Process and apparatus for producing spiral resistors

Abstract

 A process for producing spiral electrical resistors, comprises the steps of: winding a preset length of resistive wire (4) with a presettable pitch around a swift (1) having adjustable width to obtain a plurality of turns; blocking in position said turns on at least part (1a) of said swift; reducing the width of said swift; engaging at least some of said turns with at least an electrically insulating support (19; 23); releasing said turns from said swift; withdrawing the resistor (18; 20) thus obtained from the swift having reduced width; and repeating said steps, restoring the original width of the swift before winding the subsequent length of wire.

Description

[0001] The present invention concerns a process and an apparatus for the manufacture of spiral-type electrical resistors. "Spiral" electrical resistors are already known, particularly for use in air conditioners, consisting of a couple of strips made of insulating material, such as for instance micanite, each provided with a plurality of holes through which a wire, or strap, is passed, of resistive material so as to form a plurality of half turns projecting from the same side of the supporting strip. The two strips are then coupled to form a single structure provided with a plurality of resistive "spirals", each consisting of two half turns opposite to one another and positioned on different strips.

[0002] In order to simplify the structure of this type of resistor, resistors with elliptical spirals were proposed, provided with two insulating strips positioned near the ends of the resistor turns and housing said turns in a corresponding plurality of slits.

[0003] Said resistors are the object of Italian patent application n. 19355-A/85 as well as of Italian patent application n. 21428-A/89, both filed in the name of the Applicant.

[0004] The major disadvantage of said resistors lies in the difficulty to apply the techniques known in the art to their production, which results in a high percent of manual labor for their manufacture.

[0005] Object of the present invention is therefore to overcome said problems by providing a process for the manufacture of spiral resistors in an easy, economic and reliable way. Another object of the present invention is to provide an apparatus to perform said process.

[0006] Said objects are achieved by the present invention that provides a process for producing spiral electrical resistors, characterized in that it comprises the steps of:
winding a preset length of resistive wire with a preselectable pitch around a swift having adjustable width to obtain a plurality of turns;
blocking in position said turns on at least part of said swift;
reducing the width of said swift;
engaging at least some of said turns with at least one electrically insulating support;
freeing said turns from said swift;
withdrawing the resistor thus obtained from the swift having reduced width; and
repeating said steps, restoring the original width of the swift before winding the subsequent length of wire.

[0007] The invention moreover comprises an apparatus for producing spiral electrical resistors, characterized in that it comprises:
a swift having adjustable width;
means to feed a length of resistive wire to said swift;
means to reciprocally move the swift and said wire feeding means to obtain a plurality of turns with preset pitch; and
blocking means to temporarily block in position said turns on at least part of said swift.

[0008] The swift width is preferably adjusted by means of one or more blades positionable sideways to a fixed and rotatable portion of said swift.

[0009] The process and apparatus according to the invention allow to automate the manufacture of the above described spiral resistors and to vary in a very simple way the size of said resistors, by replacing the side blades according to the width desired for the resistor, thus obtaining a considerable reduction in manufacturing costs.

[0010] The invention will be now further described by way of illustrative and non-limiting example with reference to the accompanying drawings, in which:

- figure 1 is an overall schematic view of an apparatus according to the invention;

- figure 2 is a section view of a detail of figure 1 embodiment;

- figure 3 is a top view of another detail of figures and 2 embodiment;

- figure 4 is a perspective view of a resistor in an intermediate step of the process according to the invention;

- figure 5 is a partial perspective view of the resistor of figure 4 in a subsequent step of the process; and

- figure 6 is a partial side view of a resistor of the radial type as obtainable by way of the process according to the present invention.

[0011] With reference to figure 1, the apparatus according to the invention comprises a swift having adjustable width as a function of the manufacturing steps for the production of spiral resistors, means to secure and to feed a length of resistive wire 4 to said swift, means to reciprocally move the swift and said wire feeding means so as to obtain a plurality of turns with preset pace, and blocking means 6 to block temporarily in position on said swift a portion of the turns formed thereon.

