US3901145A

US3901145A - Pivoted actuator arm assembly

Info

Publication number: US3901145A
Application number: US441191A
Authority: US
Inventors: Egon S Babler
Original assignee: Teletype Corp
Current assignee: AT&T Teletype Corp
Priority date: 1972-09-18
Filing date: 1974-02-11
Publication date: 1975-08-26
Anticipated expiration: 1992-08-26

Abstract

A row of actuator arms, such as electromagnet armatures used in operating a teleprinter, are pivotably mounted in closely spaced parallel relationship. A support frame or chassis is formed with a positioning plate assembly defining a sharp crotch at approximately a 90* angle, which defines the desired axis of pivoting. The arms are formed with a portion along one surface formed at an acute angle defining a knife edge. The arms are mounted in the frame, as with individual springs, so that the knife edges are urged into the crotch and the arms are freely pivotable in the crotch between first and second positions, such as the actuated and de-actuated positions of an electromagnet armature. Slotted guides are provided on either side of the pivot to limit the pivoting movement to preset parallel planes. The armatures are initially assembled with a guide and carrier bracket, outside of the machine, prior to final assembly of the bracket and the chassis. Flat end surfaces of electromagnet cores, which serve as stops for the arms in the actuated positions, are machined to be precisely coplanar with one flat surface of the positioning plate assembly defining the crotch.

Description

United States Patent [191 Babler 2 [4 1 Aug. 26, 1975 PIVOTED ACTUATOR ARM ASSEMBLY [75] Inventor: Egon S. Babler, Northbrook, Ill.

[73] Assignee: Teletype Corporation, Skokie, Ill.

[22] Filed: Feb. 11, 1974 [21] Appl. No.: 441,191

Related US. Application Data [63] Continuation-in-part of Scr. No. 292,003, Sept. 18,

1972, Pat. No. 3,805,695.

Primary ExaminerEdgar S. Burr Assistant Examiner-Edward M. Coven Attorney, Agent, or Firm l. L. Landis 5 7 ABSTRACT A row of actuator arms, such as electromagnet armatures used in operating a teleprinter, are pivotably mounted in closely spaced parallel relationship. A support frame or chassis is formed with a positioning plate assembly defining a sharp crotch at approximately a 90 angle, which defines the desired axis of pivoting. The arms are formed with a portion along one surface formed at an acute angle defining a knife edge. The arms are mounted in the frame, as with individual springs, so that the knife edges are urged into the crotch and the arms are freely pivotable in the crotch between first and second positions, such as the actuated and de-actuated positions of an electromagnet armature. Slotted guides are provided on either side of the pivot to limit the pivoting movement to preset parallel planes. The armatures are initially assembled with a guide and carrier bracket, outside of the machine, prior to final assembly of the bracket and the chassis. Flat end surfaces of electromagnet cores, which serve as stops for the arms in the actuated positions, are machined to be precisely coplanar with one flat surface of the positioning plate assembly defining the crotch.

17 Claims, 8 Drawing Figures PATENTEB AUG 2 61975 SHEET 2 UF 6 PATENTfinmszsims 3.901 145 saw 3 OF 5 PIVOTED ACTUATOR ARM ASSEMBLY CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part, of my copending application, Ser. No. 292,003, filed Sept. 18, 1976, now U.S. Pat. No. 3,805,695, issued Apr. 23, 1974.

BACKGROUND This application relates generally to a pivoted actuator of assembly, and more particularly to a system for mounting a plurality of pivoted armatures in precisely spaced relation to each other and to corresponding printing mechanisms of a teleprinter having a row of printing mechanisms.

In my parent application, and my related copending applications (A) Ser. Nos. 268,236 now U.S. Pat. No. 3,795,187, issued Mar. 5, 1974); (B) 268,237 now U.S. Pat. no. 3,823,667, issued July 16-, 1974; and (C) 268,238 now U.S. Pat. No. 3,822,641, issued July 9, 1974; all filed July 3, 1972, and all herein incorporated by reference, there is disclosed an essentially line-ata-time teleprinter including an endless carrier or belt that conveys a font of type members past an array of print hammers, one for each possible printing column on a page. As the type pallets pass the hammers, selected hammers are individually fired to strike the pallet on-the-fly and print a character.

This application and its parent relate particularly to an improved armature and electromagnet coil assembly for individually operating such closely spaced hammer's, typically 80-120 of them depending on the width of the page, rapidly and efficiently and with a minimum of movement of the armature.

Specific objects of this invention are to provide a simple and compact assembly for mounting a large number of pivoted armatures in a closely spaced row, with precise and nearly permanent alignment of the armatures in banks and with respect to the printing elements. Also, it is desired to provide an improved subassembly of the bank of armatures with a mounting plate, that can easily be assembled with and disassembled from the printer, for ease in assembling and disassembling the printer and for replacement of individual armatures.

More generally, an object of this invention is to provide an improved assembly for pivotably mounting an actuator arm in a frame or chassis of a machine, for precisely located movement between first and second positions for operating a controlled mechanism.

SUMMARY With the foregoing and other objects in veiw, a mounting assembly in accordance with this invention includes an actuator arm having a portion along one surface formed at an acute angle defining a knife edge. The machine frame or chassis includes a positioning member defining a sharp crotch at approximately a 90 angle. The crotch extends along a preset line defining the desired axis of pivoting for the arm. and the arm is mounted in the chassis so that the knife edge is urged into the crotch and the arm is freely pivotable in the crotch for movement between preset first and second operating positions.

Preferably, a row of such arms are arranged at precisely spaced intervals along the length of a single positioning plate, each being detachably retained in its preset position in the plate, so that the subassembly of plate and arms may readily be assembled with the controlled mechanism, such as a teleprinter. The arms may be electromagnet armatures having flat surfaced portions of magnetic material along one surface. The actuating members in this embodiment preferably comprise electromagnets having cores mounted in the chassis with flat outer surfaces facing the flat-surfaced portions of the corresponding arms. The outer surfaces of the magnet cores are precisely located, as by grinding, to be coplanar with the crotch, in which case the magnet cores define an operated position of the armature, limiting the pivoting movement of the armature in that direction. An additional stop is provided for limiting movement in the opposite or de-activated direction. A double slotted guide bracket is provided for locating and positioning the arms for pivoting in a preset plane perpendicular to the pivot axis.

Other objects, advantages, and features of the invention will be apparent from the following detailed description of specific embodiments thereof, when read in connection with the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGSS FIG. 1 is a perspective view of an impact printer according to my parent application, including an armature-mounting assembly embodying one form of this invention. Parts have been broken away and parts omitted for the purpose of illustration.

FIG. 2 is a vertical section according to line 22 of FIG. 1.

