BACKGROUND OF THE INVENTION Field of Invention

This invention pertains to a high precision drive mechanism for transmission of power and/or motion from an input shaft to an output shaft, which also may be used for moving objects to a predetermined position or angular orientation with high precision.

This invention also pertains to an apparatus for precise and repeatable translation of objects along a track. In a particularly advantageous embodiment of the invention, two substantial assemblies are combined within an apparatus for positioning an object accurately and repeatedly along two orthogonal axes using the drive mechanism previously described.

BRIEF DESCRIPTION OF THE PRIOR ART Drive components to transmit power and motion are necessary almost on every machine. Well-known chain drives, gears and flexible belt drives are used

throughout the industry. Each of the above drives has advantages over another depending on the application.

Gear drives are expensive with demands for high precision, zero backlash and silence. They do not provide as smooth a transmission of motion as belt drives. Disadvantages of belt drives include the needed tensioning of the belts periodically to avoid slippage; deterioration because of severe exposure to chemicals and lubricants; and the requirement that damaged belts must be replaced rather than repaired. Conventional belts cannot be used where input and output shafts must be synchronized. Synchronous timing belts have relatively high cost and demand a fairly accurate alignment of pulleys.

Furthermore, inherently prior art belt or chain drive mechanisms impose certain restrictions on the orientation of their pulleys and on the distances between the shafts thereof.

In the modern age of automation in production and inspection processes, it is often required to position an object in two orthogonal coordinates, such as XY or XZ coordinates. Usually, this is accomplished by stacking two one-axis positioners on top of each other, so that the top positioner is perpendicular to the

bottom one. For example, a dual axis Model MT160 stage is constructed by mounting one stage on top of the other, as shown on page 56 in catalog 588 by Klinger Scientific, 999 Stewart Avenue, Garden City, NY 11530. The resulting assembly is very bulky. It is difficult to provide precise orthogonality of two positioners. The weight of the top positioner is loading the bearing system of the bottom positioner. Furthermore, such an assembly can not be used in applications, where an object, positioned in two coordinates, must be transparent, for example, for a light source in the inspection process.

So-called open frame tables are designed for applications which require a large center opening through which light can pass or objects can be mounted. For dual axis positioning, open frame tables are also mounted on top of each other. Such an assembly is shown on page 88 in the 1989-1990 catalog "Positioning Systems and Components" by Daedal, Box 500, Harrison City, PA 15636. It is obvious that both openings are aligned only in a stationary position. When an object mounted on the upper open frame is positioned in two coordinates, there is always a moving dead zone for

passing light, wherever the bottom frame interferes with the opening in the upper frame.

So-called Gantry type XY positioners are assembled from three one-axis positioners. For example, a model GV 88 XY is shown on page 65 in catalog 588 by Klinger Scientific. A single X axis slide is supported and translated by two Y axis slides. Such an assembly is complicated and therefore expensive and very sensitive to an alignment of both Y slides. Other manufacturers control each Y positioner by a separate motor and have problems in synchronizing those motions.

Therefore, there is a need for integral, low profile, inexpensive XY positioners, suitable for applications where an object positioned in two coordinates is transparent for a light or optical beam without a dead zone.

SUMMARY OF THE INVENTION In view of the above mentioned disadvantages of the prior art, it is an objective of this invention to provide a very precise drive mechanism, which provides smooth, synchronous transmission of power and/or motion with zero backlash and low noise.

A further objective is to provide a durable and rugged drive mechanism which is easily adjusted for normal wear and tear.

A further objective is to provide a drive mechanism which comprises of a relatively small number of parts with simple shapes, thereby reducing the cost and size of the mechanism.

A transmission constructed in accordance with this invention is comprised of a driving member with pulley means coupled to a drive means and rotatively mounted on a base, a driven member with pulley means rotatively mounted on said base, and a rigid endless coupling member, being in a frictional engagement with said driving and said driven pulley means for transmitting power and/or motion from said driving member to said driven member. The mechanism also includes a tensioning means for assisting in a frictional engagement of said coupling member with said driving and driven members.

A drive mechanism constructed in accordance with this invention may also be used for translating objects or work pieces with the rigid ring replaced by a rigid rod.

