A PARTICLE RETRIEVING APPARATUS

Abstract: A particle retrieving apparatus (10) is provided for individually retrieving particles (58) such as diamond particles using a reciprocating vacuum needle (48). A balance arm (20) is provided having a hopper (46) at its free end for receiving the diamond particles. The balance arm is adjusted so that it is in a position of equilibrium. As the needle tip (48A) contacts a particle (58A), the balance arm is displaced downwardly, with such downward displacement being sensed by an opto-sensor (38) which is thereby used to sense the contact position (81) of the needle as it comes into contact with the diamond particle (58A). The contact position is recorded at a micro-processor-based controller (52), which is then used to control the subsequent motion of the needle (48) in the next retrieval cycle on the basis of the recorded contact position.

Description: A PARTICLE RETRIEVING APPARATUS BACKGROUND TO THE INVENTION THIS invention relates to a retrieving apparatus, and in particular to a retrieving apparatus for retrieving and sampling particulate material. Co-pending South African patent application 97/8874 discloses a method of locating individual particles, and in particular diamond particles, on a target surface for quality testing purposes. In an initial step in the process, a hollow vacuum needle is used to deliver individual diamond particles from a batch in a sampling receptacle to the target surface. The needle is lowered slowly into the stack of particles until the needle tip is about 0.1mm from the rigidly mounted particle receptacle. As a result, the needle tends to wear rapidly, and diamond particles are sometimes forced into the mouth of the hollow needle, thereby jamming it. If the needle is speeded up so as to ensure that sampling takes place more quickly, particles are often scattered out of the receptacle, and the wear and jamming problems are increased. In both scenarios, as a result of the inter-action arising between the needle and the particles as the needle tip dips into the batch of particles, the tip of the needle tends to abrade and/or bend after a relatively short time, and therefore needs to be replaced regularly. SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a particle retrieving apparatus comprising a particle receptacle for receiving particulate material, a collecting probe for retrieving particles from the particulate material in the receptacle, drive means for driving the probe, a sensing arrangement for sensing the contact position of the probe as it comes into contact with the particulate material, recording means for recording the contact position of the probe and control means for controlling the motion of the probe via the drive means in a subsequent retrieval cycle on the basis of the recorded contact position. In a preferred form of the invention, the particle receptacle is supported on the sensing arrangement, such that the particle receptacle is displaceable in response to initial contact between the probe and the particulate material, with the sensing arrangement including a sensor for sensing such displacement. Conveniently, the sensing arrangement comprises a balance having a balance arm sensitive to the probe contacting the particulate matter, with the sensor being arranged to sense the resultant displacement of the balance arm. Advantageously, the balance arm includes adjustment means for adjusting the balance arm to a position of equilibrium in response to the variations in loading of the receptacle, the sensor being arranged to sense deviation of the balance arm off the position of equilibrium. Typically, the balance arm is suspended pivotably from a support table, the table being formed with an aperture through which the particle receptacle is - J arranged to protrude. The collecting probe may comprise a hollow vacuum needle which is driven reciprocally along its axis by the drive means, the vacuum being sufficient to lift individual particles and the inner diameter of the hollow needle being smaller than the average particle size. Preferably, the control means is responsive to a signal from the sensing arrangement, and is arranged substantially contemporaneously to halt the probe via the drive means and to enable the halted position of the probe to be recorded in the recording means. The invention extends to a method of retrieving a particle from particulate material in a receptacle comprising the steps of: a) advancing a collecting probe towards the particulate material; b) sensing a first position at which the probe makes contact with the particulate material; c) recording the first position; and d) using the record to provide a first reference position to control the motion of the probe during a subsequent particle retrieval cycle as it approaches the particulate material. Advantageously, the method includes the steps of retrieving a first particle with which the probe has first made contact, releasing the first particle, and, - 4 during the subsequent retrieval cycle, of advancing the probe towards the particulate material at a first velocity and then at a second reduced velocity which is lower than the first velocity as it reaches the first reference position so that it travels relatively slowly just before contacting the particulate material. Typically, the method includes the further iterative steps of updating the reference position for a particular collection cycle on the basis of the previously stored reference data corresponding to the position at which the probe last contacted the particulate material. