Resistance carrier for a grinding potenziometer, grinding potenziometer and manufacturing process for the resistance carrier

Description

[0001] The invention relates to a resistor carrier for a grinding potentiometer, a grinding potentiometer and a manufacturing method for the resistor carrier, in particular for a grinding potentiometer that is used as a dual potentiometer sensor in foot brake modules of commercial vehicle brakes.

[0002] A current design for a resistor carrier used in a grinding potentiometer involves manufacturing the resistor carrier from a glass fiber-reinforced epoxy resin molding compound, particularly thermosets. Such a resistor carrier is well-suited for grinding potentiometers because it can be produced with a high surface finish and good adhesion for screen printing. In this process, a resistive ink, paste, or varnish is applied to the surface of the resistor carrier in several screen printing stages to form a resistive track. After printing, the resistive ink, paste, or varnish is cured or normalized for an extended period at temperatures exceeding 200 °C.

[0003] Materials used for the resistor substrate, which allow the resistive ink, paste, or lacquer to dry or normalize at such high temperatures, include the aforementioned thermosets, as well as ceramics or printed circuit boards. However, ceramics and printed circuit boards offer only very limited shaping possibilities, as they can only be manufactured economically in sheet form and differ only in their round or square contours. Therefore, a customized shape for the resistor substrate, and thus for the grinding potentiometer, is only possible using thermosets, although processing these materials is very complex.

[0004] In the German patent application DE 42 18 938 C2, a thermoplastic can indeed be used as a resistive substrate, whereby a resistive layer is applied to another substrate material and dried on this other substrate material in an oven. This pretreated resistive layer is then embedded in a plastic core, which can be formed from the thermoplastic, but this entails additional manufacturing steps.

[0005] German patent application DE 39 28 036 A1 discloses a resistor carrier for a grinding potentiometer, which has a printable flat surface with printed conductor tracks, a resistor track printed directly on the printable surface and contact elements connected to the resistor track by the conductor tracks, wherein one material of the resistor carrier is a thermoplastic polymer.

[0006] The object underlying the invention is therefore to eliminate the aforementioned disadvantages and to provide a grinding potentiometer with a resistance carrier that allows for the most flexible customer-specific shaping possible while processing it cost-effectively.

[0007] The problem is solved by a resistor according to claim 1, a grinding potentiometer according to claim 10, a dual potentiometer according to claim 11, and a manufacturing method according to claim 12. Advantageous further developments of the invention are contained in the dependent claims.

[0008] According to one aspect of the invention, a resistance carrier for a grinding potentiometer has a printable flat surface, a resistance track printed directly onto the printable surface, and contact elements connected to the resistance track, wherein a material of the resistance carrier comprises a thermoplastic polymer.

[0009] The use of a thermoplastic material allows for flexible adaptation to customer-specific shaping requirements, while still enabling cost-effective production of the resistance carrier. Direct printing, unlike printing on a separate substrate, eliminates additional manufacturing steps.

[0010] According to an advantageous embodiment of the resistance carrier, the material of the resistance carrier is designed to be dimensionally stable in a temperature range up to over 200°C.

[0011] This property makes it possible to use a previously known resistance ink or resistance paste or resistance lacquer that needs to be dried or normalized at temperatures above 200° Celsius.

[0012] In an advantageous embodiment of the resistor carrier, the material of the resistor carrier comprises a glass fiber reinforced polyphenylene sulfide.

[0013] The use of this plastic allows the component to be heated to a temperature of over 200° Celsius in order to dry or normalize the resistance ink, resistance paste or resistance lacquer without the component deforming due to the influence of the temperature.

[0014] In a further advantageous embodiment of the resistor carrier, the contacting elements are designed to be connected to the resistor carrier by casting, in particular by virtue of their non-rotationally symmetrical contour in a directed and rotation-inhibiting orientation.

[0015] By casting, it is possible to connect the contact elements securely and form-fittingly to the resistor carrier at suitable points in a cost-effective manner.

[0016] In a further advantageous embodiment of the resistor carrier, a conductive layer connected to the contacting elements is provided on the printable surface, and the resistive track is applied in an overlapping section on the conductive layer.

