US3631372A

US3631372A - Variable resistor of lead screw actuated-type with contact engaging screw threads

Info

Publication number: US3631372A
Application number: US45777A
Authority: US
Inventors: Takashi Yamamura
Original assignee: Victor Company of Japan Ltd
Current assignee: Victor Company of Japan Ltd
Priority date: 1969-06-12
Filing date: 1970-06-12
Publication date: 1971-12-28
Anticipated expiration: 1988-12-28
Also published as: DE2028677A1; DE2028677B2; JPS4740362Y1; DE2028677C3; NL7008656A

Abstract

A variable resistor comprises a rotatable screw shaft having a screw on the outer periphery thereof, a resistor disposed in parallel with the screw shaft, a movable member formed of a bent leaf spring of electroconductive metal, and a movable member holder through which the screw shaft passes. The movable member holder holds the movable member. The movable member has at one end thereof a slidable contact portion contacting with the resistor. The other end of the movable member contacts with the portions of the grooves of the screw having the effective screw diameter. The movable member also has a protuberant middle portion contacting with adjacent crests of the screw. The edge line of the other end of the movable member has an inclination angle with respect to a vertical plane to the axis of the screw shaft, which angle is reverse in direction to the lead angle of the screw and substantially equal to the lead angle in absolute value.

Description

United States Patent Takashi Yamamura lwai-Machi, Sashima-gun, Japan 45,777

June 12, 1970 Dec. 28, 1971 Victor Company of Japan Ltd. Yokohama, Kanagawa-ken, Japan June 12, 1969 Japan Inventor Appl. No. Filed Patented Assignee Priority VARIABLE RESISTOR 0F LEAD SCREW ACTUATED TYPE WITH CONTACT ENGAGING SCREW THREADS 2 Claims, 8 Drawing Figs.

US. Cl 338/202, 3 38/ l 80 Int. Cl H0lc 9/02 Field of Search 338/ 160,

References Cited UNITED STATES PATENTS 8/1968 Soulakis 338/180 3,124,780 3/1964 Hulbert 338/180 X FOREIGN PATENTS 722,284 1/1955 Great Britain 338/l 80 Primary Examiner- Lewis H. Myers Assistant Examiner-Gerald P. Tolin Attorney-Waters, Roditi, Schwartz and Nissen ABSTRACT: A variable resistor comprises a rotatable screw shaft having a screw on the outer periphery thereof, a resistor disposed in parallel with the screw shaft, a movable member formed of a bent leaf spring of electroconductive metal, and a movable member holder through which the screw shaft passes. The movable member holder holds the movable member. The movable member has at one end thereof a slidable contact portion contacting with the resistor. The other end of the movable member contacts with the portions of the grooves of the screw having the effective screw diameter The movable member also has a protuberant middle portion contacting with adjacent crests of the screw. The edge line of the other end of the movable member has an inclination angle with respect to a vertical plane to the axis of the screw shaft, which angle is reverse in direction to the lead angle of the screw and substantially equal to the lead angle in absolute value.

PATENTED DEB28 I97! SHEET 1 [IF 2 FIG. 2

FIG.

-21/7 ,Tlo

mimiuumzam 363L372 SHEET 2 [IF 2 VARIABLE RESISTOR OF LEAD SCREW ACTUATED- TYPE WITH CONTACT ENGAGING SCREW THREADS This invention relates to a variable resistor, and more particularly to a structure of a variable resistor of lead screw actuated type used for a noncontact system tuner in a television receiver.

In the television receiver which receives the television broadcasting signals in VI-IF and UHF frequency ranges, generally a noncontact-type electronic tuner has been proposed as a tuner for switching respective channels of VHF and UHF. A conventional VHF tuner has employed a system of switching the circuit of each channel by means of contacts, while a conventional UHF tuner has adopted a system for tuning each channel by means of a variable capacitor. In contrast with these tuners the noncontact-type electronic tuner employs a variable capacitance element as a tuning element, which varies its capacitance by applied voltage. A DC voltage applied in the variable capacitance element should be appropriately changed so as to select the low channels of VHF, high channels of VHF, and channels of UHF. Therefore, in the appropriate adjusting of the DC voltage, the tuner needs a variable resistor of extremely small and simple construction operating accurately.

