n, the duration of deenergization of the transistor T, (that is, the duration of interruption of the base current of the transistor T,, represented by the time t, t,) is short, so that the contacts S S, and S, are maintained closed by the charging current of the condenser C, (passing through the coil L and the contact S, is maintained in an open position. As the rotating speed of the main shaft 2 a rpaches the value of n, the deenergization time of the transistor T, or the time t, t becomes longer and the charging current of the condenser C, is no longer able to sufficiently energize the electromagnetic relay coil L,, so that the contacts S S, and S, are opened and the contact S, is closed. Consequently, the current supply to the auxiliary motor M, is interrupted and the electromagnetic brake coil 88 is energized. The brake disc 83 is attracted by the coil to be in engagement with the lining 89 and thus the auxiliary motor M stops rotating. Therefore, the worm wheel 45 stops rotating and the rotary disc 53, the clutch shaft 49 and the pulley 54 also stop rotating, whereby the main shaft 2 of the sewing machine is stopped at a prescribed angular position. In this case, the needle bar 5 which is reciprocated vertically incident to the rotation of the main shaft 2 is held stationarily in its lowest position (with the needle stabbing into a cloth). At the same time, the transistor T, is energized, upon closure of the contact S,,, by a current flowing through a circuit of the coil L, the resistor r the base of the transistor T and thereby the transistor T, is deenergized. The current is supplied to the base of the transistor T, through the resistors r,, and r,,, but will not be supplied again to the coil L, as the contact 8,, is opened.

Then, the treadle 8 is stepped tp pivot it in an opposite direction, whereupon the lever cover 62 is pivoted in a direction opposite to the direction of arrow Q about the pivot pin 63 against the biasing force of the spring 64, under a force imposed thereon in the direction of arrow F so that the button of the microswitch 65 is disengaged from the set screw 67 and thus the contact S is closed. Therefore, a current flows through a circuit of the electromagnetic coil L, the contact 8,, the contact 8 the contact S, the resistor r the gate of the thyristor SCR the diode D the transistor T, (this transistor T, is in the energized state as the current is supplied to the base thereof), to energize said thyristor SCR,. Consequently, a circuit of the coil L, the diode D the thyristor SCR the diode D 8 the transistor T and a circuit of the electromagnetic relay coil L the diode D the thyristor SCR the diode D the transistor T are energized, with the result that the contacts S 8,, S S S S and S are closed and the contacts 8,, S S, and S are opened. In this case, the thyristor SCR, becomes deenergized at the point when the contact S is closed, with the anode and cathode thereof shorted. However, the coil L is maintained energized as the contact S is closed. Upon opening of the contact 8,, the electromagnetic brake coil 88 is deenergized to place the auxiliary motor M in motion and the main shaft 2 of the sewing machine is driven at a low speed in the same way as described before.

l-Iere, the pulse voltage generated in the coil 13 by the movement of the magnet 22 across the coil 13, is amplified by the transistors T T and part of the amplified pulse voltage is supplied to the base of the transistor T and the other part to the base of the transistor T through the resistor r In this case, it is to be noted that since the transistor T has previously been energized with a current supplied to the base thereof through the resistors r r as described before, the bistable multivibrator circuit is not inverted even when the pulse voltage is newly impressed thereon. The pulse voltage generated in the coil 13 is amplified and strikes the thyristor SCR The electromagnetic relay coil L is energized, for the contacts S S: are closed. When the magnet 22 moves across the coil 14 incident to further rotation of the main shaft 2 of the sewing machine, the pulse voltage e is generated in said coil, so that the transistor T is energized and the base current of the transistor T is interrupted. As a result, the coil L is deenergized, and the contacts S 8, and 8,, are opened and the contacts S, and S closed. Therefore, the current supply to the auxiliary motor M is interrupted and the electromagnetic brake coil 88 is energized to apply a brake force to the auxiliary motor M Thus, the main shaft 2 of the sewing machine is stopped in a prescribed angular position. In this case, the needle bar 5 is immovably located in its lifted position (with the needle lifted), and the contact S is opened to interrupt the current supply to the coil L The lifted position of the needle bar 5 may be adjusted by the position of the angle adjusting plate 16. It will, therefore, be understood that'the electromagnetic relay coil L is energized, during shifting of the needle bar 5 from its lowered position to the lifted position, at a point when the magnet 22 has moved an angle of 6 past the coil 12, and is maintained energized until the magnet has advanced further through an angle of y. The coil L is deenergized when the magnet 22 moves across the coil 14.

In a sewing machine with thread cutting means, these angles 8 and y are important for cutting the upper thread and the lower thread simultaneously, and by employing the rotational position detecting device of this invention these angles can be selected freely.

around an iron core 153, a stationary magnet I54 mounted on the plate 151, a rotary disc 158 made of a non-magnetic material carrying an iron plate 159 having high permeability. Of all four coils, the coils 152 and 155 are in pair and the coils 156 and 157 are in another pair. A two point control is possible by shifting the coils 152 and 155, or the coils 156 and 157 from each other.

The operation of the rotational position detectingdevice having a construction as described above will be explained. When the rotary disc 158 is rotated in the direction of arrow N, pulsative voltages e and e: are generated in'two coils, e.g. coils 152 and 155, as shown in FIGS. 8(a) and (b), with a time difference of t t (This time difference corresponds to the angular position difference a between the two coils.) These voltage pulses e, and e are amplified by the wave-form shaping amplifying circuit A, and fed to the bi-stable multivibrator circuit W as gate pulse, as shown in FIG. 7, whereby a voltage V of rectangular wave form as shown in FIG. 8(c) is obtained fromthe power amplifier A Although in the preceding embodiment, the rotational position detecting device comprises two pairs of coils 152, 155 and 156, 157 for selectively detecting the positions of two points on a rotary element, a .de-

A further embodiment of the rotational position device adapted for detecting the positions of three or more points may be obtained based upon the same principle.

