Discontinuous Or "on-off" Control Patents (Class 318/672)
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Patent number: 10773349Abstract: A machine tool having a tool magazine for changing a tool attached to a spindle is equipped with an initial operation speed setting unit configured to set the operation speed of the tool magazine to an initial operation speed, an operation speed adjusting unit configured to be operated by the user to thereby adjust the operation speed of the tool magazine relative to the initial operation speed, an actuator configured to actuate the tool magazine, an operation speed acquisition unit configured to acquire the operation speed of the tool magazine after adjustment of the operation speed made by the operation speed adjusting unit, and an actuator control unit configured to control the actuator to actuate the tool magazine at the operation speed acquired by the operation speed acquisition unit.Type: GrantFiled: September 18, 2018Date of Patent: September 15, 2020Assignee: FANUC CORPORATIONInventor: Gaku Isobe
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Patent number: 8786240Abstract: The invention realizes a method for controlling an electric cylinder and a control system for the cylinder that can prevent a load for pressurizing from significantly exceeding a target load and can shorten the time for the pressurization. A servo controller 17 can set the speed of the rod 11 and a load for stopping Ps that is used for determining whether the rod 11 should be stopped so that the load for pressurizing Pm does not significantly exceed the target load Pt. The servo controller 17 drives the rod 11 under the position control mode and determines whether the load for pressurizing Pm that is detected by a load detector 13 is bigger than or equal to the load for stopping Ps.Type: GrantFiled: September 1, 2010Date of Patent: July 22, 2014Assignee: Sintokogio, Ltd.Inventors: Yoichiro Shirai, Masahiko Nagasaka
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Patent number: 8725351Abstract: An active suspension system for a suspended device. The system has an electromagnetic actuator that produces force on the suspended device and that is powered by a power source, and a control system that provides control signals that cause the electromagnetic actuator to exert force on the suspended device. The control system is adapted to receive a turn-off signal that results in disabling the electromagnetic actuator from producing force on the suspended device. When the control system receives a turn-off signal it provides actuator turn-off control signals that cause the force exerted by the electromagnetic actuator to progressively transition to zero over a transition time period.Type: GrantFiled: October 31, 2012Date of Patent: May 13, 2014Assignee: Bose CorporationInventors: Brian Selden, Antonio Sangermano
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Patent number: 8710787Abstract: A servomotor control circuit for an air conditioner apparatus of a vehicle includes a drive control section for controlling drive of a servomotor so that the servomotor attains a target stop position, a rotation position change detection section for detecting a change in the rotation position of the servomotor, and an operation limit check section for checking, based on the change in the rotation position of the servomotor, whether the servomotor has attained the operation limit position. The drive control section stops drive of the servomotor without reception of a servomotor drive stop command produced from a main control apparatus, when the servomotor is determined as having attained the operation limit position.Type: GrantFiled: May 12, 2010Date of Patent: April 29, 2014Assignee: Denso CorporationInventor: Nobuaki Koshobu
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Patent number: 8159176Abstract: A motor-driving device comprising: a switching element to control a current passed through a first coil of a stepping motor including the first and a second coils electromagnetically coupled; a rectifier element to be energized in a ground-side-to-second-coil direction; a coil-current-detection unit to detect a current passed through the first coil; a regeneration-current-detection unit to detect a current passed through the rectifier element; a control unit to turn off the switching element when the current passed through the first coil reaches a predetermined-set current based on a detection result of the coil-current-detection unit; and a negative-current-detection unit to detect whether a negative current greater in absolute value than a predetermined-set value is passed through the rectifier element based on a detection result of the regeneration-current-detection unit, the control unit keeping the switching element off when the negative current is not passed, based on a detection result of the negative-Type: GrantFiled: August 13, 2010Date of Patent: April 17, 2012Assignees: Sanyo Electric Co., Ltd., Sanyo Semiconductor Co., Ltd.Inventors: Mitsuji Arai, Takeshi Oike