A variable resistor of lead screw actuated type which is used in the conventional noncontact-type electronic tuner usually has a movable member which has at an end a contact portion to slidably contact the resistor and at the other end a bent portion engaging with spiral screw grooves of a rotating screw shaft. In this mechanism, the movable member engages with the bottom of the screw thread or the root at the only bent portion. The conventional variable resistor of the described type has yet the following disadvantages. In the event that the pressure of the contact is intensified, the engagement of the bent portion is worsened thereby producing racings or idle rotations of the screw shaft. Inversely when the contact pressure is weakened for obtaining a good engagement of the bent portion it causes a bad contact with the resistor. The weak contact also causes undesired displacements of the sliding position of the movable member by small shocks. Moreover there is an increased backlash member between the bent portion and the screw groove of the screw shaft. Therefore the accurate movement of the movable member is made impossible relative to the rotation of the screw shaft.

Another variable resistor of lead screw actuated type in the prior art employs a movable member comprising a spring wire having a contact portion for slidably contacting the resistor and a portion for threading with a part of the groove of the screw shaft. The variable resistor of the type has contained the drawbacks as below. The resistor could not have a large contact pressure or a large area for the contact portion. This resulted a bad contact and accordingly a complicated procedure for assemblage. Other drawbacks are that pitches and grooves of the screw shaft need particular sizes and configurations; ordinary screw shaft cannot be applied in use; shape of the spring wire is greatly complicated and not easy for manufacture; and the backlash is very great.

Therefore, it is a general object of the present invention to provide a novel and useful variable resistor of lead screw actuated type which has overcome and removed the abovedescribed disadvantages.

. Another object of the invention is to provide a variable resistor of lead screw actuated type which is very simple in construction and small in size. and is accurately operable.

Another object of the invention is to provide a variable resistor of lead screw actuated type in which a movable member can desirably contact the resistor with appropriate intensive pressure without causing bad contact.

Another object of the invention is to provide a variable resistor of lead screw actuated type in which the movable member can move in good engagement with the screw without having large backlash or idle rotation of the screw shaft by intense contact pressure.

Another object of the invention is to provide a variable resistor of lead screw actuated type in which the screw shaft can make idle rotations relative to the movable member at a movable end of the shaft even though it erroneously continues its rotation.

Another object of the invention is to provide a variable resistor of lead screw actuated type in which the movable member will not displace by external shocks but performs accurate slide movements as all times.

Still another object of the invention is to provide a variable resistor of lead screw actuated type which can employ an ordinary screw shaft and which is assembled readily and in low manufacturing cost.

These and other objects and features of the invention will become apparent from the description set forth hereafter when read in conjunction with the accompanying drawings, in which:

FIG. I is a longitudinal sectional view of one embodiment of the variable resistor according to this invention;

FIG. 2 is a perspective view of the movable member accommodated in the variable resistor shown in FIG. 1;

FIG. 3 is partially sectioned perspective viewof a movable member holder;

FIG. 4 is a bottom view illustrating the meshing engagement of an end of the moveable member with a screw shaft;

FIGS. 5A and 5B are respectively views illustrating a relationship between a lead angle of the screw shaft and an inclination angle of an end of meshing engagement portion;

FIG. 6 is a perspective view of the variable resistor according to this invention as applied in a noncontact-type tuner;

FIG. 7 is a perspective view of another embodiment of this invention with the movable holder removed.

