Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1998-07-20
2001-05-08
Grant, William (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C710S063000
Reexamination Certificate
active
06230078
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention pertains to pre-programmed computer (PC) control of controllable devices having variable settings. In one example, the present invention may be applied to mechanical animation of imitation human or animal figures and can be used in advertising, window displays, trade shows, amusement parks & movie making, providing lifelike movements of limbs and other parts of these figures. The motive force for these movements can be from electric motors, or from hydraulic (or pneumatic) actuators controlled by solenoid valves activated by the control system. A separate reversible motor or actuator (channel of control) can be used for each part of the figure being animated. A script defining the real time movements of each motor is scanned within the PC and data is sent to the motors to control their speeds and directions of rotation.
In another example the present invention may be applied to Computer Numerical Control (CNC) of machine tools and manufacturing processes. By this method, cutting tools, machine elements and materials are moved by stepper motor drives to pre-planned positions according to a prepared file in the PC. Currently, most existing higher quality animation and CNC systems employ closed loop servo-systems. These systems have accurate control of positioning by encoder feedback. However these systems are somewhat complex and since a multi-axis CNC system with associated workell control may need thirty or more axes of movement, cost is a very big factor.
In my prior U.S. Pat. No. 5,784,541 I dislose a method and apparatus for controlling the speed of stepper motors according to the varying frequencies of pulses produced by a stable multi-vibrators. The frequency of the scanning of the script within the PC is also controlled by pulses produced by an a stable multi-vibrator. However pulse frequencies produced in this manner are not very accurate. This inaccuracy causes a less than perfect coordination between motor control pulse frequency and scan frequency. As a result, during the time span of any single scan, it can not be certain that an exact number of complete motor control pulses will be produced. This may result in some incomplete step cycles of the stepper motors, and thus some positioning inaccuracy. In most animation applications this does not present a problem since these slight inaccuracies are not noticeable, and since methods for making corrections for inaccurate positioning are also disclosed in that pending application. But in CNC operation these inaccuracies cannot be tolerated. Additionally in some animation applications it would be an improvement to avoid these inaccuracies and the need to make corrections for them.
In the present invention I disclose a method and apparatus for using frequency dividers that divide one master clock frequency into multiple various frequencies. These frequencies are used for producing: (a) various pulse frequencies to control the speed of stepper motors at different speeds, and (b) a pulse frequency to control the scanning of the script in the PC. This arrangement produces motor speed control pulses that can be synchronized with the frequency of the scanning of the script in the PC. With this arrangement an exact number of complete motor speed control pulses can be assured during the time span of each scan, regardless of motor speed. This eliminates positioning inaccuracies and produces a system ideal for CNC and higher quality animation applications.
Additionally in the present invention I disclose a method and apparatus for selectively using either of two stepper motors, each with a different drive gear ratio, to drive a single axis output, by the use of a two input, single output differential gear system. In CNC operation this enables a high resolution feed drive with one motor activated, or a high speed rapid positioning drive with the other motor activated.
The objective of the present invention is to provide an improved system for PC control of multiple controllable devices (e.g. speed and direction of animation or CNC motors) in accurately controlled repeatable performances (or operations), which is simpler to operate and less expensive than currently available systems.
SUMMARY OF THE INVENTION
The simplified system, as applied to electric stepper motors for mechanical animation of figures and machine CNC (which are examples of only two of its many applications) uses open loop control, controlling the speed of each motor by varying the frequency of pulses sent to it. The pulse frequency sent to a given motor can be increased in progressive steps, causing higher motor speeds, or it can be decreased, causing the motor to run at lower speeds. In a typical embodiment of the present invention, eight steps of variation can be specified in the writing phase, (and reproduced in the playback phase) by letters of the alphabet using the ASCII code. Forward movement is prescribed by choosing upper case letters, and reverse movement (at the same speeds) is prescribed by the same letters in lower case. A line of the script (as displayed on the monitor) contains a letter of the alphabet for each of the (typical number of) thirty motors being controlled. The priority of the letter determines the speed of that particular motor at that part of the script. For example: a letter “A” typically specifies the fastest speed in a clockwise rotation, while a letter “H” typically specifies the slowest speed, with the symbol “@” specifying a dead stop. The letters “a” and “h” (in lower case) then specify the fastest and slowest speeds in an anti-clockwise rotation. On each of the subsequent lines of script there is always the same number of letters, and the letters for the various motors are always presented in the same order, so that the letters for a given motor are present in a vertical column. This arrangement makes it easy to see what each motor is to be doing at a given time, and to compare it with other motor movements at that same time. This is important in animation applications since coordination of the movements of different parts of a figure is usually necessary. It can be seen that setting the speed of a motor at a specific time is very easy, usually requiring only one keystroke.
When the script has been prepared it is saved to disc and the contained data then outputted through the PC parallel port to control the motors. In the process of outputting the data, each character in each line of script is scanned consecutively at a scan rate controlled by a constant frequency pulse source. The outputted data corresponding to each character is distributed to the appropriate motors, causing each motor to run at the prescribed speed until the scan of the next line of script, when the speed may be changed (or not changed), as prescribed by the script. For precise positioning, the present invention uses synchronized pulse sources, in which the scan frequency, and all he motor speed pulse frequencies are obtained by frequency dividers that divide into a master clock frequency. In this way it is possible to ensure that during the time span of each scan an exact number of complete motor speed pulses are produced, at any given motor speed.
The present invention can have applications with CNC systems, using position sensors to control positioning at machine zero & critical work-piece mensions, and providing an overall simpler, less expensive system. Because our ample multiple axis capability a machine tool can be included in a work-cell with synchronized multi-operational handling of work-pieces before machining operation; all included in the same control system. This might include sorting, conveying, positioning, clamping & chucking of parts before machining or other processing operations. Also, unclamping, conveying, assembly & packaging after processing. Since the CNC application of the current invention uses synchronized pulse sources, and the motor pulse frequencies are divided and maintained outside the PC, there is no likelihood of computer interrupt delays that might corrupt the integri
Grant William
Hartman Jr. Ronald D
LandOfFree
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