[0017] By providing the resistive track on the conductive layer, there is an improved way to connect the resistive track to the contacting elements.

[0018] According to a further advantageous embodiment of the resistance carrier, additional layers, in particular at least one insulating layer, are provided.

[0019] Additional layers enable further functionalities. For example, a switching function can be implemented by including an insulating layer and a conductor track running along the printable surface. Alternatively, a capacitor function can be implemented by adding another layer on top of the insulating layer.

[0020] In a further advantageous embodiment of the resistor carrier, the contacting elements and the printable surface are designed coplanarly.

[0021] Due to the coplanar nature of the contact elements and the printable surface, the area formed by the printable surface and the contact elements is a flat surface. Therefore, it is easy to connect the contact elements to further layers via the conductive layer.

[0022] According to a further advantageous embodiment of the resistor carrier, the resistor carrier has an annular area and in the annular area sections with a uniform thickness of the resistor carrier and a predetermined surface roughness are provided around the perimeter.

[0023] This property makes it possible, with a suitably designed and adjusted housing, to clamp the resistance carrier through the housing with a defined frictional force, so that resistance values ​​can be easily set to positions of sliding springs or switching points of sliding springs without the frictional force changing after a rotation.

[0024] In a further advantageous embodiment of the resistance carrier, it has protruding and / or recessed form elements on a surface opposite the printable surface and / or a circumferential surface, which are designed to define a position and orientation of the resistance carrier during a production process of the grinding potentiometer.

[0025] Such protruding or recessed design elements make it possible to insert the resistor carrier, for example when mounting it in a housing of a grinding potentiometer, in a defined position and orientation, thus simplifying the assembly.

[0026] According to another aspect of the invention, a grinding potentiometer comprises a resistance carrier, a spring carrier with at least one grinding spring and a housing in which the resistance carrier and the spring carrier are arranged.

[0027] Such a grinding potentiometer enables cost-effective manufacturing, where customer-specific shaping requirements can be easily accommodated.

[0028] According to another aspect of the invention, a double potentiometer has two grinding potentiometers, wherein the double potentiometer is designed to move the spring carriers simultaneously or individually.

[0029] This dual potentiometer allows for cost-effective adaptation to customer-specific shaping requirements, while also providing redundancy, as resistance changes of both grinding potentiometers can be simultaneously recorded and evaluated.

[0030] According to another aspect of the invention, a manufacturing process for a resistance carrier for a grinding potentiometer comprises the following steps: injection molding of the resistance carrier from a thermoplastic material and application of a resistance track to a flat, printable surface of the resistance carrier.

[0031] This process makes it easy to flexibly accommodate customer-specific shapes while still allowing the resistance carrier to be manufactured cost-effectively, which is made possible by injection molding.

[0032] According to an advantageous embodiment of the method, the application of the resistive track to the flat printable surface of the resistive substrate comprises the following steps: cleaning the resistive substrate, activating the printable surface by means of a plasma process, applying the resistive track by means of screen printing, or a painting or ink-jet process, and curing the resistive track.

[0033] This method makes it possible to provide the resistive track to the resistive carrier using a known and proven method, even though this resistive carrier can be flexibly adapted to a customer-specific shape.

[0034] According to the invention, a conductive layer is applied to the printable surface.

[0035] This step makes it possible to easily connect further layers, which are applied at least partially to the conductive layer, with other areas of the printable surface of the resistor carrier.

[0036] According to a further advantageous embodiment of the method, it includes the step: resistance adjustment of at least one area of ​​the resistive track by means of laser trimming.

[0037] Laser trimming makes it possible to change the electrical resistance in the area by removing the resistive track and, especially when manufacturing a dual potentiometer, to adjust the resistance values ​​to each other.

[0038] The invention is explained below by means of exemplary embodiments based on the accompanying drawings.

[0039] In particular, it shows: Fig. 1 is an exploded view of a dual potentiometer with resistor carriers according to the invention; Fig. 2 is a top view of a printable surface of the resistor carrier with printed conductive and resistive tracks; Fig. 3 is a perspective view of the resistor carrier on a surface opposite the printable surface; Fig. 4 is a side sectional view of the resistor carrier; Fig. 5 is a flowchart of a manufacturing process for the resistor carrier; and Fig. 6 is a flowchart of applying a resistive track to the printable surface.

