EP0292016B1 - Actuator, especially for a linear potentiometer - Google Patents

Description

The invention relates to an actuator according to the preamble of claim 1.

Such an actuator - a linear potentiometer - is known from US-A-3 732 521. The potentiometer is composed of two housing parts, which after assembly form a guide element with an elongated hole. A sliding body is slidably guided in this slot. The sliding body has a plate-shaped base arranged on the upper side of the guide element with upper sliding segments protruding laterally beyond the elongated hole, as well as a section adjoining the base and arranged inside the elongated hole and adjoining lower sliding segments. The sliding segments with their surfaces facing the guide element are in sliding contact with the top and bottom of the guide element. They are at least partially offset from one another in the longitudinal direction of the elongated hole, but overlap to such an extent that they can jam in harsh environmental conditions.

From DE-A-26 27 346 an actuator is known in which the guide element and the sliding body are made of different plastics, which differ in particular in terms of their softening temperature. First, the guide element is produced, which is then inserted into an injection mold and thus itself forms part of the injection mold, the sliding body then being injection molded onto the guide element in a further injection molding process.

In this known actuator, the guide element has in all cases one or more grooves in which the sliding body is held in a form-fitting manner with a thickening or widening (see FIGS. 8 and 10 of DE-A-26 27 346). This results in material accumulations of the sliding body, which are disadvantageous from an injection molding point of view, particularly in the area of the groove, since the shrinking behavior of plastics depends to a large extent on the shape of the material accumulations and can therefore be non-uniform. This then leads to deteriorated sliding properties of the sliding body and to the tendency for the sliding body to tilt and thus jam when displaced.

Another type of actuators used in linear potentiometers, which are commercially available, are constructed so that the actuators have a guide element with an elongated hole, in which a sliding body is slidably guided. The sliding body, which carries the sliding contact springs on a potentiometer as a so-called spring support, is secured as security against falling out of the elongated hole by inserted pins which are inserted into a bore in the sliding body and protrude laterally beyond the elongated hole. So far, the guide element with an elongated hole on the one hand and the sliding body on the other hand were each manufactured separately and then assembled together. In these known actuators, it is disadvantageous that the tolerances to be observed increase the manufacturing effort. If the sliding body is "too tight" to the guide element and the elongated hole, it slides, if at all, only with difficulty and not smoothly. If, on the other hand, the adjustment is "too loose", the sliding body can on the one hand jam during its movement and thus jam and on the other hand it is no longer guided with sufficient precision so that, for example, with a linear potentiometer between the mechanical position of the sliding body relative to the guide element and the electrical setting Resistance value there is no clearly reproducible relationship. When manufacturing these actuators, therefore, very tight manufacturing tolerances must be observed, which in turn is complex. Even then, the tolerances set in each production can still be in add unfavorable direction so that the risk of rejects is still relatively large. The problem of tolerances is already solved in a certain way in the actuator of DE-A-26 27 346 in that the tolerances relevant to the sliding properties only depend on the shrinking properties of the plastic and no longer on the shape accuracy of the injection mold. However, the sliding bodies of this document are still designed so that the sliding properties are not always satisfactory.

The object of the invention is therefore to improve the actuator of the type mentioned in such a way that the sliding properties of the actuator are further improved. This object is achieved in the generic actuator by the features of claim 1. Advantageous refinements and developments of the invention can be found in the subclaims.

In the invention, those parts of the sliding body which serve as guide elements are injection-molded in such a way that no unfavorable distortions or bending occur when the plastic is shrunk. You also get multi-point bearings of the sliding body on the guide element, with which tilting or jamming of the sliding body is prevented even more effectively, while simultaneously reducing the frictional forces, taking into account the peculiarities of injection molding technology, in particular with regard to cooling behavior, shrinkage and formation of voids.

