Safe mobile robots
Dr Martin Kidman of Sick UK describes how the latest safety scanning is enabling human-robot collaboration to go mobile.
Human-robot collaboration is already showing its potential to revolutionise factory automation. Before long we will be used to working with robot ‘assistants’ that not only interact safely with us in stationary applications, but also move around production and logistics environments autonomously.
The safety laser scanner has played a key role in development of this collaboration. For a long time now, safety laser scanners have facilitated more productive manufacturing and supported machine integrators in delivering more compact, robust and versatile machines while ensuring safe working to the required standards. In automated guided vehicles (AGVs), they have enabled safe non-contact detection of personnel and obstructions in the path of moving vehicles, even when they are travelling through complex production layouts.
Safety laser scanners meeting PLd (EN ISO 13849) and SIL2 (IEC 62061) are widely used in both stationary and mobile applications for the non-contact, two-dimensional monitoring of hazardous points and areas, and access points. They can trigger a machine or vehicle to safely slow down or stop as soon as they detect a person, part of a body, or an unexpected obstacle inside the protective field. This prevents people from being put at risk as a result of dangerous machine movements.
Using the time-of-flight measurement principle, a safety laser scanner measures distances around a radius in a horizontal or vertical plane. When integrated with encoders on an AGV, speed can also be measured, so that safe motion control can be implemented and controlled deceleration and accelaration can occur, rather than emergency stopping. Warning fields can also be configured to introduce alarm, slow down, or field-switching signals with respect to the distance of a person or object.
Technology developments in safety laser scanners have delivered greater variation in device size, differing protective field ranges, scanning angles, evaluation scenarios and integration options to enable the precise needs of an application to be met. Increasingly compact and rugged scanning devices have been built into mobile vehicles to enable machine builders to overcome space restrictions in factory or warehouse environments. The use of multiple scanners on vehicles, integrated via safety controllers such as the Sick Flexi Soft, has reduced onboard wiring on AGV’s as well as enabling increased control and diagnostic functions for engineers.
With the help of safety laser scanner technology from Sick, Kuka’s KMR iiwa (intelligent industrial work assistant) is already demonstrating what is possible. The KMR iiwa, combines Kuka’s LBR iiwa lightweight robot with the OmniMove heavy-duty mobile platform. The Sick S300 safety laser scanner provides both a protective function and navigational support in the KMR iiwa, allowing workers to interact directly with the robot, which moves autonomously.
In its production workflow, the KMR iiwa picks boxes containing materials and delivers them to the production line as and when they are needed. New materials are ordered automatically through Kuka’s ERP system and suppliers, then distributed among workstations by the KMR iiwa entirely autonomously. It shares the routes it travels, as well as the shelving areas, with tugger trains and workers.
Sick’s S300 safety laser scanners have proved a compact and rugged partner for the KMR iiwa, when integrated into the design of the OmniMove platform. The S300’s 270° scanning angle ensures all-round surveillance and the scanner’s 16 freely-configurable protective fields allow the platform to adapt to a range of travelling situations and environmental conditions.
The KMR iiwa either moves along defined paths from one specific point to another, or it navigates freely. To achieve autonomous navigation, the Kuka navigation software continually evaluates distance measurements taken by the Sick safety laser scanner and creates a ‘map’ of the environment, determining the KMR iiwa’s position within the coordinates. Fixed objects along the route are interpreted as established reference points, while moving objects are ‘ignored’ and the KMW iiwa is able to avoid objects in its way by itself. In future, mobile systems like the KMR iiwa will also link stages of work in networked production environments, as part of a ‘smart’ Industry 4.0 process.
Further developments in active scanning safety laser scanners are opening up the possibilities for both mobile and stationary applications. The established principle of time-of-flight measurement has a limited number of individual pulses and analog distance evaluation. Now, new scanning technology, which Sick calls safeHDDM (safe High Definition Distance Measurement), provides a high-resolution, digital solution for safety-related time and distance measurement.
The technology is incorporated into the Sick microScan3 safety laser scanner, developed to make it easy for users to optimise workflow efficiency and productivity without compromising the safety of personnel.
The uniquely-developed and patented algorithms used for the safeHDDM use multi-signal evaluation to achieve a level of measurement reliability never before seen in safety scanners. The multi-pulse concept of safeHDDM generates approximately 80,000 individual pulses per scan – compared to some 500 generated with conventional technology. These 80,000 individual pulses are then used to create measured values.
Every single safeHDDM measured ‘value’ is not just composed of a single time-of-flight measurement, but now includes evaluated information from 140 pulses. The digitised echoes are compiled into data packages which overlap during evaluation. This guarantees a significantly more stable time and distance measurement. Additionally, the pulse frequency is not only almost 170 times greater in relation to previous measurement procedures but the laser pulses themselves are also coded by a time delay of a few nanoseconds which is not specific to every scanner.
The sequence is continually regenerated on a constant basis by an integrated random generator. The safeHDDM technology enables highly stable measured values for increased detection reliability; a fourfold reduction in sensitivity to sunlight and ambient light; increased resistance to dust and deposit formation and virtually no mutual interference between devices. This enables a huge increase in availability for machines and vehicles.
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