[0012] As during the manufacture of the aforedescribed spiral resistors a step is also envisaged to position supports made of electrically insulating material on the turns of the resistor wound about the swift 1, which step will be described more in detail hereinbelow, the apparatus according to the invention preferably comprises also means (not shown) for bringing said insulating supports into engagement with said turns as well as means (not shown) to withdraw the resistor provided with one or more insulating supports from the winding swift 1.

[0013] In the preferred embodiment of figure 1, the swift 1 is mounted through shaft 1′ on a spindle 7 or similar means to be rotated about its own axis. The means to secure and feed a length of resistive wire to the swift during the winding operation and the means to reciprocally move swift and feeding means are comprising a securing means 2 blocking the free end of the wire 4, a wire tightener 3 and a worm screw 5 on which the wire tightener 3 is movabble. For a better comprehension of the drawing, in figure 1 securing means 2 is shown exploded with respect to its actual position, that is laterally to swift 1, e.g. on spindle 7, in order to rotate with swift 1. In figure 3 is disclosed the actual position of means 2. In the preferred embodiment disclosed, the swift is rotated but it remains fixed without translational motion, and the feeding means moves with respect to the swift; however the invention obviously comprises also embodiments where the reciprocal motion is reversed and those where the swift does not rotate while the wire is wound around it.

[0014] In order to adjust the swift 1 width as a function of the manufacturing steps and thus enable the positioning of the aforesaid insulating supports on the turns and the subsequent withdrawal of the finished resistor, the swift 1 is preferably provided with a first fixed portion 1a fastened to the spindle 7 and rotatable about its own axis and at least a second portion securable to said fixed portion and movable in relation to the same to vary the swift width; in particular said second portion or portions are interchangeable as a function of the width desired for the winding swift.

[0015] In the embodiment disclosed in figure 1 to 3, said movable portions consist of blades 8 that can be positioned laterally to the fixed portion of the swift 1 by means of slots or similar guide means provided in a complementary way on said blades and on said fixed portion, as can be better seen in figure 2 (where one of the blades is shown in an exploded view to make the drawing better understandable), and indicated by references 9 and 10. Furthermore, as shown in figure 3, the fixed portion of the swift is preferably provided with means 11 to urge the blades 8 towards the outside when these are positioned onto the fixed portion 1a of the swift, sideways thereto. In figure 3 the preferred embodiment shown comprises a couple of side blades 8 mounted on a portion 12 of a piston or similar means of translation, said portion 12 and said blades 8 being rotatable together with swift fixed part 1a. Piston portion 12 is also provided with securing means 2′ to secure wire 4 before the next winding of a resistor, as better disclosed hereinbelow. The blades 8 are preferably elastically hinged in 13 to portion 12, to allow their slight lateral movement effected by the urging means 11 provided inside the fixed portion of the swift 1a, consisting in this case of a couple of cams. Said cams, as shown, can be actuated by a rod 14 integral to the piston 12 and translatable therewith and with said blades, to urge the blades 8 towards the outside, once the correct positioning of the blades in respect to said fixed portion of the swift 1 has been obtained. A longitudinal hole 14b is provided in the fixed portion of the swift 1 to temporarily house rod 14.

[0016] Alternatively rod 14 can be permanently housed in hole 14b and be actuated by a pivot projecting from the piston 12 (not shown).

[0017] Figure 2 shows a particular configuration of the fixed portion of the swift 1a and of the blocking means 6, wherein said fixed portion 1a and said blocking means are provided with complementary shapings, such as male and female matching bulges 15 and 16 respectively, to shape on the turns of the resistor still wound about the swift a plurality of positioning saddles in which said insulating support, or supports, will be housed. The shapings 15 are provided on the fixed portion of the swift 1 for reasons which will become obvious in the light of the process steps hereunder described.

[0018] The blocking means 6 are by stoppers, such as those shown in figure 2, or by combs or similar devices capable of keeping the pitch (i.e. the distance) of the turns during the step of positioning the insulating support.

