GB2208568A

GB2208568A - Method of manufacturing electrical circuits in small domestic electrical appliances

Info

Publication number: GB2208568A
Application number: GB8818566A
Authority: GB
Inventors: Willi J Schmidt; Jurgen H Cammann; Karl Birkert; Rolf Thomas
Original assignee: Rowenta Werke GmbH
Current assignee: Rowenta Werke GmbH
Priority date: 1987-08-04
Filing date: 1988-08-04
Publication date: 1989-04-05
Also published as: FR2619277B1; FR2619277A1; GB8818566D0

Abstract

A method and apparatus for automating the assembly and wiring of electrical connections in small domestic electrical appliances in which connecting contact members 1, 2, 3 are formed during manufacture of the individual sub-assemblies 6.6''' so that they terminate in a contact plane 4 in the assembled position of the subassemblies. The terminal portions 9 of the members 1, 2, 3 in the plane are electrically connected by means of electrically conductive substances in the form of paste, liquid, fusible material, powder or the like, disposed, for example, in grooves 10 and subsequently hardened. <IMAGE>

Description

Method of manufacturing small domestic electrical appliances The invention relates to methods of manufacturing small domestic electrical appliances, for example coffee makers or the like, wherein a plurality of sub-assemblies are arranged in an electric circuit disposed in a chamber of a said appliance, and to apparatus for carrying out such methods.

The numerous small domestic electrical appliances include, for example, mixers, stirrers, irons, toasters, deep-fat fryers, mouth strays, hair care equipment, vacuum cleaners, waffle irons, food processors, juice extractors, salad spinners or the like. These are examples of appliances to which the invention relates. However, the following specification will refer in particular to electric coffee making machines, for the sake of simplicity, as these constitute a preferred application. The methods disclosed herein, however, are applicable to all small domestic electrical appliances in which several contact points have to be connected up inside a space in the appliance.

When manufacturing coffee makers, i.e. when the individual parts are assembled to form the appliance, it is known first to place the required sub-assemblies and modules, e.g. the throughflow heater, thermostat switch, overheating cut-out, on and off switches, connections for the mains and similar components, in the socket region and then to wire up the individual contact points to one another. The sub-assemblies used will in some cases already have flexible electric leads, so called litzes, already fitted to them, which are connected to the appropriate contact point in the appliance with the corresponding opposite contacts, frequently at places which are not easily accessible.

Even in the steps preceding this operation, known as preassembly, all the sections of wire are individually pretreated. The pieces of wire are cut to length, insulated and, depending on their use, provided with mutli-core cable ends, cable shoes or the like. This laborious preparation is carried out using semi-automatic apparatus.

The final assembly of the appliance is also done by hand, whilst specific sub-assemblies, e.g.

the throughflow heaters, have undergone further preassembly. In this case, also, mechanical components and electrical components are supplied already partly coupled and are fitted in on the assembly belt. All in all, the manual wiring operation and the job of installing the sub-assemblies, which is made more difficult by its varying nature, have proved to be particularly labour-intensive. The costs of preassembly and final assembly can be determined exactly and, from the point of view of production, they constitute a substantial proportion of the manufacturing costs. To reduce these assembly costs the operations are grouped as follows: semiautomatic preparation of the wire connections, manual preassembly of the throughflow heaters, manual assembly of the electrical wiring and, lastly, final manual assembly of the appliance as a whole.

In order to improve these operations attempts have been made to automate these processes still further. This was supposed to be achieved by fixed wiring of the sub-assemblies. However, fixed wiring will suit only a small fraction of the wiring as a whole, with the result that the operation could not be automated. Moreover, automatic bending of the individual wires for fixed wiring requires the use of apparatus of above-average technical complexity without coming any closer to the final objective of automation.

Viewed from one aspect the invention provides a method of manufacturing small domestic electrical appliances, wherein a plurality of sub-assemblies are arranged in an electric circuit disposed in a chamber of a said appliance, the sub-assemblies being provided with connecting contact members having terminal portions which end substantially in the region of a common contact plane, the process including contacting the contact members with electrical connectors so as to connect the sub-assemblies in said circuit.

Viewed from another aspect the invention provides apparatus for carrying out such a method wherein the connecting contact members comprise flat conductors and/or pins which, by virtue of their shape and dimensions, project into the region of the contact plane and terminate there.

With such arrangements, during manufacture of the individual sub-assemblies, the connecting contact members may be prepared so that after they have been installed in e.g. a socket of the appliance the terminal portions of the members end substantially in the region of a common plane. It is thus possible for electrical connectors to be contacted with these terminal portions in the common plane, thereby enabling substantial and even full automation of the assembly process. It is also possible to produce the required connections by automatic wiring and soldering, adhesive bonding or the like.