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Publication number: 20100291853Abstract: A servomotor control circuit for an air conditioner apparatus of a vehicle includes a drive control section for controlling drive of a servomotor so that the servomotor attains a target stop position, a rotation position change detection section for detecting a change in the rotation position of the servomotor, and an operation limit check section for checking, based on the change in the rotation position of the servomotor, whether the servomotor has attained the operation limit position. The drive control section stops drive of the servomotor without reception of a servomotor drive stop command produced from a main control apparatus, when the servomotor is determined as having attained the operation limit position.Type: ApplicationFiled: May 12, 2010Publication date: November 18, 2010Applicant: DENSO CORPORATIONInventor: Nobuaki Koshobu
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Publication number: 20100102598Abstract: The invention relates to an electromotive drive (1) for a motor vehicle actuating part (2) which can be moved into at least one defined target position (16), said drive having a detection device (14) for detecting whether the motor vehicle actuating part (2) is in a tolerance range (19). The invention provides for the tolerance range (19) to be able to be determined on the basis of the stop position (18) of the motor vehicle actuating part (2).Type: ApplicationFiled: January 8, 2008Publication date: April 29, 2010Applicant: Robert Bosch GMBHInventors: Heiko Frey, Hubert Lamm, Christian Stolz
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Patent number: 7696713Abstract: Driving of a pulse motor is controlled in such a manner that a rotating body driven by the pulse motor rotates at a uniform angular velocity. Angular displacement of the rotating body is detected, a difference between a detection value of the angular displacement and a target value of angular displacement set in advance is calculated, and a drive pulse frequency of a drive pulse signal to be used for driving the pulse motor is calculated based on the difference and a reference drive pulse frequency. Whether the difference is added to the reference drive pulse can be selected.Type: GrantFiled: March 12, 2007Date of Patent: April 13, 2010Assignee: Ricoh Company, LimitedInventors: Makoto Komatsu, Toshiyuki Andoh, Yoshihiro Sakai
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Patent number: 7609016Abstract: A control system includes a controller configured to provide a drive signal, and a switching device configured to generate an output control signal as a function of the drive signal in an on-state mode of operation. The control system also includes a timing network configured to receive the drive signal and output a gated signal to the switching device, wherein the gated signal maintains a relationship with a predetermined threshold during the on-state of operation of the switching device.Type: GrantFiled: February 23, 2006Date of Patent: October 27, 2009Assignee: Infineon Technologies AGInventor: Richard Alan Kraus
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Publication number: 20090224718Abstract: In driving a target body only by one of actuators, the target body is smoothly driven. A drive unit (1) includes a stage (3), a first ultrasonic actuator (4A) for driving the stage (3) in an X direction and a second ultrasonic actuator (4B) for driving the stage (3) in a Y direction. When the stage (3) is driven only in one of the X direction and the Y direction, one of the first and second ultrasonic actuators (4A and 4B) which corresponds to the direction generates composite vibration of longitudinal direction parallel to a contact surface of the stage (3) and bending vibration perpendicular to the contact surface of the stage (3). On the other hand, the other one of the first and second ultrasonic actuators (4A and 4B) generates only longitudinal vibration parallel to the contact surface of the stage (3).Type: ApplicationFiled: May 20, 2009Publication date: September 10, 2009Applicant: PANASONIC CORPORATIONInventors: Kenichi HONJO, Hideaki MUKAE, Yusuke ADACHI
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Patent number: 7365508Abstract: A motor comprises: coil on/off switching devices for switching between an on-state wherein current is supplied to the coils, and a first off-state wherein the coil terminals are open-circuited or a second off-state wherein the coil terminals are short-circuited; and a coil current control device for controlling switching operations of the coil on/off switching devices according to commands input to the motor. In the event that motor movement with great mechanical compliance is required, the ratio of the period of the first off-state is increased, and on the other hand, in the event that motor movement with great viscosity resistance is required, the ratio of the period of the second off-state is increased. This solves the problems of torque loss and cogging during a period wherein no current is applied to the coil.Type: GrantFiled: November 28, 2003Date of Patent: April 29, 2008Assignee: Sony CorporationInventors: Masatsugu Iribe, Hajime Yamanaka, Yoshihiro Itoh, Shinya Suzuki
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Patent number: 7285930Abstract: A method is specified for controlling a multiphase motor that is commutated by an inverter-side bridge circuit, in the course of which a particularly precise and technically simple detection of a control-relevant variable of a considered motor phase, in particular of a motor phase current and/or a back EMF voltage and/or a variable derived therefrom, takes place. It is provided here to determine the control-relevant variable with the aid of the current state of a freewheeling diode that is disposed in a phase half bridge, assigned to the respective motor phase, of the bridge circuit, the current state being detected during an on time in which a power switch, connected in parallel with the freewheeling diode, of the phase half bridge exhibits a conducting state, and a power switch connected in series with the freewheeling diode exhibits a blocking state.Type: GrantFiled: February 22, 2006Date of Patent: October 23, 2007Assignee: Diehl AKO Stiftung & Co. KGInventors: Martin Weinmann, Alexander Müller, Stefan Zeh
