Presses – Methods
Reexamination Certificate
2001-01-03
2002-11-05
Bray, W. Donald (Department: 3725)
Presses
Methods
C100S280000, C100S282000, C072S020400, C072S021100
Reexamination Certificate
active
06474227
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of controlling synchronous drive of a plurality of pressing machines so that a position of a slide of each of the pressing machines is synchronous each other and a pressing machine usable in such a method.
The present invention also relates to a method of controlling synchronous drive of a plurality of pressing machines so that a position of a slide of each of the pressing machines is synchronous each other with a predetermined phase difference and a pressing machine usable in such a method.
2. Description of the Related Art
It has been attempted to synchronously drive a plurality of pressing machines, for example, with zero phase difference. In such a case, the output of a motor is first transmitted to the flywheel of a pressing machine, the rotational power being then transmitted to the drive shaft of the pressing machine through a clutch. The drive shaft may be in the form of a crankshaft for driving a slide (or ram). Thus, the stamping die of the pressing machine can be driven.
In the conventional phase synchronization, one of the pressing machines is used as a master machine while the other pressing machines are used as slave machines. Such a control is called “master/slave system”.
In the prior art, the master machine controlled the velocity of the motor thereof by comparing the encode output of the motor with reference velocity information and using the difference therebetween so that the motor will be rotated with the reference velocity. In other words, the master machine did not perform the control which is based on the positional information of the crankshaft.
On the other hand, the slave machines compensatively controlled the positions thereof, based on the positional information of the crankshaft in the master machine so that the slave machines will match the master machine in phase. More particularly, an encoder was provided on each of the crankshafts to take the positional information of the rotating crankshafts in the master and slave machines. The motor of each of the slave machines was controlled to cancel the difference between the crankshaft position of the master machine and the crankshaft position of each of the slave machines.
The pressing machines may synchronously be driven with a predetermined phase difference. In this case, the motor in each of the slave machines may be controlled to create a predetermined phase difference between the crankshaft position of the master machine and the crankshaft position of each of the slave machines.
However, it is actually difficult to provide a phase difference between the master and slave machines since the rotational-position information of the master machine depends on the reference position information of the slave machines. In the first place, the prior art did not have the technical concept of phase-difference synchronous operation.
In the synchronous control mentioned above, the motor control in the slave machines will adversely be affected by any disturbance such as a load change characteristic of the master machine due to the energy released from the flywheel of the master machine on pressing. In a pressing machine having an increased load inertia, thus, it is difficult to provide an highly accurate synchronization.
In the prior art, thus, the master machine is in its characteristic driving state while the slave machines must forcibly be matched to the master machine in phase. Even though the synchronization between the master and slave machines is controlled by such a method, excessive load will be exerted to the slave machines when they are controlled in the presence of the disturbance from the master machine. This unnecessarily changes the velocity in each slave machine and degrades the accuracy in synchronization.
When the master and slave machines are to run synchronously, it is preferred that the crankshafts thereof are synchronized in phase immediately after clutch engagement.
In the prior art, thus, the crankshafts in all the pressing machines must have been stopped in a certain narrow range of angle before clutch engagement. However, such a procedure is complicated.
When the master and slave machines are to run synchronously, it is also preferred that the crankshafts thereof are synchronized with any phase difference immediately after clutch engagement.
On the other hand, when the master and slave machines are to run synchronously with phase difference, it is further preferred that the crankshafts thereof are synchronized while maintaining any phase difference therebetween, immediately after clutch engagement.
In the prior art, thus, the crankshafts of all the pressing machines must have been stopped while being aligned with one another before the clutch engagement. Alternatively, when it is required to provide a predetermined phase difference between the master and slave machines, each of the crankshafts must have been stopped with a predetermined angle corresponding to that phase difference. However, such a procedure is complicated.
When the pressing machines are synchronously running with zero phase difference, this restricts the operating cycle time for a supply device which supplies materials to the pressing machines or a delivery device which delivers products between the pressing machines. Thus, such peripheral devices have executed and been completed in operation within a limited short time period. This provides a severe limitation to the peripheral devices, leading to reduction of the maximum velocity of production in the entire press line.
SUMMARY OF THE INVENTION
It is thus an objective of the present invention to provide a method of controlling synchronous drive of a plurality of pressing machines with zero phase difference or any phase difference, which can realize an improved accuracy of synchronization without adverse affection of a load change in any one pressing machine to the remaining pressing machines as a disturbance, and to provide a pressing machine usable in such a method.
Another objective of the present invention is to provide a method of controlling synchronous drive of a plurality of pressing machines, which can effectively drive the pressing machines and avoid any overload to the pressing machines due to a transitional increase of control by reducing the positional control rate between the pressing machines immediately after clutch engagement to relieve the load on the motors, and to provide a pressing machine usable in such a method.
Still another objective of the present invention is provide a method of controlling synchronous drive of a plurality of pressing machines, which can reduce the control of the positions between the pressing machines immediately after the clutch engagement to relief the load on the motors and to avoid any increased transitional control, which can initiate the control of synchronization relating to a predetermined phase difference immediately after the pressing machines have been started with the same angle of stoppage and which can set and change the phase difference even during operation under load, and to provide a pressing machine usable in such a method.
A further objective of the present invention is to synchronously drive a plurality of pressing machines intentionally with a phase difference therebetween to extend the operating cycle time for the peripheral devices, to relieve the limitation applied to the peripheral devices and to increase the maximum velocity of production.
A further objective of the present invention is to provide a method of controlling synchronous drive of a plurality of pressing machines, in which the pressing machines will not adversely be affected by any disturbance due to a load change in any one of the pressing machines and can quickly and accurately respond to a command of motor speed change, irrespective of the engagement/de-engagement of clutch, and to provide a pressing machine usable in such a method.
A further objective of the present invention is to provide a method of controlling synchronous drive of a plu
Aida Engineering Ltd.
Bray W. Donald
Cislo & Thomas LLP
Hoffman Esq. David L.
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