AUTOMATIC APPLICATIONS1 February 1999
Stephan Bekel explains how and why automated crane systems are moving into new areas of application
Automated crane systems are not just useful for the safe preservation of materials or for working in dangerous or polluted environments. Effective use of personnel, maximum precision and the ability to reproduce operation sequences are also all good reasons for having automatic cranes.
Automated suspension and overhead travelling cranes as we now know them were not possible until the advent of adequate computer capacities in the early to mid 1980s, when miniaturised computers became state of the art. Parallel to this development, the first serviceable and economical stored-program controllers (SPC) appeared. But it is not just the advent of these electronic “wonder boxes” that has allowed automatic cranes to develop.
Automatic crane systems have actually existed since the turn of the century when the first overhead travelling and suspension cranes, typically still rivetted, were used. Interconnected contactors acted as the first semi-automatic control – a target control. Modern automatic crane controls independently measure the path travelled, or, via onboard laser measuring systems, feed the control computer with information and data, for example on the load distribution in the operating range of the crane. The computer then calculates the positions to be approached. Automatic cranes thus are not strictly “artificial intelligence”, but they are developing into partially adaptive material flow components which can be integrated into complex processes and systems.
Electric monorail systems, mainly used in the automobile industry, must be regarded as the “fathers” of modern automatic cranes. On the basis of their sequence of motions and the integration of track switch controls and also possibly hoists, electric trolleys (remote controlled by a computer and equipped with various load attachment devices) were effectively small automatic crane systems, even if they only operated in two dimensions.
The German materials handling manufacturer R Stahl Fördertechnik gained its first experiences with small automatic conveying systems at the end of the 1970s. They were based on monorail trolleys and special rail profiles. Increasingly, customer enquiries were translated into cranes which in the 1990s have been monitored by modern SPC and process controls.
Anyone investing in expensive and complex automatic material handling equipment wants to accelerate processes, shorten cycles, approach fixed points more accurately, or economise on or transfer personnel to other departments. Coordinating manufacturing processes too can be achieved on a previously unknown level by using automatic cranes. By taking up loads more accurately, setting them down to the millimetre, or transporting them diagonally over great distances, products can be manufactured faster and better and with lower unit costs.
Stahl has been devoting attention to crane automation since the mid 1980s. Parallel to this development the company’s own electronic components, such as the WCS position encoding system or SLB conductor line bus, have come into being. These are used for automating cross and long travel, for load attachment devices and also for machines working in conjunction with the crane. With the aid of the POS1 positioning control, a crane can now be automated to approach preselected positions without the necessity for an expensive and complex SPC.
One of the largest automatic cranes yet manufactured by Stahl is a double girder overhead travelling crane with 22.4m span and an 8t safe working load. This crane, equipped with a 3.2m3 clamshell grab, is used in the plaster industry. A particular feature of this crane, offering a long travel speed of up to 120m/min (40m/min cross travel speed, 32m/min hoisting speed) is the laser scanning, linked with the crane control, of the surface of the bulk material, which of course changes with each cycle. This feature redefines for each grab charge all parameters for long and cross travel and for lowering the load attachment device.
Automatic cranes are establishing themselves in other branches of industry too. Recently, the aluminium processor Alcan reorganised production in its Göttingen factory and needed two semi-automated double girder overhead travelling cranes, each with 16t SWL and 6m span, one of which is to function fully automatically in the near future. These cranes, integrated into the production process, transport coils of up to 10t in weight. For example, aluminium coils must be taken up from AGVs and loaded into machining apparatus. This process of removal and loading is now to become fully automatic. The cranes, equipped with an electrohydraulically driven (adjustment and rotation) coil grab have a 4/2-1 reeved hoist of the AS 7080 type. The cranes are controlled by a Siemens S5 SPC, in addition WCS2 and SMC1 electronic components from the Stahltronic programme are fitted. These cranes and a further 16t EOT crane with 24.5m span are equipped with an electronic oscillation damping system.
