Electromagnetic driven variable resistance device
United States Patent 3900816
An electromagnetic driven variable electrical resistance device has a variable resistor mounted onto the front side of a case and provided with a rotatable shaft to which a drive-gear is attached. A pair of solenoids are mounted onto the bottom panel portion of the case. A pair of movable driving-pawl members are pivotally supported by the recess portions of an E-shaped spacer attached to the case and are biased by a pair of spring means and held in an upper limit position by a T-shaped stopper plate. A wide blade portion of each driving-pawl member is positioned above each solenoid respectively. The T-shaped stopper plate has a central projecting blade-portion borne by the rotatable shaft of variable resistor. Each of the movable driving-pawl members is twisted. The E-shaped spacer is made of non-metallic material and has a thin central flap-portion and a pair of thick side flap-portions.
US Patent References:
/1681924.html
Creveling - August 1928 - 1681924
Electrical remote control device
Conway - April 1946 - 2397922
Voltage regulating apparatus
Somerville - February 1950 - 2499200
Electric controllers
Morton - April 1959 - 2884504
Function programmers
Fosdick et al. - January 1960 - 2921284
/1681924.html
Creveling - August 1928 - 1681924
Electrical remote control device
Conway - April 1946 - 2397922
Voltage regulating apparatus
Somerville - February 1950 - 2499200
Electric controllers
Morton - April 1959 - 2884504
Function programmers
Fosdick et al. - January 1960 - 2921284
Application Number:
05/518950
Publication Date:
08/19/1975
Filing Date:
10/29/1974
View Patent Images:
Export Citation:
Assignee:
Alps Electric Co., Ltd. (Tokyo, JA)
Primary Class:
Other Classes:
338/103, 338/189
International Classes:
H01C10/14; H01C10/00; H01C13/00
Field of Search:
338/103,107,116,189
US Patent References:
| 3335385 | Rectilinear actuator and potentiometer | August 1967 | Mower et al. |
Primary Examiner:
Mayewsky, Volodymyr Y.
Attorney, Agent or Firm:
Shoup, Guy W.
Claims:
What is claimed is
1. An electromagnetic driven variable resistance device comprising
2. A variable resistance device as set forth in claim 1, wherein
3. A variable resistance device as set forth in claim 1, wherein
4. A variable resistance device as set forth in claim 1, wherein said spacer being an E-shaped.
5. A variable resistance device as set forth in claim 4, wherein
6. A variable resistance device as set forth in claim 4, wherein
1. An electromagnetic driven variable resistance device comprising
2. A variable resistance device as set forth in claim 1, wherein
3. A variable resistance device as set forth in claim 1, wherein
4. A variable resistance device as set forth in claim 1, wherein said spacer being an E-shaped.
5. A variable resistance device as set forth in claim 4, wherein
6. A variable resistance device as set forth in claim 4, wherein
Description:
This invention relates to a variable resistance device, and more particularly to a variable resistance device adapted for remote control and driven by an electromagnetic mechanism.
Recently, in television and radio receivers, it has been desirable to make one or more adjusting means operable by remote control, e.g., the sound volume control. Consequently, there has arisen a need for a variable resistance device which can be operated remotely as well as manually. A currently popular remote control system makes use of pulsative control signals typically transmitted by ultrasonic means. Therefore it is required that such a variable resistance device have a mechanism discretely driven by remote control means, and be able to complete the reciprocating action necessary for each discrete drive-step, accurately at a considerably high speed, and in accordance with each remote control pulse-signal. Furthermore, to facilitate efficient production and easy mounting, the variable resistance device must be of a simple and compact construction.
An objective of this invention is to provide an electromagnetic drive-variable resistance device able to fulfill the above-described requirements. In detail, a further objective of this invention is to provide an electromagnetic driven variable resistance device having an electromagnetic gear-drive mechanism in which the reciprocating action of driving-pawl members is completed smoothly at high speed in accordance with each of remote control pulse-signals.
According to this invention, an electromagnetic driven variable resistance device comprises a case, a variable resistor mounted onto the front face of the case, a drive-gear attached to the rotatable shaft of the variable resistor, a pair of solenoids mounted onto the bottom panel portion of the case, a pair of movable driving-pawl members of magnetic material which are pivotally mounted in the recess portions of E-shaped spaces and have a wide blade portion positioned above each solenoid respectively. A T-shaped stopper plate, for position-limitation of the movable driving-pawl members, is attached to the case. The drive-gear is rotated intermittently when either of the movable driving-pawl members is moved to strike a tooth of the drive-gear by the driving-pawl-portion thereof.
