This invention relates to shaking tables such as are used in laboratories to agitate liquid in flasks.

Such tables conventionally comprise a motor driving a cam, crank or eccentric, which acts on the table top, and are subject to the usual requirements for prolonged satisfactory operational life of such "moving part" mechanical components, which means they are expensively constructed and/or require frequent maintenance and repair. They are also not very controllable.

The present invention provides a shaking table which does not have these disadvantages.

The invention comprises a shaking table having a direct electromagnetic drive.

The table may have a bi-directional shaking motion, and may have separate electromagnet means effecting movement in different directions, and may comprise two opposed pairs of electromagnet means arranged orthogonally.

The table may comprise a base mounting electromagnet coil means and an armature moved by said coil means and connected to said table top.

The table top may be mounted to the base by flexible post means.

The table may comprise drive means pulse-energising said electromagnet coil means.

Control means for the drive means may be adapted to control pulse frequency and/or amplitude, and may also alter the energising pulse pattern whereby to produce different shaking modes.

Embodiments of shaking tables according to the invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a plan view of one embodiment.

Figure 2 is a part-sectional elevation of the embodiment of Figure 1,

Figure 3 is a front elevation of the embodiment of Figure 1,

and Figure 4 is a diagrammatic illustration of a driving and controlling arrangement.

The drawings illustrate a shaking table having a direct electromagnet drive 12. The table 11 has a bi-directional shaking motion, that is to say, regarding one edge 11a of the table 11 as an x-axis and an adjacent edge lib as a y-axis, shaking movement of the table top 13 takes place in both x- and y-directions.

The table 11 has separate electromagnet means 14, 15 effecting movement in different directions. Each separate means 14, 15 comprises an opposed pair 14a, 14b; 15a, 15b of electromagnets, the pairs being arranged orthogonally. The pairs 14, 15 are arranged diagonally on the table 11.

Armatures 16 are connected to a hub 16a by pairs of snap fitting joints 18. The hub 16a is then attached to the table top 13.

Four flexible corner posts 22 stand up from the table 11 and project slightly above the main housing 23 thereof. The top 13 locates on the upper ends of the posts when it is engaged on the armature 16, so that movements of the armature 16 are reflected in movements of the table top 13 on the flexible posts 22.

It will now be seen that energising either magnet of the pair 14a, 14b will move the table top 21 along the diagonal towards that magnet, and likewise for the other magnet pair 15a, 15b. The armature 16 is articulated by having its pole pieces 16b pivotally connected to the hub 16a to allow such movement.

It will now be seen at once that sequentially switching the magnets 14a, 15a, 14b, 15b will effect a corresponding movement of the table top.

The snap fit of the top 13 to the hub 16a enables it to be removed for cleaning and for servicing access to the housing 23.

The driving and controlling arrangement illustrated in Figure 4 is very much like a stepper motor drive arrangement and comprises a sequencing logic circuit 41 driving the electromagnets 14a, 15a, 14b, 15b sequentially. An amplitude control 42, which might be a decade switch, controls the pulse current through each magnet, and a frequency control 43, which might also be a decade switch, controls the frequency with which the circuit 41 sequences through the switching cycle. A manual on/off 44 is provided in parallel with a timer 45 which can be used to pre-set a shaking time and switch off and/or give an audible warning on termination.

This may be a luxury, but it is possible to incorporate a shaking mode selector 46 which simply alters the switching pattern of the sequencer logic so that any of several shaking modes may be selected such for example as a straightforward circular mode in which the magnets are energised in the order 14a, 15a, 14b, 15b (or the reverse) or a unidirectional mode in which only magnets 14a and 14b are used, or a mode in which the uni¬ directional mode diagonal changes periodically, and so on

The various controls are conveniently brought out to a front panel 23a of the housing 23, which, of course, accommodates the driving and controlling arrangement of Figure 4 as well as the necessary power pack and mains transformer.

It would, of course, be possible to simplify the design considerably. For example, three electromagnets could be used instead of four, and these three might be arranged at the apexes of an equilateral triangle; or designs could be envisaged using only two electromganets and indeed only one such, on a push-pull basis or with a spring bias, which would be limited as regards its shaking modes but probably nonetheless effective for most purposes.

A similar electromagnetic drive could also be used to drive a flask stirrer.