BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to indexing apparatuses and, more particularly, is directed to fluid-actuated indexable apparatuses for selectively orienting objects such as workholding devices in precise predetermined positions.

Description of the Invention Background

A number of different apparatuses have been developed for indexing a variety of articles between manufacturing operations to increase the efficiency of the manufacturing process. For example, various types of indexing apparatuses are typically used to accurately present a workpiece in a predetermined orientation relative to the spindle of a machining device such as a milling machine or the like.

One type of such indexing device is disclosed in U.S. Patent No. 2,339,986 to Engert. The device in that patent comprises an indexable device for indexing a shaft into a variety of different machining orientations about a single axis. While this device advantageously can support a shaft in various orientations to enable, for example, keyways to be cut in different locations on the shaft, the device can only hold a single shaft at a time and is ill-suited for supporting non- cylindrical workpieces .

Another indexable device is disclosed in U.S. Patent No. 3,020,998 to Webb. That device comprises a turntable adapted to be indexed by the cyclic operation of a ratchet and pawl mechanism. A plurality of vise-like workholders are supported on the table and are adapted to be indexed about an axis such that the workholders can be positioned in various orientations relative to metal bending or crimping apparatus. This device, however, can only support workpieces in single planar orientations about the device's axis. Moreover, the ratchet and pawl system cannot be used to index the workholders to very precise and minute different angular orientations. U.S. Patent No. 2,369,425 to Becker discloses an indexable workholding device that comprises a frame that is adapted for attachment to the machining table of a machining device such as drill press. A disk is rotatably attached to the frame and may be rotated about an axis and secured in a predetermined position by clamping members attached to the frame. The top of the disk is also configured to accept workpiece holding clamps thereon. The outer edge of the disc is provided with a vernier scale that cooperates with an indicator on the frame to very precisely indicate the rotational position of the disc relative to the frame. The workpiece accuracy is dependent upon the secure clamping of the disk in position and the secure clamping of the workpiece on the disk. If either the workpiece or the disk moves even slightly, the workpiece accuracy will be compromised. A similar apparatus for retaining workpieces at selective angles is also disclosed in U.S. Patent No. 2,406,043 to Sorensen.

That device also comprises a rotatable plate member that is equipped with a plurality of threaded apertures adapted to receive workholding clamping members therein. Although this device is capable of indexing a workpiece at relatively precise angular orientations, if the clamping assemblies attaching the workpiece move, the workpiece accuracy is compromised.

Today, many machine tools are computer or numerically controlled which enables such tools to outproduce their manually operated counterparts. In an effort to reduce the time necessary to index a workpiece or a series of workpieces for presentation to the machine tool, pneumatically and hydraulically operated indexing devices, which can be automatically controlled by the machine tool control system, have been developed. Such systems enable the workpieces to be automatically indexed to various predetermined orientations consistent with successive machining operations. The locking forces generated by such devices, however, are dependent upon the constant supply of the pressurized fluid to the device. Thus, if the fluid pressure is accidently lost or discontinued, those indexing apparatuses can become unlocked and expose their payloads to damage from inadvertent contact with the machine tool .

In addition, indexing apparatuses are often exposed to large torques generated when large machining forces are applied at considerable distances from the central axis of the indexing apparatus. For example, drilling a 22.2mm (.875") diameter hole in steel would require a thrust of about 10,000

N (2300 lbs.) . This force, if applied 100mm (3.9") from center, would apply lOOON-m (750 Ft-lbs.) of torque to the indexing apparatus . Such forces can cause the support member to inadvertently slip during a machining operation. Thus, large locking forces are desired for retaining the indexing device in a locked position during machining. However, because the locking forces generated by prior fluid-actuated indexing apparatuses are dependent upon the magnitude and maintenance of the pressurized fluid to the device, if there is an undetected leak in the fluid supply system, the locking forces can be compromised.

Also, prior fluid-actuated indexing apparatuses that are automatically controlled by the machine tool controller lack means for automatically confirming that the indexing apparatus is in a "home" or starting position prior to initiating the machining operations. Thus, the operator must inspect the position of the indexing apparatus prior to starting the machining process. If the indexing apparatus is not in a starting position and the machining operation is accidentally commenced, the workholding devices and/or the workpiece (s) could be damaged by the machine tool .

