Abstract: A failure monitor designed to monitor a failure in operation of a motor drive control system. The system works to drive a motor-driven member through an output shaft and an electric motor and includes an output shaft angular position sensor for determining an angular position of the output shaft and an encoder for determining an angular position of the motor for use in controlling the motor. The system works to discriminate among failures in operation of the output shaft angular position sensor and the encoder and another type of a failure using outputs of the sensors.

Abstract: A diagnostic system is disclosed for analyzing a limited rotation motor system. The diagnostic system includes a first transform unit, a second transform unit, a closed loop frequency response unit, and a diagnostic system. The first transform unit is for receiving a first digital signal that is representative of a motor control signal, and is for providing a motor control frequency domain signal that is representative of a frequency domain representation of the motor control signal. The second transform unit is for receiving a second digital signal that is representative of a position detection signal, and is for providing a position detection frequency domain signal that is representative of a frequency domain representation of the position detection signal. The closed loop frequency response unit is for identifying a representation of the frequency response of the limited rotation motor responsive to the position detection frequency domain signal and the motor control frequency domain signals.

Abstract: A method for evaluating a condition of a switching device. The switching device includes contact parts, an electric motor and a mechanical coupling device for transforming motion from the electric motor to at least one of the contact parts. A self-diagnostic test is performed on a component of the switching device. The test includes making at least one small movement with the electric motor. A switching device includes contact parts, an electric motor, a mechanical coupling device for transforming motion from the electric motor to at least one of the contact parts, and tester for making self-diagnostic tests, wherein the tester makes small motor movements that are a fraction of a full breaking movement, thereby producing data for evaluating a condition of the switching device.

Abstract: A controller for a variable frequency drive monitors electrical power from a variable frequency drive motor while a brake is maintaining a load driven or moved by the motor without requiring additional feedback components of a closed loop configuration. If excess electrical power is being generated by the motor, an undesirable condition in the brake is indicated. Support or maintenance of the load is assumed by the motor in that event. Appropriate alarms or indicators are also activated.

Abstract: A brushless motor control apparatus detects a phase current flowing in a brushless motor, converts the phase current to a vector current including a d-axis current of a magnetic flux direction component and a q-axis current of a torque direction component orthogonal to the d-axis current, calculates a vector voltage instruction value based on differences between a vector current and a vector current instruction value, calculates a phase voltage instruction value and controls rotation of the brushless motor based on the phase voltage instruction value. The apparatus further calculates electric power produced in the brushless motor and protects the brushless motor based on the magnitude of electric power.

Abstract: An actuator and movement linkage system for moving a load, such as a control surface of aircraft, in relation to a carrying structure includes an electric motor system, an actuator device connectable or connected to the load to move the load, the actuator device connected to the electric motor system to be driven thereby, and transfer units provided for mechanically connecting the actuator device to move the load.

Abstract: According to the present invention, a fail-safe circuit for controlling an actuator is provided with an input voltage which is rectified and converted to a DC voltage. The DC voltage is boosted to a high level, and high voltage storage capacitors are charged at this high voltage level resulting in smaller, less expensive capacitors. The high voltage from the storage capacitors is then converted back to a smaller DC voltage to drive the motor of the actuator. Reduced size and increased energy storage is based on the relationship between capacitance and voltage in the equation: E=½ CV2.

Abstract: It is so arranged in a robot as to monitor the over-current state of each motor and that of two more than two motors when put together by seeing the total current value of the motors being monitored in parallel with absorption of both the static load torque and the dynamic load torque of each actuator/motor. Additionally, it is so arranged as to check if each of the predetermined unit members including the arm sections and the leg sections of the robot is in an over-current state or not and also if the entire robot is in an over-current state or not, while each of the motors are not in an over-current state.

Abstract: A resistor member having a resistance value substantially equal to a resistance of a relay in an ON state is inserted into a current supply path which is not inserted with the relay in current supply paths for supplying currents from a driving circuit to a brushless motor. Further, in the driving circuit, widths of bus bars forming wirings are set such that resistances of the wirings (contact resistance) from a branch point on power source side to Hi side FET (source terminals thereof) are equal to each other and widths of bus bars forming the wirings are set such that the resistances of the wirings from a ground side branch point NL to Lo side FET (source terminals thereof) become equal to each other.

Abstract: A servo control device comprises a current supply unit for supplying a drive unit with a drive current for driving a target to be controlled, a first detector for detecting at least the drive current value, and a logical arithmetic section. The logical arithmetic section introduces a current command determining the drive current for controlling the drive speed of the drive unit to move the target to a predetermined position, and introduces the drive current value fed back from the first detector. The logical arithmetic section outputs the current command to the current supply unit after converting the current command by a digital logic process on the basis of the drive current value by using a custom LSI.

