Indexing rotary actuator with clutch pistons

An indexing rotary actuator is provided for unidirectionally rotating an output shaft through a specific angle per each indexing operation accurately without cumulative error. A pair of symmetrical housing members are mounted together to form an actuator housing. Within the actuator housing are formed a main piston chamber and a clutch piston chamber. Within the clutch piston chamber, a pair of piston mounting rings are mounted opposing each other, wherein a pair of respective main pistons within the main piston chamber are affixed to outer diametrical surfaces of the piston mounting rings. Furthermore, a pair of clutch pistons are provided within the clutch piston chamber slidably supported along the output shaft within the clutch piston chamber. The main pistons are air or fluid powered to be rotatable about the annular main piston chamber. The opposing faces of the piston mounting rings include respective raised arcuate sectors which are cooperable to limit rotation of the main pistons within the main piston chamber through the specified angle per each indexing operation, thus limiting rotation of the output shaft. Application of pressurized air or fluid through inlet ports within a first or second end of the actuator housing serves to drive the main pistons within the main piston chamber and to drive the clutch pistons along the output shaft within the main chamber. The clutch pistons are therefore alternately engaged with the output shaft, thus alternately translating rotational energy of the main pistons to the output shaft.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an indexing rotary actuator which is 
preferably used in industry for automation of rotary motion of indexing 
conveyors and rotary indexers. 
2. Description of the Background Art 
Fluid or air-powered rotary actuators are commonly used in industry for 
automation of rotary motion. Four conventional rotary actuator types 
include a vane type, a piston type with rack and pinion, a piston type 
with a lever actuated shaft, and a piston type with a chain and sprocket. 
Vane type actuators use fluid power to force a vane, which is fastened to 
an output shaft, to rotate through an arc less than 360.degree.. The 
output shaft of the vane type rotary actuator must reciprocate to be reset 
to the start position. 
The piston type rotary actuator with rack and pinion utilizes linear double 
acting piston motion to actuate the rack and pinion mechanism wherein the 
output shaft is fastened to the pinion. Angular displacement generally up 
to 360.degree. may be achieved. Reciprocation is necessary to reset the 
rotary actuator shaft to the start position. The piston type rotary 
actuator with lever activated shaft utilizes linear piston motion to 
actuate the lever mechanism which rotates the output shaft. Angular 
displacements are usually 180.degree. or less. Reciprocation is necessary 
to reset the rotary actuator to the start position. The piston type rotary 
actuator with chain and sprocket utilizes linear piston motion to actuate 
the chain and sprocket mechanism, wherein the output shaft is fastened to 
the sprocket. This type of rotary actuator provides angular displacements 
up to five full revolutions. Reciprocation is necessary to reset the 
rotary actuator to the start position. 
A variation of the piston type rotary actuator with rack and pinion as 
described above uses a pawl and ratchet mechanism together with roller 
bearing/cam clutches, which transmit torque in one direction and which run 
freely in the reverse direction. This permits the rack and pinion to drive 
the output shaft through a fixed angular displacement in the same 
direction each time the unit is cycled. While the linear piston completes 
a full return stroke, the output shaft remains stationary due to the 
roller bearing/cam clutch. Available angular displacements are limited to 
simple fractions of a whole revolution, from about 30.degree. to 
360.degree. per step. 
All of the above mentioned rotary actuators, with the exception of the 
piston-type rotary actuator with rack and pinion variation described 
above, require additional mechanical elements such as pawls and ratchets 
to attain positional accuracy necessary for complete rotary and linear 
indexing. Consequently, the requirement of additional mechanical elements 
increases manufacturing costs of the conventional rotary actuators. 
Furthermore, the pawls and ratchets are subject to mechanical wear which 
decreases accuracy of indexing and which eventually results in system 
failure. In the piston type rotary actuator with rack and pinion variation 
described above, the additional mechanical elements are disposed 
internally within the rotary indexer. System repair is difficult and 
costly. 