[0040] Fig. 1 Figure 1 shows an exploded view of a dual potentiometer 1 with two sliding potentiometers 2. The dual potentiometer 1 is used in foot brake modules for commercial vehicles, but can alternatively also be used in other applications where redundant detection of a movement is required.

[0041] Each of the grinding potentiometers 2 has a resistor carrier 3, a spring carrier 4 with two sliding springs 5, and a housing 6 in which the resistor carrier 3 and the spring carrier 4 are arranged. In the illustrated embodiment, the housings 6 of the grinding potentiometers 2 are integrally formed. Alternatively, separate, interconnected housings 6 can also be provided. Furthermore, each of the grinding potentiometers 2 has a lever 7, which is pre-tensioned by means of a torsion spring 8. By means of the lever 7, the spring carriers 4 of the grinding potentiometers 2 can be moved simultaneously by a driver of a brake pedal (not shown) of the foot brake module.

[0042] Fig. 2 Figure 1 shows a top view of a printable flat surface 9 of the resistor carrier 3 with printed conductive tracks 10 and resistive tracks 11. The conductive tracks 10 connect the resistive tracks 11 to contact elements 12. This makes it possible to detect a resistance value depending on the position of one of the slip springs 5 ​​when it connects two adjacent resistive tracks 11, in order to determine the position of the slip spring 5 and thus the position of the lever 7, thereby determining the degree of actuation of the brake pedal. Further conductive tracks 10 continue as conductive tracks 10', whereby two adjacent conductive tracks 10' can be connected by means of the slip springs 5 ​​to perform a switching function.

[0043] The resistor 3 is made of a material comprising a thermoplastic polymer. In particular, the material comprises glass fiber-reinforced polyphenylene sulfide. In alternative embodiments, the thermoplastic base material comprises a different thermoplastic polymer, which, however, like the glass fiber-reinforced polyphenylene sulfide, has the property of being dimensionally stable in a temperature range up to over 200°C.

[0044] Fig. 3 shows a perspective view of the resistance carrier 3 on one of the surfaces 13 opposite the printable surface 9.

[0045] In Fig. 3 It can be seen that the contact elements 12 are designed as pins. Furthermore, in Fig. 3 It can be seen that the resistor carrier 3 has protruding features 14 on the surface 13 opposite the printable surface 9, as well as a recessed feature 15 on a circumferential surface of the resistor carrier 3. In alternative embodiments, the resistor carrier 3 also has one or more recessed features on the surface 13 opposite the printable surface 9 and / or one or more protruding features on the circumferential surface of the resistor carrier 3. In further alternative embodiments, no such features 14, 15 are provided. These features 14, 15 make it possible to define the position and orientation of the resistor carrier 3 during a production process of the grinding potentiometer 2.

[0046] The resistor carrier 3, as also shown in Fig. 3 It is recognizable that an annular region 16 is present. In the annular region 16, the resistive element 3, in conjunction with the protruding annular segment-shaped regions 16' ( Fig. 2 ) on the printable surface 9, circumferential sections with a uniform thickness and with a predetermined surface roughness.

[0047] In this embodiment, the resistor carrier 3 is provided with a non-rotationally symmetrical engagement contour 22 at its center. The engagement contour 22, here designed for a Torx® screwdriver, allows the resistor carrier 3 to be rotated to enable initial adjustment of the potentiometer. This initial adjustment is achieved by applying a precisely controlled pressure of the housing 6 to the circumferential sections of the annular area 16 and the annular segment-shaped areas 16', while still ensuring a permanent position of the resistor carrier 3 within the housing 6.

[0048] Fig. 4 shows a lateral sectional view of the resistance carrier 3.

[0049] In Fig. 4 It can be seen that the pin, as one of the contacting elements 12, is connected to the resistor carrier 3 by being cast in place. In alternative embodiments, in which the contacting element 12 is not designed as a pin but, for example, as an angled solder lug, the contacting element 12 can have a non-rotationally symmetrical contour in the section cast into the resistor carrier 3, which allows for a directed and rotationally inhibiting orientation. In alternative embodiments, the contacting elements 12 are not cast in place but are connected to the resistor carrier in another way, for example, by screws.

