GB2060904A - Galvanometer with rigid synthetic resin outer layer - Google Patents

Abstract

A limited rotation galvanometer in which a thermoplastic layer 19 that solidifies and shrinks upon cooling is molded around the exterior of the stator 18 and serves to set up hoop tensions which rigidly fix the stator parts 20, 38 against movement; molded thermoplastic portions integral with the layer may encase and insulate a set of electrical connectors and position them to receive mating members of an external circuit. <IMAGE>

Description

SPECIFICATION Galvanometer with rigid synthetic resin outer layer This invention relates to galvanometers and their stator assemblies. Such assemblies must be rigidly constructed to assure accuracy during operation and to withstand honing of the interior cylindrical pole faces of the stator assembly which define the space for the galvanometer rotor.

To provide rigidity, the laminated stator pieces with coils in place are ordinarily aligned with each other and with interposed magnets by suitable jigs, they are clamped between top and bottom plates with rivets or screws, the jigs are removed. and the assembly is plotted into an aluminum can. Honing of the stator pole faces is thereafter performed to achieve proper alignment of the faces with the rotor that is subsequently inserted.

One drawback of such current constructions is that, when the jigs are removed, there is a release of stresses and a certain amount of spring-back of the lamination pieces causing misalignment of individual laminations and an increased need for honing. A substantial percentage of assemblies may be rejected because the misalignment is too severe to be corrected by honing. Another drawback of such construction is that epoxy potting is labor intensive, requiring partial filling and evacuation of bubbles before complete filling.

Finally, epoxy potting is somewhat elastic, permitting movement of the stator relative to its mounting. This can result in detrimental hysteresis. Welding of the laminations to overcome some of these difficulties adds considerably to production cost.

We have discovered that injection molding a rigid thermoplastic outer layer that cools, solidifies, and shrinks around the galvanometer stator will set up hoop tensions which can serve to rigidly fix the stator parts and result in a less costly and more efficient galvanometer. The rigid layer can avoid the need for epoxy potting or aluminum cans, can reduce the need for honing and can limit the stator to less movement than is the case with conventional assemblies. The rigid molded layer can also enable use of sintered stator pieces which eliminate additional problems and costs associated with stators formed of laminations.

The invention therefore features a limited rotation galvanometer comprising a stator having a plurality of parts and a rotor mounted to turn on an axis relative to the stator. According to the invention a molded outer layer of rigid thermoplastic material extends about the stator, this layer residing under hoop tension as a result of shrinkage and solidification of the thermoplastic material when cpoled following molding. This layer serves to rigidly fix the parts of the stator against movement.

The invention also features portions of rigid synthetic material, that are integral with the galvanometer-surrounding layer, serving to encase and position each of a set of electrical connector members for mating with external connectors. By this means, problems during molding of leaking of plastic along the previously used flexible electrical leads, can be avoided and a construction that is readily installed with external circuits is inexpensively achieved.Preferably the encased electrical connectors are rigid pins insulated from each other by the molded material; the electrical connector members are joined to a printed circuit board that is embedded in the molded material, preferably the board having a central aperture and surrounding the rotor; the electrical connector members are grouped to receive an external plug; and a detent molded of the rigid material retains the plug, preferably this detent being a molded cantilever spring.

Also in preferred embodiments: the galvanometer includes at least one permanent magnet, the rigid thermoplastic layer serves to force the stator parts and this magnet to press against each other and maintain them in a fixed position, whereby constant magnetic properties are maintained in the magnetic circuit established between the stator and magnet; there are stator parts on opposite sides of the rotor axis and there are a pair of magnets one disposed between opposed stator parts on each side of the rotor axis; the stator parts are gripped prior to molding by mechanical holding means incapable alone of properly holding the pieces in position during operation of the galvanometer, the mechanical holding means being embedded in the rigid thermoplastic layer that fixes the parts of the stator against movement; the stator comprises at least two pieces of molded sintered metal positioned around the rotor, and the molded sintered pieces include grippable formations molded on the exterior of the pieces that are gripped by the holding means; the molded sintered pieces are imperforate, the grippable formations comprise exterior channels, and the mechanical holding means comprises holding pins residing in and engaging the sides of the channels; the stator comprises a plurality of substantially identical planar metal laminations stacked vertically, the rigid thermoplastic layer is molded about these laminations and the layer serves to maintain the laminations in a fixed position relative to each other and relative to the rotor; coils wound about the stator are embedded in injection molded material that is integral with the rigid thermoplastic layer; the rigid thermoplastic layer comprises nylon reinforced with a material such as glass, this layer being at least 0.5 mm thick; the rigid thermoplastic outer layer is molded about the stator in the direction around the axis of the stator and in the direction around its end plates, in both cases the layer residing under hoop tension as a result of solidification and shrinkage of the thermoplastic material following molding, and serving to rigidly fix the parts of the stator.