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Patent number: 6831433Abstract: A drive control apparatus comprises a drive signal supply unit for generating, when a power-supply voltage is supplied to the drive control apparatus, a drive signal, which is used for driving a load from this power-supply voltage, and for supplying this generated drive signal to an output port of a microcomputer, a drive signal stop unit for stopping, when the power-supply voltage has a value that is equal to or less than a predetermined value, the drive signal supply unit from supplying the drive signal, and a drive signal delay unit for delaying the drive signal outputted by the drive signal supply unit.Type: GrantFiled: May 29, 2002Date of Patent: December 14, 2004Assignee: Yazaki CorporationInventor: Shinichi Furui
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Patent number: 6719677Abstract: The present invention is an automatic tool changer. The automatic tool changer is adapted to perform a tool magazine indexing operation in response to an indexing command and perform a tool changing operation in response to a tool changing command. If an indexing command is not output within a predetermined time period after completion of a tool changing operation, power to the servo motor driving the tool magazine is temporarily stopped and when the next indexing command is output, the power to the servo motor is resumed to perform the indexing operation. If a tool changing command is not output within a predetermined time period after completion of the tool magazine indexing operation, the power supply to the servo motor is temporarily stopped and when the next tool changing command is output, the power to the servo motor is resumed to perform the tool changing operation.Type: GrantFiled: December 11, 2001Date of Patent: April 13, 2004Assignee: Mori Seiki Co., Ltd.Inventor: Satohiro Izumi
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Patent number: 6636010Abstract: A liquid dispensing system increases the precision, reliability, and safety of dispensing medications and other liquids. An electronic brake grounds a power terminal of a pump motor to absorb the kinetic energy of the motor and other mechanically coupled components. The electronic brake reduces overage and overage variation in the dispensing of liquids at very little cost or complexity. A watchdog circuit monitors a controller heartbeat signal and disables the motor in the absence of a regular beat. The watchdog circuit along with redundant power switches greatly reduce the possibility of motor runaway in the event of component failure. A controller begins or ends each dispensing cycle with a diagnostic which determines whether the liquid dispensing system is fully operational. If not, the controller may disable the motor, emit an alarm tone, and display an alarm message.Type: GrantFiled: October 1, 2001Date of Patent: October 21, 2003Assignee: Zevex, Inc.Inventors: James Malmstrom, David Soss
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Patent number: 6541934Abstract: In a method for controlling an electric drive, a controlled variable is adjusted to a desired value. To protect the electric drive, the controlled variable is first adjusted to the desired value in a precise manner. Thereafter, the control operation is interrupted, AND the difference between the controlled variable and the desired value is check continuously to see whether it exceed a preset threshold. Interruption of the control operation is terminated when the threshold has been reached or exceeded.Type: GrantFiled: February 16, 2001Date of Patent: April 1, 2003Assignee: Bayerische Motoren Werke AktiengesellschaftInventors: Klaus Hirschfelder, Christian Schmidt
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Patent number: 6307464Abstract: In a receiver circuit module (22) having a microcontroller (U1), an output line (FILTER_LED) connectable to a source circuit module (20) is also used as an input. A switch (SW2) disposed in the source circuit module is closed to change the wave form which is read by the microcontroller as an input signal to drive a 5V signal to the gate of a solid state switch (Q1) turning it on to thereby energize an output device in the source circuit module via the same output line (FILTER_LED). By means of the dual function of the output line the control can notify a user of an HVAC system, for example, of system problems with a blinking light and/or an audible alarm as well as serving to notify the user at a remote location that selected maintenance is due, such as a need to change filters without additional control lines. The source circuit module can be mounted near the thermostat of the HVAC system or on the central heating and cooling unit.Type: GrantFiled: May 1, 2000Date of Patent: October 23, 2001Assignee: Texas Instruments IncorporatedInventors: Mark E. Miller, Timothy L. Anderson, Ronald E. Garnett
