GB2187531A

GB2187531A - Sieving apparatus

Info

Publication number: GB2187531A
Application number: GB08702610A
Authority: GB
Inventors: John Monteith
Original assignee: Russell Finex Ltd
Current assignee: Russell Finex Ltd
Priority date: 1986-02-13
Filing date: 1987-02-05
Publication date: 1987-09-09
Also published as: DE3764278D1; EP0233066B1; GR3000785T3; ES2018012B3; EP0233066A2; US4816144A; EP0233066A3; GB2187531B; GB8702610D0

Description

GB2187531A 1 SPECIFICATION the present invention has minimum impedance at

resonance and this impedance can be Sieving apparatus sensed and used to control the output of a free running oscillator by which the transducer This invention relates to sieving apparatus. 70 is powered.

In GB-A-1462866 there is described such The impedance can be sensed by sensing apparatus, for sieving dry particulate material, the voltage across a resistor connected across comprising a base, a frame mounted on the the supply to the transducer, the sensed vol base for vibratory movement with respect tage being used as a feedback signal for con thereto, a grating attached to the frame, 75 trol of the oscillator.

means for vibrating the frame relative to the Although in the known apparatus described base, and ultrasonic means coupled to the above the frame is vibrated relative to the grating to effect ultrasonic vibration thereof base, this is not essential for apparatus ac relative to the frame. cording to this invention. It is otherwise pos- In this known apparatus the ultrasonic 80 sible for the material being sieved to be conmeans comprises an electro-mechanical trans- veyed to and from the grating by vacuum or ducer, and in particular a magnetostrictive pressure differential means, the vibration of transducer, the body of which is rigidly the grating reltative to the frame imparted by mounted with respect to the frame and which the transducer being sufficient to effect siev- is coupled to the grating by means of a metal 85 ing.

probe. This invention will now be described by With such apparatus the low frequency vi- way of example with reference to the draw bration of the grating effected by the oscilla- ings in which:

tion of the frame serves for bulk movement of Figure 1 is a vertical sectional view through material on the grating so that all layers of 90 an ultrasonic transducer arrangement for use material are presented to the grating, while in apparatus according to the invention; and the high frequency vibration of the grating ef- Figure 2 is a circuit diagram of a supply fected by the ultrasonic means serves to pre- circuit for use in the apparatus of Fig. 1.

vent blinding of the apertures of the grating Suitable vibratory sieving apparatus to be otherwise caused by material adhering to the 95 modified to embody the present invention is grating or by particles of the material locking disclosed in GB-A-1426866, and will not together to bridge the apertures. therefore be described in detail herein. Fig. 1 A disadvantage of such known apparatus is of the drawings shows an ultrasonic vibration that the magnetostrictive transducer becomes means which replaces the magnetostrictive hot and requires a supply of large volumes of 100 transducer of the known apparatus shown in cooling air to maintain a satisfactory tempera- GB-A-1462866.

ture during operation. Further, the transducer Referring to Fig. 1, a piezo-electric trans is relatively large and heavy, and adds signifiducer 1 is bonded by means of adhesive 2 to cantly to the mass to be oscillated. the grating 100 of the known sieving appara- According to this invention there is provided 105 tus. The transducer 1 is covered by a spun sieving apparatus comprising a base, a frame metal shroud 3 secured thereto at its peri mounted on the base, a grating attached to phery by adhesive 4.

the frame, and ultrasonic means coupled to The shroud 3 carries a termination 9 for an the grating to effect ultrasonic vibration electric supply cable 5 having two wires 6 thereof relative to the frame, in which the ul- 110 and 7 connected to the transducer 1 and an trasonic means comprises a piezo-electric earth wire 8 connected to the shroud 3, and transducer directly bonded to the grating. also two terminations 10 for cooling air sup The apparatus of this invention has the ad- ply pipes 11. The cable 5 and pipes 11 are vantage that the transducer is relatively small encased in a heat-shrunk cover 12 which is and light, and does not require significant 115 secured to the shroud 3 by a length of heat cooling during operation. Further, the trans- shrunk tubing 13.

ducer is tunable, and can be provided with In use of the apparatus energisation signals means for frequency control, and preferably are supplied to the transducer 1 over the automatic control, whereby the optimum am- cable 5 thereby to produce the required vibra- plitude range of the ultrasonic vibrations of 120 tion of the grating 100, while cooling air is the grating for most effective operation of the supplied through the pipes 11 to cool the apparatus can be achieved and maintained. transducer 1 particularly to prevent overheat Preferably the transducer in energised by a ing of material (not shown) being sieved by supply circuit including means to sense reso- the apparatus.

nance of the grating and any deviation there- 125 The signals supplied to the transducer 1 are from, and feedback means operative in re- controlled in dependence upon the operation sponse to the output of said sensing means of the apparatus, in order to obtain a required to control the supply to the transducer to vibration of the grating 100 in order to maintain resonance of the grating. achieve the required sieving operation, and A transducer as used in the apparatus of 130 Fig. 2 shows a circuit for such purpose.