Furthermore, according to this invention, the T-shaped stopper plate has a central projecting blade-portion which is borne by the rotatable shaft of the variable resistor so as to secure a predetermined movement-distance of the movable driving-pawls.
Still further, according to this invention, the driving pawl-portion of each of the movable driving-pawl members, which engages with the drive-gear, is twisted so that the driving pawlportion contacts with a tooth of the drive-gear by a lessened contact-area on the way of returning-action thereof, that causes a decrease in friction and therefore results in the smooth returning-action of the driving-pawl member.
Still further, the E-shaped spacer is made of non-metallic material so as to decrease operational noise and is made to have a thin center flap-portion and a pair of thick side flap-portions so as to permit the movable driving-pawl members to return to a correct position for the next driving-action thereof.
FIGS. 1 to 8 illustrate a preferred embodiment of the electromagnetic driven variable resistance device according to this invention:
FIG. 1 is a side view thereof;
FIG. 2 is a partially sectional side view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a sectional view thereof taken along lines A, A in FIG. 4;
FIG. 6 is a sectional view of a part thereof for illustrating the relationship between the solenoid and the movable driving-pawl member;
FIG. 7 is a perspective view thereof, partially broken away, for illustrating the mounting-state of the movable driving-pawl member; and
FIG. 8 is a schematic diagram for illustrating the operation thereof.
FIG. 9 illustrates another embodiment of the electromagnetic driven variable resistance device according to this invention.
Referring now to FIGS. 1 to 8, in which there is shown an embodiment of the electromagnetic driven variable resistance device according to this invention, a case 1 having a rectangular shape which is constructed of sheet metal which is bent into the form shown. Variable resistor 2 is mounted onto the face panel-portion 1a of case 1 and comprises a cover 3, in which a resistance element and a sliding tap (not shown) are mounted, and a rotatable shaft 5 which has a projecting portion 4 projecting rearwardly through cover 3. The value of the resistance of variable resistor 2 is varied by rotating the shaft 5. Drive-gear 6 is fixedly mounted onto projecting portion 4 of rotatable shaft 5, so that the gear 6 rotates along with shafts. The drive gear 6 is made of, for example, synthetic plastic resin.
A pair of solenoids 7 and 7' are mounted onto the bottom panel-portion 1c of case 1 and are parallel to the rear panel-portion 1b of case 1.
As shown in FIGS. 6 and 7, each solenoid 7, 7' is comprised of an iron core 11, a cylindrical bobbin 8 of synthetic plastic resin and a wire coil 9 wound onto the bobbin. The pair of winding-ends of coil 9 are respectively connected to a pair of terminals 10 and 10 fixed into bobbin 8. The top flange-portion 11a of iron core 11 is received in the expanded opening-portion 8a at the upper end of bobbin 8, as shown in FIG. 6, and the top thereof is slightly lower than the upper edge 8b of bobbin 8.
As can be seen in FIG. 5, a T-shaped stopper plate 12 of synthetic resin, which comprises central projecting blade-portion 12b and a pair of wing-portions 12a and 12a, is attached into case 1 by fitting the ends of wing-portions 12a and 12a into slots provided in both sides of panel-portions 1d and 1d of case 1 and by inserting projecting portion 4 of rotatable shaft 5 of variable resistor 2 into the hole of central projecting blade-portion 12b.
An E-shaped spacer 13 of rubber or other resilient material is attached to case 1 such that the spacer 13 covers the upper portion of rear face panel-portion 1b of case 1 as shown in FIG. 7. Central flap-portion 13a thereof is formed thin and a pair of side flap-portions 13b and 13b are formed thick, and therebetween a pair of recess-portions 13c and 13c are provided.