Briefly, an apparatus for positioning objects consists of a track carrying rail means, and a carriage disposed on the track and including pulley means with

two facing surfaces disposed at a critical angle for frictional engagement thereby with the rail means. Rotation of the pulley means forces the carriage to move with respect to the track. For one-dimensional positioning, the track could be fixed and the object to be moved can be mounted on the carriage, or the carriage could be fixed and the object could be mounted on the movable track. For two-dimensional positioning, a second track with another rail means and a second carriage is coupled to the first track. The second carriage is also equipped with a second pulleys means for engaging the second rail means. Rotation of the two pulley means results in a very smooth, accurate, and repeatable two dimensional motion.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 shows a plan view of a preferred embodiment of the invention;

Figure 2a - 2c are side sectional views on an enlarged scale of different embodiments of the driving pulley and coupling member for the mechanisms of Figure

1, 5, 6, 7, and 8;

Figure 3a - 3c are side sectional views on an enlarged scale of different embodiments of the driven

pulley and coupling member for the mechanisms of Figure 1, 5, 6, 7, and 8;

Figure 4a and 4b show a side sectional view on an enlarged scale of the tensioning bearing for the mechanisms of Figure 1, 5, 6, 7, and 8;

Figure 5 is a plan view illustrating a different arrangement, wherein a tensioning bearing is mounted inside a coupling ring;

Figure 6 is a plan view illustrating a different arrangement, wherein a driving and driven pulley of equal diameters are mounted outside a coupling ring;

Figure 7 shows another alternate embodiment of the invention, wherein the transmission coupling member is a rigid rod;

Figure 8 shows another alternate embodiment for a linear motion mechanism;

Figure 9 shows a perspective view of an apparatus for positioning an object in two orthogonal directions constructed in accordance with this invention;

Figure 10 shows a partial plan view of the apparatus of Figure 9;

Figure 11 shows a partial side-sectional view taken along lines XI-XI in Figure 10;

Figure 12 shows a partial top view of the disassembled apparatus of Figures 9-11 with the top assembly removed;

Figure 13 shows a partial side-sectional view of the apparatus of Figure 12;

Figure 14 shows a cross -sectional view taken along line XlV-xrv in Figure 12;

Figure 15 shows a side view of a first alternate embodiment of the invention for positioning an object in a single dimension with the carriage stationary;

Figure 16 shows a plan view of a second alternate embodiment of the invention for positioning an object in a single dimension with the track stationary;

Figure 17 shows a side view of the embodiment of Figure 16;

Figure 18 shows a side-sectional view of the embodiment of Figure 16 taken along line XVIII-XVIII;

Figure 19 shows a plan view of the third alternate embodiment of the invention for positioning an object in a single dimension for long travel lengths;

Figure 20 shows a side-sectional view of the embodiment of Figure 19 taken along line XX-XX;

Figure 21 shows schematically a first embodiment of a gantry-type positioner constructed in accordance with this invention;

Figure 22 shows a plan view for a second embodiment of a gantry-type positioner constructed in accordance with this invention; and

Figure 23 shows a side view of the embodiment of Figure 22.

DETAILED DESCRIPTION OF THE INVENTION

DRIVE MECHANISM

In the following description, directional terms like up, down, left and right are used for purposes of illustration only. The drive mechanism described herein functions in any position or orientation.

A preferred embodiment of the invention is shown in Figures 1-4. Mechanism 10 constructed in accordance with this invention includes a support 12 and a driving pulley 14 secured to an input shaft 16 rotatively mounted on support 12. Input shaft 16 is coupled to a rotating device 18, as shown in Figure 2a - 2c. A rotating device 18 may be coupled to the opposite end of shaft 16 if desired, provided that this opposite end extends beyond the driving pulley. Rotating device 18

may be, for example, a hand wheel secured to a shaft 16 for manual operation or an electric motor or any other well-known means for motorized construction.

Driving pulley 14 has a circumferential groove 20. As shown in Figure 2a and 2b, sidewalls 22 and 24 of the groove 20 are oppositely inclined and form an acute critical angle A with a plane perpendicular to shaft 16. Preferably, angle A is in the range of 2-3°.

The mechanism 10 also includes a driven pulley 26 secured to an output shaft 28 rotatively mounted on support 12. The pulley 26 has a circumferential groove 30 with the side walls similar to groove 20, as shown in Figure 3a and 3b.

A work piece or any object, which requires rotation may be mounted on end 32 or 34 of the shaft 28. Alternatively, the work piece may be mounted directly on the pulley 26.

