Abstract: In an agricultural machine, sensor signal variability is identified, over a period of time. A control system deadband is identified, based upon the sensor signal variability. A control system uses the control system deadband to control the agricultural machine.

Abstract: A motor control device includes a velocity controller configured to calculate a torque command from a velocity command and a motor velocity; a compensation torque calculation unit configured to calculate a compensation torque command by multiplying an error between the motor velocity and a velocity of a driven part by a compensation gain and a compensation filter; a torque control unit configured to control torque of a motor based on a value obtained by adding the torque command and the compensation torque command; and a setting change part configured to change a gain of the velocity controller according to an operating condition of the motor control device, and change at least one of the compensation gain and the compensation filter in accordance with a change in the gain of the velocity controller.

Abstract: An example system includes a transmission having a first plurality of gears and an extent of backlash. The system also includes a first motor connected to an input shaft of the transmission and a second motor connected to an output shaft of the transmission through a second plurality of gears. A first gear ratio of a first plurality of gears is greater than a second gear ratio of the second plurality of gears. The system may receive a command to change a direction of rotation of the output shaft from a first direction to a second direction. In response to the received command, the first motor may drive the transmission through a first portion of the extent of backlash deadband. The second motor may drive the transmission through a second portion of the extent of backlash deadband. The second portion may be greater than the first portion.

Abstract: An electric fader drive unit includes a drive portion, a fader position control portion, and an electric fader control portion. The drive portion drives an electric fader by supplying drive power to the electric fader. The fader position control portion indicates a target position of the electric fader. The electric fader control portion receives an indication of the target position from the fader position control portion, and, when controlling the drive portion to move the electric fader to the target position, moves the electric fader to the target position by changing the drive power maintained at preparation drive power less than the minimum drive power that is the lowest drive power required for moving the electric fader to a predetermined drive power not less than the minimum drive power.

Abstract: A servo control device having a position control unit and a speed control unit to control a front end point of a machine of a machine tool, comprising: a position detecting unit for detecting a position of a motor; a first position error calculating unit for calculating a first position error based on a position command to a motor and position feedback from the position detecting unit; a torsion estimating unit for estimating an amount of torsion of the front end point of the machine; a second position error calculating unit for adding the first position error and estimated amount of torsion to calculate a second position error; a coefficient adapting unit for determining a coefficient of feedforward control so as to minimize the second position error; and a higher order feedforward control unit for performing feedforward control by using the determined coefficient and the position command.

Abstract: A multi-actuator motion control system includes a control methodology that coordinates the motion of multiple actuators while limiting the force-fight between the actuators. Control logic is provided in a relative coordinate system that allows control of the mean actuator position. Force-fight between the actuators is decoupled from the actuator position by estimating load forces on the actuator using reduced-order observers.

Abstract: A positioning control system for positioning a moving element on a basis of position command data is provided with a feedback loop. The system is also provided with a loop gain modifier for determining a loop gain, which is to be used in a following positioning operation, on a basis of a difference between an amount of overshoot measured in a current positioning operation and a predetermined tolerance or on a basis of a difference between an amount of overshoot measured in a current positioning operation and a first predetermined tolerance and a difference between an amount of undershoot measured in the current positioning operation and a second predetermined tolerance. The first and second tolerances may preferably be the same in absolute value. The moving element may specifically be a steerable mirror for drilling holes in a work by reflecting a laser beam. Also disclosed is a laser drilling machine including the system.

Abstract: A control apparatus for a motor includes, a position detection unit which detects the position of a driven body, a positional error acquiring unit which acquires for each sampling cycle a positional error representing a deviation between the position command given to the motor and the position of the driven body detected by the position detection unit, a dead-zone processing unit which outputs the positional error by replacing the positional error with zero if the positional error acquired by the positional error acquiring unit lies within a predetermined dead-zone range, and a repetitive control unit which calculates an amount of correction such that the positional error output from the dead-zone processing unit is reduced to zero, and wherein: the motor is controlled based on the positional error acquired by the positional error acquiring unit and the amount of correction calculated by the repetitive control unit.

Abstract: A system and control method mitigates hysteresis of an adjustable component in the system. A control module can allow small control changes to be effected to the component within limits of the component's and/or the system's normal hysteresis band. The control method can allow finer, more accurate and more aggressive control to be obtained from the component. The system and method can utilize two separate control regimes to control adjustments to the component. The first control regime can control changes larger than a hysteresis band and/or changes in a same direction as the last adjustment that was performed with the first control regime. The first control regime can be a feedback-based adjustment to the component. The second control regime can be utilized to control changes within the hysteresis band. The second control regime can use open-loop based adjustments to the component.

