How Radar Can Be Used for Vehicle Detection and Collision Avoidance in Challenging Environments

Motion monitoring and position sensors can enable collision avoidance, ensure safety, and enhance productivity in logistics, manufacturing, mining, transport, agriculture, and other industries. The sensors can be mounted on vehicles or placed at strategic fixed locations.

They must be configurable to fit specific application needs and have multi-functional sensing capabilities, including object detection based on distance, angular position, and velocity. The ability to detect multiple targets at once is needed in busy or complex environments.

Applications like loading docks and forklift speed control benefit from using a technology unaffected by dirt, dust, wind, precipitation, and other environmental conditions. Customizing parameters like the detection window shape and target setpoints can further enhance performance.

This article starts with a review of the importance of the operating frequency on several key radar specifications, then moves to a comparison of available radar technologies like frequency modulated continuous wave (FMCW) and pulsed coherent radar (PCR), detection schemes, beam patterns, and sensing zones. Next, a software suite is presented that can speed the development of advanced systems using radar sensors.

It closes with application examples of how all those factors are used in the Banner Engineering Q90R series of radar sensors to provide multi-functional sensing capabilities for reliable detection in demanding environments, including sensing the presence of trucks at a loading dock and controlling forklift speed for enhanced safety.

Radio detection and ranging (radar) is an active sensor technology that emits high-frequency RF energy. The energy is reflected off objects in its path, and the characteristics of the reflected energy can be used to detect objects, determine their distance, and, in some cases, measure the speed they are moving toward or away from the sensor.

The operating frequency is a fundamental characteristic that determines the performance of a radar sensor. Industrial radar sensors are available that operate at 24 GHz, 60 GHz, and 122 GHz, parts of the industrial, scientific, and medical (ISM) frequency bands, and can be used without a special license.

The operating frequency of a radar sensor has a significant impact on several specifications, including:

• Range- Low-frequency radar sensors like 24 GHz have the longest range.
• Accuracy - High-frequency radar sensors like 122 GHz have higher accuracy and can detect smaller objects.
• Dead zone - A radar sensor's dead zone, or blocking distance, is caused by the target being too close. In general, higher-frequency sensors have smaller dead zones.
• Weather resistance - Sensing functions are immune to wind, fog, steam, and temperature changes. Radar is generally resistant to interference from rain or snow. 24 GHz radar has the best ability to ignore interference from rain and snow.
• Target materials - While it’s most resistant to interference from weather, 24 GHz radar is the most limited in its ability to sense a wide range of materials. 60 GHz or 122 GHz radar sensors can detect high and low dielectric materials (Figure 1).

Figure 1: The operating frequency of radar sensors has a strong influence on the ability to identify a range of target materials based on their dielectric characteristics. (Image source: Banner Engineering)

Beyond frequency

Frequency is a defining characteristic of radar sensors. Still, other important specifications include radar technology like FMCW versus PCR, detection schemes including adjustable field versus retro-reflective sensors, and the field of view, window shape, and target setpoints.

FMCW emits a continuous signal that’s modulated and increases or decreases in frequency over a fixed bandwidth. By measuring the frequency of a reflected signal, the radar knows the time it has taken for the signal to reflect off the target and return. That time of flight (ToF) information determines the target range.

Some benefits of FMCW include simultaneous measurement of range and velocity without needing separate antennas or pulses, superior range resolution, the ability to distinguish between closely spaced targets, and higher accuracy in challenging environments.

PCR radar transmits a pulse, turns the transmitter off, waits to receive an echo from the target, then turns the transmitter back on to send a new pulse and continue the cycle. Like FMCW, a form of ToF analysis is used to determine the range and velocity of the target. The use of pulses means that PCR radar uses less power than FMCW. PCR is often preferred in battery-powered systems and is well-suited for low-power short-range applications.

Adjustable field vs retro-reflective sensors

Adjustable field radar detects objects by sensing reflected RF waves. They are well-suited to detect objects with a large radar cross-section that reflects a lot of RF energy. Objects with large metallic surface areas, especially surfaces that are perpendicular to the radar beam, typically have large radar cross-sections.

Adjustable field radar sensors can have configurable set-point distances. The sensor uses ToF calculations to determine the target range and only signals the presence of targets within the set-point distance.

A retro-reflective radar sensor relies on the presence of a reflective reference target like a wall. It detects objects by identifying disruptions in the return signal from the reference target. These radar sensors can be optimized to sense objects even if they don’t have large radar cross-sections.

60 GHz, FMCW radar sensors

The Q90R series of FMCW adjustable field radar sensors operate at 60 GHz and provide balanced performance in terms of accuracy, range, and material detection capabilities. In addition, they are IP69K-rated and suited for use in demanding environments (Figure 2). They are available with 120° by 40° or 40° by 40° fields of view. Parameters like range and detecting the nearest or the strongest object can be modified for specific application requirements.