Abstract: The present invention discloses a robotic manipulator, comprising at least one joint, each joint having a drive axis and at least one microelectromechanical system (MEMS) inertial sensor aligned with at least one drive axis providing sensing of a relative position of the drive axis. The robotic manipulator can include an inertial measurement unit (IMU) coupled to the robotic manipulator for determining the end effector position and orientation. A controller can be used, receiving a signal from at least one MEMS inertial sensor and controlling at least one joint drive axis in response to the signal to change the relative position of the joint drive axis. Rate information from MEMS sensors can be integrated to determine the position of their respective drive axes.

Abstract: Two emergency stop lines are provided. Due to contacts being opened by commands from emergency stop factors and from first and second CPUs, conducting to first and second contactors are stopped. Contacts of the contactors are opened, and power supply to the motor is interrupted, whereby an emergency stop is performed. Further, the first CPU on the first line transmits an abnormality signal to the second CPU when the states of the contacts on the self emergency stop line, detected by digital inputs, are abnormal, and the second CPU opens a contact on the self emergency stop line so as to cause the contactor to be non-excited to thereby stop power supply to the motor.

Abstract: This resolver/digital converter has a resolver, a resolver/digital converting portion and an exciting signal generator. The exciting signal generated from the exciting signal generator is supplied to the resolver, and the resolver signals produced from the resolver are supplied to the resolver/digital converter. This resolver/digital converter further has a conversion trigger generator that generates a conversion trigger signal on the basis of the exciting signal generated from the exciting signal generator, an A/D converter that converts the resolver signals produced from the resolver to digital values in response to the conversion trigger signal generated from the conversion trigger generator, and computing means that detects the failure status on the basis of the digital values produced from the A/D converter.

Abstract: An apparatus monitors performance of a power inverter to detect malfunctions. A first signal indicates the direction that electric current exists between a first voltage bus and an output terminal of the power inverter. A second signal indicates the direction that electric current exists between a second voltage bus and the output terminal. A third signal indicates the direction that electric current occurs between the output terminal and a load. Other signals designate a commanded conductivity of switches that control the current within the power inverter. A controller analyzes the values of those signals to determine whether a malfunction has occurred.

Abstract: Servo motor controls are disclosed for passivation in the event of failures with at least two independent control paths and validation of positional information. A sensor assembly generates signals indicative of the position of the motor rotor, and a signal validation detector is used to validate the generated signals and inhibit rotation of the motor rotor when the sensor assembly generates an invalid signal. A first information processor is provided in communication with the sensor assembly for receiving the generated signals to establish an A Lane decision-making channel control path to the PWM interface, and a second information processor is in communication with the sensor assembly to establish a B Lane decision-making channel control path to the PWM interface. Control logic provided with a PWM interface also inhibits rotation of the motor rotor when a decision from the A Lane differs from a decision from the B Lane.

Abstract: In an electric motor-driven power steering apparatus which comprises a bridge circuit for connecting a power source between input terminals and also connecting an electric motor between output terminals and energizes the electric motor by this bridge circuit and operates electric motor power to a steering system, the bridge circuit includes a predetermined number of arms constructed by connecting circuits for connecting switching elements in parallel with diodes in series so that the diodes mutually become reverse polarity.

Abstract: An operational check of the safety unit or the safety circuit takes place within the delay time of the relay, assigned to each motor, caused by the pick-up delay or the release delay. Also, the control unit can be equipped such with at least one safety component and/or safety circuit for controlling the control unit that an operational check of the control unit takes place between the operation of an operating element of the hand switch and the starting of the motor or motors. The operating time and the release time of the relay may be delayed by a suitable component so that sufficient time is available for the operational check.

Abstract: An apparatus for selecting, monitoring, and controlling electrically powered devices is disclosed. In one embodiment, the apparatus includes an electrically powered device having a key operating line and switching control circuitry to control usage of the electrically powered device by interrupting continuity of the key operating line. In another embodiment, the apparatus monitors usage of an electrically powered device. The apparatus includes a circuit which is coupled to the device to provide a power output of the device, an analog to digital converter coupled to receive the power output and convert the same to digital form, and a controller to receive a user input, process the user input by establishing communication with a remotely located device to request approval of a financial transaction, and generate control signals in response to receiving approval. The controller receives the digital form of the power output and monitors the operation of the electrically powered device.

Abstract: A method of providing pitch torque compensation for planar motors in which pitch torque is not inherently provided includes calculating and summing a given set of forces ideally required to be applied by each forcer in the planar motor. Correction forces for each forcer are determined such that the net effect of the corrections is equal and opposite to the pitch torques previously determined.

Abstract: A system for controlling and/or monitoring a control-unit group having at least two control units, a first control unit and at least one second control unit, the first control unit being designed for performing its control function and for monitoring this control function, as well as for monitoring the control function of the at least one second control unit.