Abstract: Provided is a technique to suppress hunting in a range of a minimum resolution of a pulse encoder when a servo motor has reached a target position and stopped, thereby maintaining a stable stop state. A servo motor position control device uses a cascade configuration having a position control loop as a main loop and a velocity and current control loop as a minor loop. A proportion control is performed for a position control while a proportion integration control is performed for a velocity control and a current control. When the servo motor position has reached the target position and stopped (S201), a current instruction value for the current control is maintained at a value upon stop (S202) and the current control is switched to the proportion control (S204).

Abstract: A method of controlling an input device is disclosed. A deadband is generated about a first position when the input device is at the first position. The input device is moved from the first position to one or more additional positions. The deadband width is varied based on the position of the input device.

Abstract: A method of operating a control device having a setpoint value, an error signal, and a control output is disclosed. The error signal is representative of a difference between a controlled variable and the setpoint value, the control output operable to affect the controlled variable. The method includes generating the control output based at least in part on the error signal and holding the control output at a held value independent of the error signal when the error signal is within a dead zone. The method also includes causing an integrating portion within the control device to track the error signal and the held value when the error signal is within the dead zone.

Abstract: A control system having a floating deadband control includes an input device moveable from a first position to a second position. In addition, the control system includes a controller configured to automatically generate a first electronically defined deadband about the first position when the input device is at the first position and configured to automatically generate a second electronically defined deadband about the second position when the input device is at the second position.

Abstract: A method of operating a control device having a setpoint value, an error signal, and a control output is disclosed. The error signal is representative of a difference between a controlled variable and the setpoint value, the control output operable to affect the controlled variable. The method includes generating the control output based at least in part on the error signal and holding the control output at a held value independent of the error signal when the error signal is within a dead zone. The method also includes causing an integrating portion within the control device to track the error signal and the held value when the error signal is within the dead zone.

Abstract: A position control system uses a speed command supplied to a driving source. The speed command has a change pattern which has an acceleration section (1) for eliminating a dead zone of a power transmission mechanism, a constant-speed section (or an acceleration section with a slower acceleration than in the section (1)), an acceleration section (3) up to the maximum speed, a constant-speed section (4), a deceleration section (5), a constant-speed section (6) for eliminating the dead zone (or a deceleration section with a slower deceleration than in the section (5)), and a deceleration (7) for stopping at a target section. Even when a driven member has large inertia, the position thereof is accurately controlled to the target position in a semi-closed position control system.

Abstract: In servomechanisms, like for example used in disk drives, disturbances, for example, friction, shock and vibration, prevent the system positioning accuracy from further improvement. These disturbances occur in a relatively low-frequency range compared to the electrical dynamics. In the present invention, an acceleration feedback control loop using a frequency-separated acceleration soft sensor (350) replaces the conventionally used current control loop in the low frequency range, where the disturbances occur, so as to attenuate the influence of the disturbances enclosed in the loop. The current feedback continues to manage the electrical dynamics in the high-frequency range. Estimating the required acceleration signal by a soft sensor (350) eliminates the need for physical accelerometers, which reduce system reliability and increase system cost.

Abstract: A control device and method is provided for controlling a control element by receiving a controller demand signal and a control element sensor signal, and processing the signals to determine if there is a change in the controller demand signal and/or a change in the control element sensor signal. A first dead band range and/or a second dead band range are determined based on the change in the controller demand signal and/or based on the change in the control element sensor signal. An error signal is calculated from the controller demand signal and the control element sensor signal, and a control signal for controlling the control element is generated based on the determination of the dead band ranges and whether the calculated error signal is outside of the first and/or second dead band ranges.

Abstract: A method for controlling non-synchronous actuators using a first and second estimate of the position of the actuator to create a variable position estimate window between which the actual position of the actuator is always bound. The first and second estimates of position are calculated based on the maximum and minimum speeds at which the actuator could be moving in each of first and second directions, and further wherein motion of the actuator in a saturated direction is disabled for as long as the first and second estimates converge at one of two final positions.