Thus, there is a need for a fluid-actuated indexing apparatus that remains in a locked position when the supply of pressurized fluid is accidentally interrupted or discontinued from the apparatus.

There is a further need for an indexing apparatus that has means for signalling the operator and/or the computerized

system controlling the apparatus that the apparatus is in a starting position.

SUMMARY OF THE INVENTION In accordance with a particular preferred form of the present invention, there is provided a fluid-actuated apparatus for selectively indexing an article about an axis. The apparatus, in a preferred form, comprises a housing member and an indexable support table that is supported on the housing member. The indexable support table is selectively movable between a plurality of locked positions about the axis wherein the indexable support table is prevented from rotating about the axis and an unlocked position wherein it can be rotated about the axis. The indexable support table is also provided with means for attaching a payload thereto. The apparatus also includes an indexing assembly that is received within the housing member and is operably attached to the indexable support table. The indexing assembly communicates with a source of pressurized fluid for receiving pressurized fluid therefrom such that upon an application of a first amount of pressurized fluid to the indexing assembly, the indexable support table is retained in a locked position. When the application of the first amount of pressurized fluid is discontinued and a second amount of pressurized fluid is applied to the indexing assembly, the indexable support table is moved to the unlocked position. Upon a further application of a third amount of pressurized fluid to the indexing assembly, the indexable support table is rotated to a

predetermined angular position about the axis. When the second amount of pressurized fluid is discontinued from the indexing assembly, the indexable support table is locked in the angular position. The apparatus is equipped with means for retaining the indexable support table in a locked position when the supply of pressurized fluid is lost or discontinued to the indexing assembly. The apparatus may also be equipped with a device for detecting when the indexable support table is in a starting position and generating a useable signal for signalling the operator or for use by the system controlling the machine tool .

Thus, it is an object of the present invention to provide a fluid-actuated indexable apparatus that can be used to index a variety of different articles about an axis to very precise angular orientations.

It is another object of the present invention to provide a fluid-actuated indexable apparatus with the above-mentioned attributes that can rigidly retain the article (s) attached thereto in the predetermined angular orientation (s) . It is yet another object of the present invention to provide a fluid-actuated apparatus that will remain in a locked position should the supply of pressurized fluid be accidentally lost or discontinued.

It is a further object of the invention to provide a fluid-actuated indexable workholding apparatus that is equipped with means for automatically determining whether the indexable support table thereof is in a desired starting position.

Accordingly, the present invention addresses the foregoing problems associated with other fluid-actuated indexable apparatuses. In addition to the forgoing mentioned advantages, other details, objects, and advantages will become apparent as the following detailed description of the present preferred embodiments hereof proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings, there are shown present preferred embodiments of the invention wherein like reference numerals are employed to designate like parts and wherein:

FIG. 1 is front elevational view of a preferred fluid- actuated indexing apparatus of the present invention;

FIG. 2 is a left side elevational view of the fluid- actuated apparatus of FIG. 1;

FIG. 3 is a cross-sectional side elevational view of the indexing apparatus of FIGS. 1 and 2 in a locked position taken along line III-III in FIG. 1 with some of the elements thereof omitted for clarity; FIG. 4 is a partial cross-sectional side elevational view of the indexing apparatus of FIGS. 1-3 in an unlocked position with some of the elements thereof omitted for clarity;

FIG. 5 is a partial cross-sectional rear elevational view of the indexing apparatus of FIGS. 1-3 in the starting position taken along line V-V in FIG. 2;

FIG. 6 is a front view of a preferred selector shaft of the present invention;

FIG. 7 is a right end view of the selector shaft of FIG. 6;

FIG. 8 is a left end view of the selector shaft of FIGS. 6 and 7; FIG. 9 is a top view of the selector shaft of FIGS. 6-8; FIG. 10 is a perspective view of the selector shaft of FIGS. 6-9;

