Electricity: motive power systems – Open-loop stepping motor control systems
Reexamination Certificate
2002-11-05
2004-08-10
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Open-loop stepping motor control systems
C318S034000, C318S498000, C318S558000
Reexamination Certificate
active
06774600
ABSTRACT:
BACKGROUND OF THE INVENTION
Certain applications require remote or automated adjustment of parameters or alignments, which are effected by mechanical or electromechanical adjusters. In this case an electric motor maybe used. In certain applications it is imperative that the motor drive electronics not be in proximity to the adjustment mechanism. In such cases a large number of motors can require a large number of wires to connect the motors to the driver, especially brushless motors that are commutated by the electronic drive circuit.
A step motor's shaft has permanent magnets or magnetic material attached to it called a rotor or core. Around the body of the motor is a series of coils that create a magnetic field that interacts with the permanent magnets. When these coils are turned on or off in a certain sequence, the motor will rotate forward or reverse. This is called the phase pattern and there are several types that will cause the motor to turn. A less common of these modes is the Single Phase Mode Driven mode. To make a step motor rotate, you must constantly turn on and off the coils. If you simply energize one coil, the motor will jump to that position and stay there resisting change. Step motors can be controlled using digital computers or processors because the computers can control the motors by turning on and off the coils. The computer energizes the coils in a certain pattern and the motor will move accordingly.
Large multiples of motors can result in a number of wires do to the need to turn on and off and reverse individual coils. As an example, if a system of 60 bipolar step motors were required, then one would expect to connect 240 wires between the electronic driver and the motors, since each motor has 4 wires (60×4), two for each phase. However this invention permits this large number of drive wires to be reduced to 22 wires thereby reducing the cabling costs when it is necessary to place the electronic drive remote from the motors.
SUMMARY OF THE INVENTION
One general object of the invention is to provide a separable driver with reduced circuit requirements to drive a large number of motors connected by a minimized number of wires. A second object of the invention is to lower the cost of the electronic circuitry to drive said motors. A third object of the invention of to provide an economical method for driving the large number of motors whereby the electronics are not in the same environment as the motors. This may be motivated due to extreme temperatures (high or low), radiation, or remoteness of the environment, so that the chance of a requirement to access the hostile environment will be minimized. Only the rugged motors will be in the hostile environment, not more environmentally sensitive electronics.
The matrix-connected driver for multiple two-phase motors of this invention meets all of the above objectives as well as those not listed. The invention includes a circuit rows and columns of input and output connections for the phases of networked two-phase motors. Multiple motors share the same input line and multiple motors share the same output line but no motor phase shares both the same input and the same output. Buffers that may be transistors power each input and output line. The input and output lines may be alternatively positively powered high or grounded low using the buffers. In this fashion individual phases may be singly powered using selected pairs of the buffers without causing the other phases to be powered whether high or low. A processor such as a microprocessor drives the buffers. The usage of common input and output lines or otherwise referred to as columns and rows allows the same number of motors to be single phase mode driven with much less wires.
This invention is especially suitable where a large number of adjustments are to be set using the large number of motors where only one of the motors is run at a time. Although if the controller sequences through them it could appear they are all running at low speed. In some cases the instrument or apparatus might be built with the large number of adjustment motors mechanically built in and wired as described in this invention with the intention that the electronic controller for said motors is not normally shipped with nor built into said apparatus. This would result in a substantial cost savings. Then, using a reasonable sized number of conductors in the cable an adjustment controller can be brought to the site where it can be plugged into the apparatus, the adjustments or alignments can be made, and the controller may be disconnected. A properly mechanical design will thereafter hold its respective positions or alignments respective to each motor while disconnected and de-powered.
A particular application is the use of this invention to tune a super conducting multi-cavity RF filter. An RF filter built using multiple resonating cavities offers superior performance when built using hi temperature super conducting surfaces due to the zero resistance offered by super conductors. This system is enclosed in a vacuum-sealed enclosure. Even with the highest tolerance machining practice, it is still necessary to tune each of the cavities for optimum performance. Also, tuning a cavity can affect the tuning of the input cavity before and the output cavity after the cavity being adjusted, through coupling interactions, which requires a potentially tedious adjustment.
This procedure may be done while the filter assembly is in a normal air environment in a liquid nitrogen-cooled cooled environment. However, due to the difference of physical constants between air and vacuum, the filter must be ‘off-tuned’ in such a manner as to result in proper tuning once the unit is enclosed and operating in a vacuum chamber.
Turning a tuning stub, which consists of rotating a fine screw presently, performs the tuning, and when it is rotated it can protrude further into the cavity or less far into the cavity. Then a lock nut can be tightened to lock the adjustment in place. A large number of tuning adjustment stubs are required for a complete system. If these adjustments were to be motorized using two-phase stepper motors, it could require a very large number of wires be routed through the wall of the cabinet. Vacuum-sealed connectors are expensive and must be minimized.
REFERENCES:
patent: 4284208 (1981-08-01), Levasseur
patent: 4961507 (1990-10-01), Higgins
patent: 5023527 (1991-06-01), Erdman et al.
patent: 5087867 (1992-02-01), Kruppa
patent: 6265842 (2001-07-01), Hard et al.
patent: 6297610 (2001-10-01), Bauer et al.
patent: 6603647 (2003-08-01), Briesen et al.
Calfa Jeffrey P.
Ro Bentsu
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