Referring now to FIG. 1, a movable member 10 consists of an electroconductive leaf spring in a bent form as shown in FIG. 2. A leg 11 of the movable member 10 has at its forward end a contact 13 which slidably contacts a resistor. The movable member 10 extends through a bent portion 14 from the leg 11 to a curved protuberance l5 and a meshing portion 16. Between the protuberance l5 and the meshing portion 16 there are provided left and right projections I7. The resistor 12 has a carbon coated resistance or a conductive foil resistance. A movable member holder 18 holds the movable member I0. The member holder I8 has a hole 20 through which an electroconductive screw shaft I9 is inserted and also has a holding grooves 21 as shown in FIG. 3. The holder 18 is made of an electric insulating material. An erected portion 22 is provided at the upper part of the holder 18. An indicator needle 23 is fixed at the upper end of the erected portion 22 (FIG. 6).

The movable member 10 is held in the holding groove 21 of the holder 18 and thereafter the screw shaft I9 is inserted through the hole 20 of the holder 18. Thus the slidablc variable resistor is assembled as shown in FIG. 1. In this state, the top portion of the protuberance 15 of the movable member 10 and the tip end of the meshing portion 16 are engaged and meshed with the grooves of the screw shaft 19. The movable member 10 is electrically contacted with the screw shaft 19 at these two positions. Therefore, the movable member I0 and the screw shaft 19 in any case maintain the matual electrical contact nearly completely. The meshing portion 16, since it contacts with both sidewalls of the groove of the screw shaft 19, meshes completely with said groove without backlash.

The meshing portion 16 may preferably engage with the groove at a position distant by eight to 10 pitches from a position where the top portion of the protuberance I5 is engaged with the screw shaft 19. Thus, the distance L between the end of the meshing portion 16 and the tip portion of the protuberance IS'may be expressed by the formulazLg nP, where a pitch of the screw shaft 19 is P, and n is an integer of approximately 8 to 10. Accordingly, in case the outer diameter of the screw is for example 3 mm./ and the pitch P is 0.5 mm., the distance L may be 4 to 5 mm. desirably.

Engagement of the tip end of the meshing portion 16 of the movable member 10 with the screw shaft 19 is now shown in FIG. 4. In case the screw shaft 19 has a lead angle 0, the meshing portion 16 is inclined approximately in an angle from a perpendicular direction to the axis of the screw shaft 19 in a reverse direction to the lead angle. Therefore, the direction of the root or crest of thread of the screw shaft 19 and the inclination of the tip end of the meshing portion 16 constitutes an angle 20. Both corners of the tip end of the meshing portion are rounded in shape. The tip end of the meshing portion 16 is inclined at an angle 0 in the reverse direction to the lead angle. Thereby, as later described, when the movable member is suspended at the end of its movement the tip end of the meshing portion 16 will ride and pass over the screw crest irrespective of the rotating direction of the screw shaft in rotation.

Requirements for the meshing portion in suspension to pass over the crest of the rotating screw shaft 19 enough smoothly are now explained with reference to FIGS. 5A and 58. FIG. 5A shows a vertically sectioned front elevation of the screw shaft 19. Here, it is assumed that the diameter of a screw crest is d; diameter of a screw root d,; and effective screw diameter d It is desired that the tip end of the meshing portion 16 will engage the screw approximately in the vicinity of the effective diameter. Points A and B are now given respectively as intersecting points of the tangent to a point H on the effective diameter and the diameter of the crest. Thus, the following formula may be obtained.

HQLX/ 1) If the pitch is provided as P, the values d and d will be given as d =d-1.082532P and d =d 0.6495 l9P according to the Standard. The above formula (2) has been obtained thus in consideration of the practical values.

From the formula (2 the following will be obtained,

Also, if

I tciie.

rs ew Hence, a line SE is parallel to a line S'D'. Now, the inclination angle of the line V5 made by a direction vertical to the axis of the screw shaft may be assumed as Q. Said angle 0 may be a-Ead angle of the screw. As the line SE is parallel to the line S'I). the line SE also may have an angle 0 with respect to the vertical direction of the shaft axis. Accordingly, if the inclination angle at the end of the meshing portion 16 is B, [#6, provided that its direction is in the reverse. Thus, it is required that the inclination angle [3 at the tip end of the meshing portion 16 is reverse in the direction to the lead angle 0 of the screw of the screw shaft 19 and has approximately equal absolute value. However, the angle [3 may not strictly be equal to the angle 0 but it may substantially be B=01 or thereabout. According to the embodiment, 6 may be between about 2 and 4.