FIG. 11 is cross-sectional rear elevational view of the indexing apparatus after the rack sleeve has engaged the shock absorbing assembly;

FIG. 12 is a schematic depiction of a preferred control system for controlling the indexing apparatus of the present invention; and

FIG. 13 is an enlarged cross-sectional elevational view of a portion of the indexing assembly of the present invention in a locked position.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings for the purposes of illustrating present preferred embodiments of the invention only and not for purposes of limiting the same, the Figures illustrate a preferred indexable apparatus 10 that has a housing 12 that can be operably attached to variety of different support structures (not shown) to orient the device's axis of rotation "A-A" in a desired manner relative to, for example, the spindle of a machine tool. In a preferred embodiment, the apparatus 10 is adapted to be attached to a support member by conventional fastening screws

that extend through mounting bores 13 provided in the housing 12. As the present Detailed Description of Preferred Embodiments proceeds, the reader will appreciate that the present indexable apparatus 10 may be used in a variety of different applications wherein it is desirable to index an item or a plurality of items about an axis at predetermined degrees of accuracy (i.e., approximately + 5 arc-seconds) .

More particularly and with reference to FIGS. 1 and 2, the present indexing apparatus 10, in a preferred form, includes an indexing table 20 that is operably supported by the housing 12 and is indexable about axis A-A by an indexing assembly generally designated as 15. A plurality of (preferably four) threaded bores 22 are provided in the indexing table 20 for facilitating the attachment of a payload 25 thereto. See FIG. 3. The reader will appreciate that the payload 25 could comprise, for example, a single workpiece, a plurality of workpieces, and/or a variety of workholding devices such as vises, clamps, fixtures, etc. As can be seen in FIGS. 3 and 4, payload 25 is preferably attached to the indexing table 20 by cap screws 26. The skilled artisan will readily appreciate, however, that other means of attachment could be successfully employed to attach workpieces and/or workholding apparatuses to the indexing table 20.

Also in a preferred embodiment, to provide an indication of the angular position of the indexing table 20 about axis "A-A", a scale ring 30 is attached to the perimeter of the indexing table 20. The scale ring 30 has an annular portion 32 that is adapted to be selectively received within an

annular cavity 17 in the housing 12. See FIG. 4. In a preferred embodiment, numerical indicia 31 are provided in the scale ring 30 and cooperate with a witness mark 39 on the housing 12 to provide the operator with a visual indication of the angular position of the indexing table 20 and, ultimately, of the payload 25 that is attached thereto. See FIG. 1.

In a preferred embodiment, three commercially available wiper members (33, 34, 35) are mounted in the wall of cavity 17 as shown in FIGS. 3 and 4. As will be discussed in further detail below, wiper members (33, 34, 35) serve a two-fold purpose; namely, to prevent chips and debris from entering into the cavity 17 and to provide a sufficient amount of frictional force to retain the indexing table 20 in a momentary "disengaged" position as the table 20 is being rotated through the final portion of its radial path.

As can be seen in FIGS. 3 and 4, an annular ring of teeth 23 are formed in the rear surface 21 of the indexing table 20. Teeth 23 are adapted to selectively mesh with a second toothed ring 40 that is preferably attached to the housing 12 by a plurality of capscrews 42. Also in a preferred embodiment, the rear surface 41 of the toothed ring is fitted with an 0- ring 43 for establishing a substantially fluid-tight seal with the adjacent portion of housing 12. The toothed portion 23 of indexing table 20 in combination with the second toothed ring 40 forms a coupling generally designated as 45 that is known in the art as a "Curvic-type" or "Hirth-type" coupling. In a preferred embodiment, the annular ring of teeth 23 and the second toothed ring 40 each contain a total of seventy-two

teeth. The second toothed ring 40 has an axial bore 44 therein that is adapted to axially receive a portion of a piston member 50 that is supported on an indexing shaft 60. As can be seen in FIGS. 3 and 4, the indexing shaft 60 extends along indexing axis A-A and has a flanged end 62 that is attached to the rear surface 21 of the indexing table 20 preferably by capscrews 63. In a preferred embodiment, an O- ring 65 is mounted in the outer perimeter of the end of the indexing shaft 60 to establish a substantially fluid-tight seal between the flanged end 62 and the indexing table 20. See FIGS . 3 and 4.