Actuators of the type dealt with here are used in the most varied fields of technology, for example as a displaceable spring support in linear potentiometers, as a contact support in slide switches, as actuators for mechanical cam controls, as actuators for sensors, etc. In many areas of application Attention must also be paid to harsh environmental conditions, such as dust, oil or other dirt as well as strong temperature fluctuations up to icing. Such environmental conditions occur, for example, when used in motor vehicles when linear potentiometers are used as measuring sensors for sensing the throttle valve position or as other measuring sensors, for example for level control, headlight range adjustment, etc. Due to the special design of the actuator according to the invention, it still works perfectly even with dirt, icing, etc. (of course only to a certain degree). Further advantages can be seen in the fact that the sliding body is in one piece, so that assembly steps are eliminated and the problem of dimensional tolerances is solved satisfactorily. Even if the thickness of the guide element or the width of the elongated hole fluctuate within large tolerances, the "molded" sliding body is individually adapted to the associated guide element, since the latter is part of the injection mold. Dimensional inaccuracies of the guide element have no negative influence. Dimensional tolerances cannot add up unfavorably. When conventional plastics harden, shrinkage or shrinkage of 0.5 to 1% occurs. This is very desirable in the invention, since this shrinkage gives the necessary bearing play which allows the sliding body to be displaced relative to the guide element. This play of 0.5 to 1%, which occurs with most sprayable plastics during shrinking, has proven to be the optimal play, which both allows extremely precise guidance, prevents tilting and also moves the sliding body in the event of contamination or icing allowed.

Fig. 1

ein erstes Ausführungsbeispiel des Stellgliedes in Seitenansicht;

Fig. 2

eine Draufsicht auf das Stellglied der Fig. 1;

Fig. 3

ein zweites Ausführungsbeispiel des Stellgliedes in Seitenansicht;

Fig. 4

eine Draufsicht auf das Stellglied der Fig. 3;

Fig. 5

ein drittes Ausführungsbeispiel des Stellgliedes in Seitenansicht;

Fig. 6

eine Draufsicht auf das Stellglied der Fig. 5;

Fig. 7

eine Ansicht der Unterseite der Stellglieder der Fig. 5;

Fig. 8

einen Schnitt längs der Linie A-B der Fig. 5;

Fig. 9

einen Schnitt längs der Linie C-D der Fig. 5;

Gleiche Bezugszeichen in den einzelnen Figuren bezeichnen gleiche bzw. einander entsprechende Teile. Die Ausführungsbeispiele der Fig. 1 bis 9 zeigen verschiedene Varianten eines Linearstellgliedes, das jeweils ein plattenförmiges Führungselement 1 mit einem geradlinig verlaufenden Langloch 2 besitzt, das hier in der Draufsicht rechteckig ist. Das Führungselement 1 kann ein Metallblech sein, aus dem das Langloch ausgestanzt ist. Es kann auch aus einem hochschmelzenden (d.h. bei hoher Temperatur schmelzenden) Kunststoff sein. Die in Längsrichtung des Langloches 2 verlaufenden, einander zugewandten Seiten des Langloches bilden Führungsflächen 3 bzw. 4 für einen Gleitkörper 7, der von der Oberseite 5 des Führungselementes 1 durch das Langloch 2 hindurch bis zu der Unterseite 6 des Führungselementes hindurchragt.The invention is explained below using exemplary embodiments. It shows:

Fig. 1

a first embodiment of the actuator in side view;

Fig. 2

a plan view of the actuator of Fig. 1;

Fig. 3

a second embodiment of the actuator in side view;

Fig. 4

a plan view of the actuator of Fig. 3;

Fig. 5

a third embodiment of the actuator in side view;

Fig. 6

a plan view of the actuator of Fig. 5;

Fig. 7

a view of the underside of the actuators of FIG. 5;

Fig. 8

a section along the line AB of Fig. 5;

Fig. 9

a section along the line CD of Fig. 5;

The same reference numerals in the individual figures denote the same or corresponding parts. The exemplary embodiments of FIGS. 1 to 9 show different variants of a linear actuator, each of which has a plate-shaped guide element 1 with a straight elongated hole 2, which is rectangular in plan view here. The guide element 1 can be a metal sheet from which the elongated hole is punched out. It can also be made of a high-melting (ie melting at high temperature) plastic. The mutually facing sides of the elongated hole which extend in the longitudinal direction of the elongated hole 2 form guide surfaces 3 and 4 for a sliding body 7 which projects from the top 5 of the guide element 1 through the elongated hole 2 to the underside 6 of the guide element.