The mechanism 10 also includes a coupling ring 36, which is endless and rigid, for transmitting power and/or motion mechanically from driving pulley 14 to driven pulley 26, by being in constant frictional engagement with driving pulley 14 and driven pulley 26. As shown in Figures 2a and 3a, ring 36 preferably has two side walls 38, 40 tapered at the critical angle A

(defined above) , therefore forming an isosceles trapezoid in cross-section.

The mechanism 10 further includes a tensioning bearing 42 also rotatively mounted on support 12, by a bushing 44. A slot 46 is provided for easy manual rotation of a bushing 44 as shown in Figures 4a and 4b by means, for example, of a screw driver blade. The tensioning bearing 42 is firmly mounted on an eccentric shaft 48, which is parallel to the axis of bushing 44, and it is radially offset therefrom.

An initial tensioning applied to the ring 36 by the tensioning bearing 42 is adjusted by rotation of a bushing 44 which produces an eccentric movement of the tensioning bearing 42 toward or away from ring 36, thereby forcing a ring 36 into a frictional engagement with pulleys 14 and 26. A set screw 50 is threaded through the support 12 to secure bushing 44 in the desired position after adjustment.

Other arrangements of the elements of a mechanism 10 are possible and may be chosen depending on a specific application. For example, Figure 5 illustrates a different arrangement of a tensioning bearing 42 being mounted inside a ring 36, therefore resulting in a smaller space requirement for mechanism 10.

Many applications require a speed ratio variation. A mechanism in accordance with this invention is well- suited for such applications. The input/output speed ratio depends on the ratio of diameters of the driving and driven pulleys. For example, in the mechanism 10 of Figures 1-5, the diameter of driven pulley 26 is larger than diameter of a driving pulley 14, and therefore the output speed is reduced. It is obvious that for an increased output speed the rotating device 18 should be coupled to shaft 28 and the shaft 16 should be used for an output.

Another arrangement of pulleys is shown in Figure 6, wherein both a driving pulley 14 and a driven pulley 26 are mounted outside the ring 36. Both pulleys shown in Figure 6 embodiment are of an equal diameter, resulting in a 1:1 speed ratio.

Other arrangements of pulleys may be used. One of the pulleys may be mounted inside a coupling ring while another -outside, provided that a tensioning bearing is mounted to force a coupling ring into a frictional engagement with grooves on the pulleys.

The operation of the transmission mechanism of Figures 1-6 is apparent from the above description. The tensioning force on ring 36 from bearing 42 creates a

frictional engagement between a driving pulley 14, ring 36 and driven pulley 26. When input shaft 16 rotates, this frictional engagement causes output shaft 28 to rotate in the same direction.

The mechanism 10 shown in figures 1-6 with the coupling ring 36 being a rigid endless ring may transmit a rotary motion from an input shaft to an output shaft in a continuous mode in one direction, for example, counter clockwise or in a reciprocating mode. However, for a reciprocating rotation with predetermined angular orientation, a coupling member 136 in the shape of a rigid rod is a more convenient element. As shown in Figure 7, in drive mechanism 100, rotation of an input shaft 16, for example, in a counter clockwise direction causes a linear movement of a rod 136 to the left and rotation of an output shaft 28 in a counter clockwise direction. Similarly, a clockwise rotation of an input shaft 16 causes the same rotation of an output shaft 28 with rod 136 moving linearly to the right. A work piece secured to either end 32 or 34 of a shaft 28 or to driven pulley 26 may be moved to a predetermined angular orientation controlled by the length of a rod 136. Limiters 52 and 54 may be secured to the rod 136 to assure definite stop. Alternatively, a work piece 56

secured to the rod 136 as shown in Figure 7 may be translated along linear path.

However, a relatively large load mounted at one end of the rod 136 may cause undesirable bending of the rod. Therefore, a platform with a U-shaped groove (not shown) may be mounted on the rod 136, with the rod nested in the groove, at a position between pulleys 14 and 26. The work piece may be secured to the platform by well- known means.