As shown in FIG. 7, movable driving-pawl members 14 and 14' are formed, for example by stamping, from a plate of magnetic material, such as a steel metal plate. Each driving pawl 14, 14' has a driving-pawl-portion 14a, a wide blade-portion 14b, neck-portion 14c and spring-retaining portion 14d. Each of the movable driving-pawl members 14 and 14' is positioned above each of solenoids 7 and 7'. The neck-portion 14c thereof being put into recess-portion 13c of spacer 13 and driving-pawl-portion 14a being positioned in recess-portion 12c, so that the pawl-end of driving-pawl-portion 14a is set at the position engageable with a tooth of drive-gear 6 and wide blade-portion 14b thereof is set at the opposite position to iron core 11 of the corresponding solenoid. Coil springs 15 and 15' are connected between springretaining portion 14d of the corresponding driving-pawl member and projection 1f provided at the side edge of side panel-portion 1d of case 1, respectively. Accordingly, each of the movable driving-pawl members 14 and 14' is pivotally biased around recess-portion 13c as a pivot, that is; spring-retaining portion 14d is pulled obliquely down toward side panel-portion 1d of case 1 by coil spring 15 with neck-portion 14c acting as a fulcrum, and driving-pawl-portion 14a lifted obliquely upwards and held in an upper limit position by the corner of recess-portion 12c of stopper plate 12. Projections 1f and 1f of case 1 are formed to have a curved face-portion with a curvature nearly equal to that of ring-hooks 15a and 15a, to prevent deformation of ring-hooks 15a and 15a.
Furthermore, as shown in FIG. 8, driving-pawl-portion 14a of movable driving-pawl member 14 is slightly twisted in the counter-clockwise direction and that of movable driving-pawl member 14' in clockwise direction. This decreases friction when driving-pawl-portion 14a is removed from drive-gear 6 after driving engagement therewith, thereby securing a more stable rotation of drive-gear 6 and reducing the possibility of improper operation.
In the following description, the operation of the above-described electromagnetic driven variable resistance device embodying this invention will be made clear. It will be assumed that the invention is used for sound-volume control in a television or radio receiver. That is, sound-volume is adjusted manually by rotating rotatable shaft 5 and remotely by supplying current pulses into solenoid 7 or 7'.
In the manual operation mode, or during non-operating intervals in the remote operation mode, driving-pawl-portions 14a and 14a of movable driving-pawl-members 14 and 14' are at position X in FIG. 8 so that drive-gear 6 is freely rotatable. Rotatable shaft 5 can be rotated for manual sound control. In this state, assuming that a current pulse is supplied to solenoid 7 for remote control, solenoid 7 is thereby magnetized and will attract movable driving-pawl member 14 downwards and pivotally move it against coil-spring 15 with neck-portion 14c acting as a fulcrum, so that driving-pawl-portion 14a thereof falls vertically and then engages a tooth of drive-gear 6 as shown by position Y in FIG. 8. At this position, since driving-pawl-portion 14a is slightly twisted, the lower face thereof goes in face-contact with the inclined surface K of the tooth. Then, movable driving-pawl member 14 is further pulled down by solenoid 7 thereby moving driving-pawl-position 14a to position Z shown in FIG. 8, to rotate drive-gear 6 one step. Thus, rotatable shaft 5 is slightly rotated by the one-step-rotation of drive-gear 6 in the clockwise direction so that sound-volume is slightly increased.
In the above-described operation, driving-pawl-portion 14a falls non-vertically from position Y to position Z in FIG. 8, that is, its movement defines a circle, with neck-portion 14c acting as a fulcrum, in accordance with the rotation of drive-gear 6. When driving-pawl-portion 14a moves to position Z, wide blade-portion 14b of movable driving-pawl member 14 strikes the upper edge 8b of bobbin 8 and driving-pawl-portion 14a is thereby stopped from further falling movement. At this position, driving-pawl-portion 14a is in line-contact with the tip of a tooth of drive-gear 6 on the side face thereof, as shown in FIG. 8.
As soon as the current pulse supplied to solenoid 7 comes to extinction, the magnetic force of solenoid 7 ceases and driving-pawl-portion 14a is lifted by the biasing force of coil-spring 15 in the direction shown by the arrow in FIG. 8 and returns to position X. Accordingly, if a series of current pulses are supplied to solenoid 7 so as to intermittently excite it, driving-pawl-portion 14a of movable driving-pawl member 14 will rotate drive-gear 6 step by step, so that sound-volume is gradually increased.
On the other hand, if current pulses are supplied to solenoid 7', driving-pawl-portion 14a of movable driving-pawl-member 14' will rotate drive-gear 6, and thereby rotate shaft 5, in the counter-clockwise direction step by step, so that sound-volume is gradually decreased.
Turning now to FIG. 9, in which there is shown another embodiment of this invention, driving-pawl-portion 14a of each of movable driving-pawl members 14 and 14' is twisted to an angle of 90° such that smooth face T thereof, which is not corresponding to sections S and S made by stamping, comes in contact with the tip of a tooth of drive-gear 6 when returning from driving engagement thereof.
