Mouser - White Papers

Mouser Electronics White Paper Imagine a robotic arm or a computer numerical control (CNC) machine making a critical positioning movement when a power outage occurs. Can the equipment automatically restart when power is restored, or does it lose position awareness when the power is off? If the latter, what is required to restart, rehome, and recalibrate the system with minimal delays and without damage to the workpiece? With electric grids often relying on distributed energy sources, such as wind turbines or photovoltaic arrays, to supplement central nuclear or fossil-fuel power generation, the chances of intermittent outages can increase. As the accuracy and throughput requirements for robots and CNC machines become increasingly stringent, the need for resilient sensing solutions in industrial automation and automotive systems is growing, particularly for those that can tolerate intermittent power outages. A key to such solutions is a power-off-tolerant rotary position sensing approach that offers a variety of system-level advantages. This white paper examines the limitations of traditional rotary position tracking across power-on and power-off cycles in automation, robotics, and automotive systems. It introduces contactless magnetic sensing using giant magnetoresistance (GMR) and anisotropic magnetoresistance (AMR) technologies and details how these technologies are integrated into the Analog Devices ADMT4000 magnetic turn-count and angle sensor, which can record the number of rotations of a magnetic system even while the device is powered down. The paper also discusses magnet design guidelines, highlights system-level advantages, and outlines future trends in multiturn position sensing. ¸ Limitations of Traditional Multiturn Position- Sensing Methods Before investigating a modern approach to power-off- tolerant rotary position sensing, consider first the traditional options for rotary position sensing (Figure 1). A gear-reduction mechanism can interface a multiple-turn input with one or more single-turn sensors. With this approach, an additional single-turn sensor can provide redundancy and improve reliability. However, the mechanical gear assembly incurs size and weight penalties, is subject to mechanical gear wear, and can exhibit mechanical hysteresis and low accuracy. Another approach is to use a single-turn sensor with memory and a backup battery. This contactless approach can provide high accuracy and is more compact than the mechanical gear approach, though still considerable in size. In addition, this approach imposes battery maintenance requirements. A designer may also use a single-turn angle sensor combined with a Wiegand sensor, which can harvest energy from a reversing magnetic field while counting turns. The Wiegand Figure 1: Multiturn encoder incumbent solutions. (Source: Analog Devices)

• Cover