Electricity: motive power systems – Positional servo systems – Time-sharing or multiplexing systems
Reexamination Certificate
2001-10-17
2003-07-08
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Positional servo systems
Time-sharing or multiplexing systems
C318S041000, C318S034000
Reexamination Certificate
active
06590359
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority of International Application No. PCT/EP01/01664, filed Feb. 15, 2001 and German Application No. 100 07 201.1, filed Feb. 17, 2000, the complete disclosures of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
a) Field of the Invention
The invention is directed to a method for the synchronized control of a plurality of stepping motors SM
1
, SM
2
. . . SM
n
which serve as drives in a feed system, wherein the stepping motors SM
1
, SM
2
. . . SM
n
are controlled at a base frequency f
a
and a cycle of the base frequency f
a
is proportional to a given step length SL.
b) Description of the Related Art
It is known from the prior art to transform the predetermined step angle defined for a stepping motor into increments of a longitudinal movement by controlling and, on this basis, to operate positioning systems by means of which displacements of device component groups along an adjustment area or a path are carried out with high accuracy.
With a suitable arrangement of the coils and phase control of the stepping motor, a sensitive control can be achieved and, therefore, the rotational movement can be advanced in step angles which are so small that even in optical precision instruments, e.g., microscopes with zoom devices, the precise positioning of the individual zoom groups required for changing the magnification while retaining imaging sharpness is achieved.
In the current state of development, typical step angles are 3.75° in permanently excited stepping motors, 1.8° in hybrid stepping motors and 1° in variable reluctance stepping motors. Generally, spindle systems are used to transform the rotational movement into a longitudinal movement.
Positioning systems in which a component group to be displaced along a path is associated with each stepping motor have been developed for applications in zoom objectives as well as for other applications. Particularly in applications for zoom objectives, there is a need to displace the different component groups at different speeds so that, after a displacement, the zoom groups are at a predetermined distance relative to one another, which distance must be sufficient for the newly adjusted magnification and is also required for retaining the imaging sharpness. An “arrangement for direct control of the movement of a zoom system in a stereo microscope” which works on this principle in described, for example, in WO 99/60436.
In the prior art, when controlling a plurality of stepping motors belonging to a positioning system, a counter unit or timer unit is associated with each stepping motor and each path. All counter units and timer units are loaded with different frequencies and times which relate to an associated path and were calculated based on the corresponding positioning task.
The stepping motors are started together and, at the conclusion of a predetermined sequence of cycles of the base frequency or control frequency, the displacement is initiated via output units, wherein an output unit is always associated with a stepping motor. For a further, subsequent adjustment, the counter units or timer units are reloaded and started in corresponding manner.
This sequence is repeated for every new positioning preset and the component groups reach the predetermined destinations on their path each time. In so doing, the component groups are displaced over different path lengths at the same times, i.e., they achieve their target positions at different speeds which are achieved in that the individual stepping motors are controlled with different frequencies.
Since every path also has separate acceleration profiles, particularly for the displacement of zoom groups, a positioning system constructed in this way requires a relatively large storage capacity and, consequently, a rather long calculating time.
In addition, because of the high feed speed that is required—in the present case, the maximum path deviation should be no more than 10 &mgr;m in all drives—every counter unit or timer unit comprises at least three individual counters.
In order to achieve the maximum possible adjustment speed, the stepping motor that must carry out the greatest displacement on the path associated with it is considered as the leading drive, to which all other drives which are assigned shorter feed distances are to be oriented in that they are operated more slowly.
It is clear from the description above that the relatively high expenditure on storage capacity and calculating time is due to the fact that a separate frequency is provided for each individual stepping motor of a positioning system of this type.
OBJECT AND SUMMARY OF THE INVENTION
On this basis, it is the primary object of the invention to further develop a method of the type described in the beginning in such a way that it is possible to control the entire positioning system in a more economical manner while retaining a high positioning accuracy and optimal adjustment speed.
According to the invention, different step lengths SL
1
, SL
2
. . . SL
n
are triggered with each cycle of the same base frequency f
a
in the individual stepping motors SM
1
, SM
2
. . . SM
n
, wherein a specific step length SL
1
is associated with stepping motor SM
1
, a specific step length SL
2
is associated with stepping motor SM
2
, and so forth.
Accordingly, it is no longer required to provide separate control frequencies for every stepping motor. All stepping motors can now be controlled at the same frequency and only a counter unit or timer unit is required for all stepping motors of the positioning system.
Since every stepping motor travels over the specific step length SL
1
, SL
2
. . . SL
n
assigned to it when controlling with one and the same frequency, it is achieved in a simple manner that the individual stepping motors SM
1
, SM
2
. . . SM
n
move at different speeds and, at the conclusion of an adjusting movement, each of the component groups to be displaced has traveled over different displacement distances and has reached its target position.
In a preferred construction of the invention, stepping motor SM
1
, for example, is operated at a step length SL
1
which corresponds to the whole step of the stepping motor SM
1
during a complete rotating field rotation. The stepping motor SM
1
is coupled with a component group which must travel a greater displacement distance than the other component groups when a positioning command is initiated.
Smaller step lengths SL
2
. . . SL
n
corresponding to a partial rotating field rotation are assigned to the rest of the stepping motors SM
2
. . . SM
n
. Accordingly, the component groups coupled with these stepping motors SM
2
. . . SM
n
travel shorter displacement distances.
The whole step length SM
1
resulting from a complete rotating field rotation is divided into a plurality of partial steps, or microsteps, as they are called, based on the fact that every position of the torque vector within a rotating field rotation is adjustable in theory by adapted control of the currents to be impressed in the individual phases. This type of control is known per se and described for example in Schörlin, F., “Controlling, regulating and driving with stepping motors [Mit Schrittmotoren steuern, regeln und antreiben]”, Fransisverlag 1996, second edition, 1996.
A quantity z of discrete microsteps can be generated in this way. For practical use of this effect, division of a whole step into z=100 microsteps is sufficient and is a proven basis for the configuration of positioning systems.
In this respect, one construction of the invention consists in that SL
1
=k
1
/z, SL
2
=k
2
/z . . . SL
n
=k
n
/z is true for step lengths SL
2
. . . SL
n
, where k
1
to k
n
are equivalents of the microsteps to be predetermined per cycle of the base frequency f
a
.
Assuming that a whole step length corresponding to a complete rotating field rotation is assigned to stepping motor SM
1
, the equivalence k
1
=100 is true for stepping motor SM
1
when z&equals
Joram Ralf
Kaufhold Tobias
Carl Zeiss Jena GmbH
Dang Khanh
Reed Smith LLP
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