Advances in Sensing for Robotics Applications

Why sensing matters in robotics

Traditional industrial robots relied mainly on motor current and position feedback. That worked well enough for repetitive, isolated tasks. But in today’s world, where cobots share space with people, humanoids walk on two legs, and robots handle delicate tasks, force and torque sensing has become essential.

Embedding force and torque sensors into robot joints improves control, accuracy, and above all safety. In fact, ISO 10218-1, the international safety standard for industrial robots, typically requires force–torque sensing in cobots and humanoids. Some leading manufacturers now embed torque sensing in every joint. Tesla’s Optimus humanoid robot reportedly carries 14 torque sensors and 18 force sensors, underscoring just how central this technology has become.

There are currently two key technologies for torque measurement in robotics applications:

Strain-Gauge Sensors

This is the conventional method for measuring rotating torque by using a strain gauge attached to a flex plate in the joint of the robot. Changes in strain, because of torque, are recorded as variations in an electrical signal.

Advantages of strain gauges are they are relatively low cost and simple to apply in low volume like a test lab. However, the disadvantages of strain gauges in robotic joints include:

• They require the use of flex structures and four gauges being arranged in a Wheatstone bridge circuit to provide a measurable strain, this compromises the mechanical integrity of the system making the robotic arm less stiff than it could be without the sensors and adds bulk and mass to the joint.
• Strain gauges are typically not robust or resilient to harsh environments, their output is affected by temperature and can degrade over time.
• They are susceptible to interference from background electromagnetic radiation and magnetic fields, limiting their ability to be deeply integrated alongside electric motors in the actuator.

Displacement Sensors

This method typically uses a pair of measurement disks attached at opposite ends of a shaft. The ‘twist angle’ of the shaft is measured from the phase difference between them through an optical or magnetic measurement. This enables torque to be calculated.

The main advantage is the ability to overload the sensor to the maximum load capacity of the “twist shaft”. The disadvantages of this method include:

• Requires a reduced diameter section of the shaft known as a torsion bar to enhance the twist angle (that can be up to several degrees for a length-to-diameter ratio L/D = 5) which can have a negative effect on the mechanical stability of the system.
• Sensitive to temperature.
• Limited dynamic measurement accuracy due to high system hysteresis.
• Requires a larger packaging volume and more components due to the need to measure shaft twist along the torsion bar length.

Both approaches rely on flex or twist within the robot’s joints. This compromises stiffness, performance, and repeatability, all factors that become critical in cobots, humanoids, and advanced medical or warehouse robotics.

A new approach with Surface Acoustic Wave (SAW) sensing

The team at Transense has pioneered and patented an alternative technology that provides an improved way to measure torque, rotation and temperature in a robotic system. It virtually eliminates joint flex, creating a higher performing, more repeatable robot with more compact joints than has been possible before.

Transense SAW technology is, a wireless, passive, non-contact sensing system consisting of two main components:

1. SAW sensing elements called AQP’s, which involve an array of SAW transducers that measure strain in different directions or temperature when excited by an RF electrical signal.
2. Sensor interrogation electronics which use Transense’s proprietary ASIC to create the RF signal to stimulate the SAW transducers and read back their response.

The SAW AQP’s can be mounted onto a shaft or other moving component and, if a rotation of less than 360 degrees is required, it can be hard wired, or if a rotation of more than 360 degrees is required, it can be communicated with across a simple RF coupler, which is essentially a near field antenna system used to transmit the RF signals to and from the sensing elements. The SAW sensing elements are entirely passive and do not require any other power source, working as a passive device reflecting the interrogation signal back to the reader electronics.

The frequency of oscillation of the reflected signal is influenced by physical measurements such as strain or temperature. The interrogation electronics analyses the difference in transmitted and received signal, calculating the value of the physical strain or temperature. Measuring the principal strains caused by torsion on the shaft gives a highly accurate measurement of shaft torque, or the sensing elements can be configured to measure linear forces.

The key advantages of Transense Technologies' SAW sensors are:

• Stiffer joints, no flex required → higher performance and repeatability.
• Immunity to RF and magnetic interference → reliable even when deeply embedded near or even inside motors.
• High sensitivity (+/–400 micro-strain) → accurate measurement with minimal hysteresis.
• Compact packaging → smaller, lighter robot joints.
• Multi-axis sensing → torque, bending loads, and temperature in one sensor.
• Scalable and robust → manufactured using proven industrial processes.

This combination delivers cleaner, more accurate data for control systems, enabling faster, safer, and more precise robot movements.

Beyond torque with touch and tactile sensing

Because SAW sensors can detect extremely small strain levels, they also open new doors for tactile surface sensing. Imagine a humanoid robot not just gripping an object, but sensing pressure across its surface—feeling, adjusting, and reacting like a human hand. That level of sensitivity is now within reach.

Conclusion

The robotics industry is moving quickly from isolated, repetitive machines to intelligent, adaptive systems. Force and torque sensing is at the heart of this transition, underpinning safety, compliance, and performance.

Transense’s SAW technology offers a breakthrough: robust, compact, and highly accurate sensors that remove the compromises of traditional approaches. For cobots, humanoids, and the next generation of robotics, it could be the step change that enables safer, smarter, and more capable machines.

Ryan Maughan, Managing Director, Transense Technologies Plc

Contact our team to discuss how SAW Sensors could enhance your project