Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
2000-02-01
2001-10-23
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
C318S685000
Reexamination Certificate
active
06307345
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to stepper motors. More particularly, the invention relates to a resonant circuit control system designed to effectively conserve energy during the operation of a stepper motor.
2. Description of the Prior Art
The use and theory of stepper motors are well developed. The term “stepper motor” is known to describe, but is not limited to, switched reluctance motors, variable reluctance motors, electronically commutated reluctance motors, variable reluctance stepper motors, brushless DC motors, and other forms of stepper motors. Stepper motors may have a bipolar or unipolar construction. Bipolar motors have a rotor constructed using permanent magnets and unipolar motors have a rotor constructed of soft iron materials (or related materials) that respond to the magnetic field produced by the stator.
The general operating principle of a stepper motor relies upon a winding mounted on a stator to conduct or block current based on the position of the rotor. As such, stepper motors are generally constructed without the brushes commonly found in electric motors. In place of brushes, the stepper motor depends on switches to control the flow of electrical charge through a particular phase winding. Stepper motors advantageously offer the ability to control the exact increment of motion, or the change in a rotor angle, by the use of a control system. Each winding relates to a specific phase and each phase to a specific increment or angular change from the previous phase. This incremental change in angle is referred to as a “step”, hence the general description of this family of devices as stepper motors.
Prior art stepper motors have been designed with resonant systems for driving the motor. However, no prior art stepper motors have been disclosed which use capacitors to efficiently capture and recycle most of the charge passing through a winding.
With reference to the control system disclosed in
FIG. 1
, a two winding system for a bipolar stepper motor
1
is disclosed. In operation, the first switches
2
a
,
2
b
are turned on (all other switches are not conducting) and electrical charge flows through the first winding
3
in the forward direction as indicated by the arrow. This produces the first phase of the stepper motor sequence. The second phase is produced by turning the third switches
5
a
,
5
b
on (all other switches are turned off) to energize the second winding
6
with electrical charge flowing in the noted forward direction. The third phase is produced by turning on the second switches
6
a
,
6
b
while all other switches are off. This allows electricity to flow in the reverse direction through the first winding
3
. Finally, the fourth phase occurs when all switches are turned off except the fourth switches
7
a
,
7
b
, allowing the second winding
6
to be energized with electrical charge flowing in the reverse direction.
This conventional arrangement of switches and windings in a bipolar stepper motor is referred to as an H-bridge (where the winding is the cross member of the H and the switch circuit composes the uprights). The current flow through the switches of the H-bridge are unidirectional and the current flow through the winding is bidirectional (hence the quote bipolar stepper).
The phase process is repeated with the rotor of the stepper motor turning a discrete amount for each phase. The stepper motor is locked or held in position by leaving one phase active. In the case of holding or locking, the current flowing through the winding exerts a given magnetic force on the permanent magnets in the motor to produce a holding torque. If the phases are switched too slowly, the stepper actually locks momentarily (achieves holding torque) in each phase, causing a jerking motion often accompanied by a clicking sound.
The prior art control systems, however, expend substantial energy in cycling through the many phases. As such, a need exists for a more efficient control system to be used in the operation of unipolar and bipolar stepper motors. The present invention provides such a control system.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a stepper motor including a rotor positioned within a stator for relative motion. The stepper motor further includes a control system associated with the stator and rotor for controlling relative motion. The control system is a resonant circuit which conserves electrical charge includes a first winding positioned between a first electrical charge source and a first capacitor assembly; a first switch controlling the flow of electrical charge between the first electrical charge source and the first capacitor assembly through the first winding in a first direction; and a second switch controlling the flow of electrical charge from the first capacitor assembly and through the first winding in a second direction. In use, phase one begins with the opening of the first switch, causing the flow of electrical charge through the first winding in a first direction and a predetermined relative movement between the stator and rotor. Phase two begins by closing the first switch and opening the second switch to cause the flow of electrical charge in the second direction from the first capacitor assembly and through the first winding. This causes a predetermined relative movement between the stator and rotor.
It is also an object of the present invention to provide a stepper motor including a second winding positioned in communication with a second capacitor assembly.
It is a further object of the present invention to provide a stepper motor including a third switch controlling the flow of electrical charge through the second winding in a first direction and into the second capacitor assembly, and a fourth switch controlling the flow of electrical charge from the second capacitor assembly and through the second winding in a second direction. In use, phase three begins with the opening of the third switch causing the flow of electrical charge through the second winding in a first direction to cause a predetermined relative movement between the stator and rotor, and phase four begins with closing the third switch and opening the fourth switch to cause the flow of electrical charge in the second direction through the second winding thus causing a predetermined relative movement between the stator and rotor.
It is another object of the present invention to provide a stepper motor wherein the first and second windings are electrically linked.
It is also another object of the present invention to provide a stepper motor wherein the stepper motor is bipolar.
It is yet a further object of the present invention to provide a stepper motor wherein the stepper motor has a unipolar configuration.
It is still another object of the present invention to provide a stepper motor including a third winding positioned in communication with a capacitor assembly and a fourth winding positioned in communication with a capacitor assembly.
It is also an object of the present invention to provide a stepper motor wherein the first, second, third and fourth windings are electrically linked.
It is a further object of the present invention to provide a stepper motor wherein the first capacitor assembly includes a series of capacitors adapted to control the capacitance of the control system.
It is a still a further object of the present invention to provide a stepper motor wherein the flow of electrical charge to the series of capacitors is controlled by a series of switches associated with the series of capacitors.
It is another object of the present invention to provide a stepper motor wherein the series of capacitors are connected in parallel.
It is also an object of the present invention to provide a stepper motor wherein each capacitor in the series of capacitors has half the capacitance of the previous capacitor.
It is a further object of the present invention to provide a stepper motor wherein at least one of the first and second switches is a unidirectional
Duda Rina I.
Nappi Robert E.
Welsh & Flaxman LLC
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