This patent was edited for publication by Maurice Jones
Technical illustrations by Nick Stenning
Abstract
The invention relates to a crane installation for load moving, typically a container crane as used in ports, berths and railyards. The crane includes a programmable control unit, which, if required, receives signals from a safety-related control command to one or more electric or electro-mechanical operational elements. There is a second stored-programmable control unit configured so that it can monitor, at least partially, the operation of the first control unit based on safety-related signals transmitted to the second control unit. If these signals are improper the second control unit is able to issue its own over-riding control command to an operational element.
Background technology
Crane installations referred to in the patent are typically for container handling of typical sizes between 20 and 45ft as standard (6.10-13.72m) in which the crane loads and unloads ships, freight cars, trucks, etc. Such a crane normally has a trolley for horizontal load movement over the means of long-distance transport. From this trolley there is a load carrying device, for example, a container spreader, suspended to grab the load and move it vertically and/or hold it during horizontal movement. Loads are typically of several tons.
Figure 1: Typical crane installation
Personnel operating or working around the crane can be in hazardous situations near crane and/or load movement, so therefore the crane is equipped with safety features by which a stored-programmable control unit (as mentioned above) is able to shut down crane operation. Typical situations are emergency shutdown, emergency halt, emergency limit-switch supervision, pre-limit switch supervision, overload and slack rope hoist supervision, overload or slack rope luffing gear supervision, overspeed supervision and collision prevention.
According to the inventors, prior arrangements for these control systems have drawbacks and shortcomings relating, for example, to manufacturing techniques or in the case that the desired effect may not always be realised. The described development is intended to improve the crane installation and obviate the shortcomings of prior art.
Crane installation
In Fig 1 a typical crane installation is shown for which the invention is designed. The crane (1, typically a container crane) can move along a quay wall (3) in the longitudinal direction of the cargo transport (ship, 2). The crane installation includes a crane base (4) to support the boom (5). A trolley (6) is mounted on the boom to travel along it (double arrow A), and carries, in this case, a container spreader (8) by hoist ropes (7) to handle a container (9). B shows the trolley hoist movement.
The installation is controlled by the first stored-program (SPS) control unit (10) by issuing commands to operating elements. It also receives signals from the operating elements or other monitoring components to offer double communication (C). A second SPS control unit (11) is in bidirectional communication (D) with the first control unit to monitor its operation and to execute a safety-relevant control command to an operating element in the absence of a proper command from the first control unit. On receiving a safety-relevant signal from an operating element it can issue a control command (E) to control or shut down the operating element as suitable.
Control circuit
Fig 2 is a block diagram showing the basic mode of operation of the control units. The second control units receives only safety-relevant signals pertinent to recognising emergency situations, and possible execution of safety commands. It is not intended for general control functions, but is provided to monitor the first control unit for safety reasons. This provides a higher degree of safety because, say the inventors, the proper control command is ensured in any situation.
Figure 2: Basic mode of operation of control units
The two control units can also be configured to effect a delay in issuing a control command, allowing the first and second control units to operate with different cycle times. Thus the second control unit can operate at a faster cycle time than the first unit, so leading in response time when recognising a safety-relevant shutdown situation. Thus an improper control command from the first unit is inconsequential due to its longer operational cycle time. Thus the relevant operational unit receives the signal from the second control unit as the delay in the first unit is long enough to prevent improper intervention by this unit.
Another functional feature of the invention is that the first control unit can be constructed to execute a plausibility check of a signal transmitted to the second control unit on the basis of a signal received. In this way whilst the first control unit is monitored by the second control unit, the second unit is also monitored by the first. Thus there is verification whether the safety-relevant signals for the second control unit are plausible and congruent with the signals received by the first control unit, forming a base for the first safety unit to possibly detect an emergency shutdown.
To prevent incorrect operation in the case of both control units receiving faulty signals there is another feature. It is possible for both control units to be constructed for processing at least partially different signals resulting in generation of the same control command. Thus a possible safety-relevant situation is detected at least partially on the basis of different signals to the two control units. The second control unit receives the actual switch signals. The second control unit can detect a faulty signal from the pre-limit switch to the first control unit, such as its issuance before the trolley passes the switch. The second unit could issue a control command but the first control unit recognises that the signal is not plausible. It is also possible to construct the system for a plausibility check to test the signal transmitted by the operating element to the second control unit and to generate output of an error message. This may involve the use of a tolerance range about the signaling point to indicate a fault, which, in the case of an error of the pre-limit switch, can be displayed to the crane operator to indicate a possible switch defect. Safety can be further enhanced by checking the control units by constructing each for simulation of a signal that triggers a control command, and for checking a response time. Thus detecting possible defects in the control units.
Operational example
As an example of the system’s operation, shown in Fig 2, a pre-limit switch (15) at the free-end of the boom is being supervised. As the trolley passes the pre-limit switch in travelling to the free end, the first control unit decreases the speed by a predetermined amount. A displacement sensor on the trolley includes an angle encoder (12) to continuously transmits a displacement signal (S1) to the first control unit (10). This shows to the control unit when the trolley has passed the pre-limit switch. The control unit then instructs the operating element (converter 13 to operate motor 14 on the trolley travelling gear) to decrease the speed.
The second control unit (11) monitors the first control unit (shown by D) for proper operation in receiving the actual pre-limit switch signal (E). As long as signal E is present, the trolley is ahead of the pre-limit switch. When this switch opens the signal is no longer present. In addition control unit 11 receives the displacement signal S2 from a pulse generator (16), so that control unit 11 can determine the speed of the trolley. Thus the second control unit can check whether or not the first control unit (10) has properly decreased the speed of the trolley. If it has, control unit 11 does not intervene.
If the first control unit fails to decrease the trolley speed by some sort of faulty operation, control unit 11 recognises the error and intervenes (dashed arrow) and sending a proper signal to the converter.
The first and second control units can also communicate bidirectionally with one another by direct data exchange, further enhancing the plausibility check of the signals (S1) for the second control unit. Thus it is possible for the first control unit to cyclically query the required data or signals from the second unit. The second control unit can continuously and cyclically transmit required data to the first control unit without interrogation. Suitable cycle times for the first control’s cyclical plausibility check, depending on its general work cycle, range between 10ms and 80ms (typically 40ms).
If control unit 10 shows by a check of signal S1 that the pre-limit switch 15 has been passed it also checks that signal E=0, indicating that the signal is no longer present at control unit 11 and the pre-limit switch is open. Control unit 10 also checks whether displacement signal S2 corresponds to signal S1 or to the actual trolley speed. If so, control unit 10 recognises the transmission of proper signals to control unit 11 to realise that both are receiving the same information for a proper control decision.
About the patent
This article is an edited version of US Patent 7,308,337 B2 published on December 11 2007 from an application filed January 25 2007. The inventors are Ernst Sparenborg (of Delmenhorst), Jorg Meyer (Bremen) and Uwe Meyer (Elsdorf), all of Germany. The patent is assigned to the Siemens Aktiengesellschaft of Munich and is based on an earlier German patent 102 33 873 of July 25 2002.
Marketing
Siemens AG manufactures and installs a wide range of crane systems including crane drive technology and controls for every industry sector. Production facilities are located in Germany and the Netherlands. For more information including catalog and on-line ordering see the website at www.automation.siemens.com/mc/cranes.
Disclaimer
As an edited version of the original patent, this article may omit legally or technically important text.
