TWK has been developing encoders and sensors since 1962. This past year, they’ve highlighted how such components impact safety in automated vehicles and robots.
To protect the environment, people, and machines, AGV and AMR operation requires highly functional sensor technology. Image courtesy of TWK.
Automated guided vehicles (AGVs) and automated mobile robots (AMRs) require several measurements to operate safely. Otherwise, they and the entire fleet cannot navigate and move to target locations. The necessary measurements are speed (wheel speed) and steering angle (wheel position). Also, the lift of forks or booms must be known. These variables influence the inclination of the vehicle and, where applicable, the vibrations that occur, especially when driving with a load.
Companies such as TWK supply encoders and sensors that ensure functional safety, including certified sensors for position, speed, inclination, acceleration, and draw-wire linear transducers and accessories. Let’s look at a few examples.
Encoders for speed
Measuring speed ensures that AGVs and AMRs reach certain positions quickly and safely. Speed is measured directly at the wheels, and the speed reduces when the target point approaches. Servo drives with integrated sensors can perform this task; however, in many cases, a separate encoder must be used to protect the environment, people, and machines.
For example, where space is limited, the ultra-compact TRK38/S3 single-turn safety encoder has a diameter and housing length of only 38 mm. With the Fail-Safe-over-EtherCAT interface (FSoE), it claims full SIL2/PLd performance with a resolution of up to 16 bit and speeds up to 15,000 rpm — quickly and safely transmitted to the controller via the safety interface. The speed signal quality has been significantly improved, as the position detection accuracy on the time scale is now approximately 1 µs. This equidistance is essential for precise speed, based on calculating the position difference per time unit.
TWK’s portfolio also includes certified encoders with CANopen Safety or PROFIsafe via PROFInet interface with a safe position and speed signal. With the help of these devices, functionally safe speed detection and monitoring in the most diverse variations make machines and systems safer.
Sensors for position
Particularly in the booming sector of AGVs and AMRs, it is not the usual sensors — encoders for angle and speed measurement — that can be used. More specialized devices of the smallest possible size or devices with special functions or a specially designed communication profile are used here. Above all, they must be functionally safe to eliminate any risk of malfunction. SIL2, PLd, or SIL3 certifications are a prerequisite — sometimes together with UL, ASIL D, or ATEX for potentially explosive environments.
For example, TWK equips its NVx vibration sensors, which are used for condition monitoring, with unique functions and algorithms for signal processing. This makes machine monitoring much easier for the user — especially for AGVs that are always in motion. In addition, draw-wire sensors with an attached encoder measure fork or arm lift by converting the linear stroke into a rotary motion. The SIL2/PLd-certified inclinometers have a gyroscope and provide raw values from six axes of redundant micro-electro-mechanical system (MEMS) sensors and the dynamically corrected tilt angle. The raw signals, especially those from the accelerometers, can be used simultaneously to monitor the vehicle’s condition (oscillations and vibrations) or control the vehicle.
This NVT/S3 PLd vibration sensor consists of an acceleration sensor, controller unit, and output interface PROFIsafe over PROFINET. Image courtesy of TWK.
These are just a few examples of the wide range of compact, safe sensors that can be used for various mobile sensing applications. Whether steering angle, wheel speed, vehicle tilt, or vibration, such quantities must be quickly and reliably recorded and transmitted to the control system’s safety interface.
TWK
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Filed Under: NEWS • PROFILES • EDITORIALS, Warehouse automation, Encoders (rotary) + resolvers, SENSORS
