US2860289A - Electromagnetic transducer motor - Google Patents

Description

Nov. 11, 1958 J. E. VERARDO ELECTROMAGNETIC TRANSDUCER MOTOR Filed Feb. 3, 1955 R O m E V m Jab/n E0 Verarda,

BY WW W M m D 8 6 4 Z ATTORNEY United States Patent Office 2,860,289 ELECTROMAGNETIC TRANSDUCER MOTOR John E. Verardo, Massapeqna Park, N. Y., assignor to Fairchild Camera and Instrument Corporation, a corporation of Delaware Application February 3, 1955, Serial No. 485,948 Claims. (Cl. 317-158) This invention pertains to transducer motors, and particularly to improvements in the magnetic structure of an electromagnetic transducer graving portion of a known form of facsimile reproduction machine. However, the improvement obtained by the present invention is also applicable to other devices in which uniformity and dependability of mechanical response to a given exciting current are requirements.

The magnetic circuits of devices of this type, where the driving currents are of alternating nature, and particularly where the currents are of higher frequencies than normal power frequency, are generally made up in laminated form, the magnetic material of each lamination being continuous in the intended direction of the flux therethrough. The use of such laminations, instead of a solid magnetically permeable body, inhibits the flow of eddy currents in directions cross-Wise of the intended flux direction, which eddy currents would otherwise represent a power loss and would produce heating of the iron. In addition, the use of relatively thin laminations effect a reduction in the hysteresis loss in the magnetic circuit, in accordance with well-known principles.

While the interface contacts between adjacent laminations of iron or steel in themselves present a relatively high-resistance path to eddy currents, due to poor facial contact as well as to the presence of oxides of relatively high resistance on these faces, it has become common practice to provide between the laminations a thin layer of an adhesiveinsulating material coated onto the thin magnetic sheets before they are assembled. This insulation is particularly required where the laminations have been hydrogen-annealed, because the annealing process reduces any surface oxides which might have existed, and hence increases the surface conductivity between the laminations. Insulation is also required where the magnetic material is inherently free of an oxide layer. Since the insulating material is generally more or less plastic, it distributes the pressure of the assembly rivets or fasteners over wider areas of the laminations and is presumed to reduce the possibility of slight changes in position of laminations during use. Of course, the binding or adhesive effect of such materials inherently tends to make the laminated assembly more unitary in action, and reduces internal local vibration which would represent a further power loss.

In many applications, however, these measures have proved inadequate, especially where the transducer is one in which a relatively powerful current (perhaps of the order of an ampere) is utilized to produce a mechan ical motion of the moving part which is measured in thousandths of an inch. Such an application is represented by the output transducer of a known form of photo electrically controlled engraving machine, as a whole well described in U. S. Patent No. Reissue 23,914, issued December 21, 1954 to J. A. Boyajean, Jr. as assignor to the owner of the present application.

In that machine, the engraving transducer motor drives intended for use in the en- 2,860,289 Patented Nov. 11, 1953 a hot stylus into and out of the surface of an engravable sheet, at a fundamental frequency upwards of 350 cycles per second. Commercial models of that invention utilize frequencies as high as a thousand cycles per second or greater. However, the amplitude of motion of the engraving tool is quite small, being of the order of .015 inch or less. In order that the reaction between tool and material not affect the tool motion to a noticeable extent, it is necessary to drive the tool with considerable force, and at these frequencies a highly efficient magnetic structure is required, especially for the magnetic circuit of the moving vane or rotor, as well as one in which the excursion of the tool for a given energization of the transduccr shall be precisely controlled and accurately duplicated, not only over short periods of time, but over periods of several working hours during which the ma chine is operating more or less continuously. The satisfactory accomplishment of this aim, which can be characterized generally as an improvement in time and temperature stability, greatly improves the quality of the engraving produced, while minimizing the necessity for attention by the operator and frequent readjustments. The importance of this inherent stability can be well realized when it is considered that a machine of this type is not working on a steady load cycle, but instead has varying demands made upon it because of the tone difference of the various kinds of copy which it is called upon to reproduce. It is important that the stability of the motor be such that it performs the same whether it has been on for a short time or a long time because, although a short time might be required for a one-column cut and a long time for a four-column cut, yet it becomes fairly apparent that a short time is in effect only the initial part of a long time. The quality of an engraving would be seriously impaired if the motor changed in performance after executing a part of the engraving.