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Patent number: 5955859Abstract: The present invention concerns an interface module between a field bus and electrical equipment controlling and protecting an electric motor. The interface module includes an integrated circuit having data pins connected via input/output circuits to contacts or binary sensors or to coils or actuators of the electrical equipment. The data pins of the integrated circuit are connected via logic circuits to inputs or outputs which are greater in number than the data pins. The inputs/outputs are connected to coils or actuators and to auxiliary contacts or binary sensors of the electrical equipment.Type: GrantFiled: April 2, 1996Date of Patent: September 21, 1999Assignee: Schneider Electric SAInventors: Gilles Baurand, Andre Ganier, Fran.cedilla.ois Roussel
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Patent number: 5926002Abstract: The application describes a control pendant for controlling a multi-segment patient table to assume a variety of different positions or configurations. The pendant has safety features including automatic shutoff of power to the keys under selected conditions and backlighting of the keys when power is being supplied (e.g., when keys are operational) to provide improved visibility in low-light environments. The control pendant further has an ergonomically effective shape and key board layout. An icon representing the table and its segments is located on the keyboard, and the keyswitches are arranged with respect to the icon to facilitate rapid and accurate visual identification of keys which operate particular table segments.Type: GrantFiled: February 21, 1995Date of Patent: July 20, 1999Assignee: Getinge/Castle, Inc.Inventors: Matthew R. Cavanaugh, Kenneth A. Johnson
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Patent number: 5572104Abstract: An electric control for gas furnaces which controls a two speed main blower fan and an induction draft fan based on inputs from a room thermostat, a high limit and an ignition control including a gas valve. The control has a circuit board having a power supply for providing 24 volts DC current source to drive DC relays and a 5 volt DC power source to power a microprocessor. 24 volt AC input signals are coupled to the input ports of the microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. The output ports of the microprocessor are connected to a relay driver which in turn is connected to the relays. Several breakaway tabs in the board provide optional features such as eliminating a normally provided draft delay timing function. Test pads are provided on the board so that the board can be tested during manufacture.Type: GrantFiled: June 27, 1995Date of Patent: November 5, 1996Assignee: Texas Instruments IncorporatedInventors: Craig M. Nold, Mark E. Miller, Mitchell R. Rowlette, Robert B. Brown
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Patent number: 5568592Abstract: A system is disclosed for conserving power in a robotic arm device. The robotic arm device is responsive to a motion command and controlled by a servo loop having a motor, a motor driver, and a motor encoder. The system positions the robotic arm to a stow position when the time since a last motion command exceeds a predetermined power shut down time. When the robotic arm has reached the stow position, power is removed from the motor and the motor drivers by opening the servo loop. Thus, power is conserved while the robotic arm rests in its stow position. When a new command is received, the servo loop is closed and power is applied to position the robotic arm to its desired position.Type: GrantFiled: October 13, 1994Date of Patent: October 22, 1996Assignee: Hewlett-Pacard CompanyInventor: Kelly J. Reasoner
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Patent number: 5554916Abstract: A method of starting a sensorless motor comprising a stator provided with three-phase stator coils to which an exciting current is supplied, and a rotor provided with a rotor magnet for obtaining a rotating torque by the electromagnetic interaction of the stator wherein a first stepping step and a second stepping step for starting the rotor at the time of starting the motor are carried out. In the early period of the second stepping step, a reverse exciting operation is carried out in which an exciting current is switched off from positive to negative or from negative to positive without including a cessation period in two-phase coils out of the three-phase stator coils.Type: GrantFiled: November 30, 1993Date of Patent: September 10, 1996Assignee: Nidec CorporationInventors: Isao Kaneda, Kohei Yonemura
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Patent number: 5272427Abstract: An electric control for gas furnaces which controls a two speed main blower fan and an induction draft fan based on inputs from a room thermostat, a high limit and an ignition control including a gas valve. The control has a circuit board having a power supply for providing 24 volts DC current source to drive DC relays and a 5 volt DC power source to power a microprocessor. 24 volt AC input signals are coupled to the input ports of the microprocessor through current limiting resistors and to AC ground through pull down resistors. AC ground is also connected to the IRQ port of the microprocessor. The output ports of the microprocessor are connected to a relay driver which in turn is connected to the relays. Several breakaway tabs in the board provide optional features such as eliminating a normally provided draft delay timing function. Test pads are provided on the board so that the board can be tested during manufacture.Type: GrantFiled: May 20, 1992Date of Patent: December 21, 1993Assignee: Texas Instruments IncorporatedInventors: Craig M. Nold, Mark E. Miller, Mitchell R. Rowlette, Robert B. Brown
