FEATURE Robotics


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Multiturn position sensor for robotic applications


By Stephen Bradshaw, Product Applications Engineer, Christian Nau, Product Marketing Manager, and Enda Nicholl, Strategic Marketing Manager, all at Analog Devices


M


odern factories are becoming more dependent on robots and cobots to reduce their cycle times,


increase factory throughput and improve effi ciency. One of the major costs and ineffi ciencies associated with standard robots, cobots and other automated assembly equipment is the resulting downtime required for rehoming and intialising power-up following a sudden loss of power during operation. Although this issue can be solved with backup batteries, memory and single-turn sensors, they have limitations. Battery packs have a limited life span and require regular maintenance and replacement. In environments where there’s risk of explosion, the maximum energy that can be stored in the battery pack is limited, leading to more frequent replacements. Wiegand wire energy-harvesting modules are an alternative to battery backup. They use specially-treated wires, where the magnetic coercivity of the outer shell is much higher than that of the inner core. These diff erences create voltage spikes at the device output when a magnetic fi eld is rotated. The spikes can be used to power external circuitry and record the number of turns.


Multiturn sensor technology At the core of the magnetic multiturn sensor is a spiral of giant magneto- resistance (GMR) material, made up of multiple nanowires of GMR elements. The sensor’s operation is based on shape anisotropy and the generation of walls in a domain wall generator in the presence of an external magnetic fi eld. As the external magnetic fi eld rotates, the domain walls propagate through the narrow spiral tracks (nanowires) attached to generator. As the domain walls move through the spiral leg structures, the state of each spiral leg element changes. The state of each element can be determined by measuring


16 November 2023 | Automation


The ADMT4000 in a robot/cobot application


its resistance. The sensor relies only on the external magnetic fi eld, and no additional back-up power or energy-harvesting technique is needed. When power is reapplied to the sensor, a reading of the turn-count state is immediately available.


Suitable solution ADMT4000 from Analog Devices (ADI) combines a GMR multiturn sensor with a highly-accurate AMR angle sensor and signal-conditioning IC, to provide a solution that records 46 turns or 16,560° of movement with a typical accuracy of ±0.25°.


The integrated signal-conditioning IC enables further system enhancements to support harmonic calibration, which removes errors due to magnetic and mechanical tolerances from the application. The ADMT4000 provides absolute 46-turn (0° to 16,560°) digital output via an SPI or SENT interface. The ADMT4000 is positioned opposite a dipole magnet mounted on the rotating shaft. ADMT4000 capabilities are useful in many industrial applications, including robot and cobot arm joint position


tracking in the event of a power outage or powerdown. Other applications include the absolute and true power-on tracking (TPO) of x-y tables in industrial automation, machine tools and medical equipment. Rotary to linear applications include turn counting of coils, drums, spools, reels, hoists, winches and lifts when powered, or movement tracking when powered down or during power outages.


Automotive applications also benefi t


from the TPO position sensing provided by ADI’s ADMT4000 in applications such as transmission actuators, electrical power steering and steer-by-wire, parking lock actuators and seat-belt retractors among others.


The size, cost and operating temperature range of the ADMT4000 make it suitable for many applications, including safety- critical tasks in the industrial, avionics and automotive space. Automotive safety-critical applications are compliant to the ISO 26262 standard and a particular automotive safety integrity level (ASIL). The ADMT4000 will be supplied as either ASIL-QM or ASIL-B(D).


automationmagazine.co.uk


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