In stopping a rotary element rotating at high speeds, the stopping position of the rotary element cannot be controlled precisely if the rotational position of the rotary element is detected during rotation of said rotary element at a high speed, to apply av braking force thereto. In this view, a device used for this purpose must be simultaneously. capable of detecting the rotating speed of the rotary element. According to the present invention, one of the rotational position detecting devices described and illustrated herein is combined with a brake actuating relay, so that said relay is not deactivated during high speed rotation of an associated rotary element but is deactivated when a preset rotational position of the rotary element has been detected by said detecting device during low speed rotation of said rotary element, to actuate a brake associated with said relay. Therefore, it is possible to stop the rotary element precisely in a prescribed position by making use of the operation delay of the. relay. Furthermore, ac-

cording to the invention a plurality of stopping posi tions can be obtained by providing a plurality of pairs of coils and shifting the coils in each pair from each other. Another advantage of the present invention is that the device according to the invention can be used semipermanently as none of its component parts are in contact with a rotary element.

What is claimed is:

1. Apparatus for stopping a rotating member at a predetermined angular position, comprising: a rotating member;

high speed driving means for driving said rotating member at a highspeed;

low speed driving means for driving said rotating member at a low speed lower than said high speed; drive selector means for selecting between said high speed and low speed driving means;

brake means for acting on said low speed drive means;

rotational position detecting means, including magnetic means rotating with said rotating member and a pair of coils in which pulse voltages are induced by said rotating magnetic means, said pair of coils being spaced apart a predetermined rotational angular distance from each other;

a bi-stable multivibrator, the inputs of which are connected to the outputs of said pair of coils;

first switching means connected to the output of said bi-stable multivibrator, said switching means being operated by the output of said bi-stable multivibrator;

a charged circuit including a resistor and capacitor connected in series, said charged circuit being connected in parallel with said first switching means through a normally open relay contact;

an electromagnetic relay having a plurality of contacts including said normally open contact and a magnetic coil connected in series with said charged circuit; at least one of said relay contacts being connected in the power circuit of said low speed driving means;

another of said relay contacts being connected to said brake means to control the operation thereof; and

second switching means connected across said charged circuit and being connected to and operated by said drive selector means.

2. The apparatus as defined in claim 1, additionally comprising at least one further pair of coils spaced apart a predetermined rotational angular distance from each other, said further pair of coils being spaced apart from the first pair of coils by a predetermined rotational angle; and further switching means for connecting the inputs of said multivibrator to one selected pair of said pairs of coils.

I IIR =0 w mum) Elf/ YES xiwn-zr'r OFF! :1;

Patent No.

Invcntorh) MaSaO MATSUDA It is cm'tificd that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown bcloa-l;

Please insert the following priority infprmaizion Japan, Patent Appln." No, 38932/68 filed June 4, 1968; Japan Patent Appln. No. 37748/69 .filed May 12, 1969;' Japan, Patent Appln. No. 3774 9/69- filed May 12 196,9.

. i Iv I Signed and sealed fihis 23rd day of April 1 97M.

(SEAL)- Attet: V

G. MARSHALL DAN'N polnmiesi'onen of Patents EDWARD MELMQHER RL Attesting Officer c nirilrlczrm o1? commc'rmq 'qtcnt Ho. 2 Dated September 973 I Invcntofls) Masao MATSUDA ft is certified that error appears in the ab0vc-idcntiicd patent; 1nd that said Letters Patent are hereby corrected as shown below;

Please insert the following priority infprmaizion Japap, Patent Appln; No. 38"932/68 filed June 4-, 1968; Japan,, Patent Appln. No. 37748/69 .filed May 12, 1969; Japan, Patent Appln. No. 37749/69- filed May 12, 1969.

I- I i r .v Signed and sealed this 23rd day of April 197M I I '(SEAL)' Attest: y I

EDWARD PLJ EETSHERJRL .G. MARSHALL DAN'N Atte'sting Officer :Corfuniasioneza of Patents

Claims (2)

1. Apparatus for stopping a rotating member at a predetermined angular position, comprising: a rotating member; high speed driving means for driving said rotating member at a high speed; low speed driving means for driving said rotating member at a low speed lower than said high speed; drive selector means for selecting between said high speed and low speed driving means; brake means for acting on said low speed drive means; rotational position detecting means, including magnetic means rotating with said rotating member and a pair of coils in which pulse voltages are induced by said rotating magnetic means, said pair of coils being spaced apart a predetermined rotational angular distance from each other; a bi-stable multivibrator, the inputs of which are connected to the outputs of said pair of coils; first switching means connected to the output of said bi-stable multivibrator, said switching means being operated by the output of said bi-stable multivibrator; a charged circuit including a resistor and capacitor connected in series, said charged circuit being connected in parallel with said first switching means through a normally open relay contact; an electromagnetic relay having a plurality of contacts including said normally open contact and a magnetic coil connected in series with said charged circuit; at least one of said relay contacts being connected in the Power circuit of said low speed driving means; another of said relay contacts being connected to said brake means to control the operation thereof; and second switching means connected across said charged circuit and being connected to and operated by said drive selector means.

2. The apparatus as defined in claim 1, additionally comprising at least one further pair of coils spaced apart a predetermined rotational angular distance from each other, said further pair of coils being spaced apart from the first pair of coils by a predetermined rotational angle; and further switching means for connecting the inputs of said multivibrator to one selected pair of said pairs of coils.

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