A preferred embodiment for a translation of a work piece is shown in Figure 8. Rod 136 is rigidly secured in the frame members 58 and 60 with all elements of a mechanism 100 being constructed similarly to those of Figures 1-7. A frictional engagement described above affords a translation of a support 12 along rod 136. A work piece 56 securely mounted on a support 12 may be translated and/or reciprocated. This latter embodiment may be modified in a simpler manner for easy manufacturing. Since pulley 26 assists only in the guidance and support of rod 136, it may be changed to a rotatively mounted roller without a circumferential groove. For example, a flanged ball bearing may be used instead of pulley 26. Such a bearing mounted on a shaft 28 could support and guide rod 136 with its bearing

flange preventing lateral movement of rod 136. Alternatively, a similar flange may be provided on a tensioning bearing 42 or on both bearings.

A drive mechanism described so far in the present application employed a frictional engagement between grooves in pulleys and a tapered coupling member, so as to insure a relatively large contact area between interfacing surfaces. The 2-3" tapers are employed for their known, relatively significant frictional force. In the machine tool industry 2-3° tapers are called self-holding tapers. They are used to hold in place many different attachments for metal cutting mechanisms. It is understood, that interfacing members of the present invention forced into a frictional engagement may have other cross-sectional shapes, such as round, elliptical, hexagonal and so on. For example, a coupling member 36b with circular cross-section is shown in Figures 2b, 2c, 3b, 3c and 4b. The contact area of circular member 36b with the grooves 20, 30 described above is generally reduced resulting in reduced load carrying capacity for the drive mechanism, but may be preferred for commercial devices, especially in the case of the translating mechanism. To increase the contact area of the coupling member 36b with circumferential

grooves of the pulleys, these grooves may also have other cross-sectional shapes. For example, gothic arc grooves 20c and 30c formed on corresponding pulleys 14c and 26c are shown in figures 2c and 3c. Moreover, the grooves of the pulleys may have matching or unmatched cross-sections. For example, a coupling ring with circular cross-section may be in a frictional engagement with one pulley having a groove with circular cross- section, and with a second pulley having a groove with a gothic arc cross-section.

As the contact surfaces of the interfacing members (the pulleys and coupling member) wear away the coupling member is easily tensioned by the rotation of bushing 44 as described above.

A mechanism constructed in accordance with this invention comprises of rigid parts with smooth surfaces, as opposed to flexible belt and chains and gears. Furthermore, mechanisms of a prior art require additional pre-loading. All three moving interfacing parts of this mechanism are constantly preloaded by the tensioning bearing for proper frictional engagement resulting also in a take up of any possible slack from manufacturing tolerances. Therefore, compared to the mechanisms of a prior art a mechanism constructed in

accordance with this invention affords much higher precision, smoothness and synchronization in coupling motion and/or power from one shaft to another, yet is easier and less expensive to manufacture.

All parts of mechanism 10 may be made of the variety of materials from hardened metals to plastics and composites and alloys thereof depending on the application. Special coatings may be used on a ring and inside grooves of the pulley to increase a coefficient of friction if desired. A lubricant may also be applied to the moving parts.

Due to the high pressure forces between interfitting surfaces of pulleys and the coupling member a mechanism constructed in accordance with this invention permits the use of lubricants, which improve mechanism performance yet reduce useful frictional forces insignificantly.

It will be appreciated that, contrary to prior art devices, the mechanism disclosed above does not have any restrictions on space orientation and the maximum dimension of the mechanism can be equal to the sum of the radii of the pulleys plus a minor spacing for clearance.

POSITIONING APPARATUS

Positioning apparatus using the principles of the drive mechanisms discussed above are shown in Figures 9- 23. For example, an apparatus 1010 for positioning an object 1012 consists of two substantially identical assemblies 1020 and 1020' joined by the conventional bolt-and-nut arrangements 1014. Assembly 1020 consists of a track 1024 terminated at the two ends by respective pedestals 1026 and 1028 for supporting the apparatus 1010. Track 1024 has a top surface 1030 and a bottom surface 1032. On the top surface, there are two substantially semicircular parallel grooves 1034, 1036 each having a rectangular bottom trench 1038, 1038. In between these grooves, there is a rectangular groove 1040, preferably disposed centrally with respect to the grooves 1034, 1036. Within groove 1040, there is a rail 1042 which may be, for example a circular rod made of hardened ground steel and secured into a semicircular trench within the groove 1040. The rod 1042 may be secured within groove 1040 by any well known means. Assembly 1020 is provided to translate an object in one direction, such as direction X as indicated by arrow 1044.

