Simple Robot Drive for Craig Countercurrent Distribution Apparatus FREDERICK C. HICKEY, O.P. Medical Research Laboratory, Providence College, Providence, R . I .
HE great practicality of the Craig countercurrent distribution apparatus for the separation of small quantities of difficultly resolvable substances makes it a desirable addition to any synthetic, biochemical, or organic analytical laboratory. The original apparatus ( 1 ) was admittedly designed to contain the largest number of tubes R hich could be handled conveniently by one experienced operator. Obviously, smaller and more simplified versions are practical. They can now be purchased (H. 0. Post Scientific Instrument Co., 6822 60th Road, Naspeth, N. Y.). Khile completely manual operation is undoubtedly tedious, there is little advantage in partially automatic operation. If the operator must be on hand, for example, to add fresh solvent a t each cycle, ever>-2 or 4 minutes, he might as ~vellsupply the other operations in the interval. Since entirely manual and completely automatic operation are the practical alternatives, it was thought desirable to construct a simple, inexpensive robot drive which, while lacking the elegance and flexibility of the very refined original or conimerrial model, could be constructed by anyone with ordinary shop facilities a t hand. It contains 20 tubes identical with Craig's original design except that the small filling tube a t the top of each cell has been lengthened, as suggested by Craig, to 10 cm. ( I ) . With the longer tubes the solutions never reach the stoppers. Hence, corks may be used, in many cases, instead of specially ground glass stoppers. The tubes are held in holes drilled in a wooden frame. A , as shown in Figure 1. The holes are sufficientlv large in diameter to accommodate a rubber sleeve between the wood and the glass to prevent fracture XTith the sxvelling of the wood. Slits are sawed along the ayis of the holes to provide visibility. T o the ends of the vooden frame, flanges are secured by screws while the flangcxs are taper-pinned to the 3/4-inchhorizontal shaft. The latter revolves in pillon blocks bolted to a n-elded angle iron frame. The essential motions of the apparatus are: ( a ) rocking of the
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tubes through angles of 35" either side of the horizontal for 15 complete oscillations ( 2 minutes) to establish equilibrium (by a change of timing wheels, of course, the number could be varied); ( b ) period of rest, the settling position, with the upper ends of the tubes elevated a t the above angle to allom- the phases to separate (1 minute); ( e ) elevation of the tubes to the vertical position, the decantation position, for a similar interval while the upper phases drain into the traps. While the tubes are in this position, the fraction collector advances one step. The first declination of the new shaking series is maintained sufficiently long to permit transfer of the upper phases to the next tubes. This, follo\\ing Craig, is referred to as the transfer position. While the above motions are carried out automatically, provision is also made for the manual inversion of the tuhes for draining and cleaning. I n order to provide positive limits to the various motions, a 6-inch circuiar disk of steel, B, from whose rim a 53' segment l/2-inch deep was removed, is fastened to the shaft by a taper pin. On the rising stroke, the edge at one end of this segment meets the solenoid-operated stop, C. This stop is operated by a direct current solenoid consisting of 1 pound of No. 24 enameled copper wire wound on a brass spool which is bolted to the frame. Its iron plunger is held in the out position by a light spring. When 60 volts direct current are applied, the plunger is drawn inward, withdraning the stop from contact n i t h the control disk. An alternating current solenoid could be employed and the need for direct current would be eliminated. On the lowering stroke, the opposite end of the segment meets the 0.25-inch depressible pin, D. The latter may be pushed in to allow the tubes to be inverted for draining and cleaning. The same stop limits the rising motion a t the vertical, or decantation position, M hen the solenoid stop is withdrai\n as shown in Figure 1. This disk is also fitted nith the knuckle pin for the shock absorber. .4t the opposite end of the shaft, the inner collar has a short length of 0.5-inch rod, E, brazed to its edge which, in contacting a projection from the frame, acts as a permanent stop to prevent the tubes from passing the vertical on their don nward motion and eliminates the danger of breaking the filling tube against the frame. The outer collar has a similar projection, F,which acts as a brace for the filling tube and dipper. These collars are likemise held in position by taper pins. DRIVING MECHANISM
To eliminate danger from fire and to provide the simplest mechanism, a vacuum drive is used. An Alemite grease gun [No. 6290-C (now obsolete, succeeded by Model No. 7510)], G, provides a substantial cylinder, a virtually leakproof piston, and very efficient packing around the piston rod. The unneeded interior parts are eliminated and the piston is secured directly to the piston rod. The latter is shortened, threaded, and provided n-ith a crosshead TI hich is ronnected to the shaft by means of a crank. B setscrew fastens the crank to the shaft and allows proper positioning. Upper and lower castings of the cylinder 7+-jrJ& < 7 & 7 -h+=7 are drilled, threaded, and provided with 1/8-inch elbows for the attachment of the copper tubing from the valve assembly deFigure 1. Front and Right-Hand Views of Countercurrent Apparatus, Vacuum Drive, Shock Absorber, and scribed below. A 0.75-inch collar brazed to the lower casting and Control Arrangements accepting a short shaft projecting from the frame, provides the .4. Tube frame pivot mounting of the cylinder as is shown from Figure 1. T o E . Control disk C. Solenoid-operated si the lower casting is brazed the base plate of the valve assembly.