A further disadvantage of conventional rotary actuators as described above 
is energy inefficiency. The conventional systems require that the main 
motive source, either the vane or piston, completes a full return stroke 
during which no work is done. Accordingly, the conventional rotary 
actuators are 50% efficient at best. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide an indexing rotary 
actuator of increased efficiency which requires no return stroke for 
resetting of the actuator. 
An further object of the present invention is to provide an indexing rotary 
actuator which accurately indexes an output shaft through a desired range 
with no cumulative error. 
A still further object of the present invention is to provide an indexing 
rotary actuator which does not require mechanical elements such as 
ratchets, pawls or one-way clutches for single direction rotary and linear 
indexing. 
The above described objects of the present invention are fulfilled by 
providing an indexing rotary actuator including a pair of symmetrical 
identical housing members mounted together to form an actuator housing 
wherein an output shaft of the indexing rotary actuator is indexed in a 
single direction through a specific angle per each indexing operation. A 
main piston chamber is disposed annularly within the actuator housing. 
Main pistons are driven by pressurized air or fluid to be rotatable about 
the main piston chamber. A clutch piston chamber is also disposed within 
the actuator housing and includes clutch pistons. Piston mounting rings 
are mounted within the clutch piston chamber with respective first faces 
opposing each other. The main pistons are respectively affixed to an outer 
peripheral surface of the piston mounting rings and are rotatable within 
the clutch piston chamber. The clutch pistons are mounted to oppose 
respective second faces of the piston mounting rings and are slidably 
supported within the clutch piston chamber along the output shaft toward 
and away from the piston mounting rings. Passageways are provided through 
the clutch pistons, piston mounting rings and main pistons so that the 
main pistons can be driven within the main piston chamber by force of 
pressurized air or fluid. The piston mounting rings include raised arcuate 
sectors formed upon the first faces which limit rotation of the main 
pistons around the central axis of the indexing rotary actuator, thus 
limiting rotation of the output shaft through the specific angle for each 
indexing. 
Successive single-direction indexing operations of the output shaft are 
achieved by alternate application of pressurized air or fluid through the 
clutch pistons and the piston mounting rings to the respective main 
pistons. Therefore, reciprocation to reset the indexing rotary actuator is 
avoided, resulting in increased efficiency as compared to the conventional 
rotary actuators. 
In a preferred embodiment of the present invention, the raised arcuate 
sectors are formed as 90.degree. sectors. Furthermore, the specific angle 
of rotation of the output shaft is 180.degree.. 
Further scope of applicability of the present invention will become 
apparent from the detailed description given hereinafter. However, it 
should be understood that the detailed description and specific examples, 
while indicating preferred embodiments of the invention, are given by way 
of illustration only, since various changes and modifications within the 
spirit and scope of the invention will become apparent to those skilled in 
the art from this detailed description.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
FIGS. 1 and 2 generally illustrate a preferred embodiment of the rotary 
actuator of the present invention. As illustrated in FIG. 1, the circular 
actuator housing comprises identical symmetric indexer body halves 10L and 
10R mated together via machine screws 11 and nuts 45. Dowels 37, 
illustrated as disposed within an outer circumference of the indexer body 
half 10L, provide further stability along the outer housing of the rotary 
actuator. Shaft 12 is rotatable along the central axis of the circular 
actuator housing as supported by bearings 13. External retaining rings 17 
mounted within groove 49 of shaft 12 locate the inner race of bearings 13. 
Bearing retainers 18 and pre-load shims 19 locate the outer race of 
bearings 13. Lubrication O-ring seal 43 provides a seal between shaft 12 
and bearing retainer 18. As mounted together, indexer body halves 10L and 
10R partially form an annular main piston chamber 14, around which arcuate 
pistons 15 and 16 are rotated about the central axis of the circular 
actuator housing to effect rotation of shaft 12. Pilot ring 38 is placed 
within an annular groove formed in an outer circumference of the joined 
indexer body halves 10L and 10R along with pilot O-rings 39. Pilot ring 38 
provides concentric support for the circular rotary indexer housing. 