The invention also features a method of manufacturing a limited rotation galvanometer that includes the steps of providing a stator having a plurality of parts to receive a rotor that will turn on an axis relative to the stator, injection molding an outer layer of rigid thermoplastic material to extend about the stator, this material being capable of shrinking with cooling from its molding temperature, and allowing the material to cool, solidify, and shrink, whereby the material permanently resides under hoop tension, the layer serving to rigidly fix the parts of the stator against movement.

Preferably: the molding step comprises positioning a mold about adjacent stator and magnet parts and introducing the thermoplastic material in manner to produce a continuous layer surrounding said parts that causes hoop tension produced by the layer to force the stator part and the magnet to press against each other to produce a magnetic circuit having constant magnetic properties; the method includes providing the stator parts in the form of molded sintered metal pieces that have molded exterior grippable formations, gripping these pieces by mechanical holding means engaged in the grippable formations, the holding means being incapable alone of fixing the pieces during operation of the galvanometer, the injection molding step including embedding the holding means in the thermoplastic layer, and the cooling step causing the hoop tension to fix the pieces against movement relative to the rotor axis; the method includes providing the stator parts in the form of a plurality of substantially identical planar metal laminations, the clamping step comprising the steps of aligning the laminations against a mandrel in a vertical stack, the mandrel situated to align pole faces of the laminations relative to the rotor axis, the injection molding step comprising the steps of introducing the thermoplastic material while the laminations are aligned by the mandrel and allowing the material to cool and shrink substantially on the exterior surfaces of the stator thereby imparting a net inward force on the pieces forcing them into alignment against the mandrel in a fixed position relative to each other and relative to the rotor axis; the method comprises introducing the thermoplastic material both to produce a continuous layer surrounding the parts and to enter the interior of the stator parts to pot the interior of the stator.

We turn now to the structure and manufacture of preferred embodiments of the invention, after briefly describing the drawings.

Figure 1 is a perspective view of a stator of a first preferred embodiment having flexible electrical leads that protrude through the molded layer; Figure 2 is a horizontal cross-section of the stator taken along 2-2 of Fig. 1; Figure 3 is a vertical cross-section of the stator taken along 3-3 of Fig. 2; Figure 4 is a vertical cross-section taken along 4-4 of Fig. 2; Figure 5 is a diagrammatic perspective view of stator laminations and magnets exposed to hoop stresses; Figure 6 is a perspective view of an alternative embodiment with the side of the layer partially cut away; Figure 7 is a bottom view of the embodiment of Fig. 6; Figures 8 and 9 are vertical cross-section views along 8-8 and 9-9 of Fig. 7.; Figure 10 is a perspective exploded view of a preferred stator molded of sintered metal pieces;; Figure 11 is a cross-section of the stator of Fig. 10 showing a mold; Figure 12 is a slide cross-section of the stator in the mold; Figure 13 is a top view of the mold and stator; Figure 14 is a perspective view of the mold and stator.

Figure 15 is a perspective view of a preferred embodiment having a printed circuit board and electrical connector pins encased by the molded material; Figure 16 is a vertical cross-section of a portion of the embodiment of Fig. 1 5 during molding.

Figure 17 is a diagrammatic view of the printed circuit board during molding.

Figure 18 is a vertical cross-section taken along 18-18 of Fig. 15.

Figure 19 is a vertical section taken along 19-19 of Fig. 15.

Figure 20 is a perspective exploded view of parts of the embodiment of Fig. 1 5.

Referring to Figs. 1-5, stator 1 8 for a limited rotation galvanometer is of laminated construction with the rigid outer thermoplastic layer 1 9 molded around axis 44 and around the end plate 24, 28 of the stator (see Figs. 2 and 3 respectively). Pole piece assemblies 20 are formed from a large number of identical thin laminations 22 stacked vertically with die cast aluminum plates 24 and 28 respectively on the bottom and top. The assembly is riveted by aluminum rivets 30 through holes in the laminations and end plates. Wire windings 34 are wound around the assemblies through recesses 36 at opposite sides at thelong ends of the assemblies while two permanent magnets 38 are disposed between the assemblies in recesses 40 at the other sides.

A generally cylindrical recess is formed in the center of stator 1 8 by the various parts described.