According to the present invention, the problem is solved in a most satisfactory manner by the elimination of plastic or adhesive materials for binding the laminations of the magnetic rotor together, and the substitution of metallic interleavings in the nature of extremely thin laminations of aluminum or an alloy of aluminum, combined with a particular form of mechanical fastening for the laminations to maintain the desired pressure through the stack or pile. Reduction of eddy currents between laminations is accomplished by a simple anodization which renders the surfaces of these aluminum shims nonconducting prior to assembly.

The invention will best be understood by referring now to the following detailed specification of a preferred embodiment thereof given by way of example, taken in connection with the appended drawings, in which:

Fig. 1 is an isometric view, with parts broken away, of a complete transducer motor in accordance with the invention,

Fig. 2 is an exploded isometric view of representative portions of the magnetic circuit of the moving vane, and

Fig. 3 is a graph showing the effect of the invention on the travel of a stylus driving chuck in relation to the energizing current.

Referring now to Fig. l of the-drawings, the transducer motor itself is indicated generally by reference numeral 10, and is shown as mounted upon a base 12 by a pair of fiat leaf springs 14 so that the fore and aft positions of the motor 10 can be adjusted slightly with respect to base 12 by means not shown. This slight movement is in the same direction as the vibrating movement of the tool chuck 16, which direction is indicated by the arrow adjacent the arm 18 which carries the chuck. Insofar as the present invention is concerned, the main body of 'motor 10 may be considered stationary, the chuck and tool being vibrated with respect thereto by reason of being connected to the rotatable magnetic vane structure to be described.

The stator structure of the motor 10 comprises two stacks 2 and 22 of C-shaped laminations of magnetic material such as a low-loss ferrous alloy. Since these stacks are stationary insofar as the transducer output is concerned; and since they are relatively large, they may be made up by ordinary riveting together of the pre-' formed laminations with or without the adhesive coating mentioned earlier. The stator stacks 2t} and 22 are rigidly clamped with respect to one another by end castings 24 and 26 which are of box-like configuration and bolted to one another, as indicated at 28 by screws or bolts passing through the stator stacks. Both of these frames 24 and 26 are identical in shape, having a central rigid web 30 upon which webs are carried the respective end blocks 32 each having a shaft portion 34- between which shafts the moving vane 36 is mounted. Flanges such as 38 rigidly connect the inner ends of the shafts 34 to the rotor assembly 36, so that slight rotary movement of the vane is possible about the common axis of the shafts 34. While the motion is rotary, it is to be understood that no bearings are employed, the slight motion permitted to rotor 36 resulting from torsion in the shaft elements 34.

Energizing coils 40 and 42 surround the vane structure 36 above and below its pivotal axis, these coils being wound to direct their flux lengthwise of the laminations of the vane (that is, in the vertical direction in Fig. l), and they are secured within the openings of the C-shaped stator laminations in any convenient way. Spacing strips 44 are indicated in Fig. 1 as wedged between the wrapped and insulated coils to force them into the C-shaped openings of the stator bodies.

The action of a motor of this type is well described in the Boyajean patent mentioned above, and illustrated particularly in Figs. 3a and 3b of that patent.

A few of the laminations near the center of the stack comprising vane 36 are extended upwardly from its general top surface, these extended laminations being riveted to the opposite sides of a block d6 which is integral with the chuck driving rod 18. Thus, slight rotations of the vane or rotor 36 will produce the desired in and out movement of the tool chuck 16.

