US3686960A

US3686960A - Stepping device for rotating the table of a sample changing equipment

Info

Publication number: US3686960A
Application number: US35969A
Authority: US
Inventors: Cecil Sidney Charles Tarbet
Original assignee: CECIL INSTRUMENTS Ltd
Current assignee: CECIL INSTRUMENTS Ltd
Priority date: 1969-05-12
Filing date: 1970-05-11
Publication date: 1972-08-29
Anticipated expiration: 1989-08-29
Also published as: GB1306227A

Abstract

A stepping device for a sample changer turntable is driven by spring means, which may be tensioned by rotation of the turntable, and suitably coupled fluid damper means controls the stepped rotation of the turntable. A stepping escapement for the device may comprise a disk carrying pins which project on both sides thereof and a lever carrying co-operating posts.

Description

O United States Patent [151 3,686,960

Tarbet [451 Aug. 29, 1972 [54] STEPPING DEVICE FOR ROTATING 1 References Cited EHgEAMIEJETOF A SAMPLE CHANGING UNITED STATES PATENTS Q 2,438,703 3/1948 Kemeny ..185/38 X [72] Inventor: Cecil Sidney Charles Tarbet, Cam- 2,605,061 7/1952 Howe ..'..188/290 X bridge, England 1,972,971 9/1934 Barenyi ..74/ 1.5 X 2,871,702 2/1951 Tetro ..74/1.5 [73] Assgnee E3 gg Cam 3,443,442 5/1969 Schweihs ..74/1.5

Primary ExaminerMilton Kaufman 1 Flled' M 1970 Attorney-Hall & Houghton [21] Appl. No.: 35,969

[57] ABSTRACT [30] Foreign Application Priority Data A stepping device for a sample changer turntable is driven by spring means, which may be tensioned .by May 12, 1969 Great Bntain ..24029/69 rotation of the turntable, suitably couple fluid damper means controls the stepped rotation of the CCll turntable A pp g escapement for the device y [58] comprise a disk c pins which project on both Field of Search ..74/1.5; 58/121, 116; 185/38 sides thereof and a lever carrying co-operating posts.

8 Claims, 3 Drawing Figures Patented Aug. 29, 1972 2 Shets-Sheet 1 (52/4 i6. fimssz INVENTOR BY )lZ-d ATTORNEY Patented Aug. 29, 1972 3,686,960

2 Sheets-Sheet 2 (ac/4 5. C771n=a5rf INVENTOR BY zw/ M ATTORNEY STEPPING DEVICE FOR ROTATING THE TABLE OF A SAMPLE CHANGING EQUIPMENT This invention relates to a stepping device for rotating the table of a sample changing equipment, and to an escapement mechanism for use in such a stepping device.

According to the present invention, a stepping device for rotating the table of a sample changing equipment comprises a drive shaft, a drive spring coupled to the drive shaft to drive the latter, an escapement geared to the drive shaft to impose a stepped rotation to the drive shaft, and a fluid damper coupled to the drive shaft to restrain the rotation of the latter. Preferably a constant-tension drive spring is used.

The invention also comprises an escapement mechanism comprising a pivotally mounted disc carrying a number of pins spaced around a circle concentric with the disc pivot and each mounted to project on both sides of the disc, and a co-pending lever carrying a pair of posts which extend into the path of the pins on either, side of the disc, and which are staggeredalong the path of the pins to permit stepwise rotation of the disc by successively blocking and releasing the passage of each pin by reciprocation.

The lever may be caused to reciprocate by external means, thus synchronizing the operation of the escapement with reference to external events.

In sample changing equipment embodying the invention, it is possible to provide co-operating stop means on a sub-turntable and on a static portion of the machine to limit the rotation of the sub-turntable to one revolution. One member of the co-operating stop means may be movably mounted so that in spite of the thickness of the stop, the full number of turntable positions is'available. In a preferred embodiment the stop means comprise a fixed pin on a downwardly depending flange of the sub-turntable and a pivot arm mounted with suitable limit stops on the base of the machine.

The invention will now be described in greater detail with reference to the accompanying drawings, of which:

FIG. 1 is a sectional plan view of a stepping drive mechanism according to the invention;

FIG. 2 is a side elevation of the mechanism of FIG. 1, showing the section line I-I along which that figure is taken; and

FIG. 3 is a fragmentary sectional view of a sample changer embodying the invention, and provided with a rotation limiting stop.