The sliding body 7, as can best be seen from FIGS. 8 and 9, has a section 8 which is immersed in the elongated hole 2 and whose side walls 9 and 10 are guided on the guide surfaces 3 and 4, respectively. Between the side walls 9 and 10 and the guide surfaces 3 and 4 there is a "bearing play" which arises in the manufacturing process by the fact that during the injection molding process the plastic - accordingly the other shape of the sliding body - is injected into parts of the elongated hole, the guide surfaces 3 and 4 of the elongated hole serving as a shape, the plastic then shrinking during the subsequent hardening, namely by about 0.5 to 1%. Regardless of the distance between the guide surfaces 3 and 4, the total play between the surfaces 4 and 9 and 3 and 10 is always 0.5 to 1% of the distance between the guide surfaces 3 and 4.

The section 8 extending in the interior of the elongated hole 2 is in principle cuboid in the illustrated exemplary embodiments. In applications with a curved contour of the elongated hole - with circular contours in particular being considered, section 8 is of course adapted to this contour. In applications with elongated holes which have different radii of curvature, the section can be approximately cylindrical so that it can run in the elongated hole thus curved without tilting. In this case, the injection mold must ensure that it is approximately cylindrical.

In order to secure the sliding body 7 against falling out, it is equipped with protruding sliding segments 13 to 18 on the parts protruding over the top and bottom 5 and 6 from the elongated hole, which - seen in plan view of the elongated hole 2 - laterally over the Protrude elongated hole and thus directly opposite the top or bottom 5 or 6 of the guide element. In other words, the surfaces of these sliding segments facing the guide element slide along the top or bottom 5 or 6.

The sliding body 7 also has a base 11 lying outside the elongated hole, to which the sliding segments are attached in one piece and to which an actuating lever 12 of any shape is also attached. This operating lever can also be optionally already in the injection mold manufacture or screw on later, glue etc.

Up to this point, the different variants of FIGS. 1 to 9 correspond. The deviations will now be described below. In the first embodiment of FIGS. 1 and 2, a total of six sliding segments 13, 14, 15, 16, 17 and 18 are provided. Two sliding segments, which are opposite one another with respect to the longitudinal extent of the elongated hole and are arranged on one side (top or bottom) of the guide element, form a pair, i.e. the sliding segments 13 and 14, the sliding segments 15 and 16 and the sliding segments 17 and 18. On the top 5 of the guide element, four sliding elements 13, 14, 15 and 16 are provided, which project laterally at both ends beyond the elongated hole, so that the guide element rests on four surfaces on the top 5 of the guide element 1. On the underside 6 of the sliding body, on the other hand, only two sliding segments 17 and 18 are provided, which are seen in the longitudinal direction of the sliding body and are arranged approximately in the middle thereof. In this exemplary embodiment, the sliding body is thus prevented by the six surfaces of the sliding segments 13 to 18 and by the side surfaces 9 and 10 of section 8 (FIG. 8) from tipping or rotating about the three possible axes of tilt or rotation relative to the guide element 1 secured.

In the variant of FIGS. 1 and 2, bumps in the guide element or foreign bodies such as dirt or ice, even of a small thickness, can still impair the displaceability of the sliding body.

To avoid these problems, a four-point bearing arrangement is provided in the second exemplary embodiment according to FIGS. 3 and 4. Seen in the sliding direction of the sliding body, there are two laterally projecting sliding segments 13 and at one end on the upper side 5 14, while at the other end there are sliding segments 17 and 18 on the underside 6. In the top view of FIG. 4 it can clearly be seen that the sliding segments do not overlap on the top and bottom. Rather, the sliding segments 13 and 17 on the one hand and the sliding segments 14 and 18 on the other hand are at a distance from one another in the plan view of FIG. 4. However, the sliding body is still possible against tilting or twisting about an axis which lies in the plane of the guide element 1 and perpendicular to the longitudinal extent of the slot 2. In other words, the sliding body can be rotated about an axis perpendicular to the plane of the drawing in FIG. 3, namely from the limit position in FIG. 3, in which the four sliding segments bear against the guide element, a clockwise rotation is possible. To prevent this, a tension spring 19 is provided on the underside 6, which is tensioned between two pins 20 and 21, one pin 20 being fastened to the sliding body, specifically in the top view of FIG. 4 between the sliding segments 13 and 14 lies while the other pin 21 is attached to the guide element 1. This tension spring is - even if the sliding body is at one end of the elongated hole 2 at the stop, under a prestress, so that a torque acts on the sliding body, which requires tilting in the counterclockwise direction. As a result, the contact surfaces of the sliding segments 13 and 14 are pressed down against the upper side 5 and the contact surfaces of the sliding segments 17 and 18 upward against the lower side 6 of the guide element. The spring 19 also acts here as a return spring, which pulls the sliding body into a limit position, which is required for applications with sensors. In this exemplary embodiment, shrinking of the plastic during curing in a direction perpendicular to the plane of the guide element does not result in contact forces that could brace the sliding segments against the guide element.