[0019] During the process to manufacture spiral electrical resistors according to the invention, first of all a winding stage is provided to wind a preset length of said resistive wire 4 around the swift 1, which has the desired width to obtain a preset width of the resistor turns, that is, it is provided sideways with blades 8.

[0020] To this purpose, wire 4 end is secured to means 2 and, by actuating the worm screw 5 the wire tightener 3 is translated at a preset speed with respect to swift 1, that in the meantime is rotated at a preselected speed, in order to obtain a plurality of turns with a predetermined pitch that is depending on the reciprocal motion of said wire tightener and said swift. Then means 6 is actuated to block the turns thus obtained on the fixed portion 1a of swift 1, wire 4 is cut to free the turns thus obtained from the remaining length of wire on tightener 3, and the other end of wire 4 is released from securing means 2.

[0021] The swift width is then reduced to leave sufficient room, in correspondence with the end of the winded turns, for the positioning of at least one electrically insulating support which is forced on said turns to engage with at least some of them and avoid they get in contact to each other during the subsequent use as resistor.

[0022] The next step provides the release of said turns from the swift by reversely actuating the blocking means 6, and the withdrawal of the resistor thus obtained from the swift; this operation is facilitated by the fact that the swift width has been previously reduced.

[0023] The abovelisted steps are repeated to produce a subsequent resistor, taking care to previously restore the original width of the swift and to secure wire 4 end to means 2′ before winding another length of resistive wire. To obtain this next resistor, wire tightener 3 is moved along screw 5 in a direction opposite to the previous one; i.e., if the previous resistor turns were obtained by moving wire tightener 3 goes from siston 12 to spindle 7.

[0024] As mentioned hereinabove with reference to the structure of the apparatus, the width of the swift 1 is preferably adjusted by displacement and/or removal of one or more blades positionable sideways to the fixed portion of the swift and rotatable with spindle 7; the blades moreover are replaceable according to the width required for the resistor turns.

[0025] The preferred process using an apparatus of the type described in figures 2 and 3 provides to position two blades 8 sideways to said fixed portion 1a simultaneously stressing them towards the outside, for instance by means of cams 11 and rod 14, until the maximum preset width for the resistor turns is obtained. The resistor obtained at this point is similar to the resistor 18 illustrated in figure 4, where for a better understanding of the drawing the swift 1 has been omitted. In order to allow to withdraw the blades from the swift without deforming the turns thus obtained, first of all the swift width is partially reduced by translating slightly backwards piston 12, rod 14 and the blades 8, thus allowing the cams 11, which are elastically stressed towards a rest position, to be disengaged from the blades themselves. It thus is now possible to remove blades 8, withdrawing them from the fixed portion 1a and leaving a free room corresponding to their width adjacent to the turn ends.

[0026] In order to operate the subsequent step of engaging said turns with said electrically insulating support.

[0027] If desired it is possible to shape the turns in the way disclosed in figure 4 providing blocking means 6 and the fixed portion 1a with said shapings with male and female bulges 15 and 16 to obtain on said turns the previously mentioned saddles 17 for the positioning of the insulating support. This operation is carried out automatically during the stage in which the turns are blocked on the fixed portion of the swift.

[0028] After positioning the insulating support 19 on the turns of the resistor 18, as shown in figure 5, the resistor 18 is withdrawn and the original width is restored by moving again the blades 8 and the rod 14 into engagement with the fixed portion of the swift 1a and with the cams 11 by translating piston 12.

[0029] The process according to the invention also envisages the possibility of using some further steps to obtain a radial resistor 20 of the type shown in figure 6. As can be noticed from this figure, the resistor comprises a central tubular support 21 appropriately made of an electrically insulating material and radially provided with a plurality of seats 22 designed to engage the end of a corresponding plurality of turns arranged radially to said support and provided with at least one flexible electrically insulating support 23 at a preselected distance from central support 21.

