Electricity: motive power systems – Alternating current commutating motors
Reexamination Certificate
1998-09-29
2001-01-09
Sircus, Brian (Department: 2839)
Electricity: motive power systems
Alternating current commutating motors
C318S809000, C318S432000, C388S937000, C388S801000, C388S809000
Reexamination Certificate
active
06172472
ABSTRACT:
FIELD OF THE INVENTION
My present invention relates to an electric motor for a portable machine, e.g. a hand-held tool or appliance, and more particularly, to a control system for an electric motor which may be integrated in such a machine, which has two terminals connectable to the voltage supply lines and which is intended to be connected to a power supply network having two lines.
BACKGROUND OF THE INVENTION
Portable and/or hand-held machines with electric Rotors are commonly available in a variety of forms and include such machines as washing machines, electric mixers, kitchen appliances and electric tools like electric drills, electric grinders, electric saws, electric cutters operating with grinding blades, circular saws and saber saws, etc.
In the operation of such machines the load upon the electric motor can suddenly or even gradually increase and cause overloading which can result in excessive wear and other detrimental states up to complete breakdown of the machine.
With such overloading, there is even a danger to the user of the machine. For example, in the case of an electric drill, the drill bit may become jammed and the drill body itself may rotate around the drill bit to cause injury to the user.
For these reasons, such machines may be provided with electronic safety systems which prevent such overloads. Such electronic safety systems can be triggered to shut off the machine or reduce the power supplied to it upon the development of an unsafe condition. These systems can be contrasted with systems using a fuse which may burn out or a mechanical safety system with intentional break parts which rupture to prevent injury to the user. In the latter two cases, the fuse or ruptured part must be replaced.
For reliability in the electronic system it is above all important that the system be activated sufficiently rapidly to prevent injury or damage and that the triggering point be fixed with sufficient precision that the operating range in terms of load is not unnecessarily reduced.
It has been found to be a disadvantage of earlier rapidly-operating electronic safety systems that relatively complex means must be provided for determining the load current, thereby making the drill system relatively large and expensive, especially when a high degree of precision is desired. Furthermore, when the load current changes dramatically, i.e. the load current dynamics are significant, there is a tendency for the load current measurement to be inexact which requires that either the trigger point for the cut-off be lowered in terms of load current or that an unnecessarily excessive number of shutoffs be tolerated at least in the critical range.
These drawbacks, together with the fact that earlier attempts to eliminate them have increased the cost of the tool or appliance to an intolerable level or have required place for the control system to the extent that the tool or appliance is no longer sufficiently compact, have resulted in acceptance of less effective control or safety systems than have been desirable.
OBJECTS OF THE INVENTION
It is the object of this invention to provide a control system for a motor-driven machine of the type described whereby the aforementioned disadvantages are avoided.
More specifically, it is an object of th invention to provide an improved control system for a two-terminal electric motor, which can be integrated into a portable and/or hand-held machine, to be connected to a voltage supply network having two lines, which allows rapid triggering upon overload, which is of low cost, both with respect to the cost of components and to fabrication, and which can be accommodated in a comparatively small space so that compactness of the tool or appliance is not adversely affected.
Still another object of this invention is to provide a system for preventing overload of an electric motor which operates more efficiently and can be of a smaller size than conventional systems.
SUMMARY OF THE INVENTION
These objects are attained, in accordance with the invention in a system for controlling a two-terminal electric motor of a portable apparatus to be connected to a two-line supply net which comprises:
a current-measuring component connected in series with the electric motor for measuring current draw of the electric motor;
a control element responsive to the component and connected in series with the component and with the electric motor between one terminal of the electric motor and one line of the supply net, another terminal of the electric motor being connected to another line of the supply net;
a microcontroller connected to the component and to the control element for actuating the control element in response to current measured by the component to cut off operation of the electric motor or reduce power supplied thereto upon initiation in the microcontroller by the measured current of a predetermined action; and
switch means for activating the electric motor.
More particularly, the control system is designed for an electric motor integrated into a portable or hand-held machine having at least two current supply terminals (C, D) which are to be connected to a voltage supply network with two network lines (A, B).
The terminal (C) (or the terminal (D)) is connected in series with a control element and a component capable of measuring the current draw of the electronic motor and via that series network to the voltage supply network line (A) (or line (B)).
The terminal (D) (or the terminal (C)) is connected with the voltage supply network line (B) (or the line (A)).
The microcontroller, i.e. the microprocessor-based controller is connected with the component measuring the current draw of the electric motor and with the control element.
The system also has a switch like, for example an on/off switch, a potentiometer, a keyboard or push-button set, or the like for activating the electric motor.
The result is a flexible adjustable overload protection since the microcontroller can be programmed with any load state to provide an exactly defined motor controlled condition so that the operational reliability and operating life of the electric motor can be significantly increased.
Advantageously, the current-measuring component can be integrated into the microcontroller, thereby providing a further saving in space.
It has been found to be advantageous to connect at least one of the voltage supply network lines to a phase detector whose output is connected to the microcontroller so that, for example, speed control of the electric motor can be provided through the microcontroller utilizing full wave, fractional phase or pulse-width modulation control.
Optionally, the microcontroller can be programmed to ensure any desired start-up relationship or characteristic, for example, a so-called soft or gradual start-up of the motor (slow increase in the speed) or can ensure that operation of the machine is initiated only after a certain condition is reached, for example, start-up only if the machine was previously in its “off” position or its on/off switch was previously in its “off” mode.
This arrangement can avoid immediate start-up of the machine following a current interruption when the switch is in its “on” position since that could be very dangerous and detrimental to the machine. The microcontroller can also be programmed to allow the overload protection to be bridged or bypassed during start-up.
Advantageously, the phase detector can be also integrated in the microcontroller to thereby further reduce the spatial requirements.
In a preferred embodiment of the invention, the microcontroller can be supplied with at least one operating parameter which can be variable and/or adjustable and which can include, for example, the rotary speed of the motor and the torque applied to the motor or to the machine so that a variety of operating states can be set in the microcontroller and, for example, maximum values or limiting values can be established for certain of the parameters.
Advantageously, the or each parameter can be adjusted by varying the external resistance, for example by se
Dubno Herbert
Sircus Brian
Westfalia Werkzeuggompany Gesellschaft mit Beschrankter Haftung
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