AU630365B2 - High intensity laboratory agitator - Google Patents

Description

630 ipz 6j r ,A8d 1A,, ~cc Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. CI: Application Number: Lodged: Complete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: Name of Applicant: TO BE COMPLETED BY APPLICANT M.D. Pescarch Company Pty Limited ress of Applicant: Atdress of Applicant: 8 Khartoum Road, North Rydo.

Michael Wenzel Chudacek N.S.W. 2113 Actual Inventor: Address for Service: P.O. Box 22, North Ryde.

IOO-52 7 OS E-9 N.S. W. 2113 Complete Specification for the invention entitled: High Intensity Laboratory Agitator The following statement is a full description of this invention, including the best method of performing it known to me:- SNote: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

This invention relates to an improved laboratory agitation apparatus for use with test-tubes and the like.

Background The purpose of agitation can be to disperse or homogenise gases and/or particulate solids in liquids or to homogenise or emulsify liquid mixtures. Agitation is also used to enhance heat and mass transfer processes such as heating, cooling, crystallisation, dissolution and extraction, where the process kinetics are agitation intensity dependent. The froth flotation technique for minerals beneficiation is a further example involving process kinetics known to be agitation intensity dependent. The measurement of mineral flotability by subjecting a reagentized suspension of particles and air to a defined intensity of agitation for a defined time period is one of the uses of the novel apparatus described herein. Yhe appatatus described herein allows measurement of mineral floatability on a very small sample size and this is of particular importance where the amount of sample material available is limited. This invention belongs to the class of apparatus for closed, batch agitation of gas/liquid, gas/liquid/solid and gas/liquid/liquid systems. The cylindrical, laboratory test-tube with a stopper is a typical example of such a closed system. In the present context, the term 'test-tube' includes any other suchlike enclosure. Test-tubes can be agitated by many modes of manual shaking, however manual agitation is disadvantageous in that it is tedious, has very low reproducibility with respect to intensity of agitation, and it cannot yield reproducible results where the studied phenom,.non is strongly dependent on agitation intensity.

Mechanical rocking test-tube shakers of prior art provide reproducible intensity of agitation, however they are limited to a low agitation intensity. Shear impeller type agitators can provide very high intensity of agitation in a test-tube but the insertion of a shaft with impeller iray cause contamination problems. Magnetically coupled stirrers are used extensively in laboratories but are not capable of highly reproducible agitation intensity, because the position of the stirring element in the test-tube is not fixed and therefore not well defined. These stirrers are also susceptible to magnetic coupling slip and, as the transmitted torque is limited to the strength of the coupling, high agitation intensity cannot be achieved. This invention aims to improve current laboratory-scale agitation techniques according to the following objectives.

To increase the intensity of agitation while maintaining a high degree of reproducibility of agitation intensity.

(ii) To control and program the whole agitation cycle.

(iii) To operate in closed system to prevent any loss and/or contamination of the sample.

(iv) To allow a mineral floatability measurement on a very small sample size.

To provide means for monitoring agitation intensity during the whole agitation cycle.

Features of the Invention The present invention comprises an apparatus for agitation of test tubes and the like, the said apparatus being characterised as having: a support member for attachment of test tubes or the i D like said support member being attached to +-hedriven member of a driving means adapted for reciprocating rectilinear drive motion, position sensors adapted to detect proximity of the support member adjacent the extremities of its reciprocating motion, and switching means adapted to change the direction of reciprocating motion of the support menmber in response to signals detected by the position sensors and to drive the support member towards the end of motion extremity remote from the position sensor which was last activated.

In one embodiment of the invention as described herein the driving means comprises a double acting pneumatic cylinder actuated by compressed gas, and switching means comprises electro-mechanical pneumatic valves adapted to control the flow of compressed gas. The invention will now be described by way of example with reference to the accompanying drawing, Fig i, which is a schematic outline of the elements of the high intensity laboratcry agitator. According to the invention, a pneumatic cylinder and reciprocating piston assembly i, typically of the rodless type, is supplied with pressurized air via a pressure regulator 8 and electromechanical valves 7 and 10. Rigidly connected to the piston assembly of the pneumatic cylinder 1 is a test-tube support member 2 with one or more attached test-tubes 3, having axes of symmetry inclined typically 150 from the axis of reciprocating movement. Such an inclination has been found to improve the circulation of the test-tube contents 0 and reproducibility of agitation as compared with test-tubes -3mounted with axes parallel to the axis of reciprocating movement. Piston position sensing switches 4 and attached at opposite ends of cylinder 1, are connected to an electronic timer/counter 6. Electrical signals from the timer/counter 6, in response to position sensors 4 and energize electromechanical valve 7 to sequentially pressurize and depressurize opposite sides of the piston in the cylinder, reciprocating the piston and test-tube carrier assembly in a cyclic manner. The piston and test tube carrier assembly reciprocates at a frequency which is adjustable by the air pressure set from regulator 8. The intensity of the agitation is controlled by pressure to the pneumatic cylinder 1 supplied by pressure regulator 8, and by the stroke length determined by the location of the sensors 4 and 5. The number of strokes of the test tube support member 2 is preset by the timer/counter 6. An accelerometer 9 is mounted on the support member 2, and connected to suitable signal processing equipment, for monitoring the intensity of agitation as characterized by the deceleration peaks at each piston stroke reversal.