FIG. 3 is a horizontal section along line 3-3 of FIG. 2, parts broken out and parts omitted to reveal structural detail.

FIG. 4 is a vertical section along line 4-4 of FIG. 2, parts being broken out for purposes of illustration.

FIG. 5 is a vertical sectional view of a subassembly used in the printer, showing the printer chassis with magnetic cores mounted, the view being in the same plane as the plane of FIG. 2.

FIG. 6 is an'enlarged view in the same plane of one armature assembly in accordance with this invention.

FIG. 7 is a view similar to FIG. 6, showing a modified embodiment of the invention. FIG. 7 illustrates a subassembly of armatures and a carrier prior to assembly in the teleprinter.

FIG. 8 is a fragmentary perspective view of a portion of the subassembly shown in FIG. 7.

DETAILED DESCRIPTION BACKGROUND GENERAL ARRANGEMENT OF PRINTER Referring first to FIG. 1, an impact printer 10 in which this invention isutilized includes a pair of spaced apart pulleys l2 and 14, about which an endless belt or carrier 16 is trained for continuously moving a plurality of type pallets 18 in a printing path designated by arrow A in FIG. 1. A plurality of type dies 17 (FIG. 2) are carried on the front faces of the pallets 18, for movement past a page 22, such as paper or other printing medium on which printing is to take place. While any of various different printing mechanisms can be used and actuated in accordance with this invention, preferably .the printer mechanism is a belt printer as described in F. E. Huntoon-J. F. Kearney U.S. Pat. No. 3,742,848. As generally described in that patent, and in my parent application, the pulley I2 is an idler sheave while pulley 14 is continuously driven by a motor 26 through a drive train generally designated 27. The drive train 27 also includes an impeller shaft 30, which is journaled in opposed side walls 28 of the chassis or frame 29 (FIGS. 2, 4, and of the printer and is continuously driven in the direction indicated by arrow 31 during printer operation.

An inked ribbon 34 is disposed in generally standard fashion between the page 22 and the pallets 18, as illustrated in FIGS. 1 and 2. As described in more detail in the parent application, the ribbon 34 is trained about a plurality of guide rollers 38, and the ends of the ribbon are secured to a pair of adjoining

ribbon spools

40 and 42 in generally conventional fashion. The ribbon 34 is alternatively driven in opposite directions by a spool control mechanism 44, which is connected to the drive motor 26 through a generally conventional drive mechanism 48 so that the ribbon is driven in timed relation to the advancement of the pallets 18 for printing. alternatively, the ribbon 34 is preferably mounted and driven in the manner described in the commonly assigned copending application of Arthur F. Riley, Ser. No. 345,407, filed Mar. 27, 1973 (now US. Pat. No. 3,825,103, issued July 23, 1974), herein incorporated by reference.

A clutch 50, which may be conventional, is provided for intermittently operating a drive train 54 to advance the page 22 upward in direction shown by arrow 56, one or more lines at a time in generally conventional fashion, thus providing line feed driven from the main drive motor 26. The drive train 54 intermittently rotates a cylindrical drive roller 62 to advance the paper or page 22 in generally standard fashion, as particularly indicated in FIG. 2.

Printing of each character selected is accomplished by impeller wheels 66, only two of which are shown in FIG. 1. As described in more detail in copending applications, Ser. Nos. 268,236 and 268,238, each impeller wheel 66 comprises a thin generally circular disc having a plurality of radial, equiangularly spaced arms or impelling teeth 68, (FIG. 2). The impeller wheels 66 are concentrically secured to the drive shaft 30 for rotation therewith in the direction shown by arrow 31.

As best illustrated in FIG. impeller the imperller wheels 66 are axially and horizontally spaced along the shaft 30 such that each is disposed in a vertical plane opposite to a corresponding printing position or station on the page 22, and such that one impeller wheel 66 corresponds to each possible printing position across the width of the page. thus, there are a stack of eighty impeller wheels 66 for a typical 80-column printer, etc. A plurality of thin circular discs or shims 72 (FIGS. 2 and 4) are disposed between adjacent impeller wheels 66, to locate the impeller wheels and to isolate them from each other, as more particularly described in my copending applications Ser. Nos. 268,236 and 268,238.

lmpactor mans for printing comprise a plurality of equally spaced apart print hammers 76 (only two of which are shown in FIG. 1) disposed behind the page 22, to the left as viewed in FIG. 2. One hammer 76 is mounted in alignment with each impeller wheel 66, and defines'a corresponding printing position across the page 22. The hammers 76 are preferably constructed and operated as described in my copending applications Ser. Nos. 268,237 and 268,238. Each hammer is aligned with, though spaced from and disposed out of the path of movement of, the teeth 68 of an associated impeller wheel 66. The impeller 68 selectively drive the corresponding hammer 76 in a lineal'path perpendicular to the page 22, from a rest or non-printing position (FIG. 1 and 2) to a printing position (moved to the right in FIG. 2) where the hammer head 77 strikes the page 22,ribbon 34 and a selected type pallet 18 then I aligned with the hammer 76, to print the selected character.

A horizontal bumper 80, in the form of an elongated rod of resilient material, is disposed parallel to the shaft 30 and has opposed ends secured in the chassis side walls 28. The bumper 80 extends through horizontally aligned slots 82 in the hammers 76, for limiting horizontal hammer movement as described in detail in my copending application, Ser. No. 268,237. A leaf spring 84 of general vertical orientation is associated one with each hammer 76, for biasing the corresponding hammer 76 to the rest position (left in FIG. 2). The lower end portion of all of springs 84 is integrally fashioned with a front wear plate 83, which is secured to a front chassis plate 86, at the right-hand side of the printer as illustrated in FIGS. 5 and 6. A rear wear plate 85 is similarly provided at the rear, or left side of the chassis 29, as illustrated in FIGS. 2 and 5. An upper end portion of each spring 84 is engaged in a downwardly opening slot 88 in the hammer 77. Each spring 84 has a slightly tensioned condition (FIG. 2), during which its hammer 76 is in its rearward or non-printing position, and a further tensioned condition during printing, for urging or restoring the hammer 76 to the rest or non-printing position.