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a partly cross-sectional side view of a particle sampling apparatus of the invention; and Figure 2 shows a partly schematic detail of a particle receptacle or hopper forming part of the particle sampling apparatus of Figure 1. DESCRIPTION OF EMBODIMENTS Referring first to Figure 1, a particle retrieving apparatus 10 comprises a fixed table 12 having an aperture 14 formed therein for loosely receiving a hopper assembly 16. The hopper assembly 16 is in turn bolted to a support end 18 of a balance arm 20 suspended pivotably from the table 12 via a trunnion 5 - assembly 22. A counterweight 26 is located towards the opposite adjusting 28 end of the balance arm 18. A first mounting bracket 30 is bolted to the underside of the table 12, and carries an adjusting screw assembly 32 which is connected to the adjusting end 28 of the balance arm 18 via a tension spring 34. A second bracket 36 is bolted to the underside of the table adjacent the hopper assembly 16, and carries an optical switch 38 which is triggered by means of an optical switch breaker 40 extending downwardly from the free end of the arm 18. An adjustable stopper 42 is used to adjust the resting height of the hopper assembly 16 and to prevent overshoot by pivoting of the balance arm 18 on which the hopper assembly is supported. The hopper assembly 16 comprises an outer housing 44 defining an opening for receiving a cone-shaped hopper 46. A retrieval probe in the form of a hollow steel vacuum needle or cannula 48 is vertically aligned so that it points towards the base of the cone. The needle is carried on a reciprocating electric servo-actuator 50, which may also be in the form of a pneumatic actuator, for controlling reciprocal movement of the needle along its axis 51. A central microprocessor-based controller 52 is connected to the optical switch 38 via a signal input lead 54, and a signal output lead 56 extends from the controller to the reciprocating actuator 50, with output signals from the controller controlling the movement of the needle 48 via the reciprocating actuator 50. The micro-processor is typically a PLC or PC which is programmed to control the position and velocity of the needle, with the velocity and position profile being optimised for each different particle size and type. In use, the sampling apparatus is operated in the following manner. A batch of particulate matter requiring sampling, which in the particular example comprises diamond particles 58 having an average particle size of less than 1,2mm, and preferably 200μm to 600μm, is deposited in the hopper 46. The corresponding needle typically has an outer diameter corresponding to or slightly less than the average particle size. The adjusting screw assembly 32, which takes the form of a fixed threaded nut 32.1 mounted to the underside of the table 12, and a bolt 32.2, the threaded shank of which is screwed into and out of the nut, is then used to fine-tune the balance via the spring 34 to a horizontal position of equilibrium, in which the breaker 40 is just clear of the optical switch. The microprocessor-based controller 52 controls a first downward stroke of the needle 48 in such a way that it descends slowly to a position indicated in broken outline at 60, in which the tip 48 A of the needle 48 contacts one of the uppermost diamond particles 58 A which is in line with the needle. The downward movement of the needle against the particle 58A causes the support end 18 of the balance arm to move downwards in the direction of arrow 61, which in turn causes the breaker 40 to activate the optical switch 38 and signal the controller 52. The controller in turn sends an output "stop" signal via the output lead 56 to the reciprocating actuator 50, which immediately halts the downward stroke of the needle 48. The exact position of the tip of the needle is then fed into the controller 52 from a displacement transducer 62 which is attached to the reciprocating actuator 50 via an input lead 63 and this value is stored in the micro-controller as a datum value. A vacuum, which is applied to the tubular vacuum needle 48 just before the needle reaches the particle, captures the particle 58A as the needle tip contracts it, after which the needle commences an upward or withdrawal stroke. An array of tickler brushes 64 serve to ensure that only a single diamond particle is held captive by the vacuum needle by brushing off all other particles which may have adhered to the needle, typically as a result of static charge, as it is raised. The diamond - 7 particle is then deposited on a crushing anvil, measuring device or similar device. In the next downward stroke, the needle is driven downwardly and relatively rapidly to the position PI (indicated by horizontal broken line 66) which has been stored in the controller 52. Alternatively, the needle may be programmed via the controller to terminate an initial portion of its subsequent downward stroke at a slightly higher position P2 so as to ensure that there is no possibility of initial contact being made with any of the diamond particles. The controller then causes the downward velocity of the needle 48 to be slowed down to a crawl velocity of typically 10% of the initial velocity so that the tip 48 A of the needle gently contacts rather than plunges into a subsequent particle such as particle 58B, which is the next particle in the "stack" to be sampled at position P3. The position in which the downward stroke of the needle terminates may be stored during each sampling or collecting cycle, as a result of which the datum point is continuously updated. An advantage of this procedure is that sampling may take place relatively quickly, in that the speed of the needle is not compromised during its major portion of travel. At the same time, the tip of the needle does not abrade as quickly, or get clogged by smaller particles, as the downward speed of the needle is considerably slowed down over the critical portion of the sample collecting cycle. It has, for example, been found that by using the above method and apparatus, a collecting needle can last up to twenty times longer. The sampling apparatus of the invention is not confined to the sampling of particulate diamonds, but may be used to sample any particulate matter in a situation where sampling speed is important, whilst at the same time either the particles being sampled or the sampling probe is prone to being damaged if - 8 - the probe contacts the particle at anything but relatively low speeds. The sensing arrangement may be any type of floating arrangement, and is not confined to a balance arm, with the main requirement being that the floating arrangement allows displacement of the particle receptacle in response to initial contact between the probe and the particulate material.

