TECHNICAL FIELD

The invention relates to a method, system and a computer program product for controlling braking of a machine mounted for movement on rails, which machine is provided with me- chanical wheel brakes, electric drive motors for rotating the wheels and a control system for braking.

TECHNICAL BACKGROUND International Standard IEC 61800 is relating to properties of adjustable speed electrical power drive systems, thus in ^¬ cluding rail mounted gantry cranes (RMG) , automatic stacking cranes (ASC) , ship-to-shore cranes (STS) , quay cranes and trolleys used in said cranes. Particularly in the part 5-2 of said Standard are defined the functional safety require ^¬ ments for said drive systems. In the International Standard IEC 61800-5-2 the stop and brake functions of the adjustable speed electrical power drive systems are defined and divided in categories as follows:

- Stop category 0: An uncontrolled stop in which the stopping is performed by immediate removal of power to the hoisting machine actuators.

- Stop category 1: A controlled stop with power available to the hoisting machine actuators. When the stop is achieved power is removed from the actuators.

- Stop category 2: A controlled stop with power left available to the hoisting machine actuators. In stop categories 1 and 2 the braking and stop of the crane and/or trolley will happen in a controlled manner without any major problems. Problems will occur especially in stop category 0 braking which in fact is an emergency braking. This kind of situation happens e.g. when a person is detect ^¬ ed in the operating range of an automatic stacking crane (ASC) , whereby all operations of the crane are stopped imme ^¬ diately. In this type of braking a mechanical brake is switched on, said brake being always on with a constant torque. Normally the mechanical brake would be used only as a parking brake. Even though this type of braking is not happening according to a normal operating mode, in some circumstances it may occur frequently, e.g. ten times a day.

So a crane or a trolley is a machine running on rails the wheels of which machine will be locked and sliding on the rails during stop category 0 braking. The sliding of the wheels causes wheel damaging. When the wheels are sliding on the rails extremely high temperatures are formed to small areas on wheel surface causing martensitic reaction which weakens the wheel strength. Due to this phenomen the wheel surface may in worst cases come off, at least partially. Better materials for wheels as well as other mechanical so- lutions have been searched and examined but current solu ^¬ tions and materials have been found best available at least at the moment .

One prior art braking system is disclosed in U.S. Patent No. 5,573,312. This document discloses a vehicle having an elec ^¬ tric and mechanical braking system with which a braking wheel can be rotated by a motor. The mechanical brake of this system, however, is dynamic so that it does not provide a constant but variable torque. Also the vehicle itself is of a type different from the inventive one and it cannot be seen that this prior art system could be applicable in RMG cranes, especially in ASC cranes.

SUMMARY

The objective of the present invention is to provide a novel and improved method, system and a computer program product for controlling braking of a rail mounted gantry crane. To this end the inventive method is mainly characterized in that it comprises the steps of:

- monitoring the movement and operations of the machine to detect whether a stop command shall be activated to stop the machine immediately,

- switching-on the mechanical wheel brakes to stop the ma ^¬ chine if the stop command is activated, and

- activating the electric drive motors of the machine sim- ultaneously with the switching-on of the mechanical wheel brakes to rotate the wheels and prevent locking and slid ^¬ ing of wheels on the rails if movement of the machine is detected at the moment of the activation of the stop com ^¬ mand .

In one embodiment of the method, it comprises monitoring the stopping of the machine and deactivating the electric drive motors of the machine when the machine is standing still. In a further embodiment of the method, it comprises program ^¬ ming a safety time gap in the control system for braking, said time gap being calculated from the activation of the stop command, and deactivating the electric drive motors the machine after said safety time gap regardless of stopping state of the machine.

The inventive system is mainly characterized in that it com ^¬ prises :

- means for monitoring the movement and operations of the machine to detect whether a stop command shall be activat ^¬ ed to stop the crane immediately,

- means for switching-on the mechanical wheel brakes to stop the machine if the stop command is activated, and

- means for activating the electric drive motors of the machine simultaneously with the switching-on of the me ^¬ chanical wheel brakes to rotate the wheels and prevent locking and sliding of wheels on the rails if movement of the machine is detected at the moment of the activation of the stop command.

According to one embodiment of the system the means for mon ^¬ itoring the movement and operations of the machine is ar ^¬ ranged to monitor the stopping of the machine and deactivate the electric drive motors of the machine when the machine is standing still.

According to another embodiment of the system a safety time gap is programmed in the control system for braking, which time gap is calculated from the activation of the stop com ^¬ mand, whereby the electric drive motors of the machine are deactivated after said safety time gap regardless of the stopping state of the machine.