However, it is also possible to use printed circuit boards and connect them automatically to the contacts.

Thus at least in the preferred embodiments of the invention there is provided a method and an apparatus by means of which the wiring of the individual sub-assemblies and the electrical connect tions thereof in a small domestic electrical appliance can be automated as far as possible at little cost.

The safety of such appliances manufactured in this way is increased substantially since assembly errors caused by human error can be eliminated and the connection points cannot become detached.

Preferred aspects of the method of the invention are recited in subclaims 2 to 11. Subclaims 12 to 27 refer to preferred aspects of the apparatus of the invention. In preferred arrangements at least, semi-automatic preparation of wire connections is no longer required. The wiring up of the individual connections of the various sub-assemblies is automated.

The safety of a small domestic electrical appliance assembled by the preferred methods is increased substantially.

It will thus be seen that some measures by means of which the wiring of the individual subassemblies and their electrical connections in a small domestic electrical appliance can be substantially automated at low cost. There are, however, improved possibilities for the practical application of the method to small domestic electrical appliances or the like. For example, a preferred method further comprises forming at least part of the electrical connectors by applying lines of electrically conductive substances in powder form and of homogeneous or heterogeneous composition along the desired paths of the connectors, and reducing the surface area of such substances. Preferably a plurality of different substances are applied separately from one another.

In this way, it is ensured that the contact members arranged in a plane can be connected in the required circuit.

In a preferred arrangement, a sheet made of non-combustible or low-flammability material is pushed over the contact members e.g. pins which are to be connected. The electrical connectors betwen the contact pins initially consist of a flowable powdered material which is poured onto the surface of the sheet to follow the path of the desired connectors. To enable the material to be applied cleanly, a pouring mask may be used for the pouring operation. The conductive substances may range from granular to powdered and may take different three-dimensional shapes. It is possible for the substances to consist of homogeneous components such as copper, tin, brass, aluminium, silver or the like; however, they may also consist of heterogeneous materials such as a mixture of copper and tin, aluminium and tin, or the like.

After the lines of conductor have been poured onto the surface of the sheet, the conductive materials which have been applied loosely are subjected to a reduction in their surface area. The surface area may be made smaller by the effect of heat; however, it is also possible to reduce the surface area by sintering, or pouring a liquid, electrically conductive material which will harden after pouring, such as tin solder or the like.

The critical point during surface reduction is that the substances applied will normally have the effect of supporting the structure and strengthening the surface as a result of the surface reduction, so that good electrical conductivity of the powdered substances applied is ensured.

To make sure that the lines of powdered conductor run cleanly, the sheet-like carrier plate may have a surface structure (for example grooves) which predetermine the path of the conductor. The conductive substances may be poured into this structured surface before being subjected to surface reduction. To prevent damage to the sheet-like support plate, the surface of the sheet-like support plate may be covered with a mask during the surface reduction.

Due to the mask, only the predetermined conductor lines of conductive material are then exposed to the surface reduction treatment, so that the carrier plate cannot be damaged. In this way it is possible to produce the sheet-like support plate from thermoplastic material and to provide the desired conductor lines by forming groove-like depressions in the plate during the injection moulding of the plate and to recess the through-holes for receiving the electrical contact pins in such groove-like depressions.

Some preferred embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Fig. 1 shows a side elevation of apparatus in accordance with the invention; Fig. 2 shows a plan view of the apparatus of Fig. 1; Fig. 3 shows another side elevation of the invention, showing the electrical connectors; Fig. 4 also shows the electrical connectors and contacts in a corresponding plan view; Figs. 5 and 6 show an alternative embodiment.

Sub-assemblies 6, 6', 6" and 6"' are mounted on a support 11 of an electrical appliance. The contact members 1 of the sub-assemblies 6 which are to be connected up have portions on the respective subassemblies located in the region of the support ll, and the contact members 1 may be in the form of flat conductors 2 and/or as pins 3 of varying geometric configuration.

All the contact members I are aligned in the direction of jointing "A", substantially at right angles to the support 11. Their lengths are such that their ends terminate in the region of the upper surface of a generally planar member which defines a contact plane 4, this contact plane 4 having downwardly widening through-openings 5 in order to make it easier to insert the contact members into the positions of penetration. The openings 5 are adapted to the particular profiles of the contact members 1 (flat conductors 2 and/or pins 3), so that they fit closely by virtue of their shape in the through-openings 5 (or vice versa).