Pistons 15 and 16 are fixedly mounted on respective piston mounting rings 
20 and 21 via shims 46 and 48, illustrated in FIG. 2. The shims 46 and 48 
are sandwiched between the pistons and the piston mounting rings and are 
formed to include screw holes and a passageway. The gap created by the 
shim prevents the piston from locking down on the indexer body halves 10L 
and 10R. The shims 46 and 48 are preferably metal, but may be any other 
suitable material including brass. 
Piston mounting ring 20 is illustrated in greater detail in FIGS. 5a-5d, 
and as also illustrated in FIGS. 1 and 2, is manufactured to include a 
90.degree. raised, arcuate sector. Specifically, piston 15 is affixed to 
an outer peripheral surface of piston mounting ring 20 via shim 46. 
Arcuate sector 22 is formed as a raised portion on a first face of piston 
mounting ring 20. Similarly, piston 16 is affixed to an outer peripheral 
surface of piston mounting ring 21 via shim 48 and arcuate sector 23 is 
formed as a raised portion on a first face of piston mounting ring 21. The 
arcuate sectors are formed on a respective portion of the first faces of 
the piston mounting rings diametrically opposed to the area of the outer 
peripheral surfaces of the rings where the pistons are affixed thereto. 
The first faces of the piston mounting rings are mounted adjacent each 
other within indexer body halves 10L and 10R so that arcuate sectors 22 
and 23 oppose each other, limiting rotation of shaft 12 through a range of 
180.degree. per index, as will be described further. 
The piston mounting rings also include a passageway P3, shown in detail in 
piston mounting ring 20 of FIG. 5a-5d. Due to the 90.degree. view portion 
of the rotary actuator of FIG. 1 along section 1--1 of FIG. 2, only 
passageway P3 of piston mounting ring 20 is illustrated. Piston mounting 
ring 21 includes passageway P3', which is not illustrated in FIG. 1, which 
leads from chamber C4 of indexer body half 10R to piston 16. The passageway 
P3 of piston mounting ring 20 of FIG. 4 leads from the second face of the 
piston mounting ring, which is opposite the first face which includes the 
arcuate sector, 90.degree. out through the outside peripheral surface of 
the piston mounting ring to couple with the passageway of the respective 
piston. 
Piston/piston mounting ring assemblies 15, 20 and 16, 21 are supported 
within indexer body halves 10L and 10R by integral radial plain bearings 
which are machined surfaces of the indexer body halves. The main piston 
chamber is formed by indexer body halves 10L and 10R and the outside 
peripheral surfaces of piston mounting rings 20 and 21. The main piston 
chamber 14 is sealed from the inner portion of indexer body halves 10L and 
10R by cylinder chamber seals 40 and 41. Seal 40 is slightly wider 
(0.003"-0.005") than the gap provided by parts 20 and 21, so as to provide 
a slight pre-load (squeeze) upon assembly. 
Clutch piston 24 is supported on piston/piston mounting ring assembly 15, 
20 via dowel 26, which is press-fit into piston mounting ring 20. 
Similarly, clutch piston 25 is supported on piston/piston mounting ring 
assembly 16, 21 via dowel 27, which is press-fit into piston mounting ring 
21. Dowels 28 and 29 are respectively press-fit into indexer body halves 
10L and 10R. Clutch pistons 24 and 25 are slidably supported along the 
axis of shaft 12, a range of motion limited by main shaft dowel 30 is 
approximately 6 mm. 
As illustrated in FIG. 1, clutch pistons 24 and 25 have been driven along 
shaft 12 to a right-most position within the clutch piston chamber. 