As shown in Figs. 12, 13, and 14 carriage 1022 consists of a U-shaped platform 1046 and two vertical parallel sidewalls 1048 and 1050 for mounting two parallel shafts 1052 and 1054 above track 1024. Pulleys 1056 and 1058 are secured to shafts 1052 and 1054 respectively by conventional means such as a pin (not shown) , or may be made integral with the shafts. Each pulley has two facing walls 1060, 1062 disposed at a critical angle in the range of 2-3" with respect to the planes normal to the shafts 1052 and 1054. Preferably the critical angle is about 2.5° (See Fig. 14). These walls are pitched at the critical angle to frictionally engage rod 1042 as mentioned above for the drive mechanism.

Preferably, one of the shafts, such as shaft 1052, extends past one of the walls, for example wall 1050, so that it can be rotated manually, or it may be coupled to a conventional drive. In this configuration, pulley 1056 may be referred to as a driving pulley and pulley 1058 may be referred to as a bearing pulley. Rotation of shaft 1052, and the pulley 1056 mounted thereon causes the carriage to translate along track 1024. Of course, it should be understood that either shaft 1052 or 1054 may be extended past the walls and coupled to a

conventional drive. If pulley 1058 is chosen to be a driving pulley, pulley 1056 becomes a bearing pulley.

As shown in Figures 12, 13 and 14, sidewall 1048 has two vertical extensions 1064 and 1066. Similarly, sidewall 1050 has two extensions 1068 and 1070. Shafts 1052 and 1054 are rotatably mounted in these extensions as shown. The U-shaped platform 1046 is secured to side walls 1048 and 1050 by conventional bolt-and-nut arrangements 1072. These bolts and nuts are tightened during assembly to preload the apparatus and provide a tight interfit between the members with no play. Mounted on the U-shaped platform 1046 are four rotatable rollers 1074 (two on each side) , which engage a corresponding rectangular depression 1076, 1078, disposed on the bottom surface 1032 of track 1024. These rollers act as guiding bearings for the carriage 1022.

Assembly 1020' is very similar to assembly 1020, except that it is upside down and rotated by 90° with respect to track 1024. Thus the assembly 1020' includes a track 1024' with two parallel semicircular grooves 1034' and 1036,' and rail 1042'. Track 1024' also has two depressions 1076', 1078', and so on. Driving shaft 1052' with pulley 1056' is rotatably

mounted in the side walls' extensions 1064' and 1068' and shaft 1054' with bearing pulley 1058' is rotatably mounted in the side walls' extensions 1066' and 1070'. Four rotatable rollers 1074' are mounted on the U-shaped platform 1046' for the guidance and support of track 1024*, when it is translated in the Y direction. Importantly, in the configuration shown in Figure 9, track 1024 is stationary, carriage 1022 with assembly 1020' is translated in direction X with respect to track 1024 by rotating shaft 1052, and track 1024' is translated in direction Y, indicated by arrow 1079 by rotating shaft 1052'. Object 1012 is mounted on track 1024' as shown.

The transition between the two orthogonal motions is accomplished through four ground and hardened stainless steel balls 1080, nested in grooves 1034, 1036, 1034' and 1036', as shown in Figure 10 and 11. These balls insure that the track 1024' moves smoothly and independently. It was found that the trenches 1038 in the bottom of grooves 1034, 1036, 1034' and 1036' greatly improve the motion of the balls whereby the balls move more smoothly and evenly than without these trenches.

Of course, an apparatus constructed as assembly 1020 or 1020' may also be used for one-dimensional translation. One such apparatus is shown in Figure 15. In this Figure, a positioning apparatus 1110 is shown, including a stationary carriage 1122 which consists of a U-shaped platform 1146 secured to side walls 1148 and 1150 by a nut-and-bolt arrangement 1172. (Except as noted, in Figure 15 elements 1152, 1154 are identical to elements 1052, 1054 in Figures 9-14, element 1156 is identical to element 1056, and so on) . The apparatus also includes a moving track 1124, a pair of pulleys 1156, 1158 mounted on shafts 1152, 1154. Mounted on carriage 1122, there are also four rollers 1174. The pulleys engage rod 1142 on track 1124. The track also has rectangular depressions 1176 and 1178 for engagement by rollers 1174. Object 1112 is now mounted on track 1124 and rotation of either shafts 1152 or 1154 causes the track 1124 and object 1112 to be translated in a direction parallel to track 1124. In this configuration, the steel balls and semicircular grooves on the track are not necessary.

