Torque sensors help make human/robot collaborations safer for workers

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By Daniel Pintar, Senior Manager of Strategy and Business Development in Robotics and Motion, TE Connectivity

As companies continue their pursuit to increase efficiency and profitability, the use of robotics, advanced automation and control systems is becoming much more common.

Overall, the use of industrial robots in factories around the world is accelerating at a high rate: 126 robots per 10,000 employees is the new average of global robot density in manufacturing industries – nearly double the number from five years ago, according to the 2021 World Robot Report from the International Federation of Robotics (IFR).

In countries that were early-adopters of robotics, the rates are much higher. According to the World Robot Report, the Republic of Korea has installed 932 robots per 10,000 employees, while Singapore boasts a rate of 605 and Japan a rate of 390. Germany is fourth highest with a rate of 371, followed by Sweden at 289, Hong Kong at 275, and the United States at 255.

With robot density skyrocketing worldwide, collaborative robots (or cobots) are an easy entry point for bringing robotic solutions into smaller and mid-size companies. Cobots are typically lighter, simpler, and more mobile than heavy-duty industrial robots, and are used on production or assembly lines alongside humans.

Unlike standalone automated equipment with little to no human interaction, cobots are designed to interact with and assist workers. Cobots assist with product assembly, help with visual parts inspection, and perform tasks like material handling, machine tending, assembly, welding, and polishing. Historically, however, there were safety concerns for workers. As a result, cobot/human interaction was limited.

Cobots Offer Flexibility

Today, cobots offer much greater flexibility on the factory floor. Protective cages are no longer needed for safety purposes and cobots have been developed to work seamlessly with humans. Now, they can perform tasks together that neither humans nor robots could do on their own just a few years ago. This flexibility helps increase return on investment (ROI) due to increased productivity and reduced labor costs.

Cobots can also handle complex or unpleasant tasks that humans either cannot complete or cannot perform in extreme conditions. For example, cobots have the capability to perform with utmost precision in applications for chemicals, pharmaceuticals or medical equipment. For health and safety improvement, cobots can even operate in environments that are dangerous, excessively hot or cold or wet, which are considered as unpleasant for human workers.

Safety Evolves with Torque Sensors

As we further develop and expand safety requirements for cobots, we are also integrating the technologies to help monitor and control cobots. One example of this from TE Connectivity (TE) is a torque sensor that monitors the mechanical torque in a variety of the rotational pivot points on a cobot. Our torque sensor is based on an integrated load cell that can translate mechanical torque to a digital output signal that is proportional to the torque applied.

When torque sensors are used in cobots, they can detect conditions where the torque level is high enough that it could potentially harm the human or damage the cobot that are working together.

Safety torque sensors are typically integrated into the joint units of the cobot. The joint unit is a complete system and often includes one or more angular sensors, as well as a motor and gear box. The joint unit drives the movement of each arm of the robot while the torque sensor is used to sense torque within the motor and gear box. The level of torque is used by the control circuitry to shut down the joint to prevent harm to the arm itself, or, if being used collaboratively, the corresponding worker.

We are now seeing an industry shift from using power-limiting systems in robots to using the more beneficial torque sensors, which allow for a faster response time and improved accuracy. Torque sensors lead to safer and more reliable robotic systems as well as increased worker safety.

TE safety torque sensors have been designed to provide accurate torque data while significantly reducing cross load errors (axial load, radial load, and tilting moment) and can act as a sealing wall in a gear box. To comply with functional safety requirements up to ISO13849 Category 4 PL e, the design is based on a dual-channel system and includes other features to detect any safety-related failure.

Here are five ways TE’s safety torque sensors are improving performance in cobot applications:

1. High functional safety: Designed to meet functional safety requirements up to ISO13849 Category 4 PL e thanks to two electrically segregated channels with no common cause failure.
2. Low susceptibility to cross loads: For use assembled on harmonic drive gear boxes the sensor design is optimized to reduce axial, radial load and tilting moment susceptibility providing increased accuracy.
3. Customizable mechanical interfaces: Low profile sensor with overall height lower than 20mm, easily adapted in terms of size and sensing range to meet customer application requirements.
4. Digital I²C electrical interface: Standard electrical interface is an I²C serial digital interface with 400 kHz communication rate allowing ease of integration.
5. Microfused technology: Microfused technology significantly reduces age-sensitive organic epoxies, used in traditional load cell designs, thus providing long-term span and zero stability.

TE’s safety torque sensor is leading the way to improved safety and reliability in cobots as those machines continue to drive the evolution of Industry 4.0.

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