Abstract: In an apparatus for controlling the position of an object driven by a servomotor via a ball screw drive system, parameters of the ball screw drive system are determined from a position command value, an acceleration command value, a torque command value and a motor speed, based on which a dynamic deflection extent while the object is driven at an adjustable speed is calculated. To compensate for this dynamic deflection extent, a deflection compensation command section calculates a deflection compensation value, a deflection speed compensation value, and a deflection torque compensation value. These compensation values are added to their related sections in the position control apparatus individually and collectively compensate for the dynamic deflection.

Abstract: A position control device for driving a movable member by a motor to a target position prevents a re-start of the motor by the vibration after stopping of the movable member. A re-start operation is forcedly inhibited during a predetermined period after a stopping operation of the movable member at the target position, and is permitted, only after the predetermined period, is entered by the position of the movable member is different from the target position.

Abstract: A method of generating a calibrated command signal in a control system including a command device is disclosed herein. The command device (e.g., a control lever) is moveable between predefined positions (e.g., detents). A sensing circuit generates a signal representing the position of the command device. The method includes the steps of calibrating the command device and then generating a calibrated command signal based upon the command device position. The calibrating step includes moving the command device to the predefined positions, converting the sensed position signals into calibration values and storing these values. The generating step includes moving the command device to an operating position, converting the sensed position signal into an operating position signal, and generating the calibrated command signal based upon the operating position signal and the calibration values. In one embodiment, the method is used to read the control levers for auxiliary valves in an auxiliary hydraulic system.

Abstract: A method and apparatus automatically associate a sensed mechanical parameter to a range of motor velocity for controlling the rotational velocity of a motor driving a medical instrument. The method and apparatus sense or measure the mechanical parameter whose value, controlled by a human operator, through for example, a footpad, can be measured and converted to a digital signal. The method and apparatus, in response to the measured sensed mechanical parameter, automatically scale the range of parameter values to a new range of motor velocity values thereby adjusting, to the mechanical displacement (force or distance) with which the user is most comfortable. The transformation also provides deadband values around the minimum and maximum motor velocities so that maximum motor velocity is not "chased" and minimum motor velocity is not sensitive to small perturbations due to thermal effects and other events which may affect the mechanical sensor output.

Abstract: A hybrid servomechanism includes a speed control, a rotor position control and a brushless motor. When enabled, the position control commands a stationary stator mmf vector, allowing the motor's rotor to rotate until load torque and motor torque are balanced. This position control eliminates limit cycle operation and allows the motor to compensate for backdriving caused by external loads.

Abstract: A moving fader system, primarily for the processing and combining of audio signals, includes a dedicated preprocessor to implement the execution of repetious input instructions. Other features contributing to the operation of the system include (1) "Look-up Tables" included in the preprocessor for conversion purposes, (2) a fiberoptic link for transmission of digital signals between the preprocessor and the servo circuits associated with each fader assembly, and (3) circuitry for combining the outputs of a position digital-to-analog (D/A) converter, an offset correction D/A converter and a gain correction D/A converter, to provide accurate analog servo signals to each fader assembly.

Abstract: A variable speed eddy current electric motor includes a zero-torque regulating circuit that senses and responds to the current flowing through an eddy current motor field coil. As the magnitude of the field coil's current is changed by the eddy current motor's speed control circuit, the operating method of the zero-torque regulating circuit supplies varying amounts of current to flow through the field coil in a direction opposite to that of the current applied thereto by the speed control circuit. Thus, when the eddy current motor's speed control circuit no longer causes any current to flow through the field coil, the current supplied to the field coil by the zero-torque regulating circuit produces a magnetic filed that removes all torque from the eddy current motor's output shaft.

Abstract: Operating device for the cover of a sliding and lifting sunroof of a motor vehicle having a desired value transmitter and an actual value transmitter for controlling the sliding sunroof function and the lifting roof function via an actuator that is part of a control circuit. By the control circuit, the desired value signal supplied by the desired value transmitter and corresponding to the respective desired position of the cover selected is compared with an actual value signal of the actual value transmitter corresponding to the respective actual position of the cover to cause the cover position to be adjusted until the actual cover position matches that desired. The operating element of the desired value transmitter is mounted, to slide for producing for a sliding of the cover, and to swing for producing a cover tilting-out movement.

Abstract: An offset compensating circuit in a fine control servo. When the servo loop for an error signal is opened, the error signal is sampled and its positive and negative peaks are found. The average of the positive and negative peaks is determined as an offset signal to be subtracted from the error signal when the loop is closed.