When the preferred process of the invention is performed, a contact plane 4 is pushed onto the plurality of flat conductors 2 and/or pins 3, whilst adjusting cams (not shown) at the edge of the contact plane 4 fix the position of insertion precisely. The downwardly widening through-openings 5 make the jointing process easier so that the required operation can also be carried out automatically.

Locking cams (not shown either) injection moulded on the baseplate hold the ready-mounted contact plane in position.

In Figs. 1 and 2, grooves 101 for example, have been provided, to receive the conductive material which is in the form of a paste or a liquid. Fig. 1 shows the grooves 10 in the partial sections A-B, C-D, E-F and C;-H. The grooves 10 all end at the through-openings 5.

By means of a program-controlled automatic application device, the conductive material in paste or liquid form is introduced into the grooves 10 and this matrial is also applied to the contact points 9 and when it has hardened the entire wiring process is complete.

In a preferred embodiment of the process, the contact plane 4 is already prepared in an automatic machine in a previous operation. In this operation the grooves 10 are filled with the conductive material in paste or liquid form as shown in Figs. 3 and 4. The contact points 9 have not yet been applied.

The contact plane 4 thus prefabricated, and treated for example by means of a programmable robot or the like, is then inserted with its electrical connectors 8 - at one station on the assembly line in the appropriate domestic appliance, whilst the flat conductors 2 and pins 3 are inserted so as to fit almost perfectly by virtue of their shape in the through-openings 5 of the contact plane 4.

The support aids mentioned above provided on the edge ensure that the contact plane 4 is correctly located.

On the assembly line, only the contact points 9 are applied by means of a program-controlled automatic apparatus (robot or axis handling system). As transportation continues along the assembly line the initially paste-like and/or liquid conductive material hardens.

The production and configuration of the contact plane 4 can also be extended and varied as desired according to apparatus claims 12 to 27, generally with no restrictions whatever as to material or format, and similarly the sequence of the operations can be varied at will. A standardised form for the contact plane 4 is particularly advantageous, with all the necessary grooves and through-openings 5 for a particular product line being provided in the various positions and of the correct dimensions and finally only the configuration specific to the appliance is used due to the program-controlled applicator device.

It will be appreciated that in one broad sense the "contact plane" is to be understood as a purely geomtric structure. A preferred process (see for example claim 4 in conjunction with apparatus claim 27) envisages, for example, that the prefabricated electrical connectors 8 could be placed and/or contacted directly on the flat conductors 2 or pins 3, and that there may be no board- or sheetlike member supporting the electrical connectors.

Thus the physical presence of a planar member defining the contact plane 4 is by way of example and, under certain circumstances, is not essential. By way of illustration, Figs. 5 and 6 show the same arrangement of sub-assemblies (6, 6', 6", 6"') as in Figs. 1 to 4. Similarly, the electrical connectors 8 shown in Figs. 3 and 4 are shown in the same configuration, but the "prefabricated" electrical connectors 8 in this alternative embodiment are inserted and contacted in self-supporting fashion as a bridge from contact member to contact member.

The configuration of the electrical connectors 8 may also take other forms. Thus, for example, it is possible to use lengths of wire or the like in which the ends are correspondingly contacted with the flat conductors 2 and/or the pins 3, e.g.

by welding, soldering or dotting.

The invention also extends to domestic appliances manufactured using the methods and/or apparatus disclosed herein.

As has been pointed out, there are numerous possible variations on the method of the invention as already mentioned, but in general the ability to automate manufacture is improved.

It is to be clearly understood that there are no particular features of the foregoing specification, or of any claims appended hereto, which are at present regarded as being essential to the performance of the present invention, and that any one or more of such features or combinations thereof may therefore be included in, added to, omitted from or deleted from any of such claims if and when amended during the prosecution of this application or in the filing or prosecution of any divisional application based thereon. Furthermore the manner in which any such features of the specification or claims are described or defined may be amended, broadened or otherwise modified in any manner which falls within the knowledge of a person skilled in the relevant art, for example so as to encompass, either implicitly or explicitly, equivalents or generalisations thereof.

Claims

claims

1. A method of manufacturing small domestic electrical appliances, wherein a plurality of subassemblies are arranged in an electric circuit disposed in a chamber of a said appliance, the sub-assemblies being provided with connecting contact members having terminal portions which end substantially in the region of a common contact plane, the method including contacting the contact members with electrical connectors so as to connect the sub-assemblies in said circuit.

2. A method as claimed in claim 1, wherein the connecting contact members are passed through the contact plane to be contacted with the electrical connectors.

3. A method as claimed in claim 1 or 2, wherein the electrical connectors consist of conductive material applied in paste or liquid form.