By rotation of the screw shaft 19, the movable member 10 in engagement with the meshing portion 16 and the protuberance 15 moves to right or left on FIG. 1 with the holder 18 corresponding to the direction of rotation of the shaft 19. At the instant, the movable member 10 is led positively by the meshing portion 16. Since the curvature of the protuberance 15 is relatively large compared with the width of the pitch of the screw shaft, the top portion of the protuberance 15 is only engaged between adjacent crests of the screw. This causes that the movable member 10 is positively led by the meshing portion 16. Then the meshing portion 16 will not nearly have backlash with respect to the screw shaft 19. Therefore, the movable member 10 responds directly to the rotation of the shaft 19 and moves correctly. Then the leg 11 of the movable member 10 is securely contacted to the resistor 12 by its tip portion 13 with its resiliency.

By rotation of the screw shaft 19, the movable member 10 moves to the extreme left of the shaft. In this position, the holder 18 is suspended. The movable member 10 will not move further to left as its engaging portion 14 engages the end of the holder 18. If the operator continues rotation of the screw shaft 19 by error, the holder 18 and the movable member 10 are engaged at the left end so that the screw shaft 19 will make idle rotation. Herein, the forward end of the meshing portion 161s inclined at an angle reverse in direction and approximately equal in the absolute value with the lead angle of the screw. Therefore the meshing portion 16 will smoothly pass over the crest of the screw shaft 19 and is not probable to prevent the idle rotation of the shaft 19.

The movable member 10 moves toward the right end of the screw shaft 19 together with the holder 18 as the shaft 19 rotates and the holder 18 is there suspended. The movable member 10 will not move further to the right as its projection 17 is engaged in a stepped portion 24 of the holder 18 shown in FIG. 3. If the operator continues rotation of the screw shaft 19 by error the screw shaft 19 will make idle rotation as the holder 18 and the movable member 10 are engaged at the right end. The meshing portion 16 will smoothly pass over the crest of the screw shaft 19 in the similar way as described above. There may be provided a vertically cut groove for forming a forked shape at the end of the leg 11. In this instance, the contact with the resistor will become more stable and a braking force caused from the contact may be lessened.

FIG. 6 shows the variable resistor of the described construction as applied in the noncontact tuner. By depression of a shaft 30, a face gear 31 engages with a gear 32 fixed at the end of the screw shaft 19 and a gear 34. The gear 34 is electrically connected to VHF and UHF tuners (not shown) and provided on a shaft 33 which is rotated by adjustable knob (not shown). By downward movement of the shaft 30, a projection (not shown) on the shaft 30 will push a brush 35. By the pushing, the brush 35 which is electricallyconnected to the shaft 33 will contact the screw shaft 19 and is electrically connected thereto. Terminals 36a and 36b are printed on the circuit base board 37 in connection to both ends of the resistor 12. The terminals 360 and 36b are applied a predetermined DC voltage.

Now, the shaft 33 is rotated by revolving of an adjusting knob. The rotation of the shaft 33 is transmitted to the screw shaft 19 through the

gears

34, 31, and 32 resulting in the rotation of the shaft 19. By rotation of the screw shaft 19, the movable member 10 engaging the screw moves in the direction corresponding to the rotating direction of the shaft 19 together with the holder 18. By rotation of the screw shaft 19 in a definite amount, the portion 13 slidingly contacts the resistor 12 and the member 10 moves to a definite position. As a result, a DC voltage responsive to a desired selected channel is applied on the tuner through the shaft 33. The'DC voltage has a voltage value corresponding to the resistance value at the described position.

