AU2013340393B2

AU2013340393B2 - Provision of data on the froth in a froth flotation plant

Info

Publication number: AU2013340393B2
Application number: AU2013340393A
Authority: AU
Inventors: Francois Eberhardt Du Plessis
Original assignee: Blue Cube Intellectual Property Co Pty Ltd
Current assignee: Blue Cube Intellectual Property Co Pty Ltd
Priority date: 2012-10-29
Filing date: 2013-10-29
Publication date: 2016-11-17
Anticipated expiration: 2033-10-29
Also published as: WO2014068478A2; CA2886752A1; AU2013340393A1; CA2886752C; WO2014068478A3; ZA201309062B

Abstract

Methods of providing data on the movement of froth in a froth flotation plant and on the height of the froth in the plant are disclosed. The surface of the froth is generally illuminated at the predetermined wavelength and a laser (18) of the same wavelength is used to produce a light post on the froth's surface. An electronic camera (16) is used to produce digital images of the surface and these are processed to provide the requisite information.

Description

WO 2014/068478 1 PCT/IB2013/059750

PROVISION OF DATA ON THE FROTH IN A FROTH FLOTATION PLANT

FIELD OF THE INVENTION

5 This invention relates to the provision of data on the froth in a froth flotation plant. BACKGROUND TO THE INVENTION

Froth flotation is used in industry as a separation process and is very widely used for ίο separating valuable minerals from gangue.

It has long been understood that the characteristics of the froth are an indication as to whether the plant is operating efficiently. In earlier times the technician simply made visual observations of the froth. Based on his skill and knowledge he would make adjustments is based on the visual characteristics of the froth.

More recently technology has been brought to bear on the control of froth flotation plants and reference can be made to United States patents 6, 727, 990 and 6, 778,881 as disclosing camera and computer based systems for replacing or supplementing the 20 technician’s experience based control of the plant.

The present invention provides a method of, and apparatus for, providing data on the characteristics of the flotation froth of a froth flotation plant. 25

BRIEF DESCRIPTION OF THE INVENTION

According to a first aspect of the present invention is provided a method of providing data on the movement of froth in a froth flotation plant, the method comprising taking two digital 30 images in succession of part of the froth’s surface, illuminating said part of the froth’s WO 2014/068478 2 PCT/IB2013/059750 surface using a laser beam whilst one image is being taken but not whilst the other image is being taken, and subtracting one image digitally from the other so as to leave only the image of the laser. 5 Said part can be subjected to general illumination by an infrared light source, the laser’s light being of the same wavelength as said source.

According to a further aspect of the present invention there is provided a method of providing data on the height of the froth in a froth flotation plant, the method comprising ίο directing a digital camera at a part of the surface of the froth, the camera being a predetermined height above a datum level of the froth, directing a laser beam at said part, the point of origin of the laser beam being a predetermined distance from the centre of the camera lens and the beam being at a predetermined angle to a line through the centre of the camera lens, taking an image of said part so as to determine the position of the laser’s 15 light spot with respect to the edge of the image, calculating the distance from the laser “spot” on said part to the camera lens, and calculating the vertical height of the froth using the output of an accelerometer which detects the degree by which the camera’s orientation deviates from horizontal. 20 According to a further aspect of the present invention there is provided apparatus comprising a digital camera for taking images of a part of the surface of the froth in a froth flotation cell, a laser for directing a laser beam at a fixed angle to an axis passing through the centre of the lens of the digital camera for producing a light spot on said part of said surface, and an accelerometer for providing data indicative of the angle by which said axis 25 deviates from vertical.

Said apparatus can include by an infrared light source for providing general illumination of said part, the laser and the light source providing light of the same wavelength. WO 2014/068478 3 PCT/IB2013/059750

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the 5 accompanying drawings in which;

Figure 1 is a pictorial view of apparatus in accordance with the present invention;

Figure 2 is a section through the apparatus of Figure 1; 10

Figure 3 is a pictorial view similar to that of Figure 1 but with parts of a cover omitted;

Figure 4 is a wavelength diagram; is Figure 5 diagrammatically illustrates the method of operation of the apparatus of Figures 1 to 3;

Figure 6 and 7 are digital images of the flotation froth; and 20 Figure 8 illustrates the blocks of the block matching algorithm.

DETAILED DESCRIPTION OF THE DRAWINGS 25 The apparatus illustrated in Figures 1 to 3 comprises a sealed housing designated 10 only the left hand part of which is shown in Figure 3. A narrow bandwidth light source 12 is provided. This produces light in the invisible part of the spectrum and directs it downwardly to provide general illumination of the top surface of 30 the froth in the froth flotation cell. The light source can be an infrared LED. Light reflected WO 2014/068478 4 PCT/IB2013/059750 from the froth passes through an optical filter 14 to an electronic camera 16. A laser 18, which produces red light of the same wavelength as the LED, is provided for directing its light beam onto the top surface of the froth. The laser’s beam is at an angle to 5 the vertical as is described below.

The images produced by the camera 16 are transmitted by an antenna 20 to a remote location for storage and viewing. Reference numeral 22 designates the electronics which process the output of the camera 16 to a signal form that can be transmitted by the antenna ίο 20. A hood 24 is provided above the housing 10. There is an airgap gap between the housing 10 and the hood 24. The hood 24 shields the housing 10 from direct sunlight thereby to minimise the danger of overheating in the sealed housing 10. 15

An accelerometer (not shown) is provided to permit the angle of the apparatus with respect to horizontal to be determined.