Each impeller wheel 66 is adapted to fire the aligned hammer 76 through an interponent 90, s described in my application, Ser. No. 268,238. In accordance therewith, the interponents 90 are disposed in general horizontal alignment and each has: 1 a first or upper position in which it is in a projected position, with its upper free end portion disposed in the path of movement of the next oncoming impeller tooth 68, for transmitting force from its impeller wheel 66 to an aligned hammer 76 to fire the hammer and print a character; and (2) a lower, non-printing, or rest position in which said interponent has been lowered and is removed from the impeller path as shown in FIG. 2. Each interponent 90 is intermittently controlled by an assembly comprised of a magnetically latchable armature 92 and an electromagnet 94 (FIG. 2) forming the subject matter of this application. Any suitable logic circuit may be employed for energizing selected electromagnets 94 to print characters, a preferred system being described in the commonly assigned copending application of Detlef A. Brodrueck, Ser. No. 402,864, filed Oct. 2, 1973 (now US. Pat. No. 3,845,710, issued Nov. 5, 1974). When a selected electromagnet 94 is energized, its armature 92 is rocked, magnetomotively, against the restoring bias of a contractile mounting spring 96, from its open or rest position shown in FIGS. 2 and 6 upwardly to a latched position contacting the lower portions of the electromagnet 94, as will be explained in detail hereafter.

When an electromagnet 92 is operated, the associated armature 92 moves the associated interponent 90 upward (from its FIG. 2 position) into its projected position between a pair of adjacent impeller teeth 68, against the lowering bias of an associated mounting spring 98 for the interponent 90. Ensuingly, each upwardly thrust interponent 90 will be engaged by the next impeller tooth 68, which drives the interponent 90 v a New" clockwise in FIG. 2 into engagement with an associated hammer 76, to effect momentum transfer and translation of impeller torque into a lineal force, thus firing the hammer 76 for printing a character. Both momentum transfer and restoration of each interponent 90 to its second position (FIG. 2) following momentum transfer, as well as the conditioning of interponents for repeat cycles, are described in detail in my application Ser. No. 268,238. The timing of the impeller wheels 68 is synchronized with the advance of the pallets 18 with the belt 16 so that the hammers 76, when fired, strike the type face of the then-aligned die 17, and the preferred arrangement of the impellers and hammers is de scribed in my application Ser. No. 268,237. As described in detail in the Huntoon-Kearney patent, the pallets l8 ride along a back-up bar or rail 102 (FIG. 2) in the printing course, which serves as a backstop for printing.

Further details of the printing mechanism, and the method of printing are given in my copending applications cited above and in the Huntoon-Kearney patent.

Armature and Magnet Assembly This application is particularly concerned with an improved mounting assembly for an actuator arm or le ver, such as the armatures 92, and is particularly useful in mounting a row of spaced armatures for individual pivoting movement about a common axis, for operating a driven mechanism such as an interponent 90 of the teleprinter 10. The mounting assembly could also be useful in mounting and operating many other types of mechanisms, particularly for precisely mounting rows of parallel electromagnetic armatures.

In the first exemplary embodiment of the teleprinter shown in FIGS. 1-6, each electromagnet 94 comprises a pair of electrically interconnected wire coils 104A and 1048 of a windings member 104 (FIGS. 2 and 3). The coils, respectively, of each pair are wound about depending legs 106A and 1068 of a magnetic core 106 as best illustrated in FIG. 5. The cores I06 and accordingly their windings members, are uniformly spaced apart and disposed horizontally in a pair of straight parallel arrays or banks 108 and 110 (top to bottom in FIG. 3). The bank 110 on the right in FIGS. 2, 3, and 5 is aligned adjacent and parallel to the front chassis plate 86, and the bank 108 on the left is aligned along and parallel to the corresponding rear chassis plate 85, which is mounted parallel to the front chassis plate 86 as shown in FIGS. 2 and 5.

Each core 106 has an upwardly projecting anchoring lug or shank I07, which is firmly secured in a respective one of a plurality of mounting holes 112 (FIGS. 2 and 5) formed in a horizontal wall 114 constituting a base or floor of the chassis 29. The holes 112 are aligned in the two banks 108 and llllfi, the alignment of the holes in each set being parallel to the hole alignment in the other set and extending along and parallel to a respective one of the

chassis plates

85 and 86. Each core 166 and its associated hole 112 in one of the banks 108 and llththough equally spaced from adjoining core members and holes in the same bank is offset horizontally from the corresponding core and hole in the opposite bank by a distance equal to half the spacing between adjacent core members and their holes, as shown in FIG. 3.

A rear or left wear plate 116 (FIGS. 2 and 3) is secured to the rear chassis plate 85. The wear plate I16 is parallel to and corresponds to the front wear plate 83,except that it does not require the upwardly extending hammer spring portions 84. Each of the

wear plates

83 and 116 has a depending overhang I118 (FIGS. 2 and 6), which extends a set distance downward below a flat lower end face 120 (FIGS. 5 and 6) of the corresponding

chassis plate

85 or 86. This construction generates a horizontal sharp crotch I22 at approximately a angle, which extends longitudinally of each bank 168 and M6, from top to bottom in FIG. 3, and which serves as a pivot point for the rocking movement of all armatures 92 in the corresponding bank H0 or I68.

In more general terms, the wear plate 83 and overhang 118 extend in a direction Y (FIG. 6), vertically downward in the example, beyond the flat end surface 220 of the chassis plate 86. The end surface 126 of the chassis plate runs in a direction X away from the wear plate 83 and perpendicular to Y, horizontally to the left in the example of FIG. 6. The inner surfaces of the overhang 11.8 and the end surface 120 of the chassis plate define the working surfaces of the crotch 122, which is formed at the junction and extends 'along a pivot axis Z (FIG. 3, and into the page in FIG. 6) perpendicular to X and Y. The two

parallel plates

86 and 83, when assembled as shown in FIG. 6, comprise a single positioning unit or member for mounting a large number of the armatures 92 in parallel for individual pivoting movement about a single pivot axis Z, as shown in FIG. 3, for each of the two rows I68 and 110. If desired, for some applications, the two parallel plates 36-83 could be formed as a single positioning plate or member; however, that construction is not preferred, as will appear hereafter in the section on the subassembly of armatures and mounting structures. As viewed in FIG. 2, the right bank armatures 94 pivot clockwise upward about the right-side crotch 122 when the corresponding electromagnet 94 is energized (arrow B), and the left-bank armatures 9 similarly pivot counterclockwise upward (arrow B) about the left bank crotch I22 when an armature 92 in that bank is selected.

An outer guide and mounting bracket 12 5 is positioned against the outer face of each of the

wear plates

83 and 116, as illustrated in FIGS. 2, 3, and 6, and is fastened to the corresponding

chassis plate

85 or 86 in the position shown. As illustrated in FIG. 3, the mounting brackets 124 extend horizontally along the width of the machine, from top to bottom in FIG. 3, so as to cover and extend beyond the entire distance occupied by the armatures 92 and the electromagnets 94.

The brackets I2 serve to position, locate and guide the individual armatures 32 for the required pivoting movement in a fixed plane and also serve, with the

wear plates

83 or 116, as a carrier for the armatures prior to assembly of the printer as will be explained hereafter.