At the instant, the holder 18 and the erected portion 22 are moved together with the movement of the movable member 10. A dial plate 39 on chassis 38 penetrates through the vertical portion 22 of the holder 18. Therefore, the indication of the dial plate 39 by the pointer 23 is performed in response to the position of the movable member 10.

Preferably, the plate 39 may be used as a mere guide for movement and a dial plate may be provided over the pointer 23 so as to make dial indication in cooperation with the pointer 23.

Another embodiment of the variable resistor according to the invention is now illustrated with reference to FIG. 7. in H0. 7, the movable member holder is taken away. Throughout FIGS. 1, 2 and 7 like numerals denote like parts, and the detailed description thereof is omitted. A movable member 50 has the meshing portion 16 and the protuberance in engagement with the screw shaft 19 just like the movable member 10 as shown in the preceding embodiment. The movable member 50 has legs 51a and 51b of forked shape at the lower end. Slidable contact portions 52a and 52b at the forward ends of the legs 51a and 51b respectively contact the two resistors 12a and 12b provided in parallel and separated from each other. The legs may be divided into three or more parts.

In one using instance, the resistors respectively have different resistance values to form different circuits. According to the instance, one movable member will actuate the variable resistor for two circuits.

In another using instance, one resistor 12a, for example, of two resistors 12a and 12b may be applied a DC voltage as like in the resistor 12 of the above embodiment. The other resistor 12b may consist of a conductor of extremely low resistance value. Then, an output is taken from the resistor 12b instead of from the screw shaft 19. For obtaining the output from the screw shaft 19 it is required to push a brush against the rotating shaft 19 to thereby obtain an electrical contact. This would cause the bad contact of the rotating shaft and the brush. Ac-

cording to the present instance the conductor 12b is usually in a still state so that the output can be easily taken out.

Throughout the above-mentioned embodiments the protuberance 15 serves to prevent the unstable movement and to provide a parallel movement with the screw shaft 19 and the resistor 12. Therefore, if the engagement with the screw shaft 19 is made only by the meshing portion 16, the protuberance 15 may have a plane configuration contacting all over the crests in plurality in place of a curved shape.

The invention may not be confined solely to the abovedescribed embodiments in practice but various modifications can be made in the range of contribance without departing from the spirit and scope of the invention.

What I claim is:

1. A ,variable resistor comprising a rotatable screw shaft having a screw on the periphery thereof, a resistor disposed in parallel with said screw shaft, a movable member in the form of a bent leaf spring of electrically conductive metal, and a movable member holder through which the screw shaft passes, said holder holding the movable member, said movable member including at one end thereof a slidable contact portion contacting the resistor, the other end contacting the portions of grooves of the screw having an effective screw diameter and a protuberant middle portion contacting adjacent crests of the screw, the edge line of the other end of said movable member having an inclination angle with respect to a vertical plane to the axis of said screw shaft, which angle is reversed in direction to the lead angle of the screw and substantially equal to the lead angle in absolute value.

2. The variable resistor as claimed in claim 1 wherein said inclination angle of the edge line of the other end of said movable member is substantially equal to an angle [3 which is defined as follows:

l where 0 is the absolute value of the lead angle of the screw.

Claims

1. A variable resistor comprising a rotatable screw shaft having a screw on the periphery thereof, a resistor disposed in parallel with said screw shaft, a movable member in the form of a bent leaf spring of electrically conductive metal, and a movable member holder through which the screw shaft passes, said holder holding the movable member, said movable member including at one end thereof a slidable contact portion contacting the resistor, the other end contacting the portions of grooves of the screw having an effective screw diameter and a protuberant middle portion contacting adjacent crests of the screw, the edge line of the other end of said movable member having an inclination angle with respect to a vertical plane to the axis of said screw shaft, which angle is reversed in direction to the lead angle of the screw and substantially equal to the lead angle in absolute value.

2. The variable resistor as claimed in claim 1 wherein said inclination angle of the edge line of the other end of said movable member is substantially equal to an angle Beta which is defined as follows: Beta theta + or - 1* where theta is the absolute value of the lead angle of the screw.