Abstract: The present invention relates to a monitoring and control device for monitoring a technical system having at least one portable and/or mobile and/or immobile device, and more specifically, a handling device that is a arranged in a protective device, and further including at least one preferably central or decentralized control unit and actuators connected thereto to carry out dangerous actions.

Abstract: Servo motor controls are disclosed for passivation in the event of failures with at least two independent control paths and validation of positional information. A sensor assembly generates signals indicative of the position of the motor rotor, and a signal validation detector is used to validate the generated signals and inhibit rotation of the motor rotor when the sensor assembly generates an invalid signal. A first information processor is provided in communication with the sensor assembly for receiving the generated signals to establish an A Lane decision-making channel control path to the PWM interface, and a second information processor is in communication with the sensor assembly to establish a B Lane decision-making channel control path to the PWM interface. Control logic provided with a PWM interface also inhibits rotation of the motor rotor when a decision from the A Lane differs from a decision from the B Lane.

Abstract: A device for controlling the velocity of an electric motor is provided. The device combines a traditional PI (Proportional+Integral) velocity controller with a robust mapping technique that estimates the velocity of the motor. The mapping technique is based on fuzzy logic methods, and provides a robust estimate of the motor's rotational velocity by using the motor current measurement and pulse-width modulated (PWM) voltage being applied to the motor. In one embodiment the device is combined with a calibration technique which ensures the proper calibration of the motor.

Abstract: A robot has a robot structure, preferably a plurality of interconnected arms. The robot also has drives for driving the arms, and a plurality of electronic drive units for operating and controlling the drives. The electronic drive units generate heat when in operation and are distributed on the robot structure at spaced locations from each other. A thermal insulation is arranged between the robot structure and the drive electronics. A cooling device is arranged on the drive electronics and is spaced from the robot structure.

Abstract: An apparatus for estimating the time to failure acceleration factor of a large industrial motor includes a sensor, a clock for controlling sensor sampling times, and a memory address calculator for mapping output signals of the sensor to a memory address. A unit is provided for incrementing the content of a specified memory address by unity.

Abstract: An electrical machine drive system (100) includes a DC power source (102), an inverter (104) and a three-phase electrical machine (106). In response to a fault condition, power switches (122, 124) in the inverter are opened. Any short circuits are then determined by examining the phase currents of the three-phase electrical machine. If short circuits are found in the inverter, then the inverter is made balanced by shorting all upper braches (122, 126) or all lower branches (124, 128), depending on the location of the short circuit. Torque ripples are avoided by balancing the circuit during the fault mode, thereby providing comfort to a user of an electric or hybrid electric vehicle employing the electrical machine drive system.

Abstract: A fault-tolerant electromechanical actuating device for converting an electrical actuating signal into a mechanical output actuating value for use in vehicles, having two mutually independent control loops. Each loop has at least one controller and at least one electric motor which is driven by this controller and which, in each case via a self-locking transmission, drives the input to a summing transmission, which superimposes the actuating values of the actuating motors to form the output actuating value. The fault tolerance or reliability of the actuating device is ensured by a comparator controller, which monitors the functions of the other controllers. Interfaces between the controllers and between the subsystems ensure stringent isolation of electrical potential.

Abstract: A method and an arrangement mutually monitor control units. The control units are built up of three program levels. A first level is for executing the control apparatus functions and a second level is provided for monitoring the control apparatus functions and a third level is for monitoring the programs of the second level. A first control unit sends out a selected question to a second control unit which answers the same in the context of a sequence control. The second control unit sends the formed answer back to the first control unit which then, on the basis of a comparison of the formed answer to the expected answer, determines the freedom from fault of the second control unit. Correspondingly, the first control unit is monitored by the second control unit via communication.

Abstract: A method and an apparatus for controlling release of a hoisting motor brake in a hoisting apparatus, where electricity is used as the driving force and a squirrel cage motor as the hoisting motor for hoisting or lowering a load attached to a hoisting member of the hoisting apparatus. Controlling of brake release comprises measuring the current and supply voltage of the hoisting motor after the start-up period of the hoisting motor and determining a variable which describes the load of the hoisting apparatus from the current and supply voltage. The variable describing the load is compared with a pre-determined limit value and hoisting or lowering of the load is interrupted if the variable describing the hoisting apparatus load exceeds the limit value set for the hoisting movement when the load is hoisted or if it exceeds the limit value set for the lowering movement when the load is lowered.

Abstract: A method for controlling movement of an automated machine. The movement is defined by a plurality of steps. First, a buffer of a predetermined size is defined. The buffer stores a current step and one or more previous steps in the movement of the automated machine. Then a current step in the movement of the automated machine is executed. Next, the buffer is checked to see if the current step executed in the movement of the automated machine movement is the same as a predetermined step of interest. If the current step is a predetermined step of interest, the buffer is checked to determine what at least one previous step was. If the current step was the step of interest, a new step is executed in the movement of the automated machine, the new step executed depending on what the at least one previous step was.