As illustrated in FIGS. 3 and 6, each mounting plate I24 is formed with a central wall section I24, which on assembly with the

chassis plate

85 or 86 is vertical and approximately the same height as the

adjacent wear plate

83 or 116, as best shown in FIG. 6. The plate I24 is formed with lower, outwardly curved slotted flange I25 and an upper, outwardly curved slotted flange I26. The lower flange I25 is formed with a set of thin rectangular guide slots I27, one for receiving an outer portion of a corresponding one of the armatures 92, and the upper flange I26 is formed with a similar set of slots I28 for receiving and guiding portions of each corresponding armature 92. The slot pairs 127 and 128 are arranged vertically in alignment with each other, one in alignment with each position of an armature 92, as best shown in FIG. 3, so that the

slots

127 and 128 can receive and guide the outer end portion of each armature 92.

In particular, each armature 92 has an outer end section 129 (for example, to the right of the magnet 94 in FIG. 6), which passes below and projects beyond the wear plate 83 and the body 124 of the bracket 24. The outer section 129 extends outward through an associated one of the lower slots 127, and then curves upward to form an upwardly extending tip 130, which is guidingly received in the associated one of the upper slots 128. Thus, the outer end section 129 of each armature 92 is received in and is guided for pivoting movement by each of the aligned pair of

guide slots

127 and 128, which slots maintain the preset vertical attitude of the armature 92 and prevent it from moving horizontally from top to bottom in FIG. 3. More generally, the slot pairs 127-128 are aligned in parallel X-Y planes, perpendicular to the pivot axis Z, so as to locate each armature 92 in both

rows

108 or 110 and to guide each armature for free pivoting movement about the crotch 122 in a fixed predetermined X-Y plane set by the location of the guide slots.

Each armature 92 also has an inner section 132 (FIGS. 2 and 3, and 6) which terminates in a flat stand 134 (FIGS. 2 and 3) constituting the operating or driving end of the armatures. The positioning of the armatures in the two offset

banks

108 and 110 is such that all of the stands 134 are disposed in horizontal alignment (FIG. 3) at the center of the printer l0, midway between the two banks of

electromagnets

108 and 110. Each armature 92 is positioned, from top to bottom in FIG. 3, so that the stand 134 is vertically aligned below an associated one of the impellers 66. As illustrated in FIGS. 2 and 4, or other controlled mechanisms to be driven by the armature 92. Aflat broad latching section 136 of magnetic material, at the middle of each armature 92, is disposed below and in alignment with the lower end surfaces of a corresponding pair of

core legs

106A and 106B, to which such latching section 136 is drawn upon energization of the associated electromagnet 94, which serves as a stop for eah armature when pivoted to the actuated position (arrows B or B).

A flat surface 138 (FIG. 6) is formed along the outer section 129 of each armature, and extends downward at an acute angle to the upper surface of the armature 92 so as to define a horizontal knife edge 140 which serves as the pivot point for the armature 92. The knife edge 140 is received inside the inner surface of the overhang 1118 of the

wear plate

83 or 116 and is seated in the corresponding crotch 122 defined between the

chassis plate

85 or 86 and the wear plate 1 16 or 83. This serves to mount the armature 92 in the crotch 122 for pivoting movement between an open or released position (FIGS. 2 and 6) and a closed or actuated position (not shown), in which the armature 92 has pivoted upward (arrow B or B) until the latching section 136 of the armature 92 strikes and is magnetically held against its core 106.

The mounting spring 96 for each armature 92 is mounted at an angle so that the spring force (along line L, FIG. 6) urges the knife edge 140 into the crotch 122 so that the armature 92 is freely pivotable in the crotch 122, within the limits set by the acute angle of the knife edge 140, between the rest and the actuated positions,

as will be described. It should be noted that the bank of parallel springs 96 serve to mount a whole array of forty or more aramtures 92 in precisely spaced parallelism for movement about a fixed single pivot axis Z, defined by the crotch 122, and that all armatures in the row are thus precisely positioned from left to right in FIGS. 2 and 6, for exact pivoting movement about a single axis.

In particular, the spring biasing force (F in the diagram, FIG. 6), acting along the line L, has a first component F (to the right in FIG. 6) urging the armature 92 to the right until the knife edge 140 contacts and is stopped by the inner surface of the overhang 118 of the wear plate 83. A second component of biasing force, F. y (up in the example) urges the end section 129 of the armature upward to urge the knife edge 140 against the end surface of the chassis plate 86. Thus the resultant linear biasing force F urges each knife edge in the row of armatures 92 into the corresponding crotch 122, so that the armatures are freely pivotable about the axis 2 of the crotch.

The mounting springs 96 also exert a force which pivots the inner ends 132 of the armatures 92 downward to the rest or open position (arrow B in FIG. 6), where the inner end 132 of the armature rests against and is stopped by a fixed bumper 141 (FIGS. 2 and 3). Each spring 96 in the embodiment shown in FIGS. 2 and 6 has one end anchored about a lug 142 formed between the guide slots 127 in the flange 125 and the opposite end connected to a downwardly projecting arm 144 formed along the lower surface of the corresponding armature 92. Thus, each spring 96 serves to mount the armature 92 precisely in the crotch 122 for free pivoting movement and to bias the armature to the open position set by the common stop 141. The electromagnet core legs 106A and 1068 serve to stop the armature, when actuated, and set the actuated position, which in the example is set to be precisely horizontal.

A horizontally elongaged channel (FIGS. 2, 3, and 4) is mounted midway between the electromagnets 94 in

banks

108 and 110. The channel 150 is generally U-shaped in cross-section, and has upper end portions of its

opposed sides

152 and 154 suitably secured to the outside surfaces of a pair of spaced horizontally extending

hanger plates

146 and 147. The

hanger plates

146 and 147 depend from the horizontal chassis wall 114, to which they are secured by a plurality of fasteners 143 (FIGS. 2 and 4). The

plates

146 and 147 define a chamber 148 within which the interponents 90 are positioned.

The channel sides 152 and 154 are slotted, respectively, with vertical slots 156 in side 152 and vertical slots 158 in side 154 being spaced apart in horizontal alignment to receive the inner ends 132 of the armatures 92, so that the channel sides 152 and 154 serve as guide plates for the armatures 92. The armature stands 134 are disposed in the lower end portion of the chamber 148, with the inner ends 132 of the armatures 92 in the left bank 108 passing through the slots 158 on the left side and with the right-bank armatures received in the slots 156 at the right side. The

slots

156 and 158 are precisely aligned and coplanar with respect to the

slots

127 and 128 in the mounting brackets 124, so that the

inner guide slots

156 or 158 serve to locate and guide the movement of the inner ends 132 of the armatures 92 for pivoting movement in the preset vertical plane aligned with the lower end of the associated interponent 90. The bumper 141 extends along the bottom of the channel 150, below and parallel to the armature stands 134. The bumper is held in a retainer 160, which is secured along the bottom of the channel by means of a plurality of fasteners 164.