Outer layer 1 9 is injection molded nylon, which is 35 percent glass filled and shrinks and solidifies upon cooling in an amount in excess of 1 % (about 3%). The layer has a yield strength of at least 20,000 pounds per square inch (psi) and a creep modulus of 5,000 psi for a duration of 104 hours at room temperature. The flexural tensile strength modulus of the material is 12,000 psi at room temperature.

Plate 24 has a groove 46 having a resin flow space between the plate and magnet 38.

The injection molded material extends through groove 46 between magnets 38 and plate 24 and through other openings not shown to fill the interior spaces within the stator and to pot the windings and magnet as indicated by numerals 36a and 48a in Fig. 2.

Annular collar 50, which serves in the final assembly to seat a torsion bar attached to rotor 52, is molded into and secured by material, see Fig. 4. (The function of the torsion bar is explained in my U.S. pat.

3,624,574.) The molded, rigid outer layer 1 9 exists under hoop tension in the directions indicated by lines x and y and arrows in Fig. 5 as a result of solidifying and shrinking upon cooling from molding. The hoop tension is communicated to laminations 22 serving to force them together with magnets 38 (see compression arrows A, Fig. 2) and each other, and fixes them against movement under a prestressed condition that produces superior hysteresis-free performance.

Figs. 6-9 depict another embodiment in which layer 19' is molded only in the direction around axis 44' and collar 50' is integral with plate 28'. The exposed end plate 24' of the molded assembly is clamped against a metal mounting plate 51. This construction enables unimpeded heat flow from the interior of the galvanometer to the mounting plate and this plate serves as a heat sink and dissipator. The limited rotation rotor 52' is shown assembled with the stator in these figures and drives a mirror 53 as an optical scanner. Other parts corresponding to these in the first embodiment are denoted by corresponding primed numerals.

An alternate embodiment using sintered metal pole pieces in place of laminations is depicted in Figs. 9 and 1 0. Stator 100 is molded in the form of two one inch high pole pieces 102 of 50 percent nickel and 50 percent iron. Each piece includes recesses 104 for wire windings and pole faces 106 to define a cylindrical rotor space. Magnets 11 4 are disposed between pieces 102. On the exterior of pieces 102 are molded vertical channels 105. The pieces are located between plates 108 and 110 by aluminum pins 112 which are fixed to the plates and lie within and engage opposite surfaces of channels 105. Outer layer of rigid thermoplastic 11 9 is molded about the rotor axis as described above with respect to the laminated stators.

The embodiment with the improved electrical connector features of the invention is depicted in Figs. 15-20. Galvanometer 218 is encased in rigid outer thermoplastic layer 219 and is generally constructed as in the prior embodiments with pole piece assemblies 220, drive windings 234, pick-off windings 234', magnets 238, and rotor 252. The windings are connected to circuits on printed circuit board 260 and male connector pins 262 in electrical continuity with these circuits.

Board 260 is completely encased in layer 219 and has central locating aperture 261, the board surrounding rotor 252. Pins 262 are soldered to board 260 and are bent at right angles to extend through layer 219, to be exposed in recess 264. Detent member 266 in the form of a molded cantilever spring extends integrally from its root at layer 219 to define one wall of recess 264.

External plug 270, for connecting the galvanometer to external circuitry, is constructed to fit into recess 264 and has recessed female connectors 224 to engage pins 262. In sliding plug 270 into the recess, member 266 is cammed slightly upwardly so as to be biased against plug 270 until ridge 268 in the detent member engages corresponding groove 272 in plug 270 to lock the plug into place.

Metal collar 250, Figs. 1 5 and 18, is generally annular with integral tang 251 extending through layer 21 9 to the exterior wall 217. Collar 250 and tang 251 are integral with plate 210. Hole 274 extends through tang 251 and collar 250. This hole receives set screw 276 which fixes torsion bar bushing 278 to one end of torsion bar 280. As depicted in Fig. 5 of my U.S. Patent 3,624,574, the torsion bar (20' in that figure) is fixed to one end of the rotor (12' in the figure). Layer 219 is molded to be essentially flush with the end surface of collar 250.

Manufacture of the laminated stator is achieved by aligning laminations 22 with temporary jigs. Magnets 38 are temporarily fixed to the assemblies and the stator parts are clamped in position between the end plates.

Four holes 32 drilled through the plates and stamped in the laminations receive rivets 30.

The peening process for the rivets causes the rivets to compress and fill the holes and secure the assembly but not sufficiently to be satisfactory for operation of the galvanometer.