Piston member 50 preferably has a hub portion 52 and an outwardly extending flange 56. Hub portion 52 has an axial bore 53 extending therethrough through which the indexing shaft 60 axially extends. As can be seen in FIGS. 3 and 4, hub portion 52 has a forward end 54 that is sized to be slidably received within the axial bore 44 in the second toothed ring 40 and a rear end 55 that is sized to be received in axial bore 14 in the housing member 12. As can also be seen in FIG. 4, the flange 56 of the piston member 50 is sized to be slidably received in a bore 16 in the housing 12 that is coaxially aligned on axis A-A with bore 14. Piston member 50 is preferably fitted with a series of three 0-rings (57, 58, 59) for establishing substantially fluid-tight seals with the housing member 12 and the second toothed ring 40, respectively. In addition, a commercially available thrust bearing 51 is preferably provided between the forward end 54 of the hub 52 and the flanged end 62 of the indexing shaft 60.

Also in a preferred embodiment, at least one and preferably six springs 48 in compression are provided between the piston flange 56 and the second toothed ring 40 for biasing the second toothed ring 40 into meshing engagement with the teeth 23 formed on the rear surface 21 of the indexing table 20. A rotary force is selectively applied to the indexing shaft 60 by a rack and pinion drive assembly generally designated as 70. Drive assembly 70 includes a pinion gear 72 that is rotatably supported on the indexing shaft 60. Pinion gear 72 is sized to rotate freely on the shaft 60 and a thrust bearing 73 is preferably provided between the pinion gear 72 and the adjacent portion of the housing 12 to further facilitate the rotation of the pinion gear 72 on the shaft 60. Pinion gear 72 is retained on the indexing shaft 60 by a retaining member 77 preferably configured as shown in FIG. 4 and attached to housing 12. In a preferred embodiment, pinion gear 72 has a series of teeth 74 formed around three fourths of its perimeter. See FIG. 5. Thus, the pinion gear 72 preferably has a toothed portion 75 and a toothless portion 76. In addition, a ring of teeth 78 are formed on one side of the pinion gear 72 and are adapted to mesh with a toothed coupling ring 66 that is non-rotatably attached to the end of the indexing shaft 60. In a preferred embodiment, coupling ring 66 is keyed onto the shaft 60 by a stationary spline arrangement and is retained thereon by a threaded nut member 68. The skilled artisan will appreciate that the toothed portion 78 of pinion gear 72 and the coupling ring 66 cooperate to form a second "Curvic-type" or "Hirth-type"

coupling, generally designated as 80. In a preferred embodiment, coupling ring 66 and toothed portion 78 of pinion gear 72 each have the same number of teeth found in the first coupling 45 (i.e., seventy-two) . Rack and pinion assembly 70 also includes a slidable rack sleeve 90 that is adapted to mesh with the pinion gear 72. Pneumatically actuated rack sleeve arrangements are known in the art and therefore the construction of the rack sleeve assembly will not be discussed in great detail. More specifically and with reference to FIG. 5, the rack sleeve 90 is slidably received in a bore 18 in housing 12. Preferably, the axis B-B of bore 18 is substantially transverse to axis A- A. Rack sleeve 90 is preferably fabricated from aluminum and is adapted to axially slide on a rotatable selector shaft 110 along axis B-B. Rack sleeve 90 has teeth machined 92 therein that are adapted to engage the teeth 74 of pinion gear 72. In addition, as can be seen in FIG. 5, a bearing sleeve 91 is mounted near each end of the sleeve 90. Bearing sleeves 91 are preferably fabricated from acetal plastic and serve to reduce the friction between the rack sleeve 90 and the bore 18. As can also be seen in FIG. 5, a wiper seal 93 is preferably mounted in each end of the rack sleeve 90 to establish substantially fluid-tight seals between those ends of the rack sleeve 90 and the wall of bore 18. Wiper seals 93 are preferably retained in position by corresponding retainer rings 94.