Abstract: A mechanically adjustable variable speed drive includes an electric actuation apparatus which can be controlled by an analog embodiment or a digital circuitry embodiment. A speed change actuator is automatically and mechanically adjustable, such as with a controlled servomotor. A tachometer determines the actual rotational speed of a drive shaft, which is compared in a digital controller with a manually set desired rotational output speed. The digital controller (or an analog circuit in the case of the analog embodiment) controls the servomotor to adjust the mechanically adjustable variable speed drive. An automatic deadband means inhibits driving of the servomotor whenever the tachometer signal and the desired speed setting signal is within a predetermined deadband, which deadband is adaptively changed responsive to various conditions.

Abstract: The invention is a control system for generating time modulated pulse signals to effect movement of a doser type actuator. The control system is characterized in that it includes an augmenter circuit which generates a first correction signal additive to scheduled control signals when the actuator fails to respond or has a response below a predetermined limit to an actuating pulse, a second correction circuit which generates a correction signal proportional to the magnitude of the first movement of the actuator response to a pulse signal for reducing the magnitude of the pulse signal in proportion to the magnitude of the movement, and a gating signal or circuit which blocks said first and second correction signal generating circuits generating the augmentation signal when the movement of the actuator in response to a pulse signal is negative or above a predetermined limit, when the positional error changes direction, or when the actuator position is within the desired deadband limits.

Abstract: A controller for close positioning or modulating control of an electric motor is disclosed. The controller compares a signal representative of the demand on the system with a signal representative of the actual position of the motor or a valve associated therewith, and if the difference between the signals exceeds a "deadband" and no action has been taken within a first time interval, and if the last movement of the valve was in the same direction and a second time interval has elapsed, a motor run pulse is generated. If the last movement of the valve was in a direction opposite to that desired, the motor run pulse is extended to overcome "backlash" resulting from the reversal of motor rotation.

Abstract: An electromagnetic servo device for electric power steering system for vehicles including a driving control circuit (100) adapted to generate a torque magnitude signal (Sa) and a torque direction signal (Sdr, Sdl), based on an output signal (VR, VL) from a torque detection mechanism (11) for detecting steering torque (Ti) acting on an input shaft (1) connected to a steering wheel and an output signal (Vf) from a vehicle speed detection mechanism (50), and to feed, to an electric motor (18) for applying auxiliary torque to an output shaft (4) operatively interconnected with a steered wheel, an armature current (Io) of such a magnitude and in such a direction of conduction as desirous in accordance with both the torque magnitude signal (Sa) and the torque direction signal (Sdr, Sdl), and a dead zone (2K.sub.1 or Dl, Dm, Dh) set for the torque magnitude signal (Sa), wherein the dead zone (2K.sub.

Abstract: An electronic levelling apparatus using an inclinometer mounted to a platform for sensing deviations from the horizontal and generating an output signal representative thereof, filtering the inclinometer output signal to remove electromagnetic and radio frequency interference, level-shifting the filtered inclinometer output signal to establish both positive and negative threshold voltages, determining positive and negative voltage level shifts to generate a level control signal therefrom and transmitting the level control signal to an actuating mechanism for maintaining the platform level.

Abstract: A tractor control system has a work implement, an actuator for the work implement, an electronic circuit utilizing an analog/digital technique and including an analog/digital control unit and a device for measuring a factor dominating the performance of the actuator and providing a first signal representing the actual value of the control system, a second signal representing a set point value, and a third signal in analog form representing the difference between the values of the first and second signals. The difference constitutes the control deviation for governing the analog/digital control unit which controls the actuator. A converter converts the third signal to digital form by a sampling device for sampling at a sampling frequency f.sub.o to establish a dead range in a time dimension. The sampling device provides pulses. A comparator circuit processes the digital signal and includes comparators having limit values defining the dead range set therein.

Abstract: An electromagnetic servo device (200) includes a driving control circuit (100) adapted for, in accordance with an output signal (VR, VL) from a torque detection mechanism (11) for detecting steering torque (Ti) acting on an input shaft (1), providing a first control signal (Vmo), to thereby feed an armature current (Io) of a controlled quantity in a controlled direction, to an electric motor (18) for generating auxiliary torque to be applied to an output shaft (4) and a second control signal (Vcl), to thereby control, an electromagnetic clutch (41) for transmitting motor torque of the electric motor (18) as the auxiliary torque to the output shaft (4).The second control signal (Vcl) has fed back thereto a signal (Vf) according to the actual quantity of the armature current (Io).