Accordingly, chamber C1 of indexer body half 10L is opened between clutch 
piston 24 and passageway P1. Chamber C4 of indexer body half 10R is 
defined by a variable distance between piston mounting ring 21 and clutch 
piston 25. In the alternative, when clutch pistons 24 and 25 are driven 
along shaft 12 to a left-most position within the clutch piston chamber, 
chamber C1 will be opened between piston mounting ring 20 and clutch 
piston 24 and chamber C4 will be opened between clutch piston 25 and 
passageway P1'. Chamber C1 and C4 of the clutch piston chamber are sealed 
via seals 31 and 32. 
FIG. 6a-6d illustrate a clutch piston in greater detail, including dowel 
holes 33 formed therein through the base portion, offset from each other 
by 180.degree. along an outer circumference of the circular base portion. 
Although not illustrated in FIG. 1, which is cut along section 1--1 of 
FIG. 2 to illustrate a 90.degree. cutaway view of the rotary actuator, the 
piston mounting rings 20 and 21 both respectively include second dowels 
press-fit thereto, offset from illustrated dowels 26 and 27 by 180.degree. 
around an outer circumference of the piston mounting rings, to form 
respective dowel pairs. The dowel pairs protruding from each of the piston 
mounting rings 20 and 21 fit through the dowel holes 33 of the clutch 
piston. The clutch pistons 24 and 25 are slidably supported along the 
respective dowel pairs 26 and 27. 
Similarly, second dowels 28 and 29 are respectively affixed to indexer body 
halves 10L and 10R. The dowels 28 and 29 are also insertable through dowel 
holes 33 of the clutch pistons 24 and 25 to lock the respective clutch 
piston to the indexer body half to prevent rotation of the clutch piston 
with shaft 12. As illustrated in FIG. 1, clutch piston 25 is locked to 
indexer body half 10R through dowel 29 and is stationary with respect to 
rotation around the central axis of the circular actuator housing. Clutch 
piston 24, however, is engaged with dowel pair 26 of piston mounting ring 
20 and transfers rotational energy of piston 15 along the main piston 
chamber 14 to shaft 12. O-ring or quadring seals 44 are optionally affixed 
to the piston mounting rings near the dowel pairs extending therefrom. 
Clutch pistons 24 and 25 each include a pair of elongated slots 35 formed 
in the cylindrical sidewall which cooperate with shaft dowel 30 to limit 
the movement of the clutch pistons 24 and 25 along shaft 12 and to 
translate rotational energy of the pistons 15 and 16 respectively from the 
piston mounting rings 20 and 21 to shaft 12. Elongated slots 35b and 35c, 
which comprise a pair of elongated slots 35, are illustrated respectively 
in FIGS. 6a and 6d which show front and rear views of a clutch piston . 
Clutch pistons 24 and 25 further each include respective passageways P2 
and P2', as illustrated in FIG. 1. For example, passageway P2 leads from 
chamber C1/passageway P1 of indexer body half 10L through clutch piston 24 
to passageway P3 formed through piston mounting ring 20. Passageway P3 
extends further into piston 15 to permit fluid to flow from external port 
X, through passageways P2 and P3 and through piston 15, to main piston 
chamber 14. As described previously, due to the 90.degree. cutaway view 
along section 1--1, only passageway P3 through the piston mounting ring 20 
is illustrated in FIG. 1, passageway P3' through piston mounting ring 21 is 
not illustrated. 
Operation of the rotary actuator of the present invention will now be 
described. A fluid powered rotary actuator will be described in this 
embodiment although the rotary actuator of the present invention may be 
air powered. The description will begin by assuming that clutch pistons 24 
and 25 are located within the clutch piston chamber along shaft 12 at a 
left-most position, which is considered the reference position for 
purposes of description. Accordingly, shaft dowel 30 of shaft 12 is 
engaged with the elongate slots of clutch piston 25. The dowel 28 of 
indexer body half 10L therefore protrudes within dowel hole 33 of clutch 
piston 24 to lock clutch piston 24 stationary to indexer body half 10L. 
