Note: Descriptions are shown in the official language in which they were submitted.
_SCRIPTION
BACKGROUND OF THE INVENTION
1 Field of the Invention
.
The present invention relates to a drive circuit
for a step motor employing thyristors.
2. Brief Description of the Background of the Invention
Including Prior Art
The application of a step motor with a relatively
low self holding torque results in the advantage of a
correspondingly low energy requirement for performing each
step. For avoiding of undesired motions caused by
mechanical disturbances such as for example small shocks
the self holding torque can be supported by an additional
magnetic field, which can be generated from a current
flowing in the rest position in a stator winding.
The switching on of the stator windings is
performed by way of thyristors connected in series to
corresponding windings, where the conducting state of the
thyristors is maintained in each case by the current
flowing through them. In the context
.~
of the present invention a thyristor refers generically to
thyratronlike solid-state devices such as silicon
controlled rectifiers and in particular pnpn type
bistable semi.conductor devices having anode, cathode
and gate terminals and useable as an electronic switch.
For switching off of a stator winding the
corresponding thyristor has to be switched off and in
general a special quench device has to be provided for this
purpose. It is an advantage~ if the switchi.ng on step
of another stator winding can be employed for at the same
time quenching said thyristor to switch off the current flow.
SUMMARY OF THE INVENTION
1. Purposes of the Invention
-
It is an object of the present invention to
provide a particularly simple drive circuit employing
thyristors for a step motor, where a current flowing through
a stator winding of the step motor is switched off
as rapidly as possible and under low losses and another
winding is switched on.
It is another object of the present i.nvention
to provide a drive circuit for a step motor where a thyristor
of a winding to be switched on effects quenching the
previously conducting thyristor.
It is a further object of the present invention
to employ a capacitor for accepting the energy remaining
in the winding after switching off of the corresponding
thyristor.
These and other features and advantages of the
present invention will become evident from the description
which follows.
2. Brief Description of the Invention
The present inver,tion provides a drive circuit
for a step motor comprising: a constant current power
supply; stator windings of the step motor; diodes each
connected in series to a corresponding winding; capacitors
each connected in parallel to a corresponding series of a
diode connected to the winding and also connected on one
side to one terminal of the constant current power supply;
thyristors each connected to a corresponding capacitor on
the side not connected to the constant current power supply
and connected to the second terminal of the constant
current power supply; and a control device connected to the
gate inputs of the thyristors~
There is also provided a method for providing
power to a step motor comprising: charging a capacitor;
energizing a winding connected in series to a diode with
the series connection of the diode and the winding being in
parallel to the capacitor; interrupting the current flow
by instituting a corresponding cycle at a second winding;
and charging with reverse polarity the capacitor with the
energy remaining in the switched off winding and preventing
current flow in the opposite direction by connecting a
diode in series to the corresponding winding.
The novel features which are considered as
characteristic for the invention are set forth in
particular in the appended claims. The invention itself,
however, both as to its construction and its method of
operation, together with additional objects and advantages
thereof, will be best understood from the following
descrip~ion of specific embodiments when read in
connection with the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING
In the accompanying drawing in which is shown one
of the various possible embodiments of the present
invention,
Fig. 1 is a view of a schematic diagram of a
drive circuit for a step motor according to the present
invention.
DESCRIPTION OF INVENTION AND PREFERRED EMBODIME~TS
In accordance with the present invention there
is provided a drive circuit where in series to each stator
winding there is connected a diode in each case and where in
parallel to each of said series connection there is
connected a capacitor in each case. Thyristors (Thl ? Th2,
Th3) are connected in series to the windings (Ll,L2, L3),
the diodes (Dl, D2, D3) and the capacitors (Cl, C2, C3~
in each case. Such a drive circuit can advantageously be
employed for driving a step motor operating a printer
for teletype equipment or for other printing machines
For reasons of simplifying the representation
in the drawing only three windings Ll, L2, and L3 are shown
of the step motor. The dashed lines indicate in Fig. 1,
that the motoremployed in each case can be provided with a
larger number of windings. Since also the spacial
arrangement of the windings with respect to each other does
not have an immediate influence on the functioning of
the circuit shown, also the possibility of employing this
drive circuit in other types of motors exists,e.g. linear motors.