' When the rotor 36 is formed of magnetic laminations riveted to one another in a pile and with the usual cement or adhesive laminated between them under heat and pressure, it is found that the position or amplitude of the chuck 16 is not uniquely defined by the energizing current supplied to the coils 40' and 4-2 through their connecting leads 48. Specifically, it has been noted that as the temperature of the entire motor varies due to heating effects of the coils, magnetizing current and in accordance with the varying load cycles which it must'perform, the amplitude of the tool motion is changed. While the change is slight, it is sufiicient to affect adversely the quality of engravings made with the device, particularly if this change occurs during some portion of a single engraving. In addition, at the higher working temperatures, suitable cements tend to soften, so that the vane 36 acts as a flexible body rather than as a rigid mass. Due to the fact that the cement represented a material which is basically elastic there was a limit to the tightness of a stack. Obviously if there were cement between the laminations the rivets, unless they squeezed out all the cement, would not create the maximum tightness that could be obtained. in an actual embodiment, the shaft portions 34 may be each about a half inch long and about a quarter inch in diameter. Such a steel shaft is of course extremely rigid, and for accurate results it is essential that the rigidity of the rotor 36 carried by these torsion shafts shall not be impaired. It was also noted that erratic performance of the rotor 36 resulted from the fact that repeated fiexures of the armature 9.11

' the improved arrangement of this invention, in which the vane 36 caused the headed pins or rivets holding them together to become loose, permitting greater motion of the tool than called for by the signal information applied to the energizing coils. It is apparently impossible to provide permanent rigidity by a riveted structure of this kind over long periods of time.

The present invention overcomes the defects of prior constructions by eliminating all non-metallic materials in the rotor, and specifically by eliminating the resin, cement and other material formerly used between the adjacent ferro-magnetic laminations. Instead the invention utilizes between each two adjacent laminations a thin shim of aluminum or aluminum alloy, formed to the same shape as the ferrous laminations but having a thickness of the order of only one and one-half thousandths of an inch. These aluminum shims are anodized to ten der the surfaces non-conducting before assembly, and when the stack of inter-leaved magnetic laminations and shims is assembled, taper pins are driven through the aligned apertures in the stack, and at least the small end of each taper pin is headed over to complete the assembly. This heading over of the taper pin removes any possibility of the taper pin becoming loose.

Fig. 2 shows very clearly the assembly of the rotor structure. In this figure, a pair of adjacent low-loss iron alloy laminations are indicated by numerals 50, and between then is shown one of the anodized aluminum shims 52. Each of the elements has aligned holes to receive the assembly fasteners. These are tapered pins of which two designated 54 pass through the laminations as well as the end plates or flanges 38 integral with the shaft elements 34, while the two pins connecting the outer ends of the laminations only are designated 56. Preferably, the taper of successive pins vertically of the assembly is reversed, so that if one pin increases in diameter from left to right of the stack, the next one will increase from right to left and so on. At least the smaller end of each taper pin is headed over after assembly, and the larger end may be left alone or preferably pressed against the last lamination through a washer which is sized to ensmall, corresponding to the standard 2/0 machineryv taper pin of hardened steel, for a stack assembly having a width across laminations of one inch and comprising fifty-nine magnetic laminations of .015 inch thickness, and fifty-eight anodized aluminum shims having .0015 inch thickness.

The improvement in stability and the ability to duplicate movement of the tool chuck is indicated graphically in Fig. 3 of the drawings, which shows curves relating the chuck motion in thousandths of an inch to the signal current in the coils expressed in'amperes. The dashed curve A has two legs, the upper one indicating displacement of the tool or chuck measured with the amplitude going to higher valves, and the lower curve giving the displacement with the amplitude decreasing. This doublevalued curve clearly indicates the lack of reproducibility of displacements for given signal currents. The solid straight line curve B represents the results obtained with position of the chuck is linearly relatedto the energizing current, and regardless of the direction of amplitude change (increasing or decreasing) of the chuck when the measurement is made. Moreover, the relationship is practically invariable with time and temperature of the motor, as has been demonstrated in operating tests extending over as much as eight hours of operation at maximum signal level. There is no warm-upfrequired for this motor. Whether the operating time is zero plusone unit of time or zero plus units of time, the performance remains the same.