[0050] The pin, as one of the contacting elements 12, and the printable surface 9 are coplanar, meaning that a cross-sectional area of ​​the contacting element 12 facing the printable surface 9 and the printable surface 9 together form a flat surface. In alternative embodiments, the contacting element 12 can also protrude from or be recessed from the printable surface 9.

[0051] A conductive layer 17 is provided on the printable surface 9 of the resistor carrier 3. This layer forms one of the conductive tracks 10 and is connected to the contacting element 12. One of the resistive tracks 11 is conductively applied to the conductive layer 17 in an overlapping section. An insulating layer 18 is applied to the resistive track 11, and optionally, further printing layers 19, 20, 21 are provided on the insulating layer 18. The insulating layer 18 serves either to insulate the resistive track 11, for example, for the switching function, or, if at least one of the further printing layers 19, 20, 21 is provided, it can function as a capacitor. In alternative embodiments, depending on the respective function, the individual layers 11, 17, 18, 19, 20, 21 can be provided or omitted, and their sequence can be adjusted accordingly.

[0052] Fig. 5 shows a flowchart of a manufacturing process for the resistor carrier 3.

[0053] In step S1, the resistor carrier 3 for the grinding potentiometer 2 is manufactured from thermoplastic material using injection molding. Subsequently, in step S2, the resistive track 11 is applied to the flat, printable surface 9 of the resistor carrier 3.

[0054] In step S1, the contacting elements 12 are optionally placed in an injection mold, and then the thermoplastic material is injected into the injection mold and cooled until the material has solidified sufficiently.

[0055] When creating the injection mold, care must be taken to ensure that the surface of the printable area 9 is as smooth and flat as possible. This can be achieved by polishing and grinding the mold, as well as by selecting appropriate injection parameters. Furthermore, when determining the shape of the resistive element 3, care must be taken to ensure that no material accumulations are generated on the surface 13 opposite the printable area 9. Such accumulations could cause differential shrinkage during the cooling process, resulting in surface defects that would alter the local resistance characteristic of the resistive track 11.

[0056] Fig. 6 shows a flowchart of the application of the resistive track to the printable surface 9 from step S2.

[0057] First, the resistor carrier is cleaned in step S2.1 to remove impurities, such as a release agent from the injection molding process.

[0058] Subsequently, in step S2.2, the printable surface 9 is subjected to a plasma process, whereby the printable surface 9 is activated, thus enabling better adhesion of the printing.

[0059] In step S2.3, the resistive track 11 is then printed directly onto the printable surface 9. This is done via a screen printing process. In alternative embodiments, printing can also be carried out via a coating or inkjet process.

[0060] In step S2.4, the resistive track 11 is then cured. This step is first divided into a storage period at room temperature for 5–10 minutes to allow the applied print to level out. This is followed by oven drying at approximately 150°C for 5–10 minutes. This is necessary to remove any remaining solvent. Finally, curing takes place at >230°C for approximately 30 minutes. The values ​​for optimal drying and curing are determined empirically according to the specific embodiment.

[0061] To apply the subsequent layers, e.g., the conductive layer 17, steps 2.3 and 2.4 are repeated with the corresponding printing. This is done until all necessary layers have been applied.

[0062] In another alternative embodiment of the manufacturing process, prior to printing the resistive track 11, the conductive layer 17 is applied to the printable surface 9 in a section overlapping with the resistive track 11, either via the screen printing process or, alternatively, via the varnishing or inkjet printing process. Depending on the number and type of layers required, the further printing layers 19, 20, 21 are applied and cured, either instead of or on top of the resistive track 11.

[0063] In an optional process step, the resistance of at least one area of ​​the resistive track 11 is adjusted by means of laser trimming. In this process, the cross-section of the resistive track 11 is reduced in order to increase the electrical resistance in this area.

[0064] Although the present invention has been described with reference to certain features and embodiments, it is obvious that various modifications and combinations can be made to it.