Rack sleeve 90 preferably has an axial bore 95 extending therethrough that is sized to slidably and rotatably support a

selector shaft 110 therein. In addition, a counterbore 96 that is coaxially aligned with axial bore 95 is provided in the end of the rack sleeve 90. A cap member 97 is preferably received in the bottom of counterbore 96 and is attached to the rack sleeve 90 by capscrews 98. In a preferred embodiment, an O-ring 99 is mounted in the perimeter of the cap member 97 to establish a substantially fluid-tight seal between the cap member 97 and the wall of counterbore 96.

In a preferred form, the selector shaft 110 is fabricated from hardened steel and is rotatably actuatable by a knob assembly 120. As can be seen in FIGS. 6-10, a plurality of notches (112, 113, 114, 115, 116, 117) are machined into the shaft at different positions for engagement with a transverse pin 102 mounted in the wall of the rack sleeve 90. Preferably, pin 102 is fabricated from hardened steel and protrudes inwardly into the axial bore 95 to selective engage the notches (112, 113, 114, 115, 116, 117) . The skilled artisan will appreciate that by rotating the selector shaft 110 within the rack sleeve 90, the axial travel of the rack sleeve 90 in the "C" direction can be limited by virtue of the engagement of the pin 102 with one of the notches (112, 113, 114, 115, 116, 117) . For example, if the selector shaft 110 is rotated such that notch 112 is aligned with the pin 102, the rack sleeve 90 will, when actuated in the manner discussed below, travel in the "C" direction until pin 102 engages the notch 112. In a preferred embodiment, such axial travel of the rack sleeve 90 will ultimately result in the 5° rotation of indexing table 20 about axis A-A. When the selector shaft

110 is rotated to align notch 113 with the pin 102, the indexing table will, upon actuation of the rack sleeve 90, rotate 15°. Similarly, when notch 114 is aligned with pin 102, the indexing table 20 will rotate 30° upon actuation of the rack sleeve 90. When notch 115 is aligned with pin 102, the indexing table 20 will rotate 45° upon actuation of the rack sleeve 90. Likewise, when the notch 116 is aligned with pin 102, the indexing table 20 will rotate 60° upon actuation of the rack sleeve 90. When the notch 117 is aligned with the pin 102, the indexing table 20 will index 90° when the rack sleeve 90 is axially actuated.

As shown in FIGS. 5, 6 and 9, because the end of the axial bore 95 in the rack sleeve 90 is sealed, a pressure equalization channel 118 is preferably provided in the selector shaft 110 to enable the air pressure within the axial bore 95 to equalize about the selector shaft 110 when the rack sleeve 90 is axially actuated and serves to prevent the establishment of an air pocket that could hamper the axial travel of the rack sleeve 90 on the selector shaft 110. In a preferred embodiment, the selector shaft 110 is rotatably supported in the housing 12 by a knob assembly 120. As can be seen in FIG. 5, knob assembly 120 preferably comprises a first support cap 122 that is fastened to housing 12 preferably by capscrews (not shown) . More specifically, support cap 122 is sized to be received in a counterbore 18' that is coaxially aligned with bore 18. To establish a substantially fluid-tight seal between the support cap 122 and the wall of counterbore 18' , an O-ring 123 is provided in

support cap 122. Support cap 122 has an axial bore 124 extending therethrough that is adapted to rotatably receive and support end 111 of selector shaft 110. In a preferred embodiment, a collar 119 is formed on the selector shaft 110 which is adapted to abut a thrust washer 125 in support cap 122.