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Patent number: 4818924Abstract: An electric actuator apparatus particularly suitable for use as part of an automotive air conditioning system. The apparatus uses a direct current motor to drive a final output element in accordance with an input voltage signal. The apparatus is inherently protected against stalled conditions and no limit switches are required. The apparatus is self-adapting to different physical environments which define the range of travel of the final output element. The apparatus may be operated as a two-position actuator or, with the addition of a feedback signal corresponding to the postion of the final output element, may be operated as an infinite position or multi-position actuator.Type: GrantFiled: July 31, 1987Date of Patent: April 4, 1989Assignee: A.R.A. Manufacturing Co.Inventor: Charles F. Burney
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Patent number: 4714363Abstract: A print control device for use with a portable battery powered dot matrix printer has a DC motor which moves a carriage with a dot generating mechanism and is provided with a shaft position signal generator. A control circuit responds to the anglular position of the drive motor to establish a print cycle in which the DC motor and the dot generating mechanism are driven in alternation so as to minimize the rate of power consumption.Type: GrantFiled: May 20, 1985Date of Patent: December 22, 1987Assignee: Seiko Epson CorporationInventor: Masahiro Minowa
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Patent number: 4617505Abstract: A voltage supply for a servomotor (9) is effected via a wiper (10) which slides on two conductive paths (5, 6) which are displaceable in longitudinal direction. The conductive paths (5, 6) have, at their opposite ends, a driver (15, 17) against which the wiper (10) can come in its end positions upon further displacement, in order to be able to carry the corresponding conductive path (5, 6) along with it. Directly before the driver (15, 17) is reached, no voltage is tapped off from the corresponding conductive path (5, 6), so that the servomotor (9) then stops.Type: GrantFiled: April 12, 1985Date of Patent: October 14, 1986Assignee: VDO Adolf Schindling AGInventors: Andreas Sausner, Gerhard Ruschek
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Patent number: 4514667Abstract: Method and apparatus for the constant speed control of a brushless DC motor, whose pole windings receive a pulsed control voltage between their commutation points, control being a function of the speed characteristics of the motor, and the commutation points being synchronized with the drop times of the motor current and the control voltage pulses. In a state in which there are no load changes, the motor current substantially rises or drops between a maximum value I.sub.max and a minimum value I.sub.min according to the pulse mode. In the event of changes in the motor load, a mean motor sum current is retained for maintaining the speed.Type: GrantFiled: April 26, 1983Date of Patent: April 30, 1985Assignee: International Business Machines CorporationInventors: Walter H. Sakmann, Volker Zimmermann
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Patent number: 4481588Abstract: A method and apparatus for adjusting the positions of switch members such as a deceleration limit switch installed on a machine tool in a numerical control system for controlling the machine tool on the basis of numerical control data and for executing predetermined numerical control processing on the basis of signals produced by the switch members. When the switch member such as a limit switch is actuated, a display device displays the current position of a movable member on the machine tool, or a numerical value corresponding to the current position of the movable member. Whether the switch member is installed on the machine tool at the correct position is determined on the basis of the displayed current position or numerical value corresponding thereto. When it is determined that the switch member is installed at an incorrect position, the switch member is positionally adjusted on the basis of the indication given by the display device.Type: GrantFiled: October 23, 1981Date of Patent: November 6, 1984Assignee: Fanuc Ltd.Inventor: Hidetsugu Komiya
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Patent number: 4295082Abstract: A motor servo circuit is disclosed. The motor in the motor servo circuit is driven by an output which is obtained by logically adding output pulses of a pulse stretcher circuit which stretches a pulse width of error pulses generated from an OR circuit when pulses inputted to the motor servo circuit and pulses outputted from a pulse generator in response to the input pulses are different in the pulse width to pulses having a predetermined pulse width which are generated at intervals of a predetermined member of the error pulses synchronizing therewith.Type: GrantFiled: March 6, 1980Date of Patent: October 13, 1981Assignee: Futaba Denshi Kogyo K.K.Inventors: Masato Moto, Seigo Ito