[0065] The description and drawings are therefore to be regarded merely as an illustration of the invention as defined by the attached claims. REFERENCE MARK LIST

[0066] 1 Dual potentiometer 2 Grinding potentiometer 3 Resistor carrier 4 Spring carrier 5 Sliding spring 6 Housing 7 Lever 8 Torsion spring 9 Printable surface 10, 10' Conductor track 11 Resistor track 12 Contacting element 13 Surface opposite the printable surface 14 Protruding molded element 15 Recessed molded element 16 Annular area 16' Annular segment-shaped area 17 Conductive layer 18 Insulating layer 19, 20, 21 Further printing layers 22 Engagement contour

Claims

1. Resistive carrier (3) for a slide potentiometer (2) which has: a printable planar surface (9) with printed strip conductors (10), a resistive track (11) which is printed directly on the printable surface (9) and contacting elements (12) which are connected to the resistive track (11) by means of the strip conductors (10), wherein a material of the resistive carrier (3) has a thermoplastic plastics material, characterized in that additional strip conductors (10) are provided, which continue in two mutually adjacent strip conductors (10') which are constructed to be able to be connected in order to carry out a switching function.

2. Resistive carrier (3) according to claim 1, wherein the material of the resistive carrier (3) is constructed to be dimensionally stable in a temperature range of up to above 200°C.

3. Resistive carrier (3) according to claim 1 or 2, wherein the material of the resistive carrier (3) has a glass-fiber-reinforced polyphenylene sulphide.

4. Resistive carrier (3) according to any one of the preceding claims, wherein the contacting elements (12) are constructed, in particular as a result of their nonrotationally symmetrical contour, to be connected to the resistive carrier (3) in a directed and rotation-limiting orientation by means of molding.

5. Resistive carrier (3) according to any one of the preceding claims, wherein a conductive layer (17) which is connected to the contacting elements (12) is provided on the printable surface (9) and the resistive track (11) is applied to the conductive layer (17) in an overlapping portion.

6. Resistive carrier (3) according to claim 5, wherein additional layers (18, 19, 20, 21), in particular at least one insulating layer (18), are provided.

7. Resistive carrier (3) according to claim 5 or 6, wherein the contacting elements (12) and the printable surface (9) are constructed in a coplanar manner.

8. Resistive carrier (3) according to any one of the preceding claims, wherein the resistive carrier (3) has a circular-ring-like region (16), and in a manner extending in the circular-ring-like region (16) portions having a uniform thickness of the resistive carrier (3) and a predetermined surface roughness are provided.

9. Resistive carrier (3) according to any one of the preceding claims, wherein the resistive carrier (3) has on a face (13) opposite the printable surface (9) and / or the circumferential face thereof protruding and / or recessed shaped elements (14, 15) which are constructed to define a position and attitude of the resistive carrier (3) during a production process of the slide potentiometer (2).

10. Slide potentiometer (2) which has: a resistive carrier (3) according to any one of the preceding claims, a spring carrier (4) having at least one wiper (5) which is constructed to connect the mutually adjacent strip conductors (10') in order to perform a switching function, and a housing (6) in which the resistive carrier (3) and the spring carrier (4) are arranged.

11. Dual potentiometer (1) which has: two slide potentiometers (2) according to claim 10, wherein the dual potentiometer (1) is constructed so that the spring carriers (4) are moved simultaneously.

12. Production method for a resistive carrier (3) for a slide potentiometer (2) according to claim 10, having the steps of: injection-molding the resistive carrier (3) from a thermoplastic plastics material; applying a resistive track (11) to a planar printable surface (9) of the resistive carrier (3); and applying a conductive layer (17), which forms one of the strip conductors (10) and which is connected to one of the contacting elements (12), to the printable surface (9) in such a manner that two mutually adjacent strip conductors (10') which can be connected in order to perform a switching function are formed.

13. Production method according to claim 12, wherein the application of the resistive track (11) has the following steps: cleaning the resistive carrier (3); activating the printable surface (9) by means of a plasma process; applying the resistive track (11) by means of screen printing, or a painting or inkjet process; and curing the resistive track (11).

14. Production method according to either claim 12 or 13, having the step of: resistance adjustment of at least one region of the resistive track (11) by means of laser trimming.