Support cap 122 also preferably has a counterbore 126 therein that is coaxially aligned with the bore 124 and is sized to receive a portion of an actuator knob 130 that is attached to the shaft end 111. Actuator knob 130 is preferably attached to the end 111 of the shaft 110 by a capscrew 132 in the manner shown in FIG. 5; however, other fastening methods may also be used. To assist the user in rotating the selector shaft 110 to one of the settings (i.e., 5°, 15°, 30°, 45°, 60° or 90°) , a commercially available spring-biased ball plunger 134 is mounted in the actuator knob 130. The skilled artisan will understand that the spring- biased ball plunger 134 comprises a ball member 136 that is supported and retained within a housing 135 that is threaded for threaded attachment to the actuator knob 130. A spring

(not shown) is provided within the housing 135 for biasing the ball 136 to the outer end of the housing 135. A series of dimples 138 that correspond to each of the rotational settings (i.e., 5°, 15°, 30°, 45°, 60° or 90°) are provided in the bottom of counterbore 126 in support cap 122. See FIG. 5. Thus, when the user rotates the actuator knob 130, the ball 136 in the spring-biased plunger 134 will be biased into a dimple 138 when the knob 130 has been rotated to that

position. Such arrangement provides a detent when the proper rotational orientation has been achieved. In addition, numerical indicia 139 corresponding to each rotational setting are printed on the knob 130 that is adapted to cooperate with a witness mark 126 on the support cap 122 for assisting the user in establishing the desired rotational setting. See FIG. 2. Also in a preferred embodiment, to assist with the proper positioning of the actuator knob 130 during assembly, the end 111 of selector shaft 110 is fitted with a transverse pin member 113' that is adapted to be received in a corresponding slot 133 in the end of the actuator knob 130. In addition, to prevent the infiltration of debris between the support cap 122 and the actuator knob 130, an O-ring 140 is fitted in the outer perimeter of the knob 130 to establish a seal between the cap 122 and the knob 130.

To form a substantially airtight cylinder in which the rack sleeve 90 can axially travel, the other end of bore 18 is plugged by an end cap member 150. In a preferred embodiment, end cap member 150 has a flanged portion 152 that is received within a counterbore 18" that is coaxially aligned with bore 18 and is adapted to be attached to the housing 12 preferably by capscrews (not shown) . Cap member 150 also has an inwardly protruding axial portion 154 that is preferably fitted with an O-ring 161 that serves to establish a substantially fluid- tight seal between the end cap 150 and the housing 12. As can be seen in FIG. 11, axial portion 154 is sized to be received within the counterbore 96 in the end of the rack sleeve 90 to dampen the axial travel of the rack sleeve 90 when it reaches

the end of its stroke. An O-ring 155 is mounted around the perimeter of the axial portion 154 to establish a substantially fluid-tight seal with the wall of the counterbore 96 when the axial portion 154 is received therein. Also in a preferred embodiment, counterbore 96 is provided with a chamfered portion 96' to assist with the entry of axial portion 154 into counterbore 96.

When the axial portion 154 is received in the counterbore 96 at the end of the axial stroke of the rack slide 90 (FIG. 11) , air is trapped under pressure between the end of the axial portion 154 and the end cap 97. The skilled artisan will appreciate that the axial travel of the rack slide 90 in the "C" direction can be dampened by controlling the exit of air from between those two components . In a preferred embodiment, the trapped air exits through an orifice 156 provided through the axial portion which communicates with a transverse passage 157 provided through the axial portion 154. Thus, when the rack slide 90 moves in the "C" direction and the axial portion 154 is received in the counterbore 96, the air that is trapped between the end of the axial portion 154 and the end cap 97 is permitted to pass through the orifice 156 in the axial portion 154, into passage 157 and into the portion of bore 18 between the end cap 150 and the end of the rack assembly 90. In a preferred embodiment, orifice 156 is threaded for receiving a removable screw member 158 therein. Screw member 158 has an axial orifice 159 extending therethrough. The skilled artisan will appreciate that by providing screws with different sized orifices, the rate that

the air is permitted to exit from between the end cap 97 and the axial portion 154 can be set to a predetermined rate.

In a preferred embodiment, to prevent the infiltration of chips and other debris into the housing 12 which could hamper the operation of the device 10, a protective cover plate 220 is attached to the housing 12 preferably by removable fasteners (not shown) . See FIGS. 3 and 4. Also, an O-ring 222 is provided in housing 12 to establish a seal between the cover plate 220 and the housing 12 to further prevent the infiltration of debris into the interior of housing 12.