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D. E. F. G.
Depressible pin Permanent stop Filling tube brace Cylinder H. Brass valve plate I . Stainless steel plate J . Solenoid K. Shock absorber
VALVE ASSEMBLY
The valve assembly consists essentially of a circular brass disk, H , rotating about a central pin projecting from a stainless
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ANALYTICAL CHEMISTRY
1994 steel plate, I. The-latter has two 6/16-inch holes, inch apart, and a t a common radius of 7/8 inch from the center pin. These are connected by elbows and copper tubing, the left-hand hole to the top of the cylinder, the right-hand to the bottom. The close spacing required to reduce, as far as possible, the length of pull by the solenoid, necessitates silver soldering of the elbows to the base plate since there is insufficient space for rotation. The brass disk, which is ground to make a leakproof contact with the steel plate, contains three holes spaced so that in one position, the left and center holes coincide with those of the lower plate; in the second position, the center and right holes so coincide. The central hole of the upper plate is provided with a hose nipple for connection, by means of rubber tubing, to the vacuum pump. This plate is also provided with a knuckle pin for connection to the actuating solenoid and is held in firm contact with the base plate by a spring mounted on the central pin. When the return springbrings thedisk to its stop, as is shown in Figure 1, vacuumis applied to the right-hand hole of the lower plate, thence to the lower end of the cylinder, while atmospheric pressure is admitted through the left-hand holes of upper and lower plate to the top of the cylinder. When the solenoid is actuated to its full extent, rotating the disk as far as possible in the opposite direction, the vacuum is applied to the left-hand hole of the lower plate and to the top of the cylinder while atmospheric pressure is admitted through the right-hand holes to the lower end of the cylinder. The solenoid used for the valve assembly, J, is a Philtrol S o . 51Cll560.4, 110 alternating current model (Phillips Control Corp., Joliet, Ill.). A Pressovac pump is used to supply the vacuum. SHOCK ABSORBER
To eliminate excessive mechanical shock in the various motions, a n oil and spring shock absorber, K , is required. It consists of a brass pipe cylinder fitted, by lapping, with a steel piston and rod. Both piston and rod are drilled through their longitudinal axis to connect with a hole drilled transversely through the piston
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Figure 2. Top View of Timer A . Timer motor B . Mounting bars C, D . Worm and gear E , F , G: Timer wheels H . Microswitch supporting bar I . Microswitches
rod above the piston. The lower end of the piston is drilled and tapped to accept a I/*-inch brass plug through which a small hole (No. 57) is drilled to control the flow of oil. The cylinder is filled with No. 20 lubricating oil. On the downward stroke, the oil is forced through the channel in plug and piston upward. On the upward stroke, the oil is drawn through the same channel downward. On the piston rod, above the piston, is placed a spring 5 inches long, made of 0.040-inch wire, 4 turns per inch, which assists in absorbing the shock of the apparatus which would otherwise be violent on going from the settling to the decantation
position, because the pump has had time to establish a high vacuum in the lower section. This spring also assists the return of the apparatus to the transfer position after decantation. The angles are so large that the driving mechanism is perilously close to dead center in the decantation position and some experimentation is necessary to find the proper position of the driving crank. TIMER
The timer motor, A, Figure 2, was obtained from a S o . 1001 automatic sign flasher (Automatic Electric Manufacturing Corp., Mankato, Minn.) with a shaft speed of 15 r.p.m. A more powerful unit mould provide a greater margin of safety against stalling but the present unit is satisfactory. After the removal of the relay panel and its switch, the motor is bolted to two 0.5-inch square steel bars, B, to provide space for the control wheels and to serve as a means of attachment to the base plate of a radio cabinet. A worm, C, is attached to the shaft by means of a short adapter and setscrews. A Trorm gear, D,having 30 teeth, is mounted on a l/r-inch shaft, 7 inches long, and the latter is attached to the motor frame by means of brass journals cut from '/(-inch plate. Collars with setscrews (radio shaft couplings cut in half) are used to hold the shaft in position. Brass blanks of 3/32-in~h plate are silver soldered to '/,-inch collars provided with set screws, and turned down to 33/8-in~hdiameter. TTTO of the wheels, E and F , are notched a t one point on their periphery with a 25/64-inch router to a maximum depth of 1/16 inch. The third wheel, G, is provided with 15 notches of the same size equally spaced around one half of its circumference. The first notch of this wheel is elongated approximately 0.25-inch to allow sufficient time for complete transfer of the upper phases from the traps to the equilibration tubes. The notch on the wheel, E, controlling the solenoid operated stop, is positioned 90' behind the last notch on the shaking control wheel, G. The notch on the fraction collector n-heel, F , is set sufficiently farther away to prevent two switches from operating a t the same time which would be an excessive load for the timer motor. Perpendicular to a 0.25 X 0.75 inch brass bar, H , 6.75 inches long, are silversoldered three pieces of the same stock 2.375 inches long with tapped holes to secure the microsnitches. The bar, H , is bolted to the steel bars, B The microsnitches, I (lX.S.E.