The mechanism illustrated in the drawings is constructed on a frame consisting of two plates 1a, 1b, spaced by

posts

2a, 2b and 20. A drive shaft 3 is journalled in the plate la and carries the torque drum 4 of a constant-tension drive spring arrangement which further includes the constant-tension spring 5 and a take-up spool 6, which latter is also journalled in the plate 1a.

The plate 1b carries a rotary fluid damper 7. This damper has a cylindrical body provided with a set of stationary vanes, and a shaft 7a which carries a cooperating set of vanes, and contains a filling of silicone fluid which permits relatively unimpeded slow rotation of the shaft 7a, while providing strong damping to rapid rotation.

The free end of the drive shaft 3 is recessed to fit over the adjacent end of the damper shaft 7a. The two shafts are coupled for rotation by means of a ratchet wheel 8 mounted on drive shaft 3, and a co-operating pawl 8a which is carried on a gear wheel 9 which in turn is mounted on the damper shaft 7a by a mounting boss 9a, the gear 9 and its mounting boss 9a being partly counterbored to clear the end of shaft 3. The sense of the ratchet and pawl arrangement is such that driven rotation of the drive shaft 3 by the spring 5 causes the damper shaft to rotate, whilethe drive shaft is disconnected from the damper shaft when the rotation of the drive shaft is reversed to wind up the spring.

Rotation of the drive shaft 3 is regulated by an escapement mechanism consisting of an escapement wheel 10 and co-operating escapement lever 14. Three pins 10' are carried by the wheel 10 at points spaced equidistantly around a circle concentric with the axis of the wheel, and each pin 10' projects equally on both sides of the wheel in a direction normal to the plane of the latter. The escapement wheel is mounted on a shaft 12 which is journalled in the plates 1a and lb and which also carries a pinion 13 which meshes with the-gear 9 on the damper shaft. For a sampler table of 30 stations the ratio of the gear 9 and pinion 13 is 10:1.

Stepping of the escapement wheel 10 is controlled by an escapement lever 14 which is supported on a block 15 carried between the plates la and 1b. The lever is supported by means of a pivot 16 held in a transverse bore in the block, and lies parallel to a tangent to the wheel 10. The end of the lever adjacent the wheel 10 carries a pair of pallets 14a, 14b, which project one on either side of the wheel 10, and are so spaced apart laterally of the wheel and along the tangent to the wheel that each oscillation of the lever 14 to and from its reset position illustrated by broken lines in FIG. 2, allows the passage of one pin 10' as the wheel 10 rotates. FIG. 1 shows the situation after the movement of the lever to its trip position, shown in solid lines, when the lower endof the previous pin has been released by pallet 14b and the upper end of pin 10' has been intercepted by pallet 14a which moves into the path of the upper end of the pin before the full release of the lower end of the previous pin from pallet 14b. On return of the lever to its reset position the pallet will release the upper end of pin 10 and the wheel will rotate a small amount until the lower end of pin 10 is intercepted by pallet 14b. The pallet 14b also moves into the path of the pin 10' before the pallet 14a releases the upper end of the pin. Even if the tripping frequency is high, and the lever moves again to its reset position before movement of the wheel 10 is complete, pallet 14b will again intercept the lower end of the next pin 10' and stop the rotation, the error in drive shaft rotation represented by the spacing of the pallets being negligible. The lever 14 is in practice operable to trip by linkage to a movable sample probe of a sample changer, which in turn may be driven by a synchronous motor in accordance with a pre-set program. Thus, as the probe is lifted from one sample cell of a series carried by the table, the lever 14 is moved to trip, and as the probe is lowered, the lever 14 is reset, thereby causing the table to rotate by one step and bring. the next sample cell under the descending probe. In the embodiment described, rewinding of the spring is effected by rotation of the drive shaft in a clock-wise direction as seen in FIG. 1 during which time the ratchet arrangement disconnects the fluid damper.

