Industrial/Drone |

Introduction

Today’s smartphone, tablets, and advanced video-game consoles are equipped with MEMS gyroscopes enabling motion sensing and motion tracking that provide a natural user experience. Similar motion detection is also needed in a number of industrial applications such as antenna stabilization, precision agriculture, machine automation, and drilling to name a few.

However, in industrial applications these MEMS devices are subject to harsher conditions compared to their consumer counterparts that spend most of their time in living rooms or pockets of cell phone users. Industrial gyroscopes are subjected to higher temperatures, vibration, and shock. There are four basic areas where an industrial gyroscope must outperform a consumer-grade version: temperature range, bias instability, noise, and vibration performance while maintaining small form factor and low cost.

Documentation

Applications

Antenna Stabilization

Keeping SATCOM or radio antennas on a moving object such as a marine vessel, train, or vehicle pointing in the right direction can be difficult. Moving objects can rotate in pitch, yaw and roll quite quickly and the antenna must be constantly pointed in the right direction quickly and accurately. Since gyroscopes measure angular speed the antenna can determine the direction and velocity of vehicle rotation very accurately, allowing the azimuth and elevation servo-loops in the receiver to back this motion off.

Precision Agriculture

The aim is to increase the yield from a farm at the same time as reducing operator fatigue, use less material such as fertilizers, seeds, and chemicals and to extend the hours that the farm can be worked. The gyroscope is combined with GPS data to determine absolute heading. The gyro then maintains the heading between GPS updates and during GPS outages. Gyros are also used to compensate the tilt sensors under dynamic conditions in order to win back the accuracy possible from the GPS. Gyros can be used to measure disturbances introduced by unlevelled ground and to control the boom to reduce resonance.

Automotive

Gyroscopes are a component of Electronic Stability Control (ESC), which works by continuously comparing the vehicle’s actual direction with the driver’s intended direction. ESC interfaces with the ABS to maintain control when the car veers in a sudden direction, a less extreme version is when a car drifts unintentionally into another lane and an alert can be sent to the driver. Navigation and cruise control are other automotive applications that leverage the gyroscope. As noted for other applications, an inertial measurement system can be combined with GPS to get and maintain a more accurate heading.

Machine Automation

During the manufacturing process it is critical that a gyroscope help a mechanical arm maintain the correct inclination and pointing throughout the entire process. This is important in a manufacturing facility where there is a lot of vibration and noise. Accurate automation will cut lead times, increase yields, and decrease the need for user intervention allowing resources to be spent elsewhere. In an assembly line there are many moving parts that a gyroscope helps to align and orient properly to ensure the process works as planned. In shipyards and warehouses loading and unloading equipment must have precise motion control to increase safety and efficiency while moving heavy loads.

Drilling

For borehole survey and drilling instruments gyroscopes are used for navigation and positioning of the drill head. In pipeline inspection applications, the machine must know the correct location and direction in case the pipeline has shifted. When mining for oil or gas directional north must be determined and inertial systems must be used. GPS is not reliable for this application and a magnetometer is sensitive to interferences from magnetic minerals in rocks or a steel pipeline.

Important Parameters

Bias Instability

The bias of a gyroscope is its output in no-rotation mode. Bias instability is how the bias changes over time at a constant temperature and can be difficult to calibrate. The longer a gyroscope operates, the greater its bias error therefore a low bias error is critical for applications that need excellent accuracy over long periods.

Noise

Another important measure of performance is the output noise of the gyroscope. A measure of gyroscope noise performance is known as Angle Random Walk (ARW). There can be a large noise variation among the various industrial gyroscope vendors, so designers typically pay extra attention to this parameter.

Vibration

Vibration performance can be important in many industrial applications. And it can be challenging to ensure a gyroscope performs accurately in the presence of a humming motor or similar noise sources. Vibration can be modeled as noise in the gyroscope output, possibly resulting in inaccuracies that are too large to accommodate. Design considerations, such as aggressive antialias and decimation filtering, can help minimize vibration issues. But the less sensitive the gyroscope is to vibration, the less aggressive these filters need to be.

Cross Axis

Many modern industrial gyroscopes have been restricted to one or two axes. Thus, these discrete sensors have had to be combined when an application calls for three axis sensing. This requires a precise 90° alignment on a PCB. Otherwise, cross axis alignment errors propagate to the final representation of the motion. To minimize the cross-axis errors, developers must implement system-level calibration routines. In contrast, a single-chip three-axis MEMS gyroscope is calibrated during the manufacturing process to cancel out all cross axis errors. This eliminates a calibration step for system integrators.

Temp Range

Industrial applications generally entail a –40 to 105°C temperature range versus the –40 to 85°C range for consumer-grade devices. Performance will degrade as temperatures reach extreme levels and can greatly affect the bias instability, noise, sensitivity, and overall performance.