The present indexing apparatus, in a preferred form is pneumatically operated. FIG. 12 is a schematic depiction of a preferred pneumatic control system for controlling the operation of the indexing apparatus 10. However, as will be appreciated by those of ordinary skill in the art, the present indexing apparatus 10 could also be operated by other pressurized fluids such as hydraulic fluid. In this embodiment, the pneumatic control system is preferably controlled by a controller 169 that interfaces in a known manner with the controller of the machine tool. However, other controllers and control systems could also be employed. In a preferred embodiment, pressurized fluid (i.e., air preferably at 7 bar [100 psi] ) is supplied to the indexing apparatus 10 through a series of control valves attached thereto. As can be seen in FIG. 12, the pressurized fluid is supplied from the source 170 to a first control valve 172 which is piped to ports (174, 176) in the housing 12. In a preferred embodiment, control valve 172 is fabricated by Festo

KG of Esslingen, Germany under Model No. J-5/2-1/8P. However, other valves could also be successfully used. When pressurized fluid is supplied through port 174, the piston 50 is biased in the "D" direction causing the teeth 23 of the indexing table 20 to engage the teeth in the second toothed ring 40 to lock the indexing table 20 in position. See FIG. 3. As can be seen in FIG. 3, when in the locked position, the second coupling 80 is disengaged and the pinion gear 72 is free to rotate on the indexing shaft 60. When pressurized fluid is supplied through port 176, the piston 50 is biased in the "E" direction causing the first coupling 45 to become disengaged and the second coupling 80 to become engaged such that rotation of the pinion gear 72 will cause the indexing shaft 60 and indexing table 20 to rotate about axis A-A. See FIG. 4.

In a preferred embodiment, pressurized fluid is supplied to a second control valve 178 which is piped to ports (180, 182) in the housing 12. Preferably, control valve 178 is identical to the first control valve 172. As can be seen from FIG. 12, when pressurized fluid is supplied through port 180 to bore 18, the rack sleeve 90 is biased in the "F" direction in bore 18. See FIG. 5. When pressurized fluid is supplied through port 182 into bore 18, the rack sleeve 90 is forced in the "C" direction. See FIG. 5. As can be seen in FIG. 12, a collection of mechanical limit valves are employed to control the flow of pressurized fluid to the indexing apparatus 10. More specifically, a first limit valve 184 is attached to the housing 12 for

detecting whether the indexing table 20 is in the locked position. Limit valve 184 is preferably manufactured by Festo KG under Model No. 5-3-PK-3-B. However, other limit valve arrangements could also be successfully employed. As can be seen in FIG. 13, limit valve 184 has a spring-biased actuator 186 that is arranged to engage the indexing table 20 when table 20 is in the locked position (FIGS. 3 and 13) . First limit valve 184 is piped to a manually actuated valve 190. As can be seen in FIG. 12, release valve 190 is piped for fluid communication with the control valve 178 and an "or" gate valve 192. Valve 192 is piped for fluid communication with the control valve 178 and a limit valve 194 that is attached to the housing 12 and arranged to detect when the piston 72 is in the unlocked position (FIG. 4) . A preferred control system also includes a limit valve 196 that is attached to the housing 12 for detecting when the rack sleeve 90 has reached the end of its stroke (FIG. 11) . As can be seen in FIGS. 5 and 11, limit valve 196 is attached to the housing 12 such that its actuator member 198 is arranged to engage the toothed portion 75 of pinion gear 72. In addition, a pressure sensing valve 200 of the type manufactured by Festo KG under Model No. PPL-1/8 is attached to the housing 12 and is piped for fluid communication with the controller 169 through line 209. However, other pressure sensing valves could also be used.