Abstract: A driving control method for an electromagnetic servo device including a driving control circuit adapted to generate a torque magnitude signal and a torque direction signal on the basis of an output signal from a torque detection mechanism for detecting torque acting on an input shaft in relation to an output shaft and to send an armature current of such a magnitude and of such a polarity as desirous in accordance with the torque magnitude and direction signals to an electric motor for additionally providing auxiliary torque for the output shaft, comprises a step of setting the width of a dead zone of the torque magnitude signal wider than that of a dead zone of the torque direction signal.

Abstract: Described herein is a steering amplifier for use in the steering systems of watercraft. Potentiometers are mounted within the helm unit and the feedback unit of the craft and these potentiometers are used to determine the various helm and rudder positions. Circuitry is provided to determine the difference or error between the helm position and the rudder position and to energize solenoid valves which cause the rudder to move in the appropriate direction to correct the error.

Abstract: An operating system for movable parts for the selective closing or exposing of openings, especially for sliding roofs and sliding/lifting roofs of motor vehicles. The operating mechanism has a motor drive for the movable part and an actuating member for starting the drive, if required. In order to facilitate, especially, the bringing of the movable part into intermediate positions, the actuating member is developed as a desired-value transmitter for the position of the movable part, and the drive is part of a control circuit which compares the position selected at the desired-value transmitter with the actual position of the movable part and adjusts the movable part until the deviation has become zero.

Abstract: A circuit arrangement for controlling the action of an adjusting device, in particular of a patient chair, which comprises, as target value indicator, a digital-analog converter (1) and, as actual value indicator controllable by the adjusting device, a potentiometer (2), which receives an equalized feed voltage which serves to operate the digital-analog converter, and which is connected via a branch (13) to a comparator unit (12), whose other input is connected to output (8) of the digital-analog converter (1), and which controls the adjusting device (31, 32, 33). According to this circuit design, the digital-analog converter (1), and the potentiometer (2), form a Wheatstone bridge of which one diagonal is supplied with a single feed voltage, while the other diagonal contains the comparator unit (12).

Abstract: In a circuit arrangement for an alternating control a PI controller comprises a first operational amplifier having an output connected via a resistor to the non-inverting input of a second operational amplifier wired as an impedance transformer. The output of the second operational amplifier is fed back via an RC stage to the inverting input of the first operational amplifier. The output of a second controller is connected via a decoupling diode to a junction between the decoupling resistor and the non-inverting input of the second operational amplifier. Positive as well as negative signals can occur at the output of the first operational amplifier, and discontinuities in control during a switch over between the two controllers are avoided.

Abstract: A method and apparatus for controlling an electric discharge machine wherein a motor for moving an energized electrode relative to a workpiece is driven in accordance with command data.

Abstract: The present invention relates to a control system. The control system controls the displacement of a working portion of an implement with respect to a reference position. The reference position can be the ground surface in the proximity of the working portion of the implement. A sensor is provided for determining the location of the ground surface to provide a reference signal. A signal generator is provided for producing a displacement signal which is representative of a preselected displacement. A comparator produces an error signal which is proportional to the sum of the reference signal and the displacement signal minus a null point signal. A servo mechanism is provided which is operable via the error signal to control the displacement of the working portion so as to substantially move the working portion the preselected displacement from the reference position thereby causing the error signal to be reduced to approximately the null point signal.

Abstract: A servovalve device assembly is provided with an electronic matching circuit positioned upstream of the servovalve. The matching circuit supplies electric control signals whose purpose is to modify the hydraulic flowrate response curve of the servovalve as a function of the electrical control signal, so as to make it substantially identical to an ideal desired response curve.

Abstract: A system for detecting the failure of a control system and its object includes a mathematical model of the control system and its object which continuously predicts the output of the object. An error signal is continuously calculated which is the difference between the model output and the actual output of the object. Error signals exceeding a predetermined minimum value or deadband are integrated; but the integral is reset to zero whenever the error signal value falls within a predetermined range indicative of normal steady state operating tolerances. If the value of the integral reaches a specified level before being reset to zero, a failure signal is triggered. This failure detection system can be made sensitive to relatively small error signals without triggering a false failure signal if the small error was the result of only a temporary problem or due to inaccuracies in model simulation.