Claims: CLAIMS 1. A particle retrieving apparatus comprising a particle receptacle for receiving particulate material, a collecting probe for retrieving particles from the particulate material in the receptacle, drive means for driving the probe, a sensing arrangement for sensing the contact position of the probe as it comes into contact with the particulate material, recording means for recording the contact position of the probe and control means for controlling the motion of the probe via the drive means in a subsequent retrieval cycle on the basis of the recorded contact position. 2. A particle retrieving apparatus according to claim 1 in which the particle receptacle is supported on the sensing arrangement, such that the particle receptacle is displaceable in response to initial contact between the probe and the particulate material, with the sensing arrangement including a sensor for sensing such displacement. 3. A particle retrieving apparatus according to claim 2 in which the sensing arrangement comprises a balance having a balance arm sensitive to the probe contacting the particulate matter, with the sensor being arranged to sense the resultant displacement of the balance arm. 4. A particle retrieving apparatus according to claim 3 in which the balance arm includes adjustment means for adjusting the balance arm to a position of equilibrium in response to the variations in loading of the receptacle, the sensor being arranged to sense deviation of the balance arm off the position of equilibrium. 10 - 5. A particle retrieving apparatus according to either one of claims 3 or 4 in which the balance arm is suspended pivotably from a support table, the table being formed with an aperture through which the particle receptacle is arranged to protrude. 6. A particle retrieving apparatus according to any one of the preceding claims in which the collecting probe comprises a hollow vacuum needle which is driven reciprocally along its axis by the drive means, the vacuum being sufficient to lift individual particles and the inner diameter of the hollow needle being smaller than the average particle size. 7. A particle retrieving apparatus according to any one of the preceding claims in which the control means is responsive to a signal from the sensing arrangement, and is arranged substantially contemporaneously to halt the probe via the drive means and to enable the halted position of the probe to be recorded in the recording means. 8. A method of retrieving a particle from particulate material in a receptacle comprising the steps of: a) advancing a collecting probe towards the particulate material; b) sensing a first position at which the probe makes contact with the particulate material; c) recording the first position; and 11 d) using the record to provide a first reference position to control the motion of the probe during a subsequent particle retrieval cycle as it approaches the particulate material. 9. A method according to claim 8 which includes the steps of retrieving a first particle with which the probe has first made contact, releasing the first particle, and, during the subsequent retrieval cycle, of advancing the probe towards the particulate material at a first velocity and then at a second reduced velocity which is lower than the first velocity as it reaches the first reference position so that it travels relatively slowly just before contacting the particulate material. 10. A method according to claim 9 which includes the further iterative steps of updating the reference position for a particular collection cycle on the basis of the previously stored reference data corresponding to the position at which the probe last contacted the particulate material.

Inventors: ADDISON TIMOTHY PATRICK GERARD, ADDISON, TIMOTHY, PATRICK, GERARD
Applicants: ADDISON TIMOTHY PATRICK GERARD, DE BEERS IND DIAMOND, ADDISON, TIMOTHY, PATRICK, GERARD, DE BEERS INDUSTRIAL DIAMOND DIVISION (PROPRIETARY) LIMITED
Application year: 1999
Main classification: B65G47
IPC codes: B65G47, G05B19