-l Unimax switch, W. L. SIarson Corp., 460 West 34th St., Sew York 1, K. T.)are so positioned that the solid part of the timing wheels holds them in the off position-i.e., depressed-while the notches permit them to return to the on position. Final adjustment is made by enlarging the mounting holes of the switches to allow changing their position slightly and by hand filing the notches until all motions are smoothly carried out. The whole timer is mounted in a steel radio cabinet, 10 X 8 X 7 inches in size, to protect it from dust The front panel is provided with two plugs for the alternating and direct current input (differently polarized plugs are used to separate the two circuits) and three receptacles to provide one direct and two alternating current outlets. This panel also rontains a double pole, single throw switch, one side of which is used to break the alternating current circuit and the other the direct current. Across the terminals of the direct current microswitch a 1-microfarad paper condenser in series with a 10-ohm resistor is connected, and across the direct current output terminals, a 40-microfarad electrolytic condenser is introduced to minimize arcing a t the w i t c h terminals. The timer, which contains the only source of electrical sparks, can be removed as far as necessary from the apparatus to eliminate danger of fire. FRACTION COLLECTOR
While fraction collectors are described in the literature ( 2 ) and are available commerciallv, the unit required for this application could be simple. A 10.5-inch length of 0.5-inch steel shaft, A, Figure 3, is turned down to 3/s-inch diameter for 3.625 inches
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disks, the perforated ones on top, are held to the shaft between nuts. The base plate, C, 8 inches square, with rounded corners, and the bearing support, D, are cut from 3/*-inch steel. I n the lathe, the cups to accept ball bearing sets for 3/*-inch shaft are cut and 13/32-inch holes are drilled completely through the plates. The bearing support, D, is held rigidly above the base plate by pillars cut from */p-inch shaft. Tapped holes in each end allow the pillars to be bolted directly between the two plates. The shaft is inserted through the bearings and secured by a collar and setscrew below the bearing support. The driving force is obtained from an alarm clock spring, E, attached, as explained above, to the shaft and secured to a steel pedestal bolted to the bearing support. The stainless steel escapement wheel, F , is turned to 3.875-inch diameter and 0.25inch thickness. Fifty teeth of the shape shown in the figure are milled in its edge. I t is attached to the shaft by a taper pin through its hub. A ratchet, G, pivoted on a pedestal bolted to the base plate, allons one notch of the escapement wheel to pass each time the solenoid functions. The inertia of the moving assembly driven by the spring returns the solenoid, H , to its out position while the ratchet halts the motion as a fresh test tube is centered under the delivery funnel (not shown in Figure 1). Sufficient vertical length is allowed in the ratchet pivot and the link to the solenoid to permit the ratchet to be lifted above the escapement wheel for rewinding, which is accomplished by merely rotating the test tube platform in the clockwise direction with the ratchet in the elevated position. .k spring normally holds the ratchet in its lower position. The apparatus has been in use in this laboratory for several months and. Tithin the limits imposed by its small number of tubes, has proved very satisfactory. With proper allowances the same driving and control arrangements could be used with a murh larger apparatus.
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Figure 3.
Front and Horizontal Sectional Views of Fraction Collector A. B. C. D. E. F. G. H.
.Main shaft Test tube supporting disks Baseplate Bearing support Driving spring Escapement wheel Rntchet Solenoid
fi,orn one end. Tlic 0.5-inch diameter section is threaded for a length of 1.25 inches a t the end and for 2.25 inches above the shaulder. Beginnirig at R point 3.125 inches from the smaller end, two grooves 1/8-inch apart, */8-inchwide, and 1/,6-inch deep are cut. The remaining ridge brtxeen the grooves is filed away so as to leave only inch. This projection is so undercut, with a small file, as to grip securely the clock spring mentioned below. Three eirrular disks, R, of 9.375 inches radius are cut from standard 19.25 X 19.12
