FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY
Dr Martin Kidman, safety specialist for SICK UK, examines how safety can improve productivity and operating efficiency
A safe way to improve productivity
distances using the time-of-flight measurement principle. Once a safety laser scanner detects an object in the pre-programmed safe protective area, it switches off the OSSDs (Output Signal Switching Devices) which causes the vehicle to stop. Non-safe warning fields can also be defined to detect objects much further ahead of the protective field. The ability to integrate laser scanners
with other sensing technologies can also be a major advantage. In particular, SICK laser scanners can safely measure the speed of a vehicle via inputs from rotary encoders fitted to the vehicle. Based on the speed, the detection field is automatically adjusted. Such advances have enabled more
W
hy is it that manufacturers with the best safety records tend also to
be those with the highest productivity? What drives improvements to employee safety in production environments? Tougher European regulations and standards, litigation and technology improvements all play a part. There is, however, another important reason – safety can help improve productivity and operating efficiency. In the modern factory or warehouse,
automation demands high-speed operation, faster changeovers and minimum downtimes. As safety becomes a true enabler of productivity, the old barriers to productivity are on course to be swept away. Technological advances in the ‘safety
laser scanner’ have helped deliver major advances in the use of Automated Guided Vehicles (AGVs). They have achieved safe, long distance, non- contact detection of personnel in the path of moving vehicles travelling along complex paths and production layouts. The technology has also allowed the AGV to travel faster.
SAFETY The arrangement which underpins all machinery safety control installations follows the sequence typified in the flow diagram and is a basis of the European standards, EN ISO 13849 and EN 62061. Safety laser scanners scan their surroundings in a fan shape and measure
14 DEC/JAN 2016 | DESIGN SOLUTIONS
Even on a small AGV, there may be between two and five laser scanners
controlled deceleration and acceleration of vehicles with the benefit of reduced wear and tear on vehicles caused by harsh braking, as well as increasing the distances covered over time.
ADVANCES Perhaps the most significant advance so far is the close combination of safe speed monitoring (e.g. via encoders) and the use of multiple scan fields. This enables operation to be controlled, slowed down or even brought to a safe stop without the need to reset by a non-critical or planned area intrusion. On AGVs, it is common to define
The arrangement which underpins all machinery safety control installations
three fields to constitute a ‘field set’; one protective and two warning fields (although a SICK S3000 with Flexi Soft can provide up four protective fields in one set). If a pedestrian enters the outer warning field an alarm may be sounded. In the inner warning field the vehicle may decelerate; and only in the protective field would a safe stop be triggered. If appropriate, when the protective field is vacated then after a delay, the AGV can sound an alarm and then automatically restart. Different configurations of field sets
can be easily taught in and switched between to allow, for example, a vehicle to corner and dock safely. Multiple field sets (as many as 32
on the SICK S3000) can be configured to provide high-performance and flexibility for complex vehicle paths as the AGVs turn and change direction to follow their routes. Even on a small AGV, there may be between two and five laser scanners, increasing the complexity of the AGV control system. A significant degree of system design expertise is needed to reach the essential Safety Integrity Level requirements of such machinery. A safety laser scanner is a Type 3 device and can be used in safety-related parts of control systems (SRP/CS) up to PLd/SIL2 as defined by EN ISO 13849 and EN 62061. To reduce wiring, SICK has developed
a package that utilises the power of a Flexi Soft safety controller connected to four laser scanners using a safe bus system called EFi (Enhanced Function interface). This compact system controls all aspects of the scanner via safe protocols for PLd/SIL2 conformance and reduces the requirement for 10 or more core cables to be connected to each scanner. It also makes it possible to have up to 16 protective fields at once with just four scanners. With all signals connected centrally
to the local Flexi Soft controller, the safety function can easily be integrated with the speed and direction control of the AGV by using the Flexi Soft Drive monitor (FX3-MOC) and safe encoders (DFS60S). This concept extends beyond AVGs and can be applied to transfer cars and shuttles as well as complex access control applications where field switching is required.
SICK T: 01727 831121
www.sick.com
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