Also, the movable element of such motor not
shown here takes a position corresponding to the windings
controlled in each case. The movable element is in general
-- 5
a rotor and the magnetic Eield of a current containing
winding interac~s with the rotor.
The windings Ll, L2, L3 can be connected to the
power supply 10 via corresponding in series disposed
thyristors Thl, Th2, Th3. A constant current source serves
as a power supply~ In order to avoid damaging overvoltages
at the output terminals of the constant current souree a
surge protector 12 is provided in Fig. lo The switching
pulses for the gate electrodes of the thyristors Thl, Th2
and Th3 are generated by the control device 11.
The diodes Dl, D2, D3 are eonneeted in series with
the windings Ll, L2, L3. The eapacitors Cl, C2, C3 are
conneeted in each case parallel to the resulting series
conneetions.
Upon switching on of the eircuit the voltage
generated by the constant current souree L0 is initially
limited to the value predetermined by the surge protector
12, since in the eonnected eircuit no elosed eircuit paths
are present for the current as long as the thyristors Thl,
Th2, and Th3 are switched off. Initially the eapacitors
Cl, C2 and C3 are in a discharged state.
The thyristor Th2 is switched on if the rotor is
to be brought in the pvsition determined by the magnetie
~L~
fi.eld of the winding L2. The current flows via this thyristor
Th2 into the capacitor C2, such that the voltage of the
constant current source 10 collapses. With increasing
charge on the capacitor C2 the voltage increases again~
If the voltage surpasses the threshold voltage of
the diode D2, then additional current flows via the winding
L2 of the step motor disposed in parallel to the
capacitor C2. Since the winding L2 cannot initially
accept the current in total, the capacitor C2 ~urther
accepts the current difference between the current coming
from the constant current source 10 and the momentary value
of the current passing through the winding L2, until the
winding L2 has completely accepted all the current coming
from the constant current source 10. The desired motion
is now provided by the magnetic field generated by the
winding L2.
Furthermore, in addition the current through the
winding L2 flows via the switched on thyristor Th2 and
generates the desired holding moment.
If now the thyristor Thl is switched on, then
the current flows through -the capacitor Cl still being in
a discharged state, as a result of which the voltage at
the constant current source collapses and blocks the
thyristor Th2. In the circui,t belonging to the thyristor
Thl the process described above for the circuit of the
thyristor Th2 now runs and generates in the winding Ll the
desired magnetic field.
By blocking the thyristor Th2 the outer connection
of the current circuit for the winding L2 is interrupted.
However, the current in the winding L2 remains effective in
the original direction and flows now to the capacitor C2,
whereby the capacitor C2 is charged with reverse polarity.
Backflow of the charge from the capacitor C2 into the wind-
ing L2 is preYented by the diode D2, such that the charge
state generated this way remains effective until a renewed
firing of the thyristor Th2. Thereby, the thyristor Th2
is safely kept in a blocking state for the current.
If now the thyristor Th2 is again fired, then the
voltage at the capacitor C2 acts as a countervoltage to
which the voltage of the constant current source 10 falls
such that the previously fired thyristor Thl blocks rapidly
and reliably.
It is to be understood that each of the elements
described above, or two or more together, may also find a
useful application in other types of motor configurations
and electromechanical power converters differing from the
types described above.
While the invention has been illustrated and
described in the context of a step motor, it is not
intended to be limited to the details shown, since various
modifications and structural changes may be made without
departing in any way from the spirit of the present
invention.
Without further analysis 7 the foregoing will so
fully reveal the gist of the present invention that others
can, by applying current knowledge, readily adapt it for
various applications without omi.tting features that, from
the standpoint of prior art, fairly constitute essential
characteristics of the generi.c or specific aspects of
this invention.
W~lat is claimed as new and desired to be protected
by Letters Patent is set forth in the appended claims.
