Electricity: motive power systems – Braking
Patent
1998-11-10
2000-07-25
Ip, Paul
Electricity: motive power systems
Braking
318368, 318370, H02P 310, H02P 320
Patent
active
060940239
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method and a device for braking an all-mains motor, preferably to a stationary position.
STATE OF ART
Electric all-mains motors are used as drive sources for a number of different applications, e.g. for various types of hand tools such as drilling machines, rotary saws (having single as well as double saw blades, rotating in an opposed relationship to each other) and angle grinders.
Any possibility to electrically perform fast braking of such a machine is not known, and mechanical braking means are normally not used for this purpose, since such a solution is technically complicated and results in an increased weight.
To reverse the rotary direction of an all-mains motor without disconnecting the feed current is disclosed as previously known in DE-A1-3 940 849, but this solution is only intended to change the rotary direction in shortest possible time and to accomplish full rotary speed, i.e. a solution to the present problem of braking the all-mains motor to a stationary position is not disclosed.
SUMMARY OF THE INVENTION
The object of the present invention is to disclose a previously not utilized possibility of fast braking action for an all-mains motor by means of an electrical switching operation. A device according to the invention influences thus the weight of a machine to a minimal extent, and acts as a substantial protection against injuries, since a rotating and cutting tool of a machine can be stopped to a substantially stationary position substantially immediately when an operation has been completed.
The method according to the present invention for electrical braking of an all-mains motor comprises use of an electric switching operation arranged to cause a reversal rotary direction for the motor, and it is mainly characterized in that disconnection of supplied feed current to the motor causes an electric switching operation, whereby electric current arranged to cause a reversed rotary direction for the rotor of the motor is supplied, and that supplied braking power is controlled and reduced on basis of the successive reduction of rotary speed for the motor until the rotor of the motor has substantially completely ceased to rotate, whereafter supplied braking current feed is interrupted. It is advantageously monitored whether or not normal start of the motor is performed, electric switching to braking only is made possible provided that such a start sequence has been indicated.
The device for utilization of the method according to the present invention is mainly characterized in that it includes electric switch means for switching supplied electric current in such a way that the rotor of the motor attempts to take up a reversed rotary direction when the normal current feed to the motor is interrupted, and that means are arranged to control supplied braking electric power so that a successively reduced power related to present actual continuously reduced rotary speed of the motor is performed, preferably substantially corresponding to an inverted "soft start" for the motor, supplied braking current feed being interrupted when the rotor of the motor substantially or completely has stopped to rotate.
BRIEF DESCRIPTION OF THE DRAWINGS
A number of non-restricting examples of embodiments of a device for utilization of the method according to the present invention, and certain modifications, will be more fully described below with reference to the accompanying drawings, in which:
FIG. 1 is an elementary circuit diagram of an all-mains motor during normal operation, having a second and braking circuit, connectable by means of an associated switching means, shown in broken lines.
FIG. 2 is a circuit diagram corresponding to FIG. 1 when switching to a braking operation has been performed;
FIG. 3 is a circuit diagram substantially corresponding to FIG. 1, i.e. showing an all-mains motor during normal operation;
FIG. 4 is a circuit diagram after switching to a braking operation from the feeding circuit shown in FIG. 3; and
FIG. 5 is a diagram inte
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