[0030] To obtain this kind of resistor, the process according to the invention envisages the additional steps of positioning at least a resistor obtained in the previously described way and provided with a single planar and flexible insulating support 23 in correspondence with the circular support 21; said planar support 23 is then bent by preferably acting on its ends by means of a template or similar device, until said ends are brought into contact to each other, and the ends of the turns adjacent to the circular support 21 are located in said superficial seats 22 of the support itself. Once the turns positioned, said ends of the supports 23 are fixed to one another so as to obtain a resistor with radial turns.

[0031] Two opposed resistors are preferably used, which are semicircularly bent and fixed to one another at the respective ends.

Claims

1. A process for producing spiral electrical resistors, characterized in that it comprises the steps of:
winding a preset length of resistive wire (4) with a presettable pitch around a swift (1) having adjustable width to obtain a plurality of turns;
blocking in position said turns on at least part (1a) of said swift;
reducing the width of said swift;
engaging at least some of said turns with at least an electrically insulating support (19; 23);
releasing said turns from said swift;
withdrawing the resistor (18; 20) thus obtained from the swift having reduced width; and
repeating said steps, restoring the original width of the swift before winding the subsequent length of wire.

2. A process according to claim 1, characterized in that the width of said swift is adjusted by displacement and/or removal of one or more blades (8) positionable sideways to a fixed rotary portion (1a) of said swift, said blades being replaceable.

3. A process according to claim 2 characterized in that it also comprises the steps of positioning said blade or blades (8) sideways to said fixed portion (1a), simultaneously urging them towards the outside, until the preset width of the winding swift is obtained, and of reducing said width and withdrawing said lateral blade or blades before bringing said insulating support into engagement with said turns.

4. A process according to any preceding claim, characterized in shaping a plurality of saddles (17) to position said insulating supports (19; 23) on said plurality of turns, during the step in which said turns are blocked in position.

5. A process according to any preceding claim, characterized in that it also comprises the steps of:
positioning at least a resistor (20) having at least one first flexible insulating support (23) in correspondence with a circular support (21) of insulating material radially provided with a plurality of superficial seats (22); bending said first support (23) or supports until their ends are brought into contact to each other positioning the ends of the turns adjacent to said circular support (21) into said superficial seats (22) of said tubular support; and fixing to one another the ends of said first support (23) or supports to obtain a resistor with radially positioned spiral turns (20).

6. An apparatus for producing spiral electrical resistors, characterized in that it comprises:
a swift (1) having adjustable width;
means (2, 3) to feed a length of resistive wire (4) to said swift;
means (5) to reciprocally move said swift (1) and said wire feeding means (3) to obtain a plurality of turns with preset pitch; and blocking means (6) to temporarily fix in position said turns on at least part of said swift.

7. An apparatus according to claim 6, characterized in that said swift is provided with a first fixed portion (1a), secured to a spindle (7) or similar rotation means, and at least a second movable portion, that can be fixed to said first portion to vary the swift width and to be rotated with it; said second portion or portions being interchangeable according to the desired swift width.

8. An apparatus according to claim 7, characterized in that said movable portion or portions are consisting of blades (8) that can be laterally positioned to said fixed portion (1a) by way of slots (9, 10) or similar guide means provided in a complementary way on said blades (8) and on said fixed portion; said fixed portion (1a) being moreover provided with means (11) to urge towards the outside said positioned blade or blades (8).

9. An apparatus according to claim 8, characterized in that it comprises two blades (8) elastically hinged (13) on a piston (12) or similar translating means and aligned with said fixed portion, and in that said urging means (11) consist of a couple of cams provided on said fixed portion (1a) and movable under the action of a rod (14) operatable by said piston (12).

10. An apparatus according to any of previous claims 6 to 9, characterized in that said blocking means (6) and said fixed portion (1a) of the swift are shaped in a complementary way with male and female bulges (15, 16) to obtain a plurality of positioning saddles (17) on said turns.

11. An electrical resistor as obtainable by a process according to any claim 1 to 5.

12. An electrical resistor according to claim 11, characterized in that it comprises at least a central circular support (21) electrically insulating and radially provided with a plurality of seats (22) to house the end of a corresponding plurality of turns arranged radially to said support and provided with at least one flexible electrically insulating support (23), at a distance from said circular support (21).

Drawing