Piston 15 within main piston chamber 14 is in the reference position as 
illustrated in FIG. 3, which is the same position of the piston as shown 
in FIG. 2. For purposes of description, piston 16 is located in FIG. 3 at 
a reference position 180.degree. from its position in FIG. 2. Arrow A 
indicates the direction of rotation of pistons 15 and 16 within main 
piston chamber 14. Therefore, the rear face of piston 15, which includes 
the exit opening of passageway P3, is adjacent the lead face of piston 16, 
with smaller chamber portion C3 of main piston chamber 14 formed 
therebetween. The larger chamber portion C2 of main piston chamber 14, 
approximately equal to 180.degree. of diameter around the rotary actuator, 
is formed between the lead face of piston 15 and the rear face of piston 
16. 
As illustrated by arrow A, the direction of rotation of the pistons 15 and 
16, and thus shaft 12 and shaft dowel 30, is clockwise. Furthermore, in 
the reference position illustrated in FIG. 3, arcuate sector 23 of piston 
mounting ring 21 is rotated through 180.degree. from the position 
illustrated in FIG. 2. The front face of arcuate sector 23 is abutted 
against the rear face of arcuate sector 22 of piston mounting ring 20. In 
this reference position illustrated in FIG. 3, both arcuate sectors 22 and 
23 would not be visible in FIG. 1. However, piston 16 would be visible in 
the bottom portion of main piston chamber 14 of FIG. 1, in addition to 
piston 15 visible in the upper portion of the main piston chamber. 
Clutch piston bumpers 34 are mounted on the indexer body halves 10L and 10R 
within the clutch piston chamber. Accordingly, a small gap of chamber C1 
exists between indexer body half 10L and clutch piston 24 when clutch 
piston 24 is in the left-most position. With clutch pistons 20 and 21 
located within the clutch piston chamber at the left-most position and 
piston 16 located at the reference position as shown in FIG. 3, an 
indexing operation of the rotary actuator to rotate the shaft 12 through a 
range of 180.degree. begins as pressurized fluid enters port X of indexer 
body half 10L. As the pressurized fluid is forced into the small gap of 
chamber C1 between the indexer body half 10L and clutch piston 24 formed 
by clutch piston bumper 34, the gap fills with fluid. As the pressure 
increases, clutch piston 24 slides along dowel pair 26 of piston mounting 
ring 20 and shaft 12 to the right thereby disengaging from dowel 28. The 
fluid pressure drives clutch piston 24 to the right, which in turn drives 
clutch piston 25 to the right within chamber C4 of the clutch piston 
chamber of indexer body half 10R. Clutch piston 25 is slidably supported 
along dowel pair 27. Under increasing fluid pressure, elongate slots 35 of 
clutch piston 24 engage fully against main dowel 30 of shaft 12. As a 
result, clutch piston 25 is abutted against clutch piston bumpers 34 of 
indexer body half 10R. Clutch piston 25 is locked in a stationary manner 
to indexer body half 10R via dowel 29. Clutch pistons 24 and 25 are 
therefore located within the clutch piston chamber at the right-most 
position, as illustrated in FIG. 1. 
When clutch pistons 24 and 25 assume the right-most position within the 
clutch piston chamber, the pressurized fluid begins to flow through the 
passageway P2 of clutch piston 24 and through seal 36, to passageway P3 of 
piston mounting ring 20, which leads into the passageway P3 of piston 15, 
which is illustrated in further detail in FIGS. 7a-7b. With reference to 
FIG. 3, the pressurized fluid exits passageway P3 of piston 15 and enters 
into small gap C3 in the main piston chamber 14. Piston seals 42 prevent 
leakage of pressurized fluid between the pistons and the outer peripheral 
surface of the piston mounting rings. As the volume of pressurized fluid 
increases, piston 15 begins to rotate around the central axis of the 
circular actuator housing. As the piston 15 rotates, piston mounting ring 
20 rotates, which rotates clutch piston 24 coupled thereto via dowel pair 
26, to rotate shaft 12 via shaft dowel 30. 