The crane requirement of the hazardous waste recycling company F Plump GmbH in Bremen was very different. A 5t and a 10t double girder EOT with 7.26m and 11.7m spans have been in use since 1997. They remove hazardous waste, both sludge and solids, from 10 bunkers.
In this application, the stopping positions are automatically controlled with the aid of WCS2 components and special incremental encoders for the hoist position. The operator monitors the loading and unloading procedure from a cabin mounted close to the crane system and can intervene if necessary. Here too, the electronic components receive their commands from a Siemens SPC.
A completely different application can be seen in the Broschek printing house in Hamburg. Here, supersensitive impression cylinders for large-format, multicolour magazines and brochures must pass through numerous treatment and coating stations before being loaded into the photogravure presses.
A monorail system with a powered monorail trolley, fitted with an AS 2010 hoist of 4t SWL, handles the impression cylinders, up to 3t in weight and 3.6m in length, which must be transported to the printing press after engraving and coating. The use of suspension or overhead travelling cranes was prohibited by conditions in the plant. A monorail runway was chosen instead, similar to the overhead conveyors common in the automobile industry. The 80m-long monorail runway with a main link section and six spur runways consists of Stahl’s reinforced KT 2000 small crane profile. Using turntables and push-type track switches, complex runway layouts can be achieved. Special suspensions conduct the forces from trolley and hoist, load attachment device and load into the runway rails. Thus an SWL for the trolley of 4t is possible.
The next step in this system which is constantly being extended, will be the fully automatic take-up of the load from a special handling device which removes the impression cylinders from the coating baths and places them ready for onward transport. Before the cylinder is taken up by the trolley, a code number is transmitted. This defines the type and geometry of the relevant cylinder. The central control monitors the positions and destinations of all the cylinders.
Before the load is taken up, the grab is extended to the corresponding dimensions by an electromotor (spindle drive principle), then takes up the cylinder fully automatically and transports it to the engraving machines. The most important criterion for the customer was that the supersensitive impression cylinders be transported overhead, safely, more simply, and with no risk of confusion.
The term “automatic” says it all. In the case of automatic cranes the crane operator is no longer the sole element determining the sequence of operations. This is stored in one or more controls which function without human intervention. Semi- or fully-automatic operation naturally involves risk for people working within the range of operation of the crane, thus for this type of system more stringent safety precautions are in force than for conventional manned cranes.
In Germany Accident Prevention Regulations VBG 8, 9 (Cranes) and 9a (Load Attachment Devices), DIN 15018 and other regulations specify the dimensioning of crane and crane runway and the electrical and electronic protection of the area of operation of the crane.
Since January 1995 the European Union machinery directives have also applied. A basic distinction is made between a closed room in which the crane operates, and a freely accessible working area.
This determines what safety elements must be installed to react if anyone enters the range of operation of the crane and immediately halt the crane or the relevant crane motion. Light barriers, motion sensors, door contact switches, infrared switches, switching mats and cord pulls for emergency stop and other devices can be considered.
The greatest danger normally arises from the actual crane motion (bumping, crushing, jamming etc.). Further danger may arise from falling loads. To prevent this, primarily positive-locked rather than friction-locked load attachment devices are used, so that in many cases bracing or grating to prevent loads from falling can be dispensed with.
Where working areas, transport paths or manually operated storage zones are crossed by the automatic crane, protective grating or other precautions must safeguard people in the working area. All approaches to the area of operation must be secured by sensors and switches. If operators or other people are regularly in the vicinity, guard hoops, safety lines and optical spacer devices (infrared sensors) must prevent any collision.
Automatic cranes link, transport, connect and handle complex loads, relieve strain on personnel and are able, combined with laser scanning for example, to load and unload bulk material fully automatically. The continuing reductions in costs for controls, and the easy and economical combination of the crane with special positioning, position encoding and data transfer systems, will make them more attractive for small and medium-sized companies. Existing crane systems can also be semi- or fully-automated by retrofitting with external automation components.