Supports: cabinet structure – Spaced insulated wall – Refrigerator cabinet
Reexamination Certificate
1995-10-13
2001-03-06
Wysocki, Jonathan (Department: 2837)
Supports: cabinet structure
Spaced insulated wall
Refrigerator cabinet
Reexamination Certificate
active
06196650
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the improvement of a sensorless motor driving circuit.
2. Description of Related Art
Sensorless motor driving circuits for driving, for example, two-phase brushless motors are well known. These circuits for driving two-phase brushless motors use rotation detecting elements such as Hall elements and switch over the conduction of the driving current (conduction) in the excitation coils utilizing an induced voltage (counter-electromotive voltage) generated in the excitation coils.
These general sensorless motor driving circuits carry out conduction switching by detecting the induction voltage in the excitation coils and supplying a certain amount of delay with respect to the timing of the inversion of the polarity.
Spike voltages (fly-back voltages) generated at the time of conduction changeover are then removed with filters.
Further, if the motor rotor is not activated directly after conduction in the excitation coils, with the motor rotor already being in the stationary position (referred to as the reference position) that is intended, if an induction voltage for the excitation coils is not detected within a certain period of time, an activation pulse is generated and the conduction pattern is forcibly switched over.
These methods of providing a prescribed delay in relation to the timing with which the polarity inverts, providing filters for removing the spike voltages, and generating activation pulses, can be divided into analog methods and digital methods.
Circuits for the analog methods utilize CR time constants to put in phase delays, remove spike voltages and generate activation pulses. Circuits for the digital methods, on the other hand, almost all use microprocessors.
Use of the digital method is possible in systems where the circuit scale is large but is not viable in small-scale circuit applications because of the cost of the microprocessors. It is therefore more natural for the analog method to be adopted, rather than the digital method.
However, in the analog method, it is necessary to set up the time constants for each element of the CR time constant circuit in the most appropriate manner, but this proves to be difficult due to interference between the time constants for each element. Further, a large number of resistors and capacitors are necessary, which means that a large number of parts are required.
SUMMARY OF THE INVENTION
As the present invention sets out to resolve the aforementioned problems, it is the object of the present invention to provide a sensorless motor driving circuit where the number of external parts is fewer when compared with circuits structured using the analog method, where the cost is reduced and where the most appropriate drive current switching is carried out for the excitation coils regardless of the rotational speed of the motor.
A sensorless motor driving circuit therefore comprises a detection circuit for detecting a reference position for the rotating rotor based on an excitation coil induction voltage, a differential pulse generating circuit for generating a differential pulse using a detection circuit output signal, a phase-locked loop circuit capable of generating a clock pulse, having a phase comparator for comparing the differential pulse with the clock pulse after the clock pulse has been frequency divided, an activation pulse generator for counting the clock pulses and generating an activation pulse when the differential pulse is not generated within the duration of a prescribed number of counts, a latch circuit for generating a delayed pulse delayed by a prescribed amount from the reference position of the rotor by counting the clock pulses or by using the activation pulse, a generating circuit for generating conduction switching signals for the excitation coils based on the delayed pulse and a driver circuit for bringing about conduction in the excitation coils based on the conduction switching signal.
The sensorless motor driving circuit may also be further equipped with a mask signal generator for generating, by counting the clock periods, a period for suppressing an imitation pulse generated during conduction changeover.
The PLL circuit controls the amount of delay for the latch delay circuit and the imitation pulse suppression period for the mask signal generator in response to the rotational speed of the rotor.
The motor of the present invention may be a two-phase bi-directional sensorless motor used for rotating a rotating drum of a rotating magnetic head device.
The motor of the present invention may also be a two-phase bi-directional sensorless motor used for rotating an optical disc.
According to this structure, the detector
3
detects the reference position of the rotor R based on the induction voltage of the excitation coils
1
and
2
.
When the rotor R rotates, an alternating current voltage is induced in the coil. However, the reference position is the position of the rotor R when the alternating current voltage is zero volts.
A magnetic force is exerted on the rotor R when either of the excitation coils
1
or
2
conducts and the rotor R will rotate. When the rotor R rotates, counter-electromotive voltages
6
s
-
2
and
6
s
-
4
are detected at the detector
3
.
The differential pulse generator
7
generates a differential pulse
7
s
using the output signals
3
s
-
1
and
3
s
-
2
from the detector
3
. The phase comparator
40
of the PLL circuit
8
capable of generating the clock
8
s
compares the differential pulse
7
s
with a pulse
8
p
, which is the frequency-divided version of the clock
8
s.
The latch delay circuit
9
generates a delayed pulse
9
s
delayed by a prescribed amount from the reference position of the rotor R by counting periods of the clock
8
s
. The circuits
6
and
12
generate conduction-switching signals
13
s
-
1
through to
13
s
-
4
for the excitation coils
1
and
2
based on the delay pulse
9
s
and the excitation coils
1
and
2
are forcibly switched over to the next conduction pattern.
In the above way, when the rotor R is rotating due to conductions, if the rotor R is already under the influence of magnetic force and is in the position (neutral position) at which it is intended to be stopped, the rotor R is at the reference position. The rotor R will therefore not move even if there is conduction in the excitation coils
1
and
2
and an induction voltage will not be generated. In this case, the activation pulse generator
10
counts the clock periods of
8
s
and generates an activation pulse
10
s
when a differential pulse
7
s
does not occur for a prescribed number of count periods. The latch delay circuit
9
then generates a delay pulse
9
s
based on this activation pulse
10
s
. The circuits
6
and
12
then generate conduction switching signals
13
s
-
1
through to
13
s
-
4
and the excitation coils
1
and
2
are forcibly switched over to the next conduction pattern.
It is preferable for the mask signal generator
11
to generate a period T for suppressing the imitation pulse generated during conduction switching by counting the periods of the clock pulse
8
s.
It is also desirable for the PLL circuit
8
to control the amount of delay of the latch delay circuit
9
and the imitation pulse suppression period T of the mask signal generator
11
in response to the rotational speed of the rotor R.
REFERENCES:
patent: 4912378 (1990-03-01), Vukosavic
patent: 4949000 (1990-08-01), Petersen
patent: 5223772 (1993-06-01), Carbolante
patent: 5306988 (1994-04-01), Carbolante et al.
patent: 5396159 (1995-03-01), Kaneda
patent: 5428284 (1995-06-01), Kaneda et al.
patent: 5530326 (1996-06-01), Galvin et al.
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
Wysocki Jonathan
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