As described above, according to this invention, since stopper plate 12 has a central projecting blade-portion 12b which is borne by projecting portion 4 of rotatable shaft 5, the distance from rotatable shaft 5 to recess-portion 12c of stopper plate 12 will be a fixed length and consequently it will be possible to secure a uniform path of operation of movable driving-pawl members 14 and 14' in the manufacture of the invention to insure stable step by step rotation of drive-gear 6 therein.
Furthermore, since driving-pawl-portion 14a is so twisted as to make line or smooth contact with a tooth of drive-gear 6 when returning from driving engagement thereof, friction therebetween will be greatly decreased and the returning action of driving-pawl-portion 14a will cause no rotation of drive-gear 6. This insures a reliable rotation of drive-gear 6. Additionally, since E-shaped spacer 13 for pivotally supporting movable driving-pawl members 14 and 14' has central flap-portion 13a formed thin and both side flap-portions 13b and 13b formed thick, each of movable driving-pawl members 14 and 14' can be biased so that driving-pawl-portions 14a thereof will move toward the center when returning to its upper-limit position, as can be seen in FIGS. 1 and 8. This will also insure reliable action in each succeeding rotation-step of drive-gear 6.
In addition, since stopper plate 12, bobbin 8 and spacer 13 are made of non-metallic material, it will be possible to decrease operational noises.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.
Recently, in television and radio receivers, it has been desirable to make one or more adjusting means operable by remote control, e.g., the sound volume control. Consequently, there has arisen a need for a variable resistance device which can be operated remotely as well as manually. A currently popular remote control system makes use of pulsative control signals typically transmitted by ultrasonic means. Therefore it is required that such a variable resistance device have a mechanism discretely driven by remote control means, and be able to complete the reciprocating action necessary for each discrete drive-step, accurately at a considerably high speed, and in accordance with each remote control pulse-signal. Furthermore, to facilitate efficient production and easy mounting, the variable resistance device must be of a simple and compact construction.
An objective of this invention is to provide an electromagnetic drive-variable resistance device able to fulfill the above-described requirements. In detail, a further objective of this invention is to provide an electromagnetic driven variable resistance device having an electromagnetic gear-drive mechanism in which the reciprocating action of driving-pawl members is completed smoothly at high speed in accordance with each of remote control pulse-signals.
According to this invention, an electromagnetic driven variable resistance device comprises a case, a variable resistor mounted onto the front face of the case, a drive-gear attached to the rotatable shaft of the variable resistor, a pair of solenoids mounted onto the bottom panel portion of the case, a pair of movable driving-pawl members of magnetic material which are pivotally mounted in the recess portions of E-shaped spaces and have a wide blade portion positioned above each solenoid respectively. A T-shaped stopper plate, for position-limitation of the movable driving-pawl members, is attached to the case. The drive-gear is rotated intermittently when either of the movable driving-pawl members is moved to strike a tooth of the drive-gear by the driving-pawl-portion thereof.
Furthermore, according to this invention, the T-shaped stopper plate has a central projecting blade-portion which is borne by the rotatable shaft of the variable resistor so as to secure a predetermined movement-distance of the movable driving-pawls.
Still further, according to this invention, the driving pawl-portion of each of the movable driving-pawl members, which engages with the drive-gear, is twisted so that the driving pawlportion contacts with a tooth of the drive-gear by a lessened contact-area on the way of returning-action thereof, that causes a decrease in friction and therefore results in the smooth returning-action of the driving-pawl member.
Still further, the E-shaped spacer is made of non-metallic material so as to decrease operational noise and is made to have a thin center flap-portion and a pair of thick side flap-portions so as to permit the movable driving-pawl members to return to a correct position for the next driving-action thereof.
FIGS. 1 to 8 illustrate a preferred embodiment of the electromagnetic driven variable resistance device according to this invention:
FIG. 1 is a side view thereof;
FIG. 2 is a partially sectional side view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a top plan view thereof;
FIG. 5 is a sectional view thereof taken along lines A, A in FIG. 4;
FIG. 6 is a sectional view of a part thereof for illustrating the relationship between the solenoid and the movable driving-pawl member;
FIG. 7 is a perspective view thereof, partially broken away, for illustrating the mounting-state of the movable driving-pawl member; and
FIG. 8 is a schematic diagram for illustrating the operation thereof.