1 2 GB 2 187 531 A 2 The supply circuit is fed from a conventional 1. Sieving apparatus comprising a base, a 240V supply at input terminals 21 and 22, frame mounted on the base, a grating at and the transducer 1 (not shown) of the appa- tached to the frame, and ultrasonic means ratus is connected to output terminals 23 and coupled to the grating to effect ultrasonic vi 24. The input voltage is applied across the 70 bration thereof relative to the frame, in which primary winding of an input transformer 30, the ultrasonic means comprises a piezo-elec the output from the secondary winding of tric transducer directly bonded to the grating.

Claims

which is applied to a rectification and smooth-
2. Apparatus as claimed in

Claim 1, in ing network 31. which the transducer is energised by a supply The output of the network 31 is applied to 75 circuit including means to sense resonance of a centre tap on the primary winding of an the grating and any deviation therefrom, and output transformer 32, and the network 31 feedback means operative in response to the also provides an input to an oscillator control output of said sensing means to control the network 33 which functions to control a free supply to the transducer to maintain reso- running oscillator 34. 80 nance of the grating.

The output of the oscillator 34 is applied by
3. Apparatus as claimed in Claim 2, in way of a network 35 comprising a push-pull which the impedance of the transducer is arrangement of two power MOSFETs, across sensed and used to control the output of a the primary winding of the output transformer free running oscillator by which the transducer 32. 85 is powered.

The secondary winding of the output trans-
4. Apparatus as claimed in Claim 3, in former 32 is connected in series with a resis- which the impedance of the transducer is tor 36 between the output terminals 23 and sensed by sensing the voltage across a resis 24, there being a voltage feedback connection tor connected across the supply to the trans from the junction between the secondary 90 ducer, the sensed voltage being used as a winding of the output transformer 32 and the feedback signal for control of the oscillator.

resistor 36, to the control network 33.
5. Apparatus as claimed in any preceding An indicator network 37 is connected to the claim, including two or more of said trans feedback connection and the input to the con- ducers bonded to the grating, the transducers trol network 33, the network 37 including a 95 being driven at mutually different frequencies light emitting diode 38 which serves to indi- such that the vibrational nodes and antinodes cate functioning of the supply circuit. at the two or more frequencies are at different In operation of the supply circuit the output positions on the grating whereby the maxi of the oscillator 34 is applied to the trans- mum area of the grating is vibrated.

ducer 1 connected to the output terminals 23 100
6. Apparatus as claimed in any preceding and 24 to cause oscillation thereof and thus claim, in which the frame is mounted on the vibration of the grating 100 to which the base for vibratory movement relative thereto, transducer 1 is coupled. and including means for vibrating the frame For efficient working it is desirable to main- relative to the base.

tain the transducer 1 and grating 100 at reso- 105
7. Apparatus as claimed in any one of nance, under which condition the impedance Claims 1 to 5, in which material to be sieved of the transducer 1 is a minimum such that is conveyed to and from the grating by va the voltage across resistor 36 is at a maxi- cuum means.

mum. Any deviation from resonance will cause
8. Apparatus as claimed in any one of a change in the voltage across resistor 36, 110 Claims 1 to 5, in which material to be sieved and any such change in effective over the is conveyed to and from the grating (100) by feedback connection to the control network pressure differential means.

33 to effect control of the oscillator 34 as
9. Sieving apparatus substantially as here necessary to return the transducer and grating inbefore described with reference to the draw- to resonance as required. 115 ings.

Although in the apparatus specifically de Printed for Her Majestys Stationery Office scribed above there is only a single transducer by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987.

coupled to a single grating, it will be appreci- Published at The Patent Office, 25 Southampton Buildings, ated that an apparatus can be provided having London, WC2A 1 AY, from which copies may be obtained.

one or more separate gratings each with one or more transducers which can be driven as described above, bonded thereto. With two or more transducers coupled to a single grating they can be driven at mutually different frequencies such that the vibrational nodes and antinodes at the two or more frequencies are at different positions on the grating whereby the maximum area of the grating is vibrated.