Figure 2: The Q90R series of FMCW adjustable field radar sensors operate at 60 GHz and are in a rugged IP69K package. (Image source: DigiKey)

The Q90R2-12040-6KDQ features a highly-configurable 120° by 40° field of view that can be split into independent detection zones and enables precision position sensing (Figure 3). Its multidimensional sensing ability can support more intelligent object detection based on distance, radial position, and speed thresholds. Like other models in the Q90R family of radar sensors, it has a range of 0.15 to 20 m. It also offers flexible connectivity options, including IO-Link and Banner’s Pulse Pro pulse frequency modulation (PFM) technology.

Figure 3: Q90R2 radar sensors have a configurable and wide 120° by 40° field of view (Image source: Banner Engineering)

Software unlocks the performance

The powerful features of the Q90R and Q90R2 radar sensors can be unlocked using Banner’s Measurement Sensor Software, a graphical user interface (GUI) that enables designers to configure and visualize data from the sensors

The software provides a graphic that shows what the sensor is seeing, which is useful for sensors without visible beams, like radar sensors. Users can modify sensor parameters, such as response speed, output configurations, and filtering options.

The 120° by 40° field of view of the Q90R2 is highly configurable and enables precision positioning and control. Designers can use Banner’s software to customize advanced sensing parameters, such as each application's window shape and target setpoints. (Figure 4).

Figure 4: Banner’s Measurement Sensor Software enables designers to optimize the field of view (top) and the window shapes and target points (bottom). (Image source: Banner Engineering)

Vehicle detection at loading docks

Automatically and accurately detecting trucks at loading docks is important to support productivity and safety and meet environmental standards. The traditional solutions of doorbells or indicator lights are often not suitable. Loading docks can be noisy places where doorbells can’t always be heard. In addition, the presence of overhead and machine lighting and flashing lights on forklifts can make it easy to overlook an indicator light, even a blinking one.

An automated sensor solution is desirable. However, trucks come in multiple sizes, are made with various materials, and can have a wide range of colors and surface finishes. Those challenges, plus the ambiguities of ambient environmental conditions like noise, dust, rain, or snow, make it challenging to implement a reliable solution based on photoelectric or ultrasonic sensors.

Radar sensors like the Q90R2 are often the preferred choice. They ignore ambient environmental conditions. They have an IP67/IP69K-rated housing, making them suitable for driving rains and other challenging environmental conditions, and a wide -40°C to +65°C operating temperature range. They can reliably detect the presence of trucks regardless of the material and its color, texture, or reflectivity.

The independent and configurable sensing zones and the 120° by 40° beam pattern of the Q90R2 can enable one sensor to do the work of two and detect the presence of trucks at two adjacent docks (Figure 4).

Figure 5: The 120° x 40° beam pattern of the Q90R2 radar sensor means a single sensor can monitor two truck docks. (Image source: Banner Engineering)

Forklift speed control and safety

In addition to detecting vehicles, radar sensors can be mounted on a vehicle like a forklift to detect changes in its surroundings to enhance safety. For example, a Q90R2 radar sensor can be mounted on the back or sides of a forklift and configured with multiple zones at different distances.

The broad 120° by 40° beam pattern of the Q90R2 makes it especially suitable for monitoring surrounding objects that may be in motion. In addition, the Q90R2 provides radial distance, angular position, and target velocity feedback. As hazards get closer, the forklift driver can be alerted, the forklift speed can be automatically restricted, or the forklift can be stopped.

In cases where a forklift is used indoors and outdoors, a Q90R radar sensor with a beam pattern of 40° by 40° can be mounted on the roof to detect the presence or absence of a ceiling. When the forklift is outdoors, and no ceiling is detected, the machine can move at its maximum allowable speed. When the forklift moves indoors and a ceiling is present, the maximum speed can be automatically reduced to enhance safety and prevent damage (Figure 5).

Figure 6: Radar sensors can be used to monitor for people or objects around a forklift and for the presence or absence of a ceiling. (Image source: Banner Engineering)

Depending on the system needs, there are several Q90R models to choose from with different output configurations, including:

• Q90R-4040-6KDQ with dual discrete NPN/PNP, PFM, and an IO-Link output
• Q90R-4040-6KIQ with an analog current (4 to 20 mA), 1 NPN/PNP discrete, and an IO-Link output
• Q90R-4040-6KUQ with an analog voltage (0 to 10 V or 0.5 to 4.5 V), 1 NPN/PNP discrete, and an IO-Link output

Conclusion

Q90R series radar sensors are highly versatile. Their 60 GHz operating frequency enables them to detect various materials. With a range of up to 20 m and configurable beam patterns, these FMCW radars can support a variety of applications. They are available with several output options to support different system needs and can be mounted on vehicles like forklifts or placed at strategic fixed locations such as adjacent to loading docks. Finally, designers can turn to Banner’s Measurement Sensor Software to speed system design and deployment.