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Advanced Engineering 2021

NEC Birmingham(B40 1NT)

03/11/2021 - 04/11/2021

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IMUs deliver new levels of application flexibility

IMUs deliver new levels of application flexibility

Tri-axis inertial measurement sensors are widely used in car and vehicle applications from driver monitoring to fully autonomous vehicles. Here, Jon Bentley of Mclennan explores some other interesting uses that this technology is being be applied to.

As a well proven six degree of freedom sensor for vehicle motion measurement, tri-axis inertial measure-ment units (IMUs) are available in various packaging and feature styles that include low cost pitch, yaw and roll measurement sensors which might be used from fleet driver evaluation to sophisticated IMUs with integral GPS that can be as part of complete dead reckoning systems for autonomous vehicles.

For single axis vibration measurement over a typical ▒60 to 720 degree/sec range, MEMS gyro sensors provide linearity to 0.2% F.S. More sophisticated products meet the needs of measurement of attitude and three-dimensional motion for vehicles and mobile machines. Available as a low cost PCB or as a housed IMU, they are equipped with vehicular standard MEMS gyro sensors and feature outputs for tri-axial angular velocity, acceleration, and angles and is supported by stable thermal behaviour and reproducibility. With I/O interfacing for CAN, RS232C, and USB it incorporates digital input command to be composite with external information such as vehicle speed.

These IMUs can be equipped with extended functions including a Bluetooth communication board, a GPS receiver board and a battery pack. Units are supplied with data logging software. Other versions can include completely packaged IMUs in waterproof and dustproof cases as well as software, evaluation units and a full complement of accessories.

As IMUs include both gyro and accelerometer sensors they can provide certain advantages and may be used effectively for industrial and other application areas where complete orientation feedback and movement can be used to enhance performance, improve productivity, increase safety and even aid recovery in medical rehabilitation. So let’s look at some potential uses:

Robot arm control: In this example an IMU is used to detect the amount of deflection in terms of position and velocity for a robot end effector. This information may be used to optimise the dynamic performance of an assembly robot during set-up or in-situ by automatically adjusting some or all of the axes. As the position element is essentially in all six degrees of freedom, the precision of the adjustment is potentially higher than just relying on torque demand from servo feedback. The IMU is this case can help improve quality control and even speed throughput on the assembly line.

Positioning tool for a torque wrench: In this example the torque wrench is fitted with an IMU and set up to sense its exact position in space. The control system then adjusts the torque output for each individual location so that large machine assembly might be carried with increased safety and speed.

Detection of abnormal vibration of machine tools: In this example on a stamping machine the IMU’s gyro can detect abnormal micro-vibration more effectively than individual accelerometers because the vibration of materials cut by machine tools is often accompanied by rotational motion. As abnormal vibration is often a first indication of machine failure, this could improve the availability of the machine through enhanced preventive maintenance which is a requisite of Industry 4.0.

Overhead traveling cranes: In crane safety, an IMU fitted to the crane hook can provide superior X-Y axis deflection sensing than camera systems by directly detecting angular velocity and acceleration. In other types of crane application such as marine loading cranes the IMU could be used to compensate for heave.

Measurement of inclination of construction and agricultural machinery: The IMU is capable of accurately measuring the inclination of a heavy mobile machine even under extreme vibration conditions, because the inclination is measured by both accelerometer and gyro sensors. The IMU is also suitable for attitude measurement of up to 0.1 degrees for heavy construction vehicles as well as MEMS-based dead reckoning systems for autonomous guiding of agricultural vehicles.

Monitoring of movement for rehabilitation: IMUs can bring several benefits to rehabilitation with precise measurement of movement available for tracking a patient’s progress. With six degrees of freedom measurement available, complete data including acceleration, angular velocity and attitude angles forms a fundamental part of a rehabilitation when used with appropriate software.

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