The inventive computer program product comprises a com- puterreadable medium bearing a computer program code embodied therein for use with a computer, and it is mainly characterized in that the computer program code comprises:

- code for monitoring the movement and operations of the machine to detect whether a stop command shall be activat ^¬ ed to stop the crane immediately,

- code for switching-on the mechanical wheel brakes to stop the machine if the stop command is activated, and

- code for activating the electric drive motors of the ma- chine simultaneously with the switching-on of the mechani ^¬ cal wheel brakes to rotate the wheels and prevent locking and sliding of wheels on the rails if movement of the ma ^¬ chine is detected at the moment of the activation of the stop command.

According to one aspect the computer program code further comprises code for monitoring the stopping of the machine and deactivating the electric drive motors of the machine when the machine is standing still.

According to another aspect the computer program code further comprises code for programming a safety time gap in the control system for braking, said time gap being calculated from the activation of the stop command, and code for deac- tivating the electric drive motors of the machine after said safety time gap regardless of the stopping state of the ma ^¬ chine .

The term "machine" used in the claims is intended to cover all types of cranes mounted for movement on rails and trol ^¬ leys used in cranes. Because the invention is also applica ^¬ ble in railway apparatuses and equipment provided with me- chanical wheel brakes and electric drive motors, said term "machine" covers this kind of apparatuses and equipment al ^¬ so . The present invention provides considerable advantages over prior art. The inventive system is a drive assisted braking system (DAB) by which the wheels of the machine, such as a crane or trolley are kept rotating during mechanical braking thus reducing the heating of the wheels and preventing wheel damaging.

Other advantages and characteristic features of the inven ^¬ tion are set out below by detailed disclosure of the inven ^¬ tion, wherein the invention is described with reference to the figures of the accompanying drawing, to the details of which the invention is not exclusively limited.

BRIEF DESCRIPTION OF THE FIGURES Fig. 1 shows schematically the timing diagram for the acti ^¬ vating function of the braking control system when the gantry crane is moving when the stop command is given.

Fig. 2 shows schematically the timing diagram for the acti- vating function of the braking control system when the gantry crane is stopped when the stop command is given.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As already explained earlier the present invention is di- rected to handle and solve the problems relating to the sit- uation in which during normal driving, e.g. when the gantry crane is moved from one position to another the crane and/or the trolley must be stopped immediately. This kind of situa ^¬ tion occurs e.g. when a person is detected in the operating range of an automatic stacking crane (ASC) , whereby all op- erations of the crane are stopped immediately. The crane is then stopped by switching on the mechanical brakes. To pre ^¬ vent sliding during mechanical braking rotation of the wheels is assisted with the drive motors of the crane. In practice this means that the stopping ramp for a wheel axle is activated at the same time as the mechanical brakes are applied. So the inventive system and method are purely pre ^¬ senting a computer program product and a programmable way to control the rotation of the crane wheels. The program is running in the PLC of the gantry crane in which the control system of the crane is running.

The stopping ramp for the wheel axle is slightly shorter than the stopping ramp achieved with pure mechanical brak ^¬ ing. The reason for this is the fact that so the drive mo- tors will not try to extend the stopping distance. This might cause further some sliding of the wheels but even in that case the wheels will not lock to one position for a long time. This prevents extensive heat accumulation to one small area on the wheel and consequently prevents the mar- tensitic reaction on the wheel surface.

Now, referring to Figs. 1 and 2 the activating function of the system is explained in a more detailed manner. The drive assisted braking function (DAB function) is activated only if the gantry crane is moving at the moment when the Stop command is activated. This situation is illustrated by Fig. 1. When the gantry crane is standing still the DAB function is not activated. This is illustrated by Fig. 2. In the case when the DAB function is not activated, Axis enable, Infeed unit enable and Control voltage are cut down immediately. With the term "Infeed unit" is preferably meant a semicon- ductor component which generally is able to feed energy. This is shown in Fig. 2. In case that the gantry crane is moving at the moment of Stop command, Axis and Infeed unit enable as well as Control voltage are kept active as long as the gantry crane is stopping. Gantry crane stopping is moni- tored and if any difference is noticed the DAB function is deactivated immediately and stopping is continued with me ^¬ chanical brakes of the gantry crane. Also a safety time gap after which the DAB function is deactivated regardless of stopping state is included in the system. In Fig. 1 said safety time gap is set to 10 seconds. It is however obvious that the safety time gap can be set shorter or longer if needed .

The invention has been described above by way of examples and with reference to the figures of the accompanying draw ^¬ ing. Even though the present invention has above been described more closely in connection with rail mounted cranes, it is to be understood that the invention is applicable in all types of cranes mounted for movement on rails and in trolleys used in cranes. Therefore the invention is not lim ^¬ ited merely to the examples illustrated in the figures; in ^¬ stead, different embodiments of the invention may vary with ^¬ in the scope of the inventive idea defined in the accompany ^¬ ing claims.