With this arrangement, it should be apparent that the aligned inner and outer slots such as 156 and 127-128 for the right-hand armatures 92 serve to position each armature 92 for pivoting movement in a precise vertical plane set by the slots in alignment below the corresponding interponent 90 to be selectively actuated by the armature. The pivot consisting of the knife edge 140 urged into the crotch 122 by the spring 96 serves to locate the armature 92 precisely, in the left-to-right direction in FIG. 6, so that it maintains the properly oriented position below the interponent 90. The rest or open position is set by gravity and the spring 96, where the inner end of the armature 92 rests on the stop or supporting bumper 141, and the actuated or closed position is set by the flat magnetic surface 136 engaging and held by the under surfaces 180 of the core legs 106A and 1068, at which time the armature is essentially horizontal and is immobilized until, later, when the electromagnet 94 is de-actuated and the spring 96 returns the armature to the open position in preparation for a subsequent printing operation by the corresponding hammer.

Assembly of the Printer Initially, the upper portion of the frame or chassis 29 is cast, comprising the horizontal wall 114 as a casting floor; the parallel vertical side walls 28, extending upwardly from wall 114; a rigidifying vertical web 170 (FIGS. 2 and connected at its lower end to the wall 114 and at its lateral ends to side walls 28; and a horizontal frame member 172 (FIG. 2), superimposed relative to the wall 114 and which defines a chamber 173 for the hammers 76. Each wall 28 is fashioned with a hole 174 (FIG. 5) for receiving an annular bearing 176, in which one end of the drive shaft 30 is journaled. The holes 174 are fashioned such that their centers are coaxially aligned and define an axis 175 parallel to the side walls 28, and about which the shaft 30 rotates when the printer is assembled.

Next, using axis 175 as a line of reference, the vertical holes 112 are drilled in the wall 114, such that their vertical axes are parallel to each other and perpendicular to the axis 175. The holes 112 associated with each of the

banks

108 and 110 have a uniform pitch of 0.200 inch in a typical embodiment of the invention, the holes 112 of each of said banks being offset 0.100 inch from the holes in the opposed bank for a'printer with 0. I00 inch spacing between characters. The holes 112 then receive the shanks 107 of the magnet cores 106 in a press fit, such that the legs 106A and 1063 of each core extend vertically downward and perpendicular to the axis 175. Thereafter, the parallel back and front chassis plates 85 and-86 are hung from the wall 114 by a plurality of fasteners 178 (FIGS. 2 and 5), and the assembly comprised of the inner guide or

hanger plates

146 and 147 and the slotted channel 150 is hung from the wall 114 by the fasteners 143.

Subsequently, again using axis 175 as a reference, the lower end surfaces 120 of the

chassis plates

85 and 86 and the lower flat end faces 180 (FIG. 5 and 6) of the

legs

106A and 106B are located, as by machining or grinding in any known manner; in a single plane parallel to the wall 114 and a preselected distance from axis 175. This operation precisely sets the vertical position of the pivot point, crotch 122, with respect to the magnet cores 106 and the upper limit of travel of the armatures 92, when actuated to the horizontal position. This, in turn, sets the limit of travel of the interponents 90, when the electromagnets 94 are energized, thus setting a uniform vertical position forthe interponents when projected and struck by the impellers 66. Each pair of coils 104A and 1048 is mounted about the corresponding core legs 106A and 1068 an fixed thereto, and the coils are electrically connected to logic circuits, for energizing the electromagnets, preferably as described in a related patent of James .F. Kearnery, U.S. Pat. No. 3,785,283, issued Jan. 15, 1974, incorporated herein by reference. That application describes a preferred method of securing the coils to the cores, and to logic circuits for operating the electromagnets 94.

Next, the shaft 30, with impellers 66, and the hammers 76 are mounted in their proper positions. Thereafter the interponents 90 are placed in position. Lastly, a subassembly consisting of the armatures 92, the

wear plates

83 or 116, the guide bracket 124, and the mounting springs 96, is fitted into place in the printer 10 as I shown in FIGS. 2 and 6.

Subassembly of Armatures and Mounting Structure Alternative Embodiment of the Invention This subassembly, designated 200 in FIGS. 7-8, is shown in those FIGS. along with a modified embodiment of the armatures 92 and mounting structure or carrier 201 for the armatures. The parts are numbered the same as in the other FIGS. except where differences are present. To make up the subassembly 200 of FIGS. 7-8, the outer bracket 124 and wear plate, such as 83, are first assembled as. shown in FIGS. 7-8, apart from the printer 10, with the positioning or wear plate 83 received on a plurality of screws 202 provided at intervals along the length of the bracket 124 and ultimately used to mount and fasten the subassembly 200 to the printer chassis plates 86 or'85 (FIG. 5) at the desired positions.

Then, each of the 40 or more armatures 92 of that subassembly are assembled in place, as depicted in FIGS. 7 and 8, one at a time, with the outer end 129 and tip being threaded through the

outer slots

127 and 128 and the spring 96 then positioned in place. When each spring. 96 is put in place, this effectively locks each armature 92 in turn into the subassembly in the position shown in FIG. 7. In the second embodiment, the spring 96 is placed betwen a wire rod 203 running the length of the mounting plate 124 and resting on the lower flange 125, and a selected one of three notches 204 formed along the projection or arm 144 of the armature. When a few of the springs 96 are in place, the spring force draws the rod 203 against the bracket 124 to hold the rod in place, and each armature is biased to the right (F and upward F at an angle in FIG. 7, as previously described, so that the knife edges bear against the flat inner surface of the wear plate 83 and force it into place against the inner wall 124' of the bracket 124.

In the subassembly position of FIG. 7, the springs 96 tilt the armatures 92 counterclockwise (arrow B), as previously described, so that the left edge 206 of the tip 130 engages and is stopped by the inner edge of the upper slot 128 and a portion 207 along the upper surface of the outer end 129 rides against the upper edge of the lower slot 127. This is the rest or stable position for each armature 92 in the subassembly, where the armatures are locked in place prior to assembly with the printer 10. But, in this position, the armatures 92 are displaced both upward (-Y direction) and counterclockwise (B rotation), to rest against the bracket 124- at two

points

206 and 207, from the operating position in the printer 10, as shown in FIG. 6 and previously described.

