Electricity: motor control systems – Specific application: – Hand tool
Reexamination Certificate
2002-01-23
2004-02-24
Nappi, Robert (Department: 2837)
Electricity: motor control systems
Specific application:
Hand tool
C388S935000, C388S813000, C388S800000
Reexamination Certificate
active
06697570
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a startup safety routine and an associated rotary electrical hand-tool device, in particular a drilling machine, a hammer drill or a combination hammer. In large and powerful rotary electrical hand-tools, there is the danger of injury to the operator from the rotation of the housing due to stored kinetic energy resulting from sudden tool blockage. When starting the tool, there is a particularly significant risk of injury due to sudden deflection of the housing out of its stationary position as a result of startup blockage.
Usually, the sudden high angular momentum producing the blockage-induced rotation is cut-off from the blocked tool by a torque limiter or safety coupling or otherwise limited with respect to torque. The cut-off is frequently delayed, however, so that a deflection of the housing cannot be prevented from the rotational energy already transferred to the housing and considerable residual torque.
DE 3128410A1 discloses a method for measurement of the torque acting on the housing by the handle guiding the electrical hand-tool. The method includes using analog integration of a signal proportional to the torque to activate the safety device when the limit value is exceeded and thus, prevent tool blockage, jamming and twisting. The disadvantage with such a method is the requirement that the operator guides the electrical hand-tool to produce the counter-force.
EP 666148B1 discloses a process and a device for the prevention of high angles of rotation of electrical hand-tools, wherein a microcontroller, using the current angular acceleration of the housing, calculates the angle of rotation of the housing to be expected at some future time and, when a limiting value is exceeded, activates a safety device to prevent exceeding the value. In the case of blockage, upon starting, however, minor angular accelerations of the housing can occur. Particularly, when current-limited supply networks are used the advance-calculated angle of rotation of the housing does not exceed the limit value and, as a result, the safety device is not activated due to the initially slowly-building rotor acceleration of the electrical motor.
Such weak current networks occur when: the networks are generally weak; small conductor cross-sections limit the current flow; long extension lines are used; there are isolation transformers arranged in the power path or low-power generators supply the device. In power networks having 230 V/110 V, the start-up power of the performance electrical hand-tools considered in this invention are of the approximate magnitude of 30 A/60 A.
SUMMARY OF THE INVENTION
The object of this invention is to provide an improvement for the microcontroller-controlled safety routine that eliminates the above disadvantages and provides certain recognition of start-up blockages, in particular, when operating on a weak supply circuit, and to provide an associated electrical hand-tool device.
In accordance with the invention, there is generally provided a rotary electrical hand-tool comprising an electrical motor and a safety device, actuated by a microcontroller when a limit value is exceeded. Preferably the rotation of the housing is calculated in advance for the interruption of transmission of torque between a tool and the electrical motor.
Essentially, in an electrical hand-tool having a programmed microcontroller-regulated start-up safety routine, the electrical motor is supplied with the full effective voltage for an initial, brief period T
0
following the switch-on process. The rotor angular acceleration is calculated by the microcontroller by a measurement of the rotor angle of rotation &phgr; over the period T
0
. From the result, which is dependent on the internal resistance [i.e, source impedance] of the power supply circuit, at least one of the limit value &agr;
G
and the shut-off time t
A
is calculated and must be exceeded for triggering of the safety device by a rotation &agr; of the housing, wherein the rotation &agr; was calculated in advance. This adaptive adjustment, of the parameters of the start-up safety routine, is done using a representation readable by the microcontroller, at least using sample data dependent on the behavior upon starting of the rotor of the electrical motor in the period T
0
.
Preferably, in the time span T
0
, a possible phase angle control reducing the effective voltage is bypassed/bridged, whereby the electrical motor in the startup condition is definitively connected to the power supply network.
Preferably, should start-up blockage occur, the electrical hand-tool device results in only minimal rotations, for example <60°, of the housing which are possible as a result of the detected response behavior in the short period, T
0
.
Advantageously, the triggering of the safety routine is reliable. In particular, since the start-up safety routine is designed to be adaptive, the rotations of the housing can be calculated in advance, in the event of start-up blockage, even beyond the specified voltage limits of the supply circuit specified in the standards. Moreover, a country-specific adjustment due to the different supply voltages is unnecessary because of the adaptive safety routine.
The start-up safety routine is implemented, preferably, without parameter changes beyond the limit values, in an existing safety routine that calculates the rotations in advance. The start-up safety routine can, therefore, be prioritized as a program by the microcontroller temporally before or higher than, or parallel to, the existing unmodified safety routine.
The rotary electrical hand-tool with the microcontroller-controlled safety routine is connected to means for determining the angle of rotation or speed. The microcontroller is connected to means for operation of the electrical motor, on the power supply circuit, using an effective impedance, at least in the temporal medium, that is advantageously zero or infinity.
It is advantageous if the resistance operated by the microcontroller is connected with an available phase angle control that reduces the effective voltage to the speed regulator, and further advantageous if the resistance is electrically bypassed.
The control dependent on the actual speed is advantageously fully modulated during the start period, which is substantially shorter than the run-up time to the desired speed.
REFERENCES:
patent: RE33379 (1990-10-01), Bradus
patent: 6025683 (2000-02-01), Philipp
Hellmann Peter
Reiner Michael
Werdun Guido
Hilti Aktiengesellschaft
McCloud Renata
Nappi Robert
Sidley Austin Brown & Wood LLP
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