Seed counting and frequency measurement apparatus and method
An improved device for measuring the count and frequency of seeds in a stream of seeds is described. The device is useful for measuring the frequency and accuracy of seed planting devices. A seed counting system can include an imaging region, an image sensing device, and a lens between the imaging region and the image sensing device. An optical distance extender between the imaging region and the lens, creates an effective optical distance between the imaging region and the lens that is substantially greater than the physical distance between the imaging region and the lens, thereby providing a substantial depth of field.
1. A seed counting system comprising:
(a) an imaging region;
(b) an image sensing device;
(c) a lens between the imaging region and the image sensing device; and
(d) an optical distance extender between the imaging region and the lens, whereby the effective optical distance between the imaging region and the lens is at least about five times the physical distance between the imaging region and the lens.
2. The seed counting system according to claim 1 wherein the optical distance extender comprises a plurality of mirrors.
3. The seed counting system according to claim 1 wherein the optical distance extender comprises a pair of substantially parallel mirrors.
4. The seed counting system according to claim 1 wherein the image sensing device comprises a charge-coupled device.
5. The seed counting system according to claim 1 wherein the imaging region has depth that is from about ten to about sixty times the diameter of a seed to be counted by the system.
6. A particle frequency measuring apparatus comprising:
(a) a housing having an aperture therein;
(b) an image sensor located on a first side of the aperture;
(c) a light source on a second side of aperture opposite the first side;
(d) a lens for focusing light from the light source onto the image sensor, the lens being positioned a first distance from the aperture; and
(e) a pair of opposed mirrors between the lens and the aperture;
(f) whereby light emitted from the light source is reflected between the mirrors such that light from the light source must travel a distance that is at least about five times the first distance before reaching the lens.
7. The apparatus according to claim 6 wherein the image sensor comprises a charge-coupled device.
8. The apparatus according to claim 6 wherein the pair of opposed mirrors are substantially parallel to each other.
9. The apparatus according to claim 6 wherein the pair of opposed mirrors includes a pair of opposed mirror faces, and wherein each of the opposed mirror faces comprises a mirroring material thereon.
10. The apparatus according to claim 6 further comprising an analog-to-digital converter for converting an analog data signal from the image sensor to a digital signal.
11. The apparatus according to claim 10 further comprising a filter for filtering the digital signal.
12. The apparatus according to claim 6 further comprising a microprocessor configured to count images sensed by the image sensor.
13. The apparatus according to claim 6 further comprising a microprocessor configured to measure an elapsed time period between successive images acquired by the image sensor.
14. A method of measuring a characteristic of a stream of spaced particles having a stream depth that is about ten to about sixty times greater than the particle size, the method comprising:
(a) passing the stream of particles through a measurement area having a depth that is equal to or greater than the stream depth;
(b) capturing a substantially focused image of substantially every particle in the stream of particles as the stream of particles passes through an aperture, irrespective of the position of a particle within the measurement area; and
(c) analyzing the captured particle images to determine at least one characteristic of the stream of particles.
15. The method according to claim 14 wherein the characteristic is a quantity of particles in the stream of particles.
16. The method according to claim 14 wherein the characteristic is a time period between successive particles in the stream of particles.
17. The method according to claim 14 further comprising generating a digital signal that is representative of the size and sharpness of the image of each particle in the stream, and wherein analyzing the captured particle images comprises analyzing the digital signal.
18. The method according to claim 14 wherein the stream of particles comprises a stream of particles having at least two different sizes, and the characteristic is the number of particles in the stream that are equal to or larger than a pre-selected size.
19. The method according to claim 14 wherein the stream of particles comprises a stream of particles having at least two different sizes, and the characteristic is the frequency of particles in the stream that are equal to or larger than a pre-selected size.
20. A compact seed counting apparatus comprising means for acquiring a substantially sharp image of a seed in a substantially dispersed stream of seeds having a mean axis of flow, wherein the means is capable of acquiring a substantially sharp image of each seed in the stream irrespective of a distance of a seed from the axis of flow wherein the means for acquiring a substantially sharp image comprises:
(a) an image sensor;
(b) a lens for focusing seed images on the image sensor, the lens being positioned between the image sensor and the mean axis of flow, wherein the lens is a first distance from the mean axis of flow; and
(c) a plurality of mirrors arranged to provide an effective optical distance between the mean axis of flow and the lens that is about at least five times greater than the first distance.
21. The compact seed counting apparatus according to claim 20 wherein the image sensor comprises a charge-coupled device.