FIG. 9 illustrates another embodiment of the electromagnetic driven variable resistance device according to this invention.
Referring now to FIGS. 1 to 8, in which there is shown an embodiment of the electromagnetic driven variable resistance device according to this invention, a case 1 having a rectangular shape which is constructed of sheet metal which is bent into the form shown. Variable resistor 2 is mounted onto the face panel-portion 1a of case 1 and comprises a cover 3, in which a resistance element and a sliding tap (not shown) are mounted, and a rotatable shaft 5 which has a projecting portion 4 projecting rearwardly through cover 3. The value of the resistance of variable resistor 2 is varied by rotating the shaft 5. Drive-gear 6 is fixedly mounted onto projecting portion 4 of rotatable shaft 5, so that the gear 6 rotates along with shafts. The drive gear 6 is made of, for example, synthetic plastic resin.
A pair of solenoids 7 and 7' are mounted onto the bottom panel-portion 1c of case 1 and are parallel to the rear panel-portion 1b of case 1.
As shown in FIGS. 6 and 7, each solenoid 7, 7' is comprised of an iron core 11, a cylindrical bobbin 8 of synthetic plastic resin and a wire coil 9 wound onto the bobbin. The pair of winding-ends of coil 9 are respectively connected to a pair of terminals 10 and 10 fixed into bobbin 8. The top flange-portion 11a of iron core 11 is received in the expanded opening-portion 8a at the upper end of bobbin 8, as shown in FIG. 6, and the top thereof is slightly lower than the upper edge 8b of bobbin 8.
As can be seen in FIG. 5, a T-shaped stopper plate 12 of synthetic resin, which comprises central projecting blade-portion 12b and a pair of wing-portions 12a and 12a, is attached into case 1 by fitting the ends of wing-portions 12a and 12a into slots provided in both sides of panel-portions 1d and 1d of case 1 and by inserting projecting portion 4 of rotatable shaft 5 of variable resistor 2 into the hole of central projecting blade-portion 12b.
An E-shaped spacer 13 of rubber or other resilient material is attached to case 1 such that the spacer 13 covers the upper portion of rear face panel-portion 1b of case 1 as shown in FIG. 7. Central flap-portion 13a thereof is formed thin and a pair of side flap-portions 13b and 13b are formed thick, and therebetween a pair of recess-portions 13c and 13c are provided.
As shown in FIG. 7, movable driving-pawl members 14 and 14' are formed, for example by stamping, from a plate of magnetic material, such as a steel metal plate. Each driving pawl 14, 14' has a driving-pawl-portion 14a, a wide blade-portion 14b, neck-portion 14c and spring-retaining portion 14d. Each of the movable driving-pawl members 14 and 14' is positioned above each of solenoids 7 and 7'. The neck-portion 14c thereof being put into recess-portion 13c of spacer 13 and driving-pawl-portion 14a being positioned in recess-portion 12c, so that the pawl-end of driving-pawl-portion 14a is set at the position engageable with a tooth of drive-gear 6 and wide blade-portion 14b thereof is set at the opposite position to iron core 11 of the corresponding solenoid. Coil springs 15 and 15' are connected between springretaining portion 14d of the corresponding driving-pawl member and projection 1f provided at the side edge of side panel-portion 1d of case 1, respectively. Accordingly, each of the movable driving-pawl members 14 and 14' is pivotally biased around recess-portion 13c as a pivot, that is; spring-retaining portion 14d is pulled obliquely down toward side panel-portion 1d of case 1 by coil spring 15 with neck-portion 14c acting as a fulcrum, and driving-pawl-portion 14a lifted obliquely upwards and held in an upper limit position by the corner of recess-portion 12c of stopper plate 12. Projections 1f and 1f of case 1 are formed to have a curved face-portion with a curvature nearly equal to that of ring-hooks 15a and 15a, to prevent deformation of ring-hooks 15a and 15a.
Furthermore, as shown in FIG. 8, driving-pawl-portion 14a of movable driving-pawl member 14 is slightly twisted in the counter-clockwise direction and that of movable driving-pawl member 14' in clockwise direction. This decreases friction when driving-pawl-portion 14a is removed from drive-gear 6 after driving engagement therewith, thereby securing a more stable rotation of drive-gear 6 and reducing the possibility of improper operation.
