FEATURE Robotics
are these pins smaller than a standard connector, but they are also designed to conduct heat away from the drive. Dynamic gate drive tuning: The output stage consists of two key components – the gate drive IC and the MOSFET – both of which are standard, off -the-shelf components, typically used by all key players in the motor-drive world. To maximise the Nano’s thermal- management capabilities, we make critical design decisions during their selection process: • The gate driver IC We select compact, half-bridge drivers with high output-current capabilities. Because the output current limits the size of the usable output-stage MOSFET, it is important that the drivers have high- current capabilities. • The output stage MOSFET These components must feature a small package, low thermal resistance, high current and low drain-source on resistance (RDS(on)
).
In terms of thermal management, the magic happens in between these two components. Dynamic gate-drive tuning controls the timing between the power device turn-on and turn-off , to achieve low power dissipation whilst meeting electromagnetic compatibility (EMC) requirements.
Current sensing: To further reduce heat dissipation, the Nano features some clever methods for measuring current. This novel approach to current sensing uses ultra-low- resistance current-sense resistors, enabling precise current sensing with minimal power dissipation. Finally, the smallest, most-powerful servo drives also need other strategies for minimised heat build-up. In the case of the Nano, these include the overall construction and layout of power components on the board. We can also pull a number of levers within the drive’s fi rmware to further reduce dissipation, if needed. For example, one feature called “bus clamping” eff ectively reduces switching losses by as much as 33%.
At the end of the day, managing the heat on the smallest, most-powerful drives doesn’t come down to a single design principle. Instead, it’s the sum of many small, carefully-considered design decisions.
The Nano Series digital servo drives An example of a servo drive that incorporates the right power density and
automationmagazine.co.uk
thermal management features is our Nano Series. Each compact unit integrates easily into AGVs, AMRs, robotic joints and other automated equipment. Designed for space-limited applications that need precise speed and position control, the Nano Series represents the next generation of motion control technology, enabling users to achieve unparalleled accuracy and effi ciency in their applications. The Nano Series comes in a small footprint of just 35 x 30 x 23.4mm, operates from 9-180VDC and delivers up to 35A of continuous current and 70A peak current, to provide exceptional power density and effi ciency. Its compact size gives system developers great fl exibility. The optional connector-equipped PCB and CME commissioning software facilitate setup and tuning. Additional features and
specifi cations include: • Safe torque off capability with Sil 3, Category 3, PLe conformance; • Six digital inputs and four digital outputs;
• Four voltage and current combinations;
• One ±10V 12-bit analogue input;
• BiSS-C unidirectional and SSI absolute encoders (primary); • Digital incremental encoder (primary and secondary); • Frequency analysis tools; • Dual encoder feedback support; • 32-bit fl oating-point fi lters and other, advanced fi lters.
In addition, the Nano Series supports EtherCAT or CANopen communication protocols, enabling real-time data exchange. Nano Module EtherCAT NES and Nano Module CANopen NPS models are available with an EZ Board option for simplifi ed mounting.
Best-in-class power dissipation Figures 2-4 show the power dissipation in our NES-090-70 and NES-18-10 Nano drives when the pulse-width modulation (PWM) outputs are driving the motor. Adding the PWM dissipation to the Vlogic
dissipation
yields the total dissipation in watts for the drive.
For the NES-090-70, the dotted lines show a dissipation of 18W at a continuous current
Figure 1
Figure 2
Figure 3
of 28Adc and +HV = 85Vdc. For the NES- 18-10, the dotted lines show a dissipation of 5.2W at a continuous current of 4.4Adc and +HV = 180Vdc.
Relevant for all NES models, Figure 4
shows the power dissipation in the Vlogic circuits that power the drive’s control circuits and external encoders. Adding the PWM dissipation to the Vlogic
dissipation
yields the total dissipation in watts for the drive. The dotted lines in the chart show a dissipation of 3.0W at Vlogic
= 30Vdc
when the drive is in an enabled state and outputting 250mA for an encoder. Servo Components & Systems distributes Copley Controls products in the UK. Contact +44 (0)1 202 666 636
www.servocomponents.co.uk
Automation | September 2023 15
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