EP0158191B1 - Wiper for resistance or collecting paths - Google Patents

Abstract

A slider for resistor or slip conductors. The slider includes a generally U-shaped slider support having a center portion and two legs, leaf springs attached to each one of the legs and extending into the interior of the U-shaped slider support, and contact means guided by the leaf springs and kept in engagement with the resistor or slip conductor. In accordance with the invention, one of the leaf springs supports the contact means, and the other leaf spring resiliently engages the first leaf spring on the side remote from the resistor or slip conductor.

Description

• a) einen Schleiferträger, der U-Grundform besitzt mit einem Mittelteil und zwei Schenkeln,
• b) zwei Blattfedern, die an je einem der Schenkel in den Innenraum des U-förmigen Schleiferträgers ragend befestigt sind, und
• c) Kontaktmittel, die von einer der Blattfedern geführt und in Anlage an der Widerstands- oder Schleiferbahn gehalten werden.

The invention relates to a grinder for resistance and grinder tracks containing

• a) a grinder carrier, which has a U-shape with a central part and two legs,
• b) two leaf springs, each of which is attached to one of the legs in the interior of the U-shaped wiper carrier, and
• c) Contact means which are guided by one of the leaf springs and held in contact with the resistance or wiper track.

Such a grinder is known from GB-A-474406. This document shows a grinder with a grinder carrier that has two parallel legs. A plurality of leaf springs arranged at a distance from one another alternately extend from one leg and from the other leg into the interior of the grinder carrier. The leaf springs are each bent obliquely downwards from the legs and then form a section parallel to the grinder support, which rests on the resistance or grinder track as a “contact means” and ends in a bent edge.

In this arrangement, each leaf spring is clamped on one side without connection to other leaf springs. In the event of rapid positioning movements, the leaf springs “jump”.

From GB-A-684067 (Fig. 8 and 9) a grinder for potentiometers is known, which consists of a V-shaped spring plate part. The lower leg of this spring sheet metal part is held in a recess in a wiper carrier. The upper leg forms contact means which are in contact with the potentiometer resistor. A resilient tongue is bent upward from the lower leg, which rests on the upper leg on its side facing away from the potentiometer resistance.

From US-A-3982221 a grinder for resistance or grinding tracks is known, which is bent from a sheet metal blank. From a central part, which is arranged approximately parallel to the resistance or wiper track, a first bent sheet metal part extends along an edge at an acute angle to the resistance or wiper track. This sheet metal part forms a contact on its free edge, which lies against the resistance or wiper track. A second bent sheet metal part extends inward from the opposite edge of the central part at an acute angle. This second sheet metal part bears against the inside of the first sheet metal part facing away from the resistance or wiper track when the grinder is pressed against the resistance or wiper track. The second sheet metal part is shorter than the first and flexible. This should increase the contact force.

This arrangement is also asymmetrical. The spring constant is increased to increase the contact force. An increase in the contact force is quite undesirable for many applications, particularly in the case of measuring potentiometers, since this increases the friction and thus the force required for the adjustment. It is desirable to have a grinder that ensures reliable contact with a low but constant contact force. A larger spring constant due to the stiff and flexible sheet metal part makes the contact force more dependent on small movements of the grinder. The grinder's resonance frequency is also increased, which increases the risk of the contacts "jumping".

DE-A-3247410, published on July 5, 1984, describes a grinder with a grinder carrier of a U-shaped basic shape, to which a pair of prestressed leaf springs is fastened. The free ends of the leaf springs are connected to one another by a flat web which extends approximately in the same plane as the free end regions of the leaf springs and whose longitudinal axis extends transversely to the respective resistance or grinder track. A wire helix surrounding the web is in contact with its windings on the resistance or grinding track. The inside diameter of the wire helix is larger than the width of the web, and the winding axis of the wire helix is perpendicular to the resistance or grinding track. The grinder support has a central part and two legs which extend substantially perpendicularly thereto and to the resistance or grinder track. The two leaf springs are each attached to one of the legs projecting into the interior of the U-shaped grinder carrier. In their free end areas, the leaf springs overlap in the longitudinal directions at least by the width of said web. They are at a mutual distance transversely to their longitudinal directions, which is at least equal to the width of the resistance or the grinding track. The free leaf springs are bent out in relation to the plane of the middle part of the grinder carrier in the direction of the resistance or grinder track and biased by a greater distance than that of the possible movement perpendicular to the resistance or grinder track when the grinder is moved. The web and the leaf springs consist of a coherent spring plate part. In a preferred embodiment, a second pair of additional leaf springs with a second web are formed on the spring sheet metal part and extend essentially parallel to the first pair of leaf springs which bring about contact with the resistance track. A loop track runs parallel to the resistance track. The arrangement of the second pair of leaf springs, the second web and a second wire helix contacting the slideway are made to each other and to the slideway in the same way as in the case of the slider parts interacting with the resistance track. This grinder is asymmetrical and has a correspondingly asymmetrical mass distribution. It has been shown that such a grinder with fast alternating movements, such as movements with mains frequency, mechanical stress is subjected to which shorten its lifespan.

