Design and experiment of performance testing system of multi-channel seed-metering device based on time intervals

Abstract: Precision metering device is the core component of seed drills, its performance determines the seeding qualities. At present, precision metering device has difficulty achieving a top seeding performance during the working time and avoiding loss sowing. Hence a seeding performance detection system must be innovated for precision seeding device to evaluate seeding performance, especially for multi-channel seeding device of rapeseed. So to be able to detect seeding performance such as normal index, miss index and multiple index accurately for multi-channel precision rapeseed drill, a multi-channel seeding performance detection system has been developed based on seeding time intervals. The system consists of a host computer (industry touch panel computer) and a slave computer (MSP430 MCU) the two-level system. Under the control of the host computer, the slave computer is in charge of collecting the seeding signals produced by a fiber-optic sensor through the time capture interrupts and collecting rotation speed signals produced by a photoelectric sensor through the external interrupt and timer interrupt. These signals were converted into seeding time-interval sequence and rotation-speed sequence respectively. Then the slave computer transmits the sequences to the host computer through the serial port with one designed transmission protocol. The host computer analyzes the sequences and computes the seeding performance indexes such as normal index, miss index and multiple index. On one hand, in order to verify the ability of multi-channel performance detection, tests were tried out by a series of given sequences by plates with different teeth and spacing angles. Seven different of type-A plates with uneven teeth and spacing angles were designed for different and random seeding performance by the fiber-optic sensor producing high and low electrical levels which were converted time-interval sequence by MCU's Time-Capture Interrupt. Type-B plate with 25 even teeth and spacing angles was designed to detect type-A plate rotational speed by the photoelectric sensor, which was installed coaxially with type-A plate on a step-motor. During the test, each plate was tested respectively at different rotation speeds such as 15, 30, 60, 90, 120, 150, 180, 210, 230, 250 and 300 r/min. Tests showed that the protocol with an error recovery of retransmission mechanism made the serial-port communication transmit data accurately and reliably. These seeding performance indexes gotten by performance detection system were the same as theory performance indexes for every type-A plate at every different rotation speeds. At the same time, the multi-channel detection worked well and got the accurate performance indexes. It is easy to obtain conclusion that the performance detection system has the ability to detect the normal index, miss index and multiple index for multi-channel precision metering device. On the other hand, to assess the system detection precision tests were carried out on the JPS-12 test-bed of the pneumatic rapeseed precision metering device by high-speed camera system with setting of 11 000 fps, 320×480 pixels to record the seeding process of precision rapeseed drill at different rotation speeds. Time intervals extracted by counting the frames of two neighboring rapeseeds were compared with the sequence captured by MCU. The test of assessing the system detection precision indicated that: the system's maximum time-interval error is 0.876 ms and maximum average error is 0.192 ms. The composite error of performance indexes is 0.87% and the composite maximum error is 3.98%. The system has realized to detect seeding performance for pneumatic rapeseed precision metering device, and it would provide reference for the performance synchronous detection and optimal design for multi-channel precision metering device.