Thus, the entire subassembly 200 of

wear plates

83 or 86, mounting brackets 124, and a great many individual armatures 92 can readily be assembled or disassembled to replace individual armatures outside of the printer, and the individual armatures 92 and the whole assembly are locked in place after the springs 96 have been applied. Further, the entire subassembly 200 of armatures an mounting plates may very easily be inserted into and removed from the printer by merely threading the inner ends 132 of the armatures 92 through the

inner guide slots

156 or 158 at the center of the printer, and then fastening the bracket 124 and subassembly 200 to the

chassis plate

85 or 86 by tightening the screws 202. This automatically mounts and aligns all of the armatures 92 at once, but in a way such that the entire armature 92 carrier 201 subassembly 200 can easily be removed from the machine.

When the assembly is positioned in place and the screws 202 tightened, the individual armatures 92 are automatically repositioned in the printing position of FIG. 6, that is pushed downward and clockwise from the subassembly position of FIG, 7 as the bottom wall 120 of the chassis plate such as 86 pushes down on the armature 92, against the biasing spring 96, to correctly set the pivot point in the crotch 122. The tip 130 pivots slightly away from the wall of the slot 128 as the attitude is set by the bumper or stop 141, which sets the initial angular position upon assembly in the printer.

The provision of three separate notches 204 in the armature-biasing arm 14-4 allows the spring tension to be adjusted to any of three selected levels. This setting, and spring adjustment, allows one to set the armatureactuate time at any of three selected levels, thus adjusting the time interval between the movement any given electromagnet coil 104 is energized and the movement that the armature 92 has elevated the corre sponding interponent 90to the printing position, in the path of the next oncoming impeller tooth 68 in FIG. 2.

Review and Summary Advantages In view of the foregoing description of two specific embodiments of the invention, it should be apparent that there has been provided a simple and effective mechanism for mounting a row of parallel levers or arms, such as armatures 92, for precisely parallel free pivoting movement about a single axis 122. Once the knife edge 140 mount for each arm 92 has been precisely machined and the location of the crotch 122 set by positioning of the plates such as 86-83, there is no way that the pivots can become misaligned with respect to each other, such that all of the levers remain parallel and fixed in position and attitude with respect to each other and the operated mechanism (interponents 90). Also, the common stops 141 and surfaces 180 of cores 106 accurately limit the open and closed positions of each arm 92; and the aligned guide slot couples such as 127, 128 and 156 limit the pivoting movement pre cisely to the prescribed planes desired. The biasing means, springs 96, both urge the'arms 92 into the pivot to maintain the desired positions from right to left in FIG. 6 and also bias the arms 92 to the open position. Thus, the arms are mounted and supported solely by the springs 96, in combination with the upper and

lower stops

141 or 106 which set the two possible positions of the arm 92.

By machining the surfaces and in a common plane, the pivot point 122 is set to coincide with the op erated stop positon to precisely set the operated position of the actuated mechanism 90.

Also, the provision of the cage-like supporting and mounting assembly 201 is simple and efficient in assembling a large number of closely spaced armatures 92 (such as 40 armatures spaced on 0.200 inch centers) with an actuated device such as the printer 10.

While two specific examples and embodiments of the invention have been described in detail hereinabove, it will be obvious that various modifications may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. In combination with a machine of the type having a support frame and a plurality of identical, elongated actuator arms pivotably mounted in the frame for movement between first and second positions for operating a plurality of controlled mechanisms, an improved mounting assembly for the arms characterized by:

the frame comprising a chassis having a horizontal wall;

a positioning member for the arms secured to the chassis in a vertical position, the positioning member comprising a positioning plate assembly including a vertical chassis plate fixed to one end of the horizontal wall and depending vertically therefrom, the lower edge of the chassis plate being flat and horizontal, and a vertical wear plate fixed to the outer surface of the chassis plate and extending a short distance downwardly therefrom so as to provide a depending overhang, the juncture at the lower. edge of the chassis plate and the overhang portion of the wear plate defining a sharp crotch at approximately a 90 angle, the crotch extending along a line defining the axis of pivoting for the arms, the positioning plate assembly being elongated in the direction of the crotch so that all of the arms are pivotably mounted in the crotch in a parallel row at spaced intervals along the length of a single positioning member;

the arms comprising a plurality of electromagnet armatures having magnetic portions along the length thereof, each arm having a portion along one surfaceformed at an acute angle defining a knife edge;

means for mounting the arms in the frame so that each arm is freely pivotable in the crotch between the first and second positions, the mounting means including a plurality of individual biasing means, one for each arm, for urging the knife edge of each arm into the crotch so that each arm is individually pivotable in the crotch;

a plurality of individual electromagnets, one associated with each armature, for individually pivoting the corresponding armatures from the first to the second positions, the electromagnets being mounted in the frame in a row facing the magnetic portions of the corresponding armatures; an outer end of each arm including a curved portion tapering downwardly away from the knife edge, thence outwardly beneath the wear plate, and then upwardly generally parallel to the wear plate; and

the mounting means including a guide bracket secured to the outer surface of the wear plate and having upper and lower guide slots therein, in which the outer portions of the arms are received for locating the arms in the slots and containing the pivoting movement of the arms to predetermined vertical planes.

2. Apparatus as recited in claim 1, wherein the mounting means includes a plurality of springs mounted between the lower ends of the guide bracket and a plurality of depending extensions formed along the lower surfaces of the arms.

3. Apparatus as recited in claim 1, further comprising an inner guide for the armatures comprising a flat channel plate secured to the horizontal wall and depending vertically therefrom, said channel plate having a plurality of elongated vertical slots therethrough, through which the inner ends of the armatures pass, the slots being aligned with the slots in the guide bracket so as to locate and guide the inner ends of the armatures, and being long enough vertically to allow the required pivoting movement of the armatures in a vertical plane.

4. Apparatus as recited in claim 3, wherein the channel plate forms part of a U-shaped channel in which the inner ends of the armatures are enclosed, the channel having a closed bottom wall, and wherein an elongated horizontal bumper is received in the bottom of the channel, on which the inner ends of the armatures normally rest and which sets the open or de-energized positions of the armatures.

5. Apparatus as recited in claim 4, wherein:

the electromagnets include a plurality of vertically disposed core members secured to the horizontal wall at intervals along the length thereof, corresponding to the spacing of the armatures, the core members depending vertically from the horizontal wall and having fiat lower surfaces precisely flush with the lower surface of the vertical chassis plate, the core assemblies being located between the chassis plate and the channel plate, and being arranged in a horizontal row parallel to both of those plates.

6. Apparatus as recited in claim 5, wherein there are provided two banks of armatures, two rows of coils, and two vertical plate assemblies, the vertical plate assemblies being secured to the front and rear ends of the horizontal wall, with the guide slots of a front plate being parallel to those of the rear plate, but offset half the distance between the slots of the rear plate, so that the armatures in a front row alternate in position with those of the rear row, the inner ends of the armatures in both rows projecting toward each other in interleaved parallel relationship and terminating in a common vertical plane midway between the front and rear plate assemblies, the cores of the electromagnets being staggered in accordance with the positions of the armatures so that each core is centered directly above its corresponding armature.