ln'some cases, it may be preferred to limit the rotation of a sample-changer turntable to a single revolution, to avoid over-running and consequent mixing of samples in the sample cells in the event that the sample changer is left unattended for a period greater than that required for a single revolution. Limitation to a single revolution may be achieved by providing co-operating stop means on the sub-turntable indicated at 15a in FIG. 2 and on the main frame of the machine incorporating an escapement. A suitable stop arrangement is shown diagrammatically in FIG. 3, in which one of the co-operating stop members is pivotable to allow a full revolution of the sub-turntable in spite of the space occupied by the stop means. The downwardly depending rim 15b of the sub-turntable is provided with a radially inwardly projecting stop pin 16. The co-operating stop member takes the form of a lever 17 pivotally mounted on the base of a U-bracket 18 which in turn is mounted on the frame of the machine. The

upstanding side members

18a and 18b of the U-bracket act as stops for the pivotal movement of the stop member 17 about its pivot 19 and adjustment screws 20a and 20b are provided for fine adjustment of the limits of travel of the stop member 17. In the position illustrated in the drawings, the turntable is being rotated in a clockwise direction about its center 21 to tension the spring 5, and further rotation of the turntable about its center in the direction shown can be continued until the adjusting screw 20babuts the member 18b and the stop pin 16 abuts the stop member 17. This is indicated in dotted lines in FIG. 3.

Operation of the turntable can now continue until the stop pin 16 is moved through an angle almost equal to 360. The pin 16 will then abut the righthand edge of the stop member 17 and continued movement of the turntable under the influence of the spring will cause the stop member 17 to pivot in an anticlockwise direction about its pivot 19 until the screw 20a abuts the member 18a and the motion of the turntable is arrested. The final position of the stop pin 16 when the turntable is arrested is indicated at 16'.

It will be seen that the device described above permits positive stepping of the table of the sampling equipment with an adequate amount of power available for the drive, while it will be appreciated that the provision of the fluid damper controls the rotation of the table so that samples carried by the table are not spilled during stepping as a result of sudden acceleration or deceleration. Furthermore, the use of a constant-tension spring is particularly-advantageous, since it ensures constancy of operation while the spring is tensioned.

I claim; l. A stepping device for rotating the table of a sample changing equipment comprising:

a. a drive shaft; b. a drive spring means coupled to said drive shaft; c. a stepping escapement geared to said drive shaft;

and d. a fluid damper coupled to said drive shaft to restrain the rotation of the latter. 2. A device accordingto claim 1 in which said drive s 'n means co 'ses aco tantens'o s i 5 stepping vice as c aimed in c aiin l ih whlch said fluid damper is coupled to said drive shaft by a unidirectional coupling.

4. An escapement mechanism for a stepping device, said mechanism comprising:

a. a pivotally mounted disc carrying a number of pins spaced around a circle concentric with the disc pivot and each projecting on both sides of the disc; and

b. a co-operating lever carrying a pair of posts extending into the path of said pins on either side of said disc, said posts being staggered along the path of said pins.

5. A mechanism according to claim 4 in which said lever includes an extended portion for cooperation with an actuating linkage.

6. A device according to claim 1, further comprising equipment including a static portion, a sub-turntable rotatable by said shaft, and'co-operating rotation-limiting stop means on said sub-tumtable and said static portion, respectively.

7. A device according to claim 6 in which one member of the co-operating stop means is moveably mounted.

8. A device according to claim 7 wherein said subtumtable carries a downwardly depending flange and said stop means comprises afixed pin on said downwardly depending flange and a pivot arm mounted with limit stops on said static portion.

Claims

1. A stepping device for rotating the table of a sample changing equipment comprising: a. a drive shaft; b. a drive spring means coupled to said drive shaft; c. a stepping escapement geared to said drive shaft; and d. a fluid damper coupled to said drive shaft to restrain the rotation of the latter.

2. A device according to claim 1 in which said drive spring means comprises a constant-tension spring.

3. A stepping device as claimed in claim 1 in which said fluid damper is coupled to said drive shaft by a unidirectional coupling.

4. An escapement mechanism for a stepping device, said mechanism comprising: a. a pivotally mounted disc carrying a number of pins spaced around a circle concentric with the disc pivot and each projecting on both sides of the disc; and b. a co-operating lever carrying a pair of posts extending into the path of said pins on either side of said disc, said posts being staggered along the path of said pins.

6. A device according to claim 1, further comprising equipment including a static portion, a sub-turntable rotatable by said shaft, and co-operating rotation-limiting stop means on said sub-turntable and said staTic portion, respectively.

8. A device according to claim 7 wherein said sub-turntable carries a downwardly depending flange and said stop means comprises a fixed pin on said downwardly depending flange and a pivot arm mounted with limit stops on said static portion.