With the stator parts in place against central mandrel 80 (Figs. 11-14) the mold is closed around the parts. The mold has a bottom piece 82 to which are fixed mandrel 80, locating rod 84, and ejection pins 86. Middle part 88 of the mold has a hole 85 through which rod 84 extends. The stator parts of Figs. 1-4 are positioned in the mold and held off of the bottom of mold part 88 by pins 86, which also serve to prevent the layer 1 9 from covering screw mounting holes 23 in plate 24. (The stator end plate 24' of the embodiment of Figs. 6-9 engages a corresponding mold surface and in thus kept free of the injection molded material).

The molten thermoplastic material is introduced through port 92 in top mold piece 90 and flows immediately into cavity 93 around the exterior of the stator. The material then flows through the space between magnets 38 and grooves 46 so as to reach the interior and form potting 48a. The material also flows through end spaces 49 and around windings 34 to pot the windings on the inside at 36a.

Such flow to the interior takes place after the material has filled around the exterior surfaces of the stator. As a result of delayed entry to interior spaces and of greater exterior surface area, the molten thermoplastic layer will produce a net tendency to hold the magnets in place rather than force them outwardly from the recesses in the stator pieces. As the outer layer cools, solidifies and shrinks, hoop stresses thus produced impose a net inward force on the laminations. As shown by compression arrows A in Fig. 2 this forces the laminations and magnets 38 tightly together and establishes the laminations in a fixed position relative to each other, relative to the magnet and relative to axis 44.

Ejection pins 86 serve to permit gases to escape and to eject the stator from the mold.

The alternate embodiment using molded sintered metal pole pieces with molded channels 105 is manufactured by aligning and fixing the sintered pieces between plates 108 and 110 using pins 11 2 which engage channels 1 05. No through holes need be drilled, and there is no need to stamp laminated pieces.While the holding means alone would not be satisfactory for fixing the pieces during galvanometer operation, the outer continuous layer 11 9 of rigid thermoplastic material when molded as described serves to impart a net inward force on the pieces, forcing them together with the magnets under a pre-stressed condition and establishes them in a fixed position relative to each other, relative to the magnets and relative to the axis in a manner that will sustain operational forces without separation or adverse hysteresis. As with the other embodiments, the stator parts are formed to ensure that they engage the corresponding surfaces of the magnets before reaching the mandrel to ensure high pressure contact between the pole pieces and magnets.

When it is desired to mold the material only around the axis of the stator, as is the embodiment of Figs. 6-9, mold pieces 82, 88 and 90 are designed to prevent flow over the metal end plate 24. This leaves the plate exposed to transmit heat away to an adjoining surface, to effect cooling of the galvanometer, as mentioned above.

Manufacture of the embodiment of Fig. 1 5 is shown in Figs. 18 and 19. Pins 262 are soldered to printed circuit board 260, and the stator assembly is positioned in a mold around mandrel 80'. Metal mold plug form 282, secured in mold wall 88' by two rods 284, receives portions of pins 262 to prevent flowing thermoplastic material from covering them, and to position and support the pins and the circuit board during molding. Molten thermoplastic material enters through port 92' into gaps around board 260 and exposed portions of pins 262, and, upon cooling, supports and insulates them. Cantilevered detent 266 is formed in the gap between mold 90' and plug form 282, ridge 268 being formed by indentation 286. After molding, plug form 282 is removed to expose portions of pins 262. Tang 251 extends to the mold wall and thus will have an exposed surface in the finished product so as to avoid the need for drilling through layer 21 9 to install set screw 276.

Other embodiments are within the following claims. For example, additional molded sintered pieces can be stacked about the rotor to provide greater height, preferably less than 3 inches. The layer can be reinforced with other materials including but not limited to carbon.

Claims (16)

1. A limited rotation galvanometer comprising a stator having a plurality of parts and a rotor mounted to turn on an axis relative to said stator, characterized by a molded outer layer of rigid synthetic resin material extending about the stator parts, said layer residing under hoop tension as a result of shrinkage and solidification of the thermoplastic material when cooled following molding, the layer serving to rigidly fix the parts of said stator against movement.

2. The galvanometer of claim 1 wherein said galvanometer includes at least one permanent magnet, and is further characterized by said rigid synthetic resin layer serving to force said stator parts and said magnet to press against each other whereby constant magnetic properties are maintained in the magnetic circuit established between said stator and magnet.

3. The galvanometer of claims 1 or 2 further characterized in that said stator parts are gripped by mechanical holding means incapable alone of properly holding said pieces in position during operation of the galvanometer, said mechanical holding means being embedded in said rigid synthetic resin layer that fixes said parts of said stator against movement.

4. The galvanometer of claim 1, 2 or 3 further characterized in that said stator comprises at least two pieces of molded sintered metal positioned around said rotor, said molded sintered pieces include grippable formations molded on the exterior of said pieces, said formations being gripped by said mechanical holding means.

