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The application of computer imaging to sizing and inspection has increased the need for efficient singulation systems. A lateral expanding tube singulator has been developed for potatoes. Tests were carried out to assess its efficiency using three cultivars, four size grades and three operating rates. For each test, the singulation performance on 8000 potatoes was analysed.

Major improvements have taken place in the design of potato crop establishment, harvesting and grading machinery over the past decade. These changes have been consumer-driven with premium payments for quality produce, particularly for pre-packs of uniformly sized tubers. The psychological impact of freshness is fully recognized and large retail outlets often display such produce to maximum advantage at the entrance to the store. There is no place in this quality image for the bag trade — an unknown quantity of dirty, damaged and even diseased tubers.

SUMMARY The weight, length, breadth and depth were measured for each of 10 000 potato tubers. These were samples over 3 years of the 10 most commonly grown UK maincrop varieties. Volume, square-mesh riddle size and average projected area were also measured in the final 2 years. A multivariate log-normal distribution was found to give a good fit to the data. Illustrations are presented of how this distribution can be used to assess grading schemes.

SUMMARYTests were to be made to estimate the ED 10 for surface splitting of potatoes; that is the dropping height for which on average 10% of potatoes sustain a surface split. To got good estimates for the ED 10 it is necessary to drop potatoes from heights close to this level. It was decided that a sequential procedure should be used to alter drop heights so that most drops would be made from heights close to the ED 10. Several procedures were investigated by calculation of large-sample properties of estimators and computer simulation of experiments. A procedure was then chosen for the drop tests. Results show that this procedure is easy to use, and also yields satisfactory estimates of ED 10s.

A proportion of the damage sustained by potatoes at harvest time occurs during transfer from the potato harvester delivery conveyor to the trailer. A prototype delivery conveyor, designed to reduce this damage, was built and tested under commercial harvesting conditions. The conveyor has an automatic discharge height control consisting of a sensor ball mounted on the end of the conveyor and actuating an airswitch which causes a solenoid valve to operate a hydraulic lifting ram. The conveyor is in two parts, the distal part being capable of swinging sideways in the event of impact against the trailer tailboard. Results of tests show that the mean drop height can be held within the range 116–199 mm. This is an improvement on the mean drop heights of 390–780 mm measured under typical farm conditions on harvesters without automatic control of the delivery height of the discharge conveyor.

The mass, length, breadth and depth were measured for each of 6000 potatoes. Samples of approximately 200 tubers of each of the 10 most commonly grown UK maincrop cultivars from three locations in UK were use. Multivariate log-normal distributions fitted the data well. This result has been used to assess grading methods based on mass, one-dimensional measurements of size, or estimates of riddle size. Prediction of mass using the product of the three principal tuber dimensions shows an error of 10 % or less, against 30 % forthe current riddle method of sizing.