It is presumed that the use of the aluminum shims provides greatly improved frictional contact between, successive laminations by virtue of the higher clamping pressure that could be used, and that the use of taper pins rather than straight shank fasteners provides continuous tight bearing surfaces between the laminations and the pins. The elimination of all non-metallic materials is believed to be responsible for the greatly improved time and temperature stability of the motor, and its complete freedom for mechanical hysteresis effects. The maximum tightness of a stack was heretofore limited by the use of cement. The elimination of all non-metallic elements removes any upper limit to the tightness of a stack. By the use of suitable clamping devices it is possible to achieve as near to solid stack tightness as is possible Without in fact making it a solid stack.

The elimination of any non-metal material also removes any heat insulation efrects that existed. The heat transfer ability of the unit has been improved with the result that the motor heat rise is less.

To recapitulate, the invention provides a mechanically solid magnetic structure of high stability and good eddy current insulation, together with excellent thermal conductivity nearly equivalent to that of a solid block of metal. The resulting improvement in heat dissipation, and in the position stability of the driven element, eliminates some of the power losses heretofore experienced, and in many cases provides better position stability with a smaller restoring force (torsion bar cross-section) which again may effect a substantial reduction in the required power input.

While the invention has been described herein in connection with its application to a transducer motor to which extremely rigorous duty cycles are applied, it is obvious that the principles of the invention may equally well be applied to other magnetic structures in which reproducibility of position is essential. Hence, the invention is not to be limited to the details specified above except as may be required by the scope of the appended claims.

What is claimed is:

1. A rotor for electromagnetic chuck drive transducers, comprising a plurality of low-loss magnetically permeable laminations, shims of thin ductile aluminum sheet stock having anodized surfaces interposed directly between each pair of successive laminations, end plates for said rotor, and tapered pins passing through said laminations, shims and end plates and headed over to secure the same in rigid face to face contact, and an output stub shaft secured at one of its ends to at least one of said end plates.

2. In an electromagnetic transducer, a vibrating element comprising a plurality of thin, low-loss magnetically permeable metallic laminations, shims of relatively thinner ductile metallic sheet material interleaved between the successive laminations, the shims being anodized to form integral electric insulating layers on their opposite surfaces, and means for clamping the interleaved laminations and shims tightly together in immediate face contact to form a structure which will maintain its rigidity under vibration even at elevated temperatures, and an output stub shaft secured at one end to said element and lying perpendicular to the planes of said laminations.

3. The invention in accordance with claim 2, in which the clamping means comprises a plurality of tapered pins passing through said laminations and shims and headed to secure the latter together.

4. In an electromagnetic transducer, a vibrating element comprising a plurality of thin, low-loss magnetically permeable metallic laminations, shims of relatively thinner ductile metallic sheet material interleaved between the successive laminations, the shims having integral electric insulating layers on their oposite surfaces, and means for clamping the interleaved laminations and shims tightly together in immediate face contact to form a structure which will maintain its rigidity under vibration even at elevated temperatures; the thickness of said shims being of the order of one-tenth the thickness of said laminations, and an output stub shaft secured at one end to said element and lying perpendicular to the planes of said laminations.

5. The invention in accordance with claim 4, in which said shims are surface-anodized aluminum sheet material.

References Cited in the file of this patent UNITED STATES PATENTS 420,396 Thomson Jan. 28, 1890 448,644 Farmer Mar. 24, 1891 1,782,521 Trombetta Nov. 25, 1930 1,877,569 Falkenthal Sept. 13, 1932 2,410,220 Langworthy Oct. 29, 1946 2,506,637 Fog May 9, 1950 FOREIGN PATENTS 136,745 Switzerland Feb. 1, 1930

Images