The Position Sensing Playbook: Choosing the Right Technology for Motion Control

Part 1: The Modern Motion Control Landscape

If you look inside almost any modern automated system—whether it is an articulated collaborative robot arm on a manufacturing line, a steer-by-wire actuator in an electric vehicle, a sub-millimeter surgical robot, or an agile autonomous mobile robot (AMR)—you will find one common denominator: an uncompromising demand for precision motion control.

For decades, the standard recipe for closed-loop motion control was relatively straightforward. You selected a motor, paired it with a standard microcontroller or digital signal processor, placed an optical encoder or discrete magnetic Hall switch on the motor shaft, and called it a day. The control loops were simple, dynamic responsiveness requirements were modest, and packaging constraints were generous enough to accommodate bulky sensor assemblies.

Today, that paradigm is gone.

Modern motion control systems are operating in an entirely new performance envelope. Motor drives are expected to deliver higher torque densities, operate across wider thermal operating envelopes, and eliminate audible resonance and micro-vibrations—all while fitting into tighter, more irregularly shaped physical enclosures. At the heart of this performance leap is the position sensor. Far from being a passive component chosen late in the design cycle, the position sensor has emerged as one of the most critical determinants of overall drive efficiency, dynamic bandwidth, positioning accuracy, and system reliability, resolution.

The Packaging Shift: The "Hollow" Reality

At the same time that electrical requirements are tightening, mechanical architectures are evolving.

In robotics and advanced automotive actuators, power density rules supreme. Engineers are rapidly adopting smaller BLDC motors and integrated drive units (IDUs) to pack maximum torque into the smallest possible axial footprint. In these integrated joints, mechanical real estate is at an absolute premium.

The traditional "end-of-shaft" (on-axis) mounting configuration—where a dipole magnet spins neatly above an IC centered on the rotational axis—is increasingly unavailable especially in robotic applications. Joints frequently require hollow-bore shafts so power and communication lines can pass through the center of the arm without continuous twisting or needing to use slip rings.

When the center of the shaft is occupied, the position sensing solution must move off-axis. Designers are forced to consider through-bore ring magnets, multi-pole magnetic targets, arc segments, or inductive sensor coils printed directly on concentric circuit boards. Each of these mechanical shifts fundamentally alters the sensing physics, bringing challenges like mechanical runout, axial float, and geometric eccentricity to the forefront.

Even when an on-axis mounting configuration can be used, demands are increasing for smaller and higher performance solutions at reduced costs. Use of ferrite magnets for supply chain availability and cost is increasing but, thanks to their lower field strength, often come with increased demands on differential sensing for stray field resiliency.

Hostile Operating Environments

Compounding the electrical and mechanical constraints is the physical environment in which modern actuators must survive. Position sensors are operating closer to high-power electronics and harsh mechanical stress points than ever before:

Stray Magnetic Fields: With the transition to 400 V and 800 V traction systems in electric vehicles and 48 V/100 V in robotics and heavy industrial automation, magnetic fields from neighboring high-current busbars, inverter switching transients ( di/dt d i / d t ), and electromagnetic brakes routinely exceed several millitesla. Traditional unshielded magnetic sensors can register significant false angular displacements unless protected by costly, heavy magnetic shielding or built around differential sensing topologies.

Thermal Extremes and Drift: From in-wheel motors and transmission actuators reaching ambient temperatures above 160C 160 C to sealed robotic joint housings where drive dissipation accumulates, sensors face severe thermal stress. Magnetic-based designs need to consider thermal drift of the sensor as well as the magnet to ensure correct operating range.

Mechanical Tolerances and Bearing Wear: Real-world actuators are imperfect. Bearings possess radial play; gearboxes introduce axial float; dynamic shock loads create tilt and mechanical wobble. A position sensing that performs flawlessly on a rigid bench fixture can quickly fail in production if it cannot accommodate air-gap variation or mechanical eccentricities without requiring complex end-of-line (EOL) calibration.

The Fallacy of the "Universal" Sensor

Faced with these competing constraints, engineers often search for the single "best" position sensor. They scan parametric tables for the highest effective bit-count or the smallest package outline, hoping one solution will fit all requirements across their product roadmap.

In practice, there is no universal winner.

A 3D Hall-effect  sensor may offer unmatched ease of use, small size, and integrated ASIL functional safety diagnostics for actuator positioning, but it may struggle to meet speed requirements for motor commutation.

A high-sensitivity Tunnel Magnetoresistance (TMR) bridge provides exceptional bandwidth and ultra-low noise and power dissipation, making it ideal for high-speed dynamic tracking—yet it still relies on a magnetic target and requires design attention when strong external stray fields are present.

An Inductive Position Sensor (IPS) completely eliminates the magnet, sidestepping stray-field susceptibility and magnetic supply-chain volatility by using inexpensive etched PCB coils and a stamped sheet-metal target—yet it demands careful design of coils tolerance controls.

The challenge is not finding the sensor with the most impressive headline specification; it is identifying the solution whose performance, cost, and design-in efforts align directly with your mechanical envelope, thermal budget, safety goals, and total system Bill-of-Materials (BOM).

Introducing The Position Sensing Playbook

This reality is the driving force behind this blog series.

The Position Sensing Playbook is designed as a practical  guide to navigating motion control sensing options. Over the course of this series, we will unpack the trade-offs, design rules, and principles behind the three dominant technologies shaping motion control today: Hall-Effect, Tunnel Magnetoresistance (TMR), and Inductive Position Sensing (IPS).

We will break down real-world actuator challenges, compare how these technologies behave under mechanical runout and thermal drift, evaluate analog sine/cosine versus integrated digital output architectures, and explore how functional safety standards (ISO 26262 and IEC 61508) shape sensor selection.

Whether you are designing a high-speed traction inverter, a compact medical actuator, or a next-generation multi-axis robotic joint, this playbook provides the technical roadmap needed to choose the right technology for your application.