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Patent number: 4293806Abstract: A cycle control device employing a parallel switching circuit to control a single or a predetermined number of cycles of a motor driven output shaft. A latching and a cycle switch in the parallel circuit are providing an overlapping switching sequence which is initiated by a latchable pushbutton and controlled further by the motor driven output shaft to the end of the cycle. An indexing arrangement is functioning to delay the unlatching and keeping the motor circuit energized until the unlatching and motor stopping can take place in a home position after a dial readable predetermined number of ratcheting steps have been completed. The control principle is applicable to a countdown version, a memory version with an automatic return or to a unit with a shaft mechanism to one or the other mode.Type: GrantFiled: May 21, 1979Date of Patent: October 6, 1981Inventors: Leo Kull, Vello H. Ebrok
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Patent number: 4263539Abstract: Apparatus for rotating an antenna to a predetermined position and maintaining said position is disclosed. The system comprises an antenna position sensing signal source, a desired position signal source, both of which provide analog signals, position comparator means, and antenna drive means. Comparison of the desired position signal and actual position signal generates a direction relay signal and an antenna rotor drive relay signal which together activate the antenna rotor drive means for rotation in the proper direction to the desired position. Circuitry is included for automatic operation in conjunction with equipment utilizing predetermined channels, such as a radio or television receiver, and for manual override or testing and calibration of the automatic operation.Type: GrantFiled: October 4, 1977Date of Patent: April 21, 1981Assignee: Zenith Radio CorporationInventor: Stephen Barton
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Patent number: 4159429Abstract: A tracer unit for use with measuring machines is described.The main feature of this tracer unit is to comprise a plurality of tracer tools, each of which is provided with a rod arranged to come into contact with a surface to be scanned, a movable body connected to said rod, a fixed body, first means which supply a first signal either when said movable body leaves the position of equilibrium relative to said fixed body or when said movable body passes through a determined position relative to said fixed body, and second means arranged to indicate from which of the various tracer tools said first signal is originated.Type: GrantFiled: June 8, 1977Date of Patent: June 26, 1979Assignee: Dea Digital Electronic Automation S.p.A.Inventors: Gianfranco Migliardi, Francesco Germano, Ugo Cavicchioli
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Patent number: 4077000Abstract: A system for selectively aiming a directional receiving antenna in one of a plurality of different directions respectively associated with a plurality of broadcast transmitters differently located in azimuth relative to the antenna in response to the entry into a digital keyboard of the different identification numbers assigned to the different transmitters.Type: GrantFiled: January 13, 1977Date of Patent: February 28, 1978Inventor: Jerry A. Grubbs
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Patent number: 4037519Abstract: An electro hydraulic system for controlling a hydraulic function includes a pump and a reservoir connected to the function through a manually operable, electro-hydraulic control valve. The valve is positionable to either side of a neutral ports blocked position and may be held to one side by the engaging of a spring loaded detent. The detent is disengaged by an electrical signal produced by a comparator when a preset, operator-controlled, limiting signal is equalled by a feed back sensor signal proportional to the output of the function. The system will allow initial activation of the valve to provide continuous operation of the function until the limiting input is reached at which time the function will be stopped. The system further provides manual override of the electrical control system to permit operation of the valve when the feedback signal is greater than the limiting input signal.Type: GrantFiled: April 21, 1975Date of Patent: July 26, 1977Assignee: Deere & CompanyInventors: Wayne Russell Miller, Jan Vilas Seipp, Garn Farley Penfold
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Patent number: 3975669Abstract: There is disclosed a motor control circuit that is particularly useful for the control of a damper motor in a heating and ventilating system. The control circuit comprises a bridge circuit having a pair of operational amplifiers with cross connected input terminals. An input signal is provided by input signal circuit means to one of the cross-connecting conductors and a reference signal is provided to the other of the conductors by a reference signal circuit means. The operational amplifiers are provided with feedback circuit means between their output and noninverting terminals to drive the amplifiers into an unstable condition where they function as on and off switches. Dead band means in the form of a load dropping resistor is provided between the input signal circuit and the noninverting terminal of one of the amplifiers.Type: GrantFiled: November 18, 1974Date of Patent: August 17, 1976Assignee: Robertshaw Controls CompanyInventor: Hugh Jean Tyler