5. The galvanometer of claim 4 further characterized in that said molded sintered pieces are imperforate, said grippable formations comprise exterior channels, and said mechanical holding means comprise holding pins residing in and engaging the sides of said channels.

6. The galvanometer of claims 1, 2 or 3 further characterized in that said stator comprises a plurality of substantially identical planar metal laminations stacked vertically, said rigid synthetic resin layer being molded about said laminations, said layer serving to maintain said laminations in a fixed position relative to each other and relative to said rotor.

7. The galvanometer of any one of the foregoing claims further characterized in that said stator is comprised of pole piece assemblies positioned on opposite sides of said rotor, two permanent magnets being disposed between said stator assemblies and establishing magnetic circuits therewith, said magnets being positioned on opposite sides of the rotor, said assemblies being joined by mechanical holding means incapable alone of holding said assemblies in position during galvanometer operation, further characterized in that the hoop tension stresses of said layer serve to force said assemblies and said magnets to press against each other whereby constant magnetic properties are maintained in said circuits, and said layer serving to fix said assemblies and magnets against movement relative to the axis of said rotor.

8. The galvanometer of any of the foregoing claims wherein the rigid synthetic resin layer comprises a thermoplastic material.

9. The galvanometer of any one of the foregoing claims characterized in that said layer extends continuously in the direction around the galvanometer axis, one end of said galvanometer being free of said layer, said end being defined by a metal end-plate in direct heat-receiving contact with other stator parts, said end plate including mounting means for attachment of said end plate face to face with an external metal mounting surface whereby heat generated within said stator is readily dissipated.

1 0. The galvanometer of any one of the foregoing claims further characterized by a set of electrical connector members connected to deliever electrical power to the galvanometer, and integral portions of said rigid synthetic resin material surrounding and rigidly locating each of said set of electrical connector members in position to receive mating external electrical connector members for connection of said galvanometer to an external circuit.

11. The galvanometer of claim 10 further characterized in that said set of electrical connector members comprises a series of male connector pins, said pins molded in and insulated from each other by portions of said rigid material that are integral with said layer, said electrical connector members being grouped to receive an external plug, there being a molded detent member, integral with said rigid material that forms said layer, said detent positioned along the path of entry of said plug and arranged to engage and retain said external plug when the plug is connected, said detent member being in the form of a cantilever spring detent molded integrally with said layer.

1 2. The galvanometer of claim 10 or 11 further characterized in that said electrical connector members are joined to a printed circuit board, said printed circuit board being embedded in the molded rigid material.

1 3. The galvanometer of any one of the foregoing claims further comprising a torsion spring means connected between the rotary and stationary parts of said galvanometer, further characterized by a metal annular collar embedded in and rigidly fixed by said synthetic resin layer, said collar having a set screw extending through a passage and securing said torsion spring, said collar having metal side projection extending outwardly beyond said layer of synthetic resin material to an external surface of said galvanometer, said set-screw passage extending through said projection whereby said passage can be formed without the necessity of drilling through said synthetic resin material.

1 4. A method of manufacturing a limited rotation galvanometer of any of the foregoing claims, comprising providing a stator having a plurality of parts to receive a rotor that will turn on an axis relative to said stator, and characterized by injection molding an outer layer of rigid synthetic resin material to extend about the stator, this material being capable of shrinking with cooling from its molding temperature, and allowing said material to cool, solidify and shrink, whereby said material permanently resides under hoop tension, the layer serving to rigidly fix the parts of said rotor against movement.

1 5. The method of claim 14 further characterized by providing said stator parts in the form of molded sintered metal pieces that have molded exterior grippable formations, gripping said pieces by mechanical holding means engaged in said grippable formations, said holding means being incapable alone of fixing said pieces during operation of the galvanometer, said injection molding step including embedding said holding means in said synthetic resin layer, said cooling step causing said hoop tension to fix said pieces against movement relative to said rotor axis.

16. The method of claim 14 wherein said stator comprises a plurality of substantially identical planar metal laminations, said gripping step further characterized by aligning said laminations against a mandrel in a vertical stack, said mandrel situated to align pole faces of said laminations relative to the rotor axis, said injection molding step further characterized by the steps of introducing said synthetic resin material while the laminations are aligned by said mandrel, allowing said material to cooi, solidify and shrink substantially on the exterior surfaces of said stator thereby imparting a net inward force on said pieces forcing them into alignment against said mandrel, in a fixed position relative to each other and relative to said rotor axis.

1 7. A galvanometer substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

1 8. A method of manufacturing a galvanometer substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.