A potentiometer tap (DE-PS-2508530) is also known, which guarantees hysteresis-free guidance of the wire coil and a defined contact between the web and the wire coil, without particularly close tolerances being required. In this case, a flat web is formed on the free end of the leaf spring, which extends into the interior of the wire coil parallel to its longitudinal axis and whose width is smaller than the inside diameter of the wire coil and is smaller in the central region of the web than at the ends thereof. The web only loosely engages the wire helix, the inner diameter of the wire helix being significantly larger than the width of the web. As a result, no narrow tolerances need to be taken into account for the bridge and wire helix. The inherent elasticity of the wire helix is also not critical. The assembly is considerably simplified since the wire helix can easily be pushed onto the web with play. The hysteresis-free guidance and the contact between the wire helix and the web are ensured by the contact force acting on the web due to the pretensioning of the leaf spring, with which the potentiometer tap or the like can also be used. is pressed onto the resistance or slip track. With this contact force, the web is pressed into the arch of the wire helix lying against the conductor and its edges lie on it on both sides. The wire coil takes hysteresis-free, i. H. regardless of the direction of movement of the potentiometer tap or the like, a defined position to the web.

The contact between the web and the wire helix is determined by the contact force acting on the web, which can be transferred to the respective conductor track via the web and the wire helix. This contact force can easily be generated by a soft but appropriately preloaded spring, so that slight movements of the web do not noticeably influence the contact force.

Due to the fact that the width of the web in its central area is smaller than at the ends, it can be adapted to the contour of the resistance and grinder track without causing an impermissible «hysteresis».

The leaf spring is U-shaped and its middle part forms the web. In a further embodiment, the web and the wire helix arranged thereon extend transversely to a resistance and a sliding contact path. The disadvantage of this design is the inclination of the grinder to jump when the direction of rotation is reversed quickly and therefore no longer guarantee reliable contact.

The invention has for its object to provide a structurally simple grinder suitable for alternating movements without hysteresis and without jumping, in which stresses due to mass asymmetry are avoided.

• d) die erste Blattfeder die Kontaktmittel trägt, und
• e) die zweite Blattfeder federnd auf der der Widerstands- oder Schleiferbahn abgewandten Seite an der ersten Blattfeder anliegt, und
• f) die Blattfedern so ausgelegt sind, dass die durch die Trägheitskräfte bedingten, gegensinnig auf die Blattfedern wirkenden Andrück- und Abhebekräfte die Kontaktkraft zwischen Schleifer und Widerstands- oder Schleiferbahn im wesentlichen konstant halten.

According to the invention, this object is achieved in that, in order to enable rapid movement of the grinder with little contact force between the grinder and the resistance or grinder track

• d) the first leaf spring carries the contact means, and
• e) the second leaf spring resiliently abuts the first leaf spring on the side facing away from the resistance or sliding track, and
• f) the leaf springs are designed in such a way that the pressing and lifting forces caused by the inertial forces acting in opposite directions on the leaf springs keep the contact force between the grinder and the resistance or grinder track essentially constant.

