Abstract:
An actuator positioned in accordance with two signals, the first being predominant and having a noise portion of magnitude which would mask the second signal and wherein the first signal is filtered to remove the noise and is connected to the actuator independently of the second signal so that the resultant motion of the actuator is additive of the two signals.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to actuators, and more particularly to the drive for actuators, which may contain two or more inputs, one of which may be many times larger than the other. 
     2. Description of the Prior Art 
     Actuators which may be used, for example, to position a device in a desired attitude are well-known in the art. The device is positioned by a first signal, herein called the coarse signal, usually from a computer through an amplifier to the actuator. The device being positioned may also be subject to undesirable changes of position due to, for example, vibration. To avoid this problem, an additional actuator has been heretofore employed to provide a second positioning signal, herein called the fine signal, to counteract the vibration. The fine signals may be several orders of magnitude smaller than the coarse, and so the problem of noise in the coarse signal presents a special problem since it may be in the same general magnitude as the fine signals. If an attempt to drive the actuator from a combination of the coarse and fine signals is made, the noise in the coarse signal may swamp the fine signal so that the fine signals are lost. If the noise is filtered out by a low pass filter, then the fine signals may very well be filtered out also. Using a separate actuator for the fine signals is expensive, heavy and often nearly impossible without adding a second platform or stage for the device being positioned. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In the present invention, an actuator in the form of a voice coil is used and wherein the windings around the armature are two-fold. The main windings are from the coarse controller and are relatively large in number, while the fine signals are presented to a smaller number of coils around the same armature. The result is that the noise in the coarse signal may be filtered out without affecting the fine signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the present invention; and 
     FIG. 2 is a block diagram of a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, a device to be controlled which, for purposes of this description will be considered to be a camera  10  is positioned by an actuator  14 , in the form of a voice coil having an stator  16  and a movable armature  18 , which operates to position camera  10  through a mechanical connection shown as dashed line  20 . 
     A position controller,  22 , which may be a computer, is shown having a first output on a line  24  which feeds the input of an amplifier  26 . Amplifier  26  provides an output current, i coarse , at two output terminals  30  and  32  which are connected to a wire  34  wrapped a number of times, N, around the armature of the voice coil  14 . Amplifier  26  preferably has an associated low pass filter,  35 , which filters out the noise, and the output current, i coarse , acting through N turns, causes the armature  18  to exert a force F, on camera  10  through the mechanical connection  20 . A position feedback shown by box  40  returns a signal via line  42  to controller  22  so that the motion caused by force, F, controls the camera  10  to the desired position. 
     A sensor shown by box  46 , which may be an accelerometer, produces a signal on a line  48  to controller  22  informing the computer of the vibration which the camera  10  may be experiencing. Since the vibration effect is at least an order of magnitude smaller than the position effect, if the two signals were added directly, the noise in the position signal would be of the same magnitude as the vibration signal and would tend to mask it out. To avoid this, controller  22  produces an antivibration signal on an output line  50  which generally will be smaller in magnitude than the position signal on line  24 . The signal on line  50  is presented to an amplifier  52  which produces an output current, i fine , at output terminals  54  and  56  connected to a wire  58  which is wrapped a number of times, n, around the armature of the voice coil  14 . In the normal situation, the output of amplifier  52  is of the same general order of magnitude as the output of amplifier  26  and accordingly, the number of turns, N, is made to be much larger than the number of turns, n. In some cases, amplifier  52  may have a very small output compared to the output of amplifier  26  in which case, the number of turns, N, need not be so very much larger than n. The important feature is that the force produced by the antivibration signal be proportionately smaller than the force produced by the position control signal. This would normally be at least one order of magnitude. This is most easily accomplished by adjusting the number of turns N, to the number of turns n. Amplifier  52  may have an associated low pass filter,  59 , therein to filter out any noise but the magnitude of this noise is so small that filter  59  is probably not necessary. The output current i fine  adds a small force to the positioning force F which operates to null the vibration. 
     The force F may be expressed by the equation: 
     
       
           F=B ( Ni   coarse   +ni   fine ) 
       
     
     Where B is a constant of magnitude which depends on the size and geometry of the magnetics in voice coil actuator,  14 . 
     It is seen that by using a single actuator with two coils activating the armature, one coil having many turns and exerting a large influence on the movement of the armature and the other coil having few turns and exerting a proportionately smaller influence on the movement of the armature, a single actuator may be used. The position being controlled by the larger armature movement and any vibration which may exist being cancelled by the smaller movement. It is also seen that the noise in the larger signal can be filtered out without affecting the smaller signal for the vibration. 
     If desired, a third correction could be added in cases where a third and yet smaller variable is desired to be added to the force F. In this event, as seen in FIG. 3, a third output,  65 , from controller  22  would feed a third amplifier,  67 , to produce a third, and yet smaller, current into a third winding,  70 , around armature  18  to produce a third factor into the force F of considerably less effect than the position signal and the antivibration signal. When the third output is small enough to be swamped by the noise in the second signal, then the second output would be separately filtered, as shown, and the third output independently connected to the coil  70 , as shown, to provide protection in the same manner as the first and second outputs avoid the second output from being swamped by the first output. 
     It is therefore seen that I have provided a novel actuator requiring only one movable force exerting device and which produces an output force of magnitude dependent upon the main force plus additional smaller forces that might be desirable to use without allowing the noise which may exist in the larger force to mask the effect of the smaller forces. Many changes will occur to those having skill in the art. For example, while a camera-positioning device has been used in the description of the preferred embodiment, there are many other devices such as telescopes, mirrors, antennas etc., which can use the present invention, and while a voice coil type actuator has been used in the description of the preferred embodiment, there are many other actuators such as piezoelectric, electrostatic, motors, etc., which can use the present invention. I therefore do not wish to be limited to the structures and methods described in presenting the preferred embodiment but rather intend to rely on the claims to define the scope of the invention.