Another alternate embodiment of the invention is shown in Figures 16-18, wherein an apparatus 1210 for positioning an object 1212 includes stationary track

1224 mounted between two frames 1226, 1228, and having grooves 1276, 1278 on one side, and rod 1242 on the other. (Again, elements 1252, 1254, and so on in Figures 16-18 are identical to elements 1052, 1054 in Figures 9- 14, unless otherwise noted). Rollers 1274 engage the grooves 1276, 1278, while pulleys 1256, 1258 engage rod 1242. Rotation of either pulley causes carriage 1222 to translate along track 1224. Object 1212 is mounted on carriage 1222.

A further alternate embodiment of the invention is shown in Figures 19-20 especially suitable for the applications where an object is translated along a long track (i.e. over 30 cm) . In such applications undesirable bending of a long stationary track may occur under large loads. Therefore, the long track may be reinforced, for example with a rib 1082 disposed at the center of track 1324. A carriage 1322 is shown under track 1324 only for the sake of clarity. Apparatus 1310 may be operated upside down, or standing on rib 1082. Track 1324 has two rails 1342, one on each side, and driving pulley 1356 with a drive shaft 1352 is rotatably mounted in the center or the carriage sidewall 1348. Two bearing pulleys 1358 are rotatably mounted on the second wall of a carriage 1350 as close to the edges of

a carriage as possible for maximum support of the carriage 1322. All other elements are identical to the elements of apparatus 1110 and 1210. Importantly, the rails 1142, 1242, 1342 in the apparatus 1110, 1210 and 1310 are secured to the track, and no rectangular groove is required. For very long travel lengths, track 1324 may be made in short sections and secured to one long rib 1082 for simpler manufacturing. The rails 1342 may be either assembled with the track sections or made in one piece coextensive with the rib.

The principles and structures described above may be used in a gantry-type positioning device as well. For example, as shown in Figure 21, two identical positioners 1402, 1404 may be placed in parallel, each having a structure similar to the structure shown in Figures 19 and 20. For example, positioner 1402 includes a stationary T-shaped track 1406, a carriage 1408 and a drive shaft 1410. Similarly positioner 1404 includes a T-shaped track 1412, a carriage 1414 and a drive shaft 1416. The two drive shafts 1410, 1416 are connected to a common motor 1418 which rotates the shafts simultaneously in the same direction to translate the positioners along tracks 1406 and 1412. Mounted transversely on carriages 1408 and 1414 is a another

positioner 1420 also constructed in a manner similar to the positioner of Figures 19 and 20. Thus third positioner 1420 includes a transversal track 1422 with a carriage 1424 for positioning an object 1426.

A simplified version of a gantry-type positioning device is shown in Figures 22 and 23. This version is similar to the one shown in Figure 21. The device 1500 includes a stationary rib 1502, holding a track 1504. The track 1504 carries on its lower surface a circular rail 1506 , and on its upper surface has a groove or channel 1508. The device 1500 also includes a second stationery rib 1510 in parallel with first rib 1502. Secured to rib 1510 is a second track 1512 facing track 1504 and having a lower rail 1514 and an upper groove 1516. A common carriage 1517 straddles the two tracks 1504, 1512, and has two parallel substantially vertical walls 1518, 1520. Rollers 1522 and 1524 are rotatably mounted on wall 1518 to ride in groove 1508. Similarly rollers 1526, 1528 are mounted on wall 1520 to ride in groove 1516. Carriage 1517 also has two drive shafts 1530, 1532 passing through suitable holes made in walls 1518, 1520 respectively. Drive shaft 1530 supports a driving pulley 1534 which engages rail 1506. Shaft 1532 supports a driving pulley 1536 which engages rail 1514.

Preferably the driving pulleys have inner circumferen¬ tial walls such as 1538 and 1540 which are disposed at the critical angle as defined above. The two shafts are coupled to a common motor 1542 whereby when the two shafts are driven simultaneously by the motor, the carriage 1517 is translated along tracks 1504, 1512. On a top surface of the carriage 1517 there is a transversal track 1544. A carriage 1546 identical to carriage 1346 shown in Figures 19 and 20 rides on track 1544 for positioning an object 1548.

It should be understood that all the embodiments operate in any orientation and that directional terms such as up, down, top or bottom have been used merely to facilitate the description of the invention.

Obviously, numerous other modifications may be made to the invention without departing from its scope as defined in the appended claims.