When the grinder moves quickly, for example with a mains frequency, the masses of the leaf springs and the inertial forces acting on them must be taken into account. If one looks at a leaf spring lying obliquely on the resistance or grinder path, which encloses an acute angle with this resistance or grinder path, the following results: When the movement of the grinder is reversed in the direction of the tip of this acute angle, the inertia force acts on the leaf spring so that it presses the leaf spring more strongly onto the resistance or slip track. The inertial force tries to maintain the original direction of movement of the leaf spring in such a reversal of movement, so it acts in the direction of the opening of the acute angle. In this way, it exerts a moment on the leaf spring around its clamping point, which tries to increase the angle between the leaf spring and the resistance or wiper track and thus presses the leaf spring against the resistance or wiper track. If the movement reverses in the opposite direction, i.e. if the grinder first moves in the direction of the tip of the acute angle and then after reversing the movement is moved in the direction of the opening of the acute angle, then the inertial force acts on the leaf spring in the direction of the tip of the acute angle . It creates a moment of tension that the leaf spring tries to lift off the resistance or slip track. If a second leaf spring, which extends in the opposite direction, bears against the first leaf spring, then the pressing and lifting forces due to the inertial forces act on the second leaf spring in opposite directions to the forces acting on the first leaf spring: If the first leaf spring is caused by the Inertial force is additionally pressed, the pressure force transmitted by the second leaf spring is reduced by the inertial force acting thereon. If the inertial force acting on the first leaf spring tends to lift this leaf spring off the resistance and sliding path, the contact pressure transmitted by the second leaf spring is increased by the contact pressure resulting from the inertial force acting on this leaf spring. Therefore, the contact force between grinder and resistance or grinding track essentially constant even with fast movements of the grinder. It is possible to work with a relatively low contact force between the grinder and resistance or grinder path without the grinder jumping.

Embodiments of the invention are the subject of the dependent claims.

• Fig. 1 zeigt eine Draufsicht auf einen Potentiometerabgriff mit einer Potentiometerwicklung und einer zusätzlichen Schleiferbahn;
• Fig. 2 zeigt den Potentiometerabgriff nach Fig. 1 im Schnitt längs der Linie 11-11 von Fig. 1.

An embodiment of the invention is explained in more detail below with reference to the accompanying drawings:

• 1 shows a plan view of a potentiometer tap with a potentiometer winding and an additional wiper track;
• FIG. 2 shows the potentiometer tap according to FIG. 1 in a section along the line 11-11 of FIG. 1.

10 is a resistance track and 12 is a parallel slider track. The grinder contains a grinder support 14 which has a U-shaped basic shape. The grinder support 14 has a central part 16 and two legs 18 and 20 which extend substantially perpendicularly thereto and to the resistance or grinder track 10 or 12. Two leaf springs 22 and 24 are fastened on each of the legs 18 and 20, respectively, projecting into the interior of the U-shaped grinder carrier 14. Contact means are guided by the leaf springs 22 and 24 and held in contact with the resistance track 10. One of the leaf springs 22 carries the contact means. The other leaf spring 24 resiliently abuts on the first leaf spring 22 on the side facing away from the resistance track 10. As can be seen from FIG. 2, the legs 18 and 20 are angled with respect to the central part 16 of the grinder support 14 in such a way that the leaf springs 22 and 24 fastened to the legs 18, 20 relative to the plane of the central part 16 in the direction of the resistance track 10 are bent out and enclose an obtuse angle with their longitudinal axes. The free ends of the leaf springs are bent by a greater distance by means of their pretension than that of the possible movement perpendicular to the resistance track 10 when the grinder is moved over it. The leaf spring 22, which carries the contact means, has a length such that the contact means are held approximately asymmetrically with respect to the central plane 26 of the wiper carrier. The other leaf spring 24 is longer than the leaf spring 22. It overlaps it and lies on the leaf spring 22 beyond the central plane 26. The leaf spring 24 has a flat, U-shaped end 28 which bears on the leaf spring carrying the contact means. In the embodiment shown, the contact means are formed by a broom grinder 30. Instead, a wire helix of the type described at the beginning could also be provided as the contact means. As can be seen from FIG. 1, the leaf spring 24 consists of two separate arms which run essentially parallel to one another and which are connected to one another by the bent end 28. The opening formed in this way ensures that the leaf spring 24, although longer than the leaf spring 22, has essentially the same mass as the leaf spring 22.

Attached to the legs 18, 20 of the grinder support 14 is a second pair of leaf springs 36 and 38, each of which, with a leaf spring 22 or 24 of the first pair causing contact with the resistance track 10, consists of a coherent spring plate part 36 and 38, respectively. The spring plate parts 36 and 38 lie between insulating parts 40, 42 and 44, 46, which are connected to the legs 18 and 20 by rivets 48 and screws 50, respectively. As can be seen from Fig. 1, each spring sheet metal part is fastened by two rivets or two screws. The second pair 36, 38 of leaf springs extend substantially parallel to the first pair 22, 24 of leaf springs. A leaf spring 36 of the second pair carries contact means, also in the form of a broom grinder 52, which bear on the grinder track 12 in a contacting manner. The other leaf spring 38 of the second pair, in turn, rests on the first leaf spring 36, as in the wiper parts abutting the resistance track 10. Here, too, the leaf spring 38 has an opening, so that it is formed by two interconnected arms 54 and 56 and has essentially the same mass as the leaf spring 36. A circular opening surrounded by a collar is provided on the grinder carrier 14. The grinder carrier 14 can thus be placed on a potentiometer shaft. The resistance and grinder tracks, which are only indicated schematically in the figures, then naturally run concentrically around the axis of the potentiometer shaft.