Also, to avoid the problems encountered when accidentally starting the indexing sequence when the indexing apparatus 10 is not in a starting or "zero" position, a limit valve 202 is

attached to the housing 12. Limit valve 202 is piped for fluid communication with the controller 169. As can be seen in FIG. 13, limit valve 202 has an actuation member 204 that extends to a point adjacent to the rear surface 21 of the indexing table 20, but does not contact the rear surface 21. An actuator ball 206 is mounted in the rear surface 21 of the indexing table 20 such that when the indexing table 20 is in the zero position, the actuator member 204 is actuated by contact with the actuator ball 206. When limit valve 202 is actuated, it permits pressurized fluid to flow from the source 170 to the controller 169 through line 210 which causes the controller 169 to send a pneumatic starting signal to valve 178 through line 212. The skilled artisan will appreciate that the starting signal can be used to initiate various activities. For example, the controller 169 could be used to send an electronic signal to an indicator light (not shown) or sound generating device (not shown) that would inform the operating personnel that the indexing table 20 is in the starting position. In the alternative, the starting signal could be used to initiate the indexing sequence or sent to a controller that operates the machine tool for use thereby. The operation of the apparatus 10 will now be described. When the apparatus 10 is in the locked position, valve 172 permits pressurized fluid to flow from the source 170 through port 174 in housing to bias the piston 50 in the "D" direction. The skilled artisan will appreciate that, should fluid pressure be lost to the device 10 when the device is in the locked position, the springs 48 serve to retain the first

coupling 45 in intermeshing engagement. Such aspect of the present invention represents a vast improvement over prior fluid-actuated indexing apparatuses which typically become unlocked when the supply of fluid pressure to the device is lost or interrupted.

To start the indexing cycle, the controller 169 sends a pneumatic start signal to control valve 172 through line 212 which causes valve 172 to direct pressurized fluid from the source 170 through port 176. As pressurized fluid enters port 176, piston 50 is biased in the "E" direction to unlock the indexable table 20. Such movement of the table 20 actuates the table unlock limit valve 194 which permits pressurized fluid to flow through gate valve 192 to control valve 178. Control valve 178 then permits pressurized fluid to flow into bore 18 in housing through port 182 to bias the rack slide in the "C" direction. Such axial movement of the rack slide 90 causes the pinion 72 to rotate. Because the toothed portion 75 of pinion 72 is intermeshed with the coupling ring 66 which is rigidly attached to the indexing shaft 60, the indexing shaft 60 and, ultimately, the indexable table 20 are rotated about axis A-A a predetermined distance.

When the actuator 198 of limit valve 196 encounters the toothless portion of the pinion 72, indicating that the rack slide has reached the end or is nearing the end of its axial stroke, the limit valve 196 permits pressurized fluid to pass to control valve 172 which permits the pressurized fluid to flow through port 174 and bias the piston 50 in the "D" direction. If the actuator 204 of limit valve 202 contacts

ball 206 in the rear surface 21 of table 20, thus indicating that the table has been indexed to the home position, the limit valve 202 sends a pneumatic signal back to the controller 169 through line 210 which can be used to actuate an indicating light, alarm, signal, etc.

To adjust the rotational travel of the indexing table 20 to one of the predetermined settings (i.e., 5°, 15°, 30°, 45°, 60° or 90°) , the operator presses and holds the manually actuatable valve 190 which permits pressurized fluid to flow to the gate valve 192 and to the control valve 178. The pressurized fluid is permitted to flow from the valve 178 through port 182 which causes the rack slide to move to its end position (FIG. 11) . The operator then turns the actuator knob 130 to the desired setting and thereafter releases the manually actuated valve 190 thereby permitting the rack slide to return to the starting position (FIG. 5) .

The present indexable device can be used in numerous applications wherein an item or a collection of items must be very precisely indexed to positions about an axis and retained in those positions even under the influence of substantial external forces. The present indexable device is relatively compact and can be incorporated into various other support structures as desired. In addition, when compared to a number of other indexable apparatuses, the present indexable device is relatively inexpensive and easy to operate. Moreover, the present indexable apparatus will be retained in a locked position should the supply of pressurized fluid to the device be interrupted or discontinued. In addition, the present

invention provides a means for automatically determining whether the indexing table is in the home position prior to initiating any machining operations.

Thus, the present invention provides solutions to the aforementioned problems associated with prior fluid-actuated indexable apparatuses. While such advantages are apparent from the foregoing disclosure, it will be understood, however, that various changes in the details, materials and arrangements of parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims .