ELECTRIC TRANSFORMER, POSSIBLY IN COMBINATION WITH A RECTIFIER

Abstract: A lightweight, compact welding transformer (10) is particularly suited for robotic applications. It includes copla­ nar secondary pads (16), a parallel common bus (18), and a secondary coil (20) having turns each including a first end coupled to the common bus and a second end extending through the common bus (18) and coupled to one of the secondary pads (16). The transformer further includes planar diodes (22) abutting the secondary pads (16) opposite the coil and a planar rectified bus (24) abutting the diodes (22) to sandwich them against the secondary pads (16).

Description: The present invention relates to transformers, more particularly but not exclusively to welding transformers and rectifiers, for example transformers and rectifiers for robotic welders. In resistance welding, coalescence is produced primarily by resistive heat created by passing an electric current through the workpiece. A resistance welder includes primary conductors, a transformer, secondary conductors, and welding electrodes. The primary conductors couple the transformer to a power source. The secondary conductors interconnect the transformer and the electrodes. Typically, the primary power source or supply in resistance welding provides power at the line frequency--for example, 60 hertz (Hz) in the United States and 50 Hz in Europe. Welding transformers for this relatively low-frequency current are excessively heavy for many robotic welders where weight is a primary consideration. In an attempt to reduce the weight of the transformer, relatively high-frequency power sources (e.g., 400 or 1200 Hz) have been used. By so boosting the frequency, the transformer weight can be greatly reduced. However, the increased frequency requires the secondary voltage to be increased because of increased inductive reactance, which is directly proportional to frequency. In an attempt to reduce impedance, use has been made of rectified secondary voltage/current. One such construction is illustrated in United States Reissue Patent 31,444. Such constructions are relatively bulky and heavy and therefore not fully adaptable to all robotic welders. Further, the shunts between the transformer and the rectifier are "inductive throats", such that the high-frequency reactance problem remains. A further exemplary transformer, having those features set out in the pre-characterising portion of Claim 1, is shown in US-A-3826967. It is an object of the present invention to attempt to alleviate these problems, and one way in which this is done is by providing an extremely lightweight and compact welding transformer and rectifier assembly which provides a rectified secondary current. The size and weight of the unit are greatly reduced over known units; and the unit is believed to comply with all known weight and size restrictions for robotic welders. According to a first aspect of the invention, a transformer is characterised by those features set out in the characterising portion of Claim 1. Preferably the rectifier assembly directly abuts the secondary pads of the transformer to eliminate inductive throats therebetween. More particularly, the transformer includes a pair of secondary pads, and preferably has at least one diode overlying and abutting each secondary pad, and a rectified but overlying and abutting the diodes. Consequently, a rectified current is outputted on the rectified bus. The sandwiching of the diodes directly against the secondaries greatly reduces both the profile of the transformer and its weight. Inductance due to electrical connections between the transformer and the rectifier assembly, in this embodiment, are virtually eliminated. The unit therefore provides improved performance in a smaller and lighter weight package than known units. Preferably also, the common bus of the transformer is configured to further reduce the size and weight of the unit. More particularly the transformer includes a pair of coplanar secondary pads, a planar common bus overlying the secondary pads, and a plurality of secondary coil turns. Each turn includes a first end connected to the common bus and a second end extending through or beyond the common bus and connected to one of the secondary pads. Preferably, the bus defines some apertures (or void means) permitting the second turn ends to extend therethrough without electrically contacting the bus. This intermeshing of the coil turns and common bus further reduces the transformer unit size and weight. The invention may be carried into practice in various ways and one specific embodiment will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side plan view of a welding transformer and rectifier assembly; Figure 2 is a top elevational view of the assembly of Figure 1; Figure 3 is an end elevational view taken from the right side of Figure 2; Figure 4 is an end elevational view taken from the left side of Figure 2; Figure 5 is a view taken along plane V-V in Figure 2; Figure 6 is a view taken along plane VI-VI in Figure 2; and Figure 7 is an elevational view of the common bus. A welding transformer and rectifier unit or assembly constructed in accordance with a preferred embodiment of the invention is illustrated in the drawings and generally designated 10. The transformer includes a transformer portion 12 and a rectifier portion 14 (Figures 1 and 2). The transformer portion 12 includes a pair of generally coplanar secondary connectors or pads 16a and 16b, a common bus 18, and a secondary coil 20. Each turn of the coil 20 includes a first end electrically connected to the