As piston 15 rotates clockwise, fluid in large chamber portion C2 between 
the front face of piston 15 and the rear face of piston 16 is forced out 
of the main piston chamber 14 through passageway P3' of piston 16, which 
is not illustrated. The excess fluid is forced through passageway P3' of 
piston 16 and piston mounting ring 21, through chamber C4 of indexer body 
half 10R and into passageway P2' of clutch piston 25. The forced fluid 
then passes through passageway P1' of indexer body half 10R out port Y. As 
fluid volume into port X of indexer body half 10L increases to further 
rotate piston 15 around main piston chamber 14, the remaining fluid in 
chamber portion C2 is forced out port Y of indexer body half 10R. 
As piston 15 rotates clockwise in the direction of arrow A, arcuate sector 
22 of piston mounting ring 20 rotates clockwise around the shaft center 
line. Eventually, the front face of arcuate sector 22 will rotate around 
the central axis of the circular actuator housing 180.degree. to abut 
against the rear face of arcuate sector 23 of piston mounting ring 21. 
Piston mounting ring 21, which is affixed to piston 16, is coupled to 
clutch piston 25 through dowel pair 27. In the right-most position as 
illustrated in FIG. 1, dowel 29 of indexer body half 10R is engaged 
through dowel hole 33 of clutch piston 25, locking clutch piston 25 to 
indexer body half 10R so that clutch piston 25 cannot rotate. Accordingly, 
as the front face of arcuate sector 22 of piston mounting ring 20 abuts the 
rear face of arcuate sector 23 of piston mounting ring 21, rotation of 
piston 15 is stopped. At the completion of the indexing, piston 16 remains 
in the reference position of FIG. 3 while piston 15 is rotated around the 
shaft center line 180.degree. to a position immediately behind piston 16, 
as illustrated in FIG. 4. Arcuate sectors 22 and 23 effectively limit the 
index of rotation of pistons 15 and 16, thus limiting the index of 
rotation of shaft 12 to 180.degree.. 
The above operation is descriptive of indexing of the shaft 180.degree. 
resulting in rotation of the pistons 15 and 16 to positions within the 
main piston chamber 14 as illustrated in FIG. 3. A following indexing 
operation to rotate piston 16 180.degree. around main piston chamber 14 to 
a position where the front face of piston 16 abuts against the rear face of 
piston 15 operates similar to that described above, but in the reverse 
direction. Specifically, as clutch pistons 24 and 25 are located at the 
right-most position within the clutch piston chamber as illustrated in 
FIG. 1, pressurized fluid is applied to external port Y to force clutch 
piston 25 in a direction toward indexer body half 10L. The pressurized 
fluid is forced through passageways P3' of piston mounting ring 21 and 
piston 16, which are not illustrated, to drive piston 16 in a clockwise 
direction around main piston chamber 14. Accordingly, successive indexing 
operations are performed by alternately applying pressurized fluid to 
external ports X and Y. Thus, this embodiment of the present invention 
requires no reciprocation to reset the indexing rotary actuator. 
Efficiency is therefore increased as compared to the above described 
conventional actuators which require a full return stroke in which no work 
is performed. Furthermore, since the angle of rotation of output shaft 12 
is accurately controlled there is no cumulative error with respect to 
shaft rotation over successive indexing operations. 