Operation of the Invention When the test-tube agitator is started the pistonvith the test-tube support member 2 attached is driven at its natural speed from its rest position at the upper end of the cylinder towards the lower limit, determined by position sensor 5. Once the position sensor 5 is activated, timer/counter 6 energizes electromechanical valve 7 which simultaneously exhausts air from the pressurized side of the cylinder piston and injects pressurised air to the other side of the cylinder piston. This action results in abrupt -4-

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but shock-free reversal of piston movement leading to high decelerat'.ve forces acting upon the contents of the test-tube 3. As the reversal occurs well before the piston reaches its limit of movement in the pneumatic cylinder 1 the injected air acts as a pneumatic cushion, resulting in a very smooth operation while exposing the test-tube contents to a very high decelerative field. After motion reversal, the piston is accelerated by compressed air until the position sensor 4 is activated and motion is again reversed.

This periodic reversal of the piston motion produces an air cushioned reciprocating movement. Reciprocating movement causes the liquid in a partly filled test-tube to change position from one end of the test-tube tc the other, due to reversal of acceleration fields in manner similar to intense manual shaking, leading to very intensive agitation. The agitation intensity is monitored during the whole agitation period by an accelerometer 9 attached to the te--ube carrier 2. The output of accelerometer 9 is fed into a computer equipped with a suitable analog to digital Data Acquisition System. A computer program calculates the frequency, peak acceleration and deceleration of each cycle and the mean and standard deviation of each parameter during the agitation period. The intensity of agitation is thus monitored with high precision and recorded for comparison with future experiments where precisely defined agitation intensity is required. As the shakec is capable of operating at very high piston velocities, the last halfcycle is pneumatically cushioned by the electromechanical valve operating in response to a signal from the electronic timer/counter 6 to ensure that the test-tube support member I 2 comes to rest in a gentle manner. Valve 10 rapidly cuts off the air supply to valve 7 during the last piston stroke of the motion sequence. By this action the pneumatic cylinder 1 is starved of air and the test-tube support member 2 comes to rest at the start-up position in a gentle manner. The test-tube agitator is then ready for the next sequence of agitation cycles.

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Claims (9)

1. Apparatus for agitation of test tubes and the like comprising: a support member for attachment of test tubes or the c- like said support member being attached to b\kdriven member of a driving means adapted for reciprocating rectilinear drive motion, position sensors adapted to detect proximity of the support member adjacent the extremities of its reciprocating motion, and switchjr j means adapted to change the direction of reciprocating motion of the support member in response to signals detected by the position sensors and to drive the support member towards the end of motion extremity remote from the position sensor which was last activated.

2. Apparatus according to Claim 1, wherein driving means comprises a double acting pneumatic cylinder actuated by compressed gas.

3. Apparatus according to Claim 2, wherein switching means comprises electro mechanical pneumatic valves adapted to control the flow of compressed gas.

4. Apparatus according to Claim 2 or Claim 3, wherein the supply pressure of compressed gas is adjustable to provide control of reciprocating frequency and peak accelerations of the support member.

Apparatus according to Claim 3 or Claim 4, wherein the electromechanical pneumatic switching valves are controlled by an electronic control module which is adapted to drive the support member through a preset -7- number of cycles, and to indicate the elapsed time.

6. Apparatus according to any one of Claims 1 to inclusive, wherein the support member is adapted to accommodate one or more test tubes or the like.

7. Apparatus according to any one of Claims 1 to 6 inclusive, wherein the test tube axis of symmetry lies at an angle between 0 and 90 degrees to the reciprocating direction.

8. Apparatus according to Claim 5, wherein cushioning of the final drive stroke of the pneumatic cylinder is provided by isolation of the compressed gas fromnt the pneumatic cylinder by means of an electromechanical pneumatic switching valve at the commencement of the final drive stroke of the pneumatic cylinder in response to a signal fromnt the electronic control module.

9. Apparatus according to any one of Claims 1 to 8 inclusive, wherein the acceleration of the support member is monitored by an accelerometer attached to the said support member. Apparatus for agitation of test tubes and the like substantially as herein described with reference to the accompanying drawing. DATED this ELEVENTH day of AUGUST 1989. M.D. RESEARCH COMPANY PTY LIMITED -8-