7. Apparatus as recited in claim 1, wherein:

each electromagnet includes a vertically disposed magnet core member secured to the chassis and depending vertically therefrom, the core having a flat lower horizontal surface located in the same horizontal plane as the crotch and spaced therefrom so that the arm can pivot from a de-energized position where the arm is spaced from the core to an energized position where the magnetic portion of the arm engages the core and is stopped thereby in a horizontal position.

8. Apparatus as recited in claim 7, further comprising:

inner and outer guide plates mounted on the chassis,

one on either side of the crotch and core, the guide plates having coplanar vertical slots for receiving portions of the arm and permitting pivoting movement of the arm in a predetermined vertical plane set by the plane of the slots.

9. In combination with a machine of the type having a support frame and an elongated actuator arm pivotably mounted in the frame for movement between first and second positions for operating a controlled mechanism, the mounting assembly including (A) a positioning member secured to the frame and having surfaces defining a sharp crotch at approximately a angle, the crotch extending along a line defining the axis of pivoting for the arm, (B) the arm having a portion along one surface formed at an acute angle defining a knife edge, and (C) means for mounting the arm in the frame so that the knife edge is urged into the crotch and the arm is freely pivotable in the crotch about the knife edge between the first and second positions;

an improved mounting assembly, for mounting a plurality of identical arms in a parallel row at spaced intervals along the length of a single positioning member, the improved mounting assembly being characterized by:

(D) the positioning member being elongated in the direction of the crotch so that all of the arms are pivotably mounted in a single crotch;

(E) the mounting means including a plurality of individual biasing means, one for each arm, for urging the knife edge of each arm into the crotch so that each arm is individually pivotable in the crotch;

(F) the mounting means further including a guide bracket secured to the positioning member, the bracket having a pair of slotted flanges defining pairs of aligned coplanar guide slots, the slot pairs being equal in number to the number of arms and being located along the bracket according to the desired spacing of the arms so that each slot pair if aligned with one corresponding arm; and

(G) each arm including an outer end portion extending from the pivot point away from the controlled mechanism and shaped for reception in both slots of a corresponding pair, so that each pair of slots locates and guides the associated arm for pivoting movement in a fixedpredetermined plane set by the plane of the guide slots and perpendicular to the axis of the crotch.

10. Apparatus as recited in claim 9, wherein the mounting means further includes an inner guide plate secured to the frame on the opposite side from the guide bracket, the inner guide plate having a corresponding series of guide slots coplanar with those of the guide bracket for receiving and guiding an inner end portion of each corresponding arm for pivoting movement in the predetermined plane.

11. Apparatus as recited in claim 9, wherein the individual biasing means comprise a corresponding plurality of individual mounting springs mounted between portions of each corresponding arm and portions of the guide bracket, the springs being aligned to exertthe biasing force urging the knife edge of each corresponding arm into the crotch.

12. Apparatus as recited in claim 9, wherein the positioning member comprises an assembly of two parallel plates, an inner plate of which is secured to the frame and projects therefrom in a direction Y, and an outer plate of which is mounted against the inner plate and extends further in direction Y than the inner plate so as to provide an overhang running in direction 4, the inner surface of the overhang defining a first working surface of the 90 crotch, the inner plate being formed with a flat end surface running in a direction X away from the outer plate and perpendicular to Y and defining the second working surface of the crotch, the crotch being formed at the juncture of the overhang of the outer plate with the end surface of the inner plate and running along a pivot axis Z perpendicular to X and Y.

13. Apparatus as recited in claim 12, wherein the individual biasing means comprise a corresponding plurality of individual mounting springs mounted between portions of each corresponding arm and portions of the guide bracket, each spring being located along an axis arranged to exert a biasing force along a line L having components in the X and Y directions, thus biasing the knife edge of each arm into the crotch.

14. Apparatus as recited in claim 13 wherein:

the portions of the arms to which the springs are mounted extend in a direction such that the springs also pivot the arms in the crotch to the second position; and

a stop is mounted in the frame for engaging a portion of each arm and stopping it in the second position.

15. Apparatus as recited in claim 12, wherein:

the guide bracket and the outer plate of the positioning plate assembly also serve as a carrier for mounting and locating the arms and biasing means with respect to the guide bracket and outer plate prior to assembly of the guide bracket and outer plate with the inner plate; and

means are provided for securing the guide bracket and outer plate assembly to the inner plate.

16. Apparatus for mounting a row of parallel actuator arms pivotably in a carrier, which comprises:

a positioning plate having a flat inner surface;

a guide bracket;

means for mounting the guide bracket adjacent to the outer surface of the positioning plate; the bracket having a pair of slotted flanges defining pairs of aligned coplanar guide slots, the slot pairs being equal in number to the number of arms and being located along the bracket according to the desired spacing of the arms so that each slot pair is aligned with one corresponding arm, each arm including a knife edge portion formed along one surface of the arm and an outer end portion extending from the knife edge portion and shaped for reception in both slots of a corresponding pair; means for individually mounting each arm to the bracket so that the knife edge portion of each arm is urged against the inner surface of the positioning plate and so that the outer end portion of each arm is received for pivoting movement in both slots of the corresponding pair; and

stopping means formed in the bracket at the base of each slot for engaging two spaced portions of the outer end portion of each arm as the arm pivots in the slots, so that the arms are locked with the positioning plate and guide bracket, together forming the carrier, after positioning of the arms in the slots and assembly of the mounting means.

17. Apparatus as recited in claim 16, wherein the mounting means include a corresponding plurality of individual mounting springs mounted between portions of each corresponding arm and portions of the guide bracket, the springs being aligned to exert a biasing force urging the knife edge of each corresponding arm against the positioning plate, and also biasing and pivoting each arm into engagement with the stopping means of both corresponding grooves.