The variant of FIGS. 5 to 9 builds on the embodiment of FIGS. 3 and 4. It differs from the latter, however, in that a web 22, 23, 24 and 25 is formed on the sliding segments 13, 14, 17 and 18, which runs parallel to the longitudinal extent of the elongated hole 2, but is laterally offset with respect to the elongated hole so that it is in sliding contact with the top or bottom 5 or 6 of the guide element. In the side view (Fig. 5), these webs are ramped, i.e. from their free end they have a slope 26 which rises in the direction of the associated sliding segment. The webs 22 and 23 on the top side or the webs 24 and 25 on the bottom side converge towards one another, so that they are in a side view (FIG. 5 ) seen in pairs (22, 24 and 23, 25) overlap. Tilting - as in the example of FIGS. 3 and 4 - is no longer possible. Due to the ramp shape (slope 26), however, shrinking of the plastic during curing in the direction perpendicular to the plane of the guide element 1 has no negative effects. When shrinking, the webs 22 to 26 will shrink differently due to their constantly changing material thickness in the direction perpendicular to the plane of the guide element, so that the webs will bend slightly so that the free ends of the webs are slightly bent away from the guide element. This slight bending takes place in an order of magnitude that corresponds exactly to the desired bearing play in the direction perpendicular to the plane of the guide element 1.

This embodiment is also shown with a spring 19 and pin 20, 21. However, this spring 19 acts primarily as a return spring and only secondarily also applies a torque, as is required in the embodiment of FIGS. 3 and 4. If no return spring is required in the embodiment of FIGS. 5 to 9, the spring 19 can be omitted without further notice, without tilting or tilting of the sliding body is to be feared. In this exemplary embodiment too, the entire sliding body, including the sliding segments and the webs 22 to 25, is produced in one operation as an injection molded part.

A further variant, not shown, relates to a modification of the exemplary embodiment in FIGS. 1 and 2. In this case, two sliding segments are present on the upper side, that is to say on the side to which the actuating lever 12 is attached, and four sliding segments are present on the underside.

Claims (4)

1. An actuator, more particularly for a linear potentiometer, comprising a slide body (7) which is displaceably guided in a slot (2) of a guide element (1), the slide body (7) having on either side of the guide element (1) sliding segments (13-18), projecting laterally beyond the slot (2), of which the surfaces facing the guide element (1) are in sliding contact with the upper- or underside (5 or 6) of the guide element (1), the sliding segments (13-18) being respectively provided in pairs on each side of the guide element (1), and each sliding segment pair (13, 14; 15, 16; 17, 18) consisting of sliding segments (13-18) facing one another with respect to the longitudinal extent of the slot (2),
   characterised

   a) in that the slide body (7) is moulded to the guide element (1) as one piece by the plastic injection moulding method,

   b) in that the guide element (1) is in one piece, and

   c) in that the sliding segment pairs (13, 14; 15, 16; 17, 18) are offset in relation to one another in the longitudinal direction of the slot (2), entirely free of any overlap.
2. An actuator according to claim 1, characterised in that only one pair of sliding segments (13, 14; 17, 18) is provided on each side of the guide element, and in that a spring (19) is secured to the slide body (7), on the one hand, and to the guide element (1), on the other hand, the said spring acting on the slide body with a torque which is directed such that the sliding segments (13, 14; 17, 18) are pressed against the guide element.
3. An actuator according to claim 1 or 2, characterised in that a respective bar (22-25) is moulded to each sliding segment (13, 14; 17, 18) as one piece, in that these bars extend parallel to a side (5, 6) and parallel to the longitudinal direction of the slot (2), and in that the bars (22, 24 or 23, 25) on one side of the guide element, in the plan view of the guide element, at least partially overlap the bars of the other side.
4. An actuator according to claim 3, characterised in that the bars (22-25) rise in a ramp shape (slope 26) from their free end towards the associated sliding segment.

Images