Abstract: A circuit for controlling the position of a driven member is disclosed which includes a control circuit for controlling the application of electrical power to a motor and a circuit element operable for generating position error signals corresponding to the position of the load which may in one embodiment constitute a rotor element of the motor. A comparator section is provided for comparing the position error signals with position reference signals and for generating control signals to effect rotation of the load in a desired direction. In one embodiment, the error signal is generated by a feedback loop including a potentiometer having a movable element coupled to the load or motor rotor, wherein the voltage magnitude of the error signal is varied in accordance with the rotational position of the load or rotor element. In a preferred embodiment, the comparator section includes first and second comparators respectively responsive to position deviations of the rotor in first and second rotational directions.

Abstract: A control system 54 for a doser type hydraulic actuator 56 is disclosed. The doser actuator includes a pair of unequal area pistons 18, 20 on a common shaft 16 which are moved incrementally by injecting into or removing from a control pressure chamber metered quantities or doses of fluid. The doses are metered by timed openings of solenoid valves 32, 34 connecting the control pressure chambered to a supply 44 or return 48 pressure sources. The control system includes a base pulse width signal generator 106 which pulse modulates the solenoids as a function of the error between a requested position and an actual position. The base pulse width is modified by a correction means 108, 110, 112 when the error is within a predetermined band width. The correcting means compensates for the variations of the actuator when its response is uncertain with respect to the base pulse width.

Abstract: An automatic control system in which a controlled quantity of an object to be controlled is compared with a preset quantity through a comparator, the output signal of which is applied to blind controller means having a dead zone set therein. When the output from the comparator comes out beyond the dead zone, the blind controller means cooperates with operation holding means to perform a control operation continuously for a predetermined time even when the output from the comparator falls within the dead zone. The number of times at which the object is controlled may be significantly decreased.

Abstract: A control unit for automatically controlling the angular position of a reversible, motorized device, such as an antenna rotor, in response to a signal from an external sensor, such as a potentiometer coupled to the rotating shaft of a windvane. The unit includes integrated circuits and other electronic components for monitoring the windvane signal and for activating the rotor, as necessary, to maintain its alignment with the sensed wind direction. The unit also comprises means for providing: a no-response zone of adjustable width about the momentary, average wind direction; an adjustable, time delayed response to changes in wind direction; an automatic reversal of rotation if the rotor approaches the .+-.180.degree. position while searching for the wind direction; an automatic disabling of the rotor for windspeeds less than a selectable, threshold value.

Abstract: A power driver control circuit (38) provides control signals (44, 46, 48, 50, 52, 54) for switching transistors in a power driver (56) for an electromagnetic actuator (11) of the type used for controlling a servo head (12) in a closed loop servo system. The control circuit includes variable time delay circuits (70, 71) connected to threshold detectors (74, 84) so that dead zones can be created when the servo error signal changes polarity thereby isolating the switches and preventing switch burn-out.

Abstract: The lens mount of a movie camera is automatically positioned to maintain an image of a subject in focus on a focal plane of a recording station by generating periodic range pulses having a characteristic directly related to subject range, and converting each pulse to a number which represents the focus position of the lens mount. Such number is stored in a first register whose contents vary in response to changes in subject distance at a rate dependent on the pulse repetition rate of the range pulses. The actual position of the lens mount is determined in the form of a second number which is stored in a second register whose contents vary in response to changes in the position of the lens mount at a rate determined by the rate of change of position. Rotation of a reversible motor is initiated when the contents of the registers are unequal, rotation being terminated when the contents are equal. The direction of rotation is in accordance with which of the two registers has the larger contents.

Abstract: A multiple-purpose, closed-loop, automatic control system comprising:a system controlled;a detecting means for detecting a controlled variable output from the system controlled and converting the controlled variable into an electrical feedback signal;a signal converting means for receiving the feedback signal and converting said signal into an angular displacement corresponding to the feedback signal;a comparing means for comparing the controlled variable with a preset desired value and selectively opening or closing a forward or a reverse controlling circuit;a controlling means including the forward and the reverse controlling circuit selectively opened or closed by said comparing means, a braking control circuit and a driving mechanism responsive to said forward and reverse control circuits and said braking control circuit for automatic control over the system controlled to keep the controlled variable within the preset desired value.