Claims

1. In combination with a machine of the type having a support frame and a plurality of identical, elongated actuator arms pivotably mounted in the frame for movement between first and second positions for operating a plurality of controlled mechanisms, an improved mounting assembly for the arms characterized by: the frame comprising a chassis having a horizontal wall; a positioning member for the arms secured to the chassis in a vertical position, the positioning member comprising a positioning plate assembly including a vertical chassis plate fixed to one end of the horizontal wall and depending vertically therefrom, the lower edge of the chassis plate being flat and horizontal, and a vertical wear plate fixed to the outer surface of the chassis plate and extending a short distance downwardly therefrom so as to provide a depending overhang, the juncture at the lower edge of the chassis plate and the overhang portion of the wear plate defining a sharp crotch at approximately a 90* angle, the crotch extending along a line defining the axis of pivoting for the arms, the positioning plate assembly being elongated in the direction of the crotch so that all of the arms are pivotably mounted in the crotch in a parallel row at spaced intervals along the length of a single positioning member; the arms comprising a plurality of electromagnet armatures having magnetic portions along the length thereof, each arm having a portion along one surface formed at an acute angle defining a knife edge; means for mounting the arms in the frame so that each arm is freely pivotable in the crotch between the first and second positions, the mounting means including a plurality of individual biasing means, one for each arm, for urging the knife edge of each arm into the crotch so that each arm is individually pivotable in the crotch; a plurality of individual electromagnets, one associated with each armature, for individually pivoting the corresponding armatures from the first to the second positions, the electromagnets being mounted in the frame in a row facing the magnetic portions of the corresponding armatures; an outer end of each arm including a curved portion tapering downwardly away from the knife edge, thence outwardly beneath the wear plate, and then upwardly generally parallel to the wear plate; and the mounting means including a guide bracket secured to the outer surface of the wear plate and having upper and lower guide slots therein, in which the outer portIons of the arms are received for locating the arms in the slots and containing the pivoting movement of the arms to predetermined vertical planes.

5. Apparatus as recited in claim 4, wherein: the electromagnets include a plurality of vertically disposed core members secured to the horizontal wall at intervals along the length thereof, corresponding to the spacing of the armatures, the core members depending vertically from the horizontal wall and having flat lower surfaces precisely flush with the lower surface of the vertical chassis plate, the core assemblies being located between the chassis plate and the channel plate, and being arranged in a horizontal row parallel to both of those plates.

7. Apparatus as recited in claim 1, wherein: each electromagnet includes a vertically disposed magnet core member secured to the chassis and depending vertically therefrom, the core having a flat lower horizontal surface located in the same horizontal plane as the crotch and spaced therefrom so that the arm can pivot from a de-energized position where the arm is spaced from the core to an energized position where the magnetic portion of the arm engages the core and is stopped thereby in a horizontal position.

8. Apparatus as recited in claim 7, further comprising: inner and outer guide plates mounted on the chassis, one on either side of the crotch and core, the guide plates having coplanar vertical slots for receiving portions of the arm and permitting pivoting movement of the arm in a predetermined vertical plane set by the plane of the slots.

9. In combination with a machine of the type having a support frame and an elongated actuator arm pivotably mounted in the frame for movement between first and second positions for operating a controlled mechanism, the mounting assembly including (A) a positioning member secured to the frame and having surfaces defining a sharp crotch at approximately a 90* angle, the crotch extending along a liNe defining the axis of pivoting for the arm, (B) the arm having a portion along one surface formed at an acute angle defining a knife edge, and (C) means for mounting the arm in the frame so that the knife edge is urged into the crotch and the arm is freely pivotable in the crotch about the knife edge between the first and second positions; an improved mounting assembly, for mounting a plurality of identical arms in a parallel row at spaced intervals along the length of a single positioning member, the improved mounting assembly being characterized by: (D) the positioning member being elongated in the direction of the crotch so that all of the arms are pivotably mounted in a single crotch; (E) the mounting means including a plurality of individual biasing means, one for each arm, for urging the knife edge of each arm into the crotch so that each arm is individually pivotable in the crotch; (F) the mounting means further including a guide bracket secured to the positioning member, the bracket having a pair of slotted flanges defining pairs of aligned coplanar guide slots, the slot pairs being equal in number to the number of arms and being located along the bracket according to the desired spacing of the arms so that each slot pair if aligned with one corresponding arm; and (G) each arm including an outer end portion extending from the pivot point away from the controlled mechanism and shaped for reception in both slots of a corresponding pair, so that each pair of slots locates and guides the associated arm for pivoting movement in a fixed predetermined plane set by the plane of the guide slots and perpendicular to the axis of the crotch.

11. Apparatus as recited in claim 9, wherein the individual biasing means comprise a corresponding plurality of individual mounting springs mounted between portions of each corresponding arm and portions of the guide bracket, the springs being aligned to exert the biasing force urging the knife edge of each corresponding arm into the crotch.

12. Apparatus as recited in claim 9, wherein the positioning member comprises an assembly of two parallel plates, an inner plate of which is secured to the frame and projects therefrom in a direction Y, and an outer plate of which is mounted against the inner plate and extends further in direction Y than the inner plate so as to provide an overhang running in direction 4, the inner surface of the overhang defining a first working surface of the 90* crotch, the inner plate being formed with a flat end surface running in a direction X away from the outer plate and perpendicular to Y and defining the second working surface of the crotch, the crotch being formed at the juncture of the overhang of the outer plate with the end surface of the inner plate and running along a pivot axis Z perpendicular to X and Y.

13. Apparatus as recited in claim 12, wherein the individual biasing means comprise a corresponding plurality of individual mounting springs mounted between portions of each corresponding arm and portions of the guide bracket, each spring being located along an axis arranged to exert a biasing force along a line L having components in the -X and -Y directions, thus biasing the knife edge of each arm into the crotch.

14. Apparatus as recited in claim 13 wherein: the portions of the arms to which the springs are mounted extend in a direction such that the springs also pivot the arms in the crotch to the second position; and a stop is mounted in the frame for engaging a portion of each arm and stopping it in thE second position.

15. Apparatus as recited in claim 12, wherein: the guide bracket and the outer plate of the positioning plate assembly also serve as a carrier for mounting and locating the arms and biasing means with respect to the guide bracket and outer plate prior to assembly of the guide bracket and outer plate with the inner plate; and means are provided for securing the guide bracket and outer plate assembly to the inner plate.

16. Apparatus for mounting a row of parallel actuator arms pivotably in a carrier, which comprises: a positioning plate having a flat inner surface; a guide bracket; means for mounting the guide bracket adjacent to the outer surface of the positioning plate; the bracket having a pair of slotted flanges defining pairs of aligned coplanar guide slots, the slot pairs being equal in number to the number of arms and being located along the bracket according to the desired spacing of the arms so that each slot pair is aligned with one corresponding arm, each arm including a knife edge portion formed along one surface of the arm and an outer end portion extending from the knife edge portion and shaped for reception in both slots of a corresponding pair; means for individually mounting each arm to the bracket so that the knife edge portion of each arm is urged against the inner surface of the positioning plate and so that the outer end portion of each arm is received for pivoting movement in both slots of the corresponding pair; and stopping means formed in the bracket at the base of each slot for engaging two spaced portions of the outer end portion of each arm as the arm pivots in the slots, so that the arms are locked with the positioning plate and guide bracket, together forming the carrier, after positioning of the arms in the slots and assembly of the mounting means.