common bus 18 and a second end electrically connected to one of pads 16a and 16b. The common bus 18 is configured to permit the second end of each turn to extend therethrough without electrically contacting the bus. The rectifier portion 14 includes a plurality of disk diodes 22a and 22b sandwiched against the secondary pads 16a and 16b, respectively, and a rectified bus 24 sandwiched against the diodes 22. Alternating current on the secondary pads 16 is rectified to single-phase DC current on the rectified bus 24. Each of the secondary pads 16 (Figures 1 to 3 and 5) is a generally rectangular parallelepiped. Each secondary pad 16 includes a coil face 26 and an opposite rectifier face 28. The coil faces 26 of the two pads are coplanar, and the rectifier faces 28 are also coplanar and parallel to the coil faces. Optionally, wear pads 30 can be mounted on rectifier faces 28. If included, each wear pad 30 preferably extends the full height and width of the secondary pad 16 on which it is mounted. The secondary pads 16 define slots 32 in their coil faces 26 to receive the coils 20. The pads also define tapped bores 33 to receive bolts 70 as will be described. The common bus 18 (Figures 1 to 3 and 7) is generally planar and generally parallel to the secondary pads 16. The common bus 18 includes a pad face 34 and a coil face 36, which are parallel to one another. The common bus 18 includes a terminal portion 38 defining tapped bores 40 which receive electrical connectors in conventional fashion. The common bus 18 also defines a pair of rectangular apertures or voids 42b and 42d (Figure 7) which extend through the common bus to receive certain coil ends as will be descrbed. Opposite the terminal edge 38 are a pair of arms 44a and 44b which define a void or open-sided aperture 42c therebetween. A fourth void or open-sided aperture 42d is located directly below the arm 44a. A plurality of slots or recesses 46a, 46b, 46c, and 46d are formed in the coil face 36 of the common bus 18 to receive coil ends. The turns or loops of secondary coil 20 (Figures 1 to 3) are generally identical to one another. The turns are grouped into two sets of physically alternating turns or every other turn--a first set including turns 20a and 20c and a second set including turns 20b and 20d. Each of the turns 20 is extruded copper and preferably hollow to permit water cooling. The turn 20a (Figures 1 and 2) includes a bight portion 48 and a pair of legs 50a and 50b extending therefrom. The legs 50 are generally physically parallel to one another, and the leg 50a is longer than the leg 50b. The leg 50a includes a pad end 52a which extends through void 42a in the common bus and is electrically connected to the secondary pad 16b. The leg 50a therefore does not contact the common bus 18 but only the secondary pad 16b. The turn end 52a is silver soldered in the slot 32 in the secondary pad 16b. The shorter leg 50b includes a bus end 52b positioned within the slot 46a of the common bus 18. Consequently, the leg 50b does not extend through the common bus, but rather is electrically connected thereto. The turn 20c is identical to the turn 20a and includes a longer leg 50a, which extends through void 42c in the common bus 18 and is connected to the pad 16b, and a shorter leg 50b which is electrically connected to the common bus in the slot 46c. Consequently, the first set of turns 20a and 20c is electrically connected to the common bus 18 and to the secondary pad 16b. The common bus 18 is configured to receive the long legs 50a of turns 20a and 20c therethrough. The turns 20b and 20d (Figures 2 to 3) are generally identical to the turns 20a and 20c but are rotated 180 degrees or "flipped over". Consequently, the longer legs 50a of turns 20b and 20d extend through the voids 42b and 42d, respectively, in the common bus 18 to be electrically connected to the secondary pad 16a. The shorter legs 50b of turns 20b and 20d are electrically connected to the common bus 18 within the slots 46b and 46d, respectively. Consequently, the turns 20b and 20d of the second set are electrically connected to the common bus 18 and to the secondary pad 16a. The rectifier portion 14 (Figures 1 and 2) includes the generally planar disk diodes 22, the rectified bus 24, and spring assemblies 54. The spring assemblies 54 are anchored to the secondary pads 16 to urge the rectified bus 24 against the disk diodes 22 and therefore sandwich the disk diodes between the rectified bus and the secondary pads 16. The disk diodes 22 are generally well-known to those in the diode art. These diodes are preferably 52 millimetre diodes sold as Model No. R9KN0610 by Westinghouse. Typically, such disk diodes include an overflow silicon bead about the peripheral edge of one face formed during manufacture. Other diodes could be substituted therefor. The rectified bus 24 (Figures 1 to 2 and 6) is generally planar and generally parallel to the disk diodes 22 and the secondaries 16. The rectified bus 24 includes a diode face 56 and a spring face 58 generally parallel to one another. The diode face defines four circular grooves 60 to each receive the silicon bead of a disk diode 22 permitting the bus 24 to fully abut the faces of the diodes. Each groove 60 is flanked by four throughbores 62 spaced evenly thereabout. The rectified bus 24 includes a terminal portion 64 defining a pair of threaded bores 66 to receive conventional electrical connectors. The secondary pads 16, the common bus 18, and the rectified bus 24 are all fabricated of copper stock having a low-stress sulfamate nickel plate. Other suitable electrically conductive