Turning now to Figure 4, the spectral emission lines of the LED light source 12 and the laser 20 18 are shown. It will be noted that the peaks of these spectral lines coincide. The two vertical dotted lines show the limits of the wavelengths that the filter 14 permits to reach the camera. The filter is intended to prevent light from the sun and from other external sources reaching the camera 16. This limits the detrimental effects that can be caused by shadows and uneven lighting. Consequently the light which reaches the camera is almost exclusively 25 that from the two light sources 12 and 18. The chosen wavelength of 820 nm to 860 nm is a compromise. Sunlight levels are lower at most longer infrared wavelengths. However, readily available silicon based cameras are highly sensitive at shorter infrared wavelengths. Strong LED sources at 830 nm and 850 nm are commercially available. When all these factors are taken into consideration the chosen wavelength of between 820 nm and 860 nm 30 represents the best available choice. WO 2014/068478 5 PCT/IB2013/059750

The area illuminated by the light source 12 is within the field of view of the camera 16 as is the spot on the surface of the froth which is illuminated by the laser 18. Because the laser is directed at an angle to the vertical, the apparent position of the red light spot on the 5 surface of the froth, as viewed by the electronic camera 16, moves laterally with changes in froth depth.

The use of the apparatus described will now be explained. The distances and angles given below are by way of example only. 10

The laser 18 is located 145 mm in the horizontal direction from the centre point of the camera lens. The laser is positioned at an angle of between 11 and 18 degrees to the vertical. An angle of 16 degrees is preferred. is The lens of the camera 16 is 800mm above the level of the froth lip over which the froth flows. In this regard what is called the zero correction of the camera is undertaken in the factory. When the camera is positioned as described the pixel position for that set up is adopted as the zero reference. 20 The camera and the laser are in a fixed relationship to one another, both being mounted on a laser cut chassis plate of the housing 10. This means that the distance from the centre of the camera’s lens to the laser is known and fixed as is the angle of the laser which respect to a line passing through the axis of the camera lens. The angle between adjacent pixels of the camera is also fixed and known. The deviation of the housing 10 from horizontal is 25 known based on the output of the accelerometer.

The camera is triggered to take two images in quick succession. For one of the images the laser 18 is on and for the other image the laser 18 is off. The position of the point of light where the laser intersects the froth is calculated by moving the two images until they 30 coincide and then subtracting one from the other. The only remaining clear image is that of WO 2014/068478 6 PCT/IB2013/059750 the laser and the number of pixels of that point from the zero position can be calculated.

From the information available as outlined above, the distance from the spot of light to the camera lens can be calculated. This is not, however, necessarily the height of the froth 5 because the camera may be at an angle to the horizontal which means that the reading may be too high or too low. The next step is to calculate the true height of the froth using the calculated distance of the camera to the froth and the output of the accelerometer which is an indication of how far the camera is from the position it occupies when the housing 10 is horizontal. 10

The rate of movement of the froth is determined by taking two images in quick succession and using a block algorithm to locate some parts of the images that correspond. The number of pixels though which the selected part of the image has moved in the interval between images can be determined which enables the angle through which that part of the 15 image has moved to be calculated. As the froth height has been calculated as described above, the angle of movement can be used to calculate the distance through which the froth has moved in the time between images.

Two digital images of the froth are shown in Figures 6 and 7. These images were taken 20 20 milliseconds apart

Figure 8 illustrates the laser dot position, the rectangle in which the laser is searched for and each of the blocks of the block matching algorithm each with their vector of detected movement in pixels.

Claims

1. A method of providing data on the movement of froth in a froth flotation plant, the method comprising taking two digital images in succession of part of the froth’s surface, illuminating said part of the froth’s surface using a laser beam whilst one image is being taken but not whilst the other image is being taken, and subtracting one image digitally from the other so as to leave only the image of the laser.

2. A method as claimed in claim 1, wherein said part is subjected to general illumination by an infrared light source, the laser’s light being of the same wavelength as said source.

3. A method of providing data on the height of the froth in a froth flotation plant, the method comprising directing a digital camera at a part of the surface of the froth, the camera being a predetermined height above a datum level of the froth, directing a laser beam at said part, the point of origin of the laser beam being a predetermined distance from the centre of the camera lens and the beam being at a predetermined angle to a line through the centre of the camera lens, taking an image of said part so as to determine the position of the laser’s light spot with respect to the edge of the image, calculating the distance from the laser’s light “spot” on said part to the camera lens, and calculating the vertical height of the froth using the output of an accelerometer which detects the degree by which the camera’s orientation deviates from horizontal.

4. Apparatus comprising a digital camera for taking images of a part of the surface of the froth in a froth flotation cell, a laser for directing a laser beam at a fixed angle to an axis passing through the centre of the lens of the digital camera for producing a light spot on said part of said surface, and an accelerometer for providing data indicative of the angle by which said axis deviates from vertical.

5. Apparatus as claimed in claim 4 and including an infrared light source for providing general illumination of said part, the laser and the light source providing light of the same wavelength.