Automated guided vehicles (AGVs) or autonomous guided vehicles perform tasks for the transportation of goods and commodities. This transportation requires high demands on the vehicles. Harsh environmental conditions, efficiency in battery systems, variable loads, uphill and downhill slopes and interaction with humans are some of the challenges these vehicles face. Computer-controlled and wheel-based, AGVs travel along the floor of a facility without an onboard operator or driver. Their movement is directed by a combination of software and sensor-based guidance systems. For such systems, effective motion control is crucial for the successful operation of the vehicle. When a leading global supplier of AGV and material flow systems wanted to upgrade their latest AGV model, they turned to Elmo.
Read this case study to learn how:
- Powerful high-density Gold servo drives enable motion control when the system is required to switch between different load weights.
- Compact equipment fits into demanding space requirements.
- Elmo’s solution has fixed a longtime problem which caused the system to switch off.
- Elmo’s advanced gantry solution ensures smooth synchronization of the drives on PWM level.
The target vehicle was designed for carrying parts from stock/warehouse to the assembly line of small trucks, and the load weight varied from 100 kg to 1.2 tons. The vehicles operate in 3 shifts and must ensure fail-safe transportation of goods to the assembly line.
The customer’s existing AGV experienced severe efficiency and downtime difficulties, as different loads and speeds lead to misalignments between the hubs of the lifting system, which caused the motion controller to switch off the system. Because of these problems, the company has decided to re-design the lift tables on these AGVs. Upgrading the system posed a challenge considering a compact design of the hub system. The new design required reduced cabling, I/O support for limit switches, as well as the high power density of approximately 30 A RMS at 48 VDC for each drive.
Motion control solution included:
- Gold Solo Twitter drives
The lifting system was a scissor hub system of two independent Permanent Magnet Synchronous (PMSM/BLDC) motors with gear box and absolute encoder, driving a non linear spindle. Both independent systems are mechanical, connected by the pallet carrier, and the spindles lift the hubs.
Since both scissors of the lift table shall run synchronously to keep the table plate constantly staying in horizontal position, Elmo’s built-in gantry function has been suggested to the customer as the correct solution. The gantry solution has not only significantly improved the performance of the lift table regarding the synchronization of both scissors, the stability and accuracy of the positioning, but also has greatly reduced the control effort on their CANopen master side, since the synchronization of the both motors was now carried out by the Gold Solo Twitters, and the CANopen master had only to command one Gold Solo Twitter, which acted as the gantry master.
Two Gold Solo Twitter servo drives, one configured as master and one as slave, were installed on the compact hubs to control the motors. Communication is done via an internal communication interface without overloading the fieldbus system. Elmo uses highest possible synchronization at motor PWM level. Control accuracy of target position and center of the gantry system is 1 encoder increment (1 count). This gantry function is already integrated in the ELMO drives and therefore does not require any complex programming. The gantry mode and synchronization does not affect the bus bandwidth with additional traffic. Configuration is simple and fast via the ELMO’s powerful Application Studio, EASII.
During the simulation of the AGV, Elmo was able to demonstrate and test its Gantry solution with two drives, the smooth parallel run of both and the deviations in the system. Elmo’s EASII software enabled fast and easy set-up of the drives, and showed the customers all the possible failures of the system. Elmo has also helped the software team to set the CAN connection from their master to the servo drives.
Performance under payload 300 kg, motor speed 3250 rpm, acc-/deceleration 3000 rpm/s
To further reduce the space claim, Elmo’s engineering team has offered to replace the encoders, and helped the customer to select suitable partners for the multi encoder interface. Instead of an incremental encoder on each motor plus an absolute system with cable pull on the hub, Elmo recommended an absolute system on the back of the motor for commutation and positioning, which lead to cost savings.
Portal solutions can be implemented in a much more space-saving way, decentralized and with reduced cabling effort without major expenditure and conversion work. Elmo Motion Control offered a cost effective and fast solution by synchronizing the drives on PWM level, which works reliably and can be put into operation quickly. Integrating Elmo’s best-in-class high performance servo drives in the AGV has considerably enhanced the operation of the vehicle. Because of the most advanced servo control technology of Elmo drive and the unique built-in gantry function, Elmo was able to provide the optimal solution to the customer to solve their urgent problem within the shortest period of time.
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