Sheep and pig weighing and drafting (sorting) crate includes a 4-axis motion control system
Pharmweigh, based near Bury St Edmunds, is a leading designer and manufacturer of high-quality livestock and agricultural weighing equipment. Its load bars – portable weighing systems for all types of livestock, as well as feed mills and bagging etc. – are said to be highly regarded for their exceptionally long life and high reliability.
The same highly robust load-cell technology is widely adapted across many of Pharmweigh’s products which include drafting crates and platforms equipped with weighing scales, indicators, electronic ID and livestock auto markers. Pharmweigh’s latest innovation, the Draft Master Auto Drafter, is a sheep and pig weighing and drafting (sorting) crate that includes a 4-axis motion control system from Heason Technology to enable automated 3-way gate operation. With successful project funding through the UK DTI/EEDA SMART and Micro Project Development Award schemes, the portable and compact Draft Master is DC powered from electric bike-style batteries – and with autonomous operation can weigh, identify, and draft up to 600 lambs per hour by weight, daily liveweight gains or EID look up, as well as transmit recorded information to third party management apps.
The essential specifications for the development of the Draft Master called for a motion control system that maintained the long working life and high reliability reputation that Pharmweigh has cultivated over several decades. As well the efficiency under battery operation and quiet operation, safety features to ensure that the gates would retract under any resistance caused by jamming were also significant requirements. Pharmweigh’s own expertise in electronic controls for load cell-based weighing, RFID identification, grading and data export would stand them in good stead for the overall control system and Heason’s proficiency in motion control would provide the essential technology and programming skills for a standalone motion control sub-system for gate operation.
Consideration for the most economical, portable, and robust motor technology centred on Lexium MDrive integrated stepper motors from Heason’s distribution partner Schneider Electric Motion. Bringing together stepper motors and integral microstepping drives plus an on-board programmable motion controller in a single package, the compact all-in-one MDrive was specified with options including an incremental magnetic encoder and packaging in an environmentally sealed housing with IP65 rated protection.
Selecting the RS-422/485 communication protocol version Heason programmed the NEMA 23 frame sized MDrives using Schneider’s Mcode script with the individual move parameters for operating the entry gate and the three exit gates. The intelligent drives’ software capability includes logic, branching, trip and maths functions, and in combination with its complement of on-board I/O various memory-stored move sequences are called by Pharmweigh’s host controller and coordinated with the weighing and RFID identification sequences. The control system also extends to an optional semi-automatic mode for grading and handling livestock using a smartphone or tablet.
As well as provide a precise datum reference for axis homing on set-up, the MDrive’s incremental encoder option enables the use of Schneider’s hMT closed loop control algorithm which accurately tracks and compares the encoder feedback position with the commanded motor position, correcting any loss of synchronisation. In addition, to further ensure operational safety, drive current sensing is used to detect and remove gate jams by branching to a sub-routine that immediately reverses the gate direction. The choice of a magnetic encoder, rather than a more fragile optical encoder, was an important factor for the durability of the motion system. And to ensure use in all weather conditions the IP65 rated version of the MDrive includes fully sealed M12 connector sets. With programmable motor resolution up to 51,200 steps per rev and encoder resolution of 4000 counts per rev, the MDrive exceeded the accuracy the application called for.
Without the need for a separate drive cabinet, the integrated and intelligent Lexium MDrive minimises the wiring effort required, simplifies maintenance, and helps reduce overall installation costs. Furthermore, their compact size was an important factor to maintain the desired dimensions of the drafting crate which is the same size as Pharmweigh’s industry-standard manual version. The MDrive’s quiet operational characteristics ensure calmness during the weighing process and their high efficiency and low power consumption meets the Draft Master’s battery powered throughput capability.
Schneider’s Lexium MDrive is also available in NEMA 17 and 34 frame sizes in a wide choice of stack length/power output ratings. In addition to the RS422/485 comms version used, other options include Ethernet for EtherNet/IP, Profinet, and ModbusTCP as well as CANopen. To facilitate flexible use across all types of motion applications, industries and environments, the comprehensive range of options and accessories include absolute encoders, high torque versions with 50% additional motor power, IP20 or IP65 protection and a wide choice of cordsets.
The development programme for the Draft Master ran during the Covid lockdowns and, despite the inconvenience of that period, successful field trials are now complete and the product is now fully launched.