4. A method as claimed in claim 1, 2 or 3, wherein the electrical connectors consist at least partly of prefabricated conductive material.

5. A method as claimed in any preceding claim, wherein the contacting and the formation of at least part of the electrical connectors are effected simultaneously by the application of the conductive material in paste or liquid form.

6. A method as claimed in claim 1 or 2, wherein the contacting is effected by the application of a conductive material in paste or liquid form.

7. A method as claimed in any of claims 1 to 4, wherein the contacting is effected by pressing together.

8. A method as claimed in claim 2, wherein the contacting is effected by welding.

9. A method as claimed in any preceding claim, further comprising forming at least part of the electrical connectors by applying lines of electrically conductive substances in powder form and of homogeneous or heterogeneous composition along the desired paths of the connectors, and reducing the surface area of such substances.

10. A method as claimed in claim 9, wherein a plurality of different substances are applied separately from one another.

11. A method as claimed in any preceding claim, wherein the terminal portions of the contact members extend in a substantially common direction.

12. Apparatus for carrying out the method claimed in any of claims 1 to 11, wherein the connecting contact members comprise flat conductors and/or pins which, by virtue of their shape and dimensions, project into the region of the contact plane and terminate there.

13. Apparatus as claimed in claim 12, wherein the contact plane is defined by at least one member having openings therethrough, the openings corresponding to the positioning and shape of the flat conductors and/or the pins.

14. Apparatus as claimed in claim 13, wherein the or each member defining the contact plane has a surface remote from the sub-assemblies which contains the electrical connectors and wherein such connectors extend up to the edge of the openings.

15. Apparatus as claimed in claim 14, wherein before or after the or each member defining the contact plane is inserted in the electrical appliance, the electrical connectors provided on the said surface are produced by the application of a hardenable, electrically conductive material in paste or liquid form.

16. Apparatus as claimed in claim 15, wherein the application is carried out using an automatic, program-controlled applicator apparatus.

17. Apparatus as claimed in claim 13, wherein the or each member defining the contact plane is inserted into the electrical appliance after the mounting of the sub-assemblies, the flat conductors and/or pins being inserted into the openings through the member(s) so as to form a substantially snug fit therein.

18. Apparatus as claimed in any of claims 14 to 16, wherein by the application of a conductive material in liquid or paste form to the position of each opening, an electrical contact is produced between the respective electrical connector which extends up to the edge of each opening and the flat conductor or pin inserted in such opening.

19. Apparatus as claimed in claim 18, wherein the application of a conductive material in liquid or paste form to the position of each opening is carried out by means of an automatic, program-controlled applicator apparatus.

20. Apparatus as claimed in any of claims 12 to 19, wherein the electrical connectors on the contact plane consist of pre-formed material, of rectangular, square, round, oval or polygonal crosssection or the like.

21. Apparatus as claimed in any of claims 12 to 20, wherein electrical contact between the contact members and the electrical connectors is produced by upsetting, pressing, riveting, fusion or welding or the like.

22. Apparatus as claimed in any of claims 12 to 21, wherein there is provided in the contact plane additionally one or more points of electrical contact which differ from the points of contact between the contact members and the electrical connectors in their direction of jointing and in the contacting.

23. Apparatus as claimed in claim 13 and any of claims 14 to 22, wherein the or each member defining the contact plane is provided with grooves defining the layout of the electrical connectors.

24. Apparatus as claimed in claim 13 and any of claims 14 to 23, wherein the or each member defining the contact plane is produced by extrusion, deep drawing, sintering, cutting out, stamping, embossing, casting, milling, pressing or the like.

25. Apparatus as claimed in claim 13 and any of claims 14 to 24, wherein the starting material used to produce the or each member defining the contact plane is plastics, resin, ceramics, glass, impregnated cardboard, deep drawn film, hard rubber, clay mixtures, glass wool, mineral wool, mica or similar insulating materials.

26. Apparatus as claimed in claims 13 and any of claims 14 to 25, wherein the or each member defining the contact plane has contact points and/or electrical operational elements, e.g. resistors, impedence coils, fuses, thermo-switches or the like which are inserted at the time of manufacture.

27. Apparatus for carrying out the method claimed in claim 4, wherein the terminal portions of the connecting contact members are in the form of flat conductors or pins which make direct contact with prefabricated electrical connectors.

28. A method of manufacturing small domestic electrical appliances, substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 3 and 4 or Figs. 5 and 6 of the accompanying drawings.

29. Apparatus for carrying out a method of manufacturing small domestic appliances, the apparatus being substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 3 and 4 or Figs. 5 and 6 of the accompanying drawings.