materials could also be substituted. Additionally, the secondary pads 16, common bus 18, coils 20, and rectified bus 24 are water cooled in conventional fashion (not shown). The four spring assemblies (Figures 1 to 2 and 4) are generally identical to one another and are included to accommodate thermal expansion in the unit. One spring assembly 54 is positioned over each of diodes 22 so that the spring force against each diode is independently adjustable. Each assembly 54 includes a stack of spring washers 67, a back-up plate 68, and the bolts 70, already mentioned. In the preferred embodiment, the spring washers 67 are known in the industry as Belville springs. The back-up plate 68 sandwiches the spring washers 67 against the rectified bus 24. Although not fully shown, the bolts 70 extend through back-up plate 68 and the bores 62 in the rectified bus 24 and are threadedly received in the apertures 33 in the secondary pads 16. A stainless steel washer 72 and an insulated washer 74 are positioned over each of bolts 70 between the head and the back-up plate 68. Additionally, an insulated sleeve 76 (only one shown in Figure 1) is positioned over each bolt 70 and extends through the back-up plate 68 and the rectified bus 24. Therefore, the bolts 70 are electrically connected to the secondary pad 16 in which they are anchored and electrically insulated from the rectified bus 24 and the back-up plates 68. The sleeves 76 support and position the diodes 22. After the transformer is assembled as described above, a primary coil (not shown) and a core (not shown) are installed in conjunction with the secondary coil 20 in conventional fashion. The secondary connectors or pads 16, the common bus 18, the coil 20, the primary coil, and the core are potted for electrical, thermal, and structural integrity. The bolts 70 are carefully torqued to provide a desired spring force against the rectified bus 24 through spring washers 66. In the preferred embodiment, the desired spring force is 5500 pounds (24.5 KN). Electrical connectors (not shown) are secured to the common bus 18 at the bores 40 in the terminal portion 38. Similarly, electrical connectors (not shown) are secured to the rectified bus 24 in the bores 66 in the terminal portion 64. The transformer is then ready for use particularly in conjunction with a robotic welder. A primary voltage is applied to the primary coils (not shown) at approximately 1200 Hz. The relatively high frequency enables the transformer to be much smaller and lighter than those transformers utilizing line frequencies. A secondary voltage is induced in the secondary coil 20 which appears as an alternating voltage across the secondary pads 16a and 16b. This alternating current is rectified through the diodes 22 so that single-phase full-wave DC current is applied to the rectified bus 24. Consequently, the transformer and rectifier unit supplies a DC voltage to eliminate reactance problems. Further, the described configuration is extremely compact and lightweight enabling the transformer to be used in a wide variety of robotic and fixture type applications where both size and weight are significant constraints.

Claims: A transformer having a plurality of generally coplanar secondary connector pads (16); a generally planar common bus (18) generally parallel to and overlying the secondary pads; secondary coil means (20) including at least four turns (20a, 20b ...) each having a pad end and a bus end, the turns being generally orthogonal to the secondary pads and the common bus; means for electrically connecting each of the bus ends to the common bus (18); characterised by means for electrically connecting each of the pad ends to one of the secondary pads (16) through the common bus (18), the pad ends and the pad ends connecting means being electrically insulated from the common bus. A transformer as claimed in Claim 1 in which the common bus (18) defines void means through which extend selected ones of the pad ends and the pad ends connecting means. A transformer as claimed in Claim 1 or Claim 2 in which the common bus (18) is of one piece. A transformer as claimed in Claim 1 or Claim 2 or Claim 3 in which every other turn is connected to one of the secondary pads (16) and the other turns are connected to another of the secondary pads (16). A transformer as claimed in any one of the preceding claims including at least one generally planar rectifier means (22) overlying and abutting each of the secondary pads (16); a rectified bus (24) overlying and abutting the rectifier means (22) to sandwich the rectifier means between the secondary pads (16) and the rectified bus (24); and spring means (54) for biasing the rectified bus (24) against the rectifier means (22). A transformer as claimed in Claim 5 in which the spring means (54) includes means for independently adjusting the biasing force on each rectifier means (22). A transformer as claimed in Claim 5 or Claim 6 in which the spring means (54) includes one spring positioned over each of the rectifier means (22). A transformer as claimed in any one of Claims 5 to 7 including a plurality of wear pads (30), each mounted on one of the secondary connector pads (16) facing the rectifier means (22). A transformer as claimed in any one of Claims 5 to 8 in which the connector pad faces which abut the rectifier means (22) are generally coplanar, and in which the rectifier means (22) are generally flat.

Inventors: HOLT, GARY EDWARD, SIEHLING, MARK BERNARD, VAN ANTWERP, STANLEY RALPH
Applicants: MARK IV INDUSTRIES, INC.
Application year: 1986
Main classification: H01F27
IPC codes: H01F27, H01F30, H02M7