In contrast to the aforementioned patent application DE-A-3247410, the grinder described is constructed symmetrically with regard to the masses of the leaf springs. The leaf springs of each pair are also arranged at the same distance from the axis of the potentiometer shaft and are not radially offset from one another. It has been shown that this enables the grinder to achieve a significantly longer service life in the case of alternating movements, that is to say in the case of rapid reciprocating movements, for example at the mains frequency.

Claims (9)

1. Slider for resistor or slip conductors (10, 12), comprising

a) a generally U-shaped slider support (14) having a center portion (16) and two legs (18, 20),

b) two leaf springs (22, 24 and 36,38, respectively) attached to one of the legs each (18, 20) and extending into the interior of the U-shaped slider support (14), and

c) contact means (30, 52) guided by the leaf springs (22, 24 and 36, 38, respectively) and kept in engagement with the resistor or the slip conductor (10,12). characterized in that for permitting a quick movement of the slider with small contact force between slider and resistor or slip conductor

d) the first leaf spring (20 and 36, respectively) carries the contact means (30 and 52, respectively) and

e) the second leaf spring (24 and 38, respectively) resiliently engages the first leaf spring (22 and 36, respectively), on the side remote from the resistor or slip conductor, and

f) the leaf springs are designed such that the contact pressure and lift-off forces due to the inertial forces and acting on the leaf springs in opposite sense keep the contact force between slider and resistor or slip conductor substantially constant.

2. Slider as set forth in claim 1, characterized in that the leaf springs (22, 24 and 36, 38, respectively) have substantially equal masses.

3. Slider as set forth in claim 1 or 2, characterized in that the free ends of the leaf springs (22, 24 and 36, 38, respectively) are bent, because of their bias, by a larger distance than the amplitude of any possible movement perpendicular to the resistor and slip conductor, respectively (10 or 12, respectively), when the slider is moved thereover.

4. Slider as set forth in claim 3, characterized in that the legs (18, 20) are bent off at an angle with respect to the center portion (16) of the slider support (14) such that the leaf springs (22, 24 and 34, 38, respectively) attached to the legs (18, 20) are bent off with respect to the plane of the center portion (16) in the direction of the resistor and slip conductor, respectively (10, 12) and with their longitudinal axes form an obtuse angle.

5. Slider as set forth in claim 2, characterized in that

a) the leaf spring (22 and 36, respectively) supporting the contact means (30 and 52, respectively) has such a length that the contact means are held approximately symmetrical relative to the center plane (26) of the slider support (14), and

b) the other leaf spring (24 and 38, respectively) is longer than the first leaf spring (22 and 36, respectively), extends over it and engages it beyond of the center plane.

6. Slider as set forth in claim 5, characterized in that the other leaf spring (24 and 38, respectively) has a slightly U-shaped bent end which engages the leaf spring (22 and 36, respectively) supporting the contact means (30 and 52, respectively).

7. Slider as set forth in one of the claims 1 to 6, characterized in that the contact means are formed by a brush slider (30, 52).

8. Slider as set forth in one of the claims 5 to 7, characterized in that the other longer leaf spring (24 and 38, respectively) has a longitudinal aperture to reduce the mass, such that it forms two arms (32,34 and 54, 56, respectively).

9. Slider as set forth in one of the claims 1 to 8 having resistor and slip conductors (10 and 12, respectively) extending parallel to each other, characterized in that

a) a second pair of leaf springs (36, 38) is attached to the legs (18, 20) of the slider support, each of said leaf springs together with a leaf spring (22 and 24, respectively) of the first pair (22, 24) causing the contact with the resistor conductor (10), consisting of an integral part of spring sheet metal (37,39), and extending substantially parallel to the first pair of leaf springs (22, 24), and

b) a leaf spring (36) of the second pair supports contact means (52) which engage contactingly the slip conductor (12), and the other leaf spring (38) of the second pair engages the first leaf spring (36), like the slider portions engage the resistor conductor (10).

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