During rotation of pistons 15 and 16 within main piston chamber 14, 
variable frictional drag occurs due to the pressurized fluid within main 
piston chamber 14 acting on the outer peripheral surfaces of piston 
mounting rings 20 and 21. As the angle of rotation of pistons 15 and 16 is 
increased from 0.degree. to 180.degree., a radial proportion of the outer 
peripheral surfaces of the piston mounting rings 20 and 21 are uncovered 
and exposed to pressurized fluid within the main piston chamber 14. The 
resulting force due to the pressurized fluid is the product of the 
pressure (force per unit area) and the effective area, which in this case 
increases linearly during rotation of the pistons 15 and 16. As a result, 
frictional drag linearly increases as the pistons 15 and 16 complete a 
stroke, thereby creating frictional torque. The resulting force acts 
through the center of the effective area and produces a moment (a torque) 
and load that effects the piston/piston mounting ring assemblies 15, 20 
and 16, 21 since the resulting force acts off center (eccentric) to the 
radial plain bearing which supports the total load and moment. The greater 
the load, the greater the frictional torque to resist rotational motion. 
The frictional torque acts inversely to the acceleration that a normal 
mass would experience under a constant force, which is the case since the 
fluid pressure normally stays constant. As the pressurized fluid 
accelerates the pistons 15 and 16 around the main piston chamber 14, the 
pressurized fluid pushing down on the piston mounting rings 20 and 21 
decelerates the pistons 15 and 16. Therefore, the present invention has an 
inherent design mechanism for speed control. Furthermore, due to the 
absence of any cushioning device contacting the piston face, as is common 
in many rotary actuators, 100% torque is available at the beginning of the 
rotational stroke. Since cushioning devices are not included as contacting 
the piston face, the effective piston area is not reduced as in common 
rotary actuators. 
An advantage of the indexing rotary actuator of the present invention as 
described above is that the indexer body halves 10L and 10R may be 
disassembled by removing machine screws 11 and nuts 45. Accordingly, the 
interior of the indexing rotary actuator including shaft 12, piston 
mounting rings 20 and 21, clutch pistons 24 and 25 and pistons 15 and 16 
can be easily disassembled or repaired once removed from the housing. 
Furthermore, since the indexer body halves 10L and 10R and clutch pistons 
24 and 25 are identical and symmetric, and since pistons 15 and 16 and 
piston mounting rings 20 and 21 are also symmetrical and identical except 
for screw mounting holes and threads and air passages, efficiency of mass 
production of the indexing rotary actuator of the present invention is 
optimized. 
The above described embodiment of the present invention may be varied in 
many ways. For instance, the mechanism providing clutching of the clutch 
pistons to shaft 12 and the indexer body halves is not limited to the slot 
and dowel configuration illustrated. Splines and polygons may be utilized 
to provide clutching, however this alternative clutching method does not 
produce tolerances as close to those achieved using the slot and dowel 
configuration. Also, the arcuate piston cross-section is not limited to 
the shape illustrated since any practical cross-section which can 
effectively be sealed may be used. Magnetic coupling can be utilized 
between the arcuate piston with respect to the shaft and indexer body 
halves. However, use of magnetic coupling creates several design problems 
with respect to fluid porting and piston sealing. Additionally, the 
indexing body halves may be of symmetric square shape rather than 
symmetric circular shape. Also, the angle through which the raised arcuate 
sectors extend may vary, thus varying the angle of rotation of the shaft. 
In the preferred embodiment, the seals and O-rings are preferably made of 
Buna. However, sealing of the compressed air or fluid is not limited to 
the seals and materials as described, any suitable synthetic rubber may be 
used. The indexer body halves 10L and 10R, pistons 15 and 16 and pilot ring 
38 are preferably made of aluminum. The clutch piston bumpers are 
preferably made of Buna. The cylinder chamber seals are preferably teflon. 
Piston mounting rings 20 and 21, clutch pistons 24 and 25, shaft 12, ball 
bearings 13, external retaining rings 17 and bearing retainers 18, and the 
dowels are preferably steel. The above designated materials are not to be 
considered limiting as suitable variations are to be considered within the 
scope of the present invention. 
The invention being thus described, it will be obvious that the same may be 
varied in many ways. Such variations are not to be regarded as a departure 
from the spirit and scope of the invention, and all such modifications as 
would be obvious to one skilled in the art are intended to be included 
within the scope of the following claims.