How do EMI harm and help in the world of robotics?

This article is part of the TechXchange: Dive into EMI, EMC and Noise

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What you will learn:

  • How do conductive and radiative emissions affect BLDCs?
  • Impact of EMI on drones and UAVs.
  • How EMI is used to disable illegal drones and UAVs.

High-speed brushless DC (BLDC) motors are widely used in electric vehicles, automated industrial applications (eg, submarine subsystems), aerospace applications, and in the field of robotics. This article discusses the effects of electromagnetic interference (EMI) on robotics.

We know that EMI occurs when two or more electromagnetic fields interfere with each other and then become distorted.

Robot designers need to have a good understanding of EMI and know how to prevent it from affecting robot performance. What are the best approaches to minimize EMI effects on their designs?

Designers should first research the most optimal motor for their robot design. The best bet for reducing EMI in a robotic design is an ironless core motor structure because it has much lower magnetic energy when switching. Thus, the choice is clear: the BLDC motor will generally be the best option in robotics.

Conductive and radiative EMI

EMI noise can occur as both conductive and radiative noise. Radiated EMI noise is usually not much of an issue in BLDCs for robotics. Conductive EMI can flow through the common DC path or through parasitic elements or ground planes.

Conductive EMI has two types: common mode (CM) and different mode (DM). CM noise flows in the same direction through the circuit elements and back through the ground plane. DM noise flows in one direction through one element and will return through other circuit elements. A high dv/dt creates CM noise. A high di/dt creates DM noise.

Commutation is the action of directing currents or voltages to the appropriate motor phases to produce optimum motor torque. In a BLDC motor, the coils do not move, so there is no need for brushes and commutators. In this class of motor, the permanent magnet rotates by changing the direction of the magnetic fields generated through the surrounding stationary coils.

Electromagnetic field simulation software for the design and analysis of electric motors is available via Ansys Maxwell.

Integrated motor controllers

Built-in motor drivers combine everything needed to drive a BLDC motor (see picture). These integrated drivers will typically have field effect transistors (FETs), gate drivers, and state machines.

The integration will eliminate the routing of long wires from the Electronic Control Unit (ECU) to the engine. Integrated BLDC motor drivers also have the advantage of a smaller printed circuit board (PCB) size, as well as a lower overall system price.

Drones and Unmanned Aerial Vehicles (UAVs) are also robots

Remote-controlled dynamic navigation devices, such as drones and UAVs, are also (mechanical) robots. Sources of EMI that a UAV/drone may encounter are power lines, electrical substations, and communication towers. EMI shielding can be used in this case.2

As an example, consider an electrical distribution tower of several hundred kilovolts. If the UAV/drone flies below 100 feet, communications will be lost and there may be a telemetry failure. Data transmission will be interrupted at approximately 250 feet.

In this scenario, a non-conductive UAV/drone airframe will help minimize EMI interference.

EMI Disabling of Illegal Drone/UAV Use

Drones/UAVs can be deployed illegally when used for terrorist purposes and as spy cameras. Research is ongoing regarding anti-drone methods. These methods, such as the application of intentional EMI (IEMI) to drones/UAVs, are used in particular to disrupt the detection modules of drones/UAVs.3

Examples of illegally deployed drones include:

  • Contraband in prisons
  • Map/photograph prison areas for potential escape plans
  • Terrorism
  • Illegal surveillance of large crowds, stadiums or people
  • Infiltrate conferences/meetings to obtain sensitive information
  • Aircraft interference

Drones will maintain stable flight when their variety of sensors, inside and out, work in coordination. If a few sensors are affected by external interference, it may cause serious malfunction. Additionally, since sensor modules like Inertial Measurement Units (IMUs) are essential for most drones, introducing disturbances into these sensor modules is an effective way to incapacitate the drone.

Here are the targets, methods and characteristics of the different categories of anti-drones:

High-powered EMI targets electronic circuitry via an antenna that deploys a high-powered EMI wave, which will destroy or degrade the offending drone:

  • Targeting an unprotected electronic system via a Cassegrain antenna with a gain of 37 to 40 dB using a pulse method with a peak field of a few kV/m which has a pulse repetition frequency (PRF) of 300 Hz to 1 kHz.
  • Target a commercial drone, such as DJI Ghost 3with an ultra-wideband (UWB) electromagnetic pulse (EMP).
  • Targeting a commercial quadcopter drone with a horn antenna using a 100 MHz to 3.4 GHz narrowband pulse that has a PRF of 1 kHz.
  • Target a minimal sensor network (MULLE) using a 2 to 3 GHz continuous wave (CW) horn antenna with a peak field strength of 0.24 to 0.36 kV/m.
  • Target a commercial standard (COTS) quadcopter with an antenna that has a CW of 100 MHz to 2 GHz and a field of 75 to 95 V/m.

Low-power IEMI targets the following:

Non-RF methods:

  • An acoustic MEMS sensor using mechanical resonance.
  • Optical flow using a laser which will degrade the image received from the optical flow sensor, resulting in malfunction.

Drone detection systems can also be deployed to prevent the leakage of sensitive data, theft of passwords, illegal photography and thefts through access to aerial photography, recordings, CCTV, passwords pass and security locations. Again, a controlled EMI disturbance will disable the drone.

Summary

Robotics developers must fully understand EMI interference to completely prevent their robot designs from behaving erratically or even being severely damaged by rogue EMI signals. Ironless core motors can reduce EMI.

Design engineers should pay attention to potential EMI issues early in the design cycle and determine how proper motor selection could manage EMI threats. Shielded cables can help, as can proper testing throughout the design cycle. Using ferrite beads on PCBs will also help.

Read more articles in the TechXchange: Diving into EMI, EMC and Noise

References

1. Union Robotics – EMI/EMF and the Effects on Your UAV Operations – YouTube

2. EMI Shielding for Drones and UAVs, Steve Taranovich, Electronic Design

3. Examination of intentional electromagnetic interference on UAV sensor modules and experimental study

4. A Case Study of EMI Noise Negatively Affecting Performance and Reliability in Robotics and Automation – Power Quality Blog

5. Best Practices for Preventing Electromagnetic Interference in Robotics | ManufacturingTomorrow

6. EMI Filters for UAV Robotics | APITech

seven. How dangerous are EMI for drones? (manifoldrobotics.com)

8. Design of robots for electromagnetic compatibility and functional safety – Embedded computer design

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