In the following description, the operation of the above-described electromagnetic driven variable resistance device embodying this invention will be made clear. It will be assumed that the invention is used for sound-volume control in a television or radio receiver. That is, sound-volume is adjusted manually by rotating rotatable shaft 5 and remotely by supplying current pulses into solenoid 7 or 7'.
In the manual operation mode, or during non-operating intervals in the remote operation mode, driving-pawl-portions 14a and 14a of movable driving-pawl-members 14 and 14' are at position X in FIG. 8 so that drive-gear 6 is freely rotatable. Rotatable shaft 5 can be rotated for manual sound control. In this state, assuming that a current pulse is supplied to solenoid 7 for remote control, solenoid 7 is thereby magnetized and will attract movable driving-pawl member 14 downwards and pivotally move it against coil-spring 15 with neck-portion 14c acting as a fulcrum, so that driving-pawl-portion 14a thereof falls vertically and then engages a tooth of drive-gear 6 as shown by position Y in FIG. 8. At this position, since driving-pawl-portion 14a is slightly twisted, the lower face thereof goes in face-contact with the inclined surface K of the tooth. Then, movable driving-pawl member 14 is further pulled down by solenoid 7 thereby moving driving-pawl-position 14a to position Z shown in FIG. 8, to rotate drive-gear 6 one step. Thus, rotatable shaft 5 is slightly rotated by the one-step-rotation of drive-gear 6 in the clockwise direction so that sound-volume is slightly increased.
In the above-described operation, driving-pawl-portion 14a falls non-vertically from position Y to position Z in FIG. 8, that is, its movement defines a circle, with neck-portion 14c acting as a fulcrum, in accordance with the rotation of drive-gear 6. When driving-pawl-portion 14a moves to position Z, wide blade-portion 14b of movable driving-pawl member 14 strikes the upper edge 8b of bobbin 8 and driving-pawl-portion 14a is thereby stopped from further falling movement. At this position, driving-pawl-portion 14a is in line-contact with the tip of a tooth of drive-gear 6 on the side face thereof, as shown in FIG. 8.
As soon as the current pulse supplied to solenoid 7 comes to extinction, the magnetic force of solenoid 7 ceases and driving-pawl-portion 14a is lifted by the biasing force of coil-spring 15 in the direction shown by the arrow in FIG. 8 and returns to position X. Accordingly, if a series of current pulses are supplied to solenoid 7 so as to intermittently excite it, driving-pawl-portion 14a of movable driving-pawl member 14 will rotate drive-gear 6 step by step, so that sound-volume is gradually increased.
On the other hand, if current pulses are supplied to solenoid 7', driving-pawl-portion 14a of movable driving-pawl-member 14' will rotate drive-gear 6, and thereby rotate shaft 5, in the counter-clockwise direction step by step, so that sound-volume is gradually decreased.
Turning now to FIG. 9, in which there is shown another embodiment of this invention, driving-pawl-portion 14a of each of movable driving-pawl members 14 and 14' is twisted to an angle of 90° such that smooth face T thereof, which is not corresponding to sections S and S made by stamping, comes in contact with the tip of a tooth of drive-gear 6 when returning from driving engagement thereof.
As described above, according to this invention, since stopper plate 12 has a central projecting blade-portion 12b which is borne by projecting portion 4 of rotatable shaft 5, the distance from rotatable shaft 5 to recess-portion 12c of stopper plate 12 will be a fixed length and consequently it will be possible to secure a uniform path of operation of movable driving-pawl members 14 and 14' in the manufacture of the invention to insure stable step by step rotation of drive-gear 6 therein.
Furthermore, since driving-pawl-portion 14a is so twisted as to make line or smooth contact with a tooth of drive-gear 6 when returning from driving engagement thereof, friction therebetween will be greatly decreased and the returning action of driving-pawl-portion 14a will cause no rotation of drive-gear 6. This insures a reliable rotation of drive-gear 6. Additionally, since E-shaped spacer 13 for pivotally supporting movable driving-pawl members 14 and 14' has central flap-portion 13a formed thin and both side flap-portions 13b and 13b formed thick, each of movable driving-pawl members 14 and 14' can be biased so that driving-pawl-portions 14a thereof will move toward the center when returning to its upper-limit position, as can be seen in FIGS. 1 and 8. This will also insure reliable action in each succeeding rotation-step of drive-gear 6.
In addition, since stopper plate 12, bobbin 8 and spacer 13 are made of non-metallic material, it will be possible to decrease operational noises.
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described above and as defined in the appended claims.