Abstract: The present invention provides apparatus, systems and methods for fail passive servo controllers. In accordance with an exemplary embodiment of the present invention, servo controller is used with an ALS to control an aircraft during landing procedures. In accordance with one aspect of this exemplary embodiment, upon a failure (e.g., of one of the components of ALS) servo controller fails passively rather than actively. In an exemplary embodiment, the fail passive nature of the servo unit is accomplished by providing at least two independent signal and drive current paths for controlling the servo motor. As such, the servo motor will not generate torque unless the two independent signal lanes agree. For example, when a component such as processor, difference amplifier, or PWM fails or otherwise ceases to function properly, servo motor will not runaway, but rather will fail with only minor transient movement, or alternatively, servo unit will lock at its current position.

Abstract: An object of the present invention is to provide a control apparatus for a robot in which the work efficiency is improved in the whole robot peripheral system including the robot, and in which considering the increase in the consciousness of safety such as the standardization of safety apparatuses, both the reliability of the safety circuit of the control apparatus for a robot and the ensuring of the safety are improved. By connecting, to peripheral devices outside the robot, each intermediate output signal line for extracting the operation signal or the emergency stop signal of each of the plurality of switches each assigned to a factor causing the stop of the robot, a factor to cause the stop of the robot body alone can be distinguished from a factor to cause the stop of both the robot body and the peripheral devices.

Abstract: An intelligent control and regulating device, especially for use in the process technology for flowable substances and media, which is built into the housing of an adjusting drive mechanism or into the drive mechanism itself and which has an adjustment arrangement controlling an adjusting member via an auxiliary energy device depending on sensor signals. The inventive control and adjusting device, which reacts reliably and rapidly to changing ambient conditions, includes a parameterable process regulator which receives adjustment input signals from the external sensors.

Abstract: A method, computer system, and program product for optimizing a useful objective function with respect to a dynamic parameter vector and a static parameter vector. The method, called the static/dynamic control (MDC) method, either minimizes or maximizes the useful objective function subject to a state equation, initial conditions, terminal conditions, constraints, and dynamic limitations. The SDC method includes an algorithm having two formulations: a period formulation and a fully continuous formulation. With the period formulation, the dynamic optimization variables associated with the dynamic limitations are permitted to be discontinuous, parametric functions of time. With the fully continuous formulation, the dynamic optimization variables are permitted to be continuous, non-parametric functions of time. The SDC method is computer implementable and employs an iterative process including an inner loop and an outer loop.

Abstract: Motion of a substrate-transporting robot arm is controlled in order to compensate for inaccuracies and deflections encountered during operation. The compensation is effected by synchronizing elevational and planar motions of the robot arm such that the trajectory of the substrate is made coincident with the object axis of the substrate. The substrate may be a semiconductor wafer, an LCD panel or an end effector of the robot arm. The synchronized motion is achieved using a controller issuing control signals to arm actuating means based on synchronization algorithms developed during analytical or experimental robot learning sessions.

Abstract: A robot system including a robot body, a plurality of safety devices to stop the operation of the robot body, connecting portions respectively disposed between the plurality of safety devices, and output device to transmit an output signal to external equipment. The safety devices are respectively connected in series to each other, and the output device is removably connected to at least one of the plurality of connecting portions. The robot body includes a plurality of robot bodies, and respective ones of the plurality of robot bodies are connected to the plurality of safety devices.

Abstract: A method for calculating a first and second gain for a controller circuit for a plant is disclosed. The method comprises the steps of providing a reference model circuit with desired circuit characteristics, providing a reference model adaptive circuit, setting the second gain to zero, supplying a spectrally rich input signal to the reference model and to the controller circuit, determining the first gain by continuously adjusting the first gain until an output of the reference model and an output of the controller circuit are substantially equal, setting the first gain to the previously determined value, determining the second gain by continuously adjusting the second gain until an output of the reference model and an output of the controller circuit are substantially equal and setting the second gain to the previously determined value.

Abstract: In a method and apparatus for controlling current limit of a motor of an electric-powered vehicle, the current limit of the motor is initially set to a smaller first value during start-up operation of the vehicle. Thereafter, in response to operation of a twist-grip throttle of the vehicle to commence accelerating operation of the vehicle subsequent to the start-up operation, the current limit of the motor is increased from the smaller first value to a larger second value larger than the smaller first value in accordance with angular rotation of the twist-grip throttle from an initial position. When the current limit reaches the larger second value, the current limit of the motor is then maintained at the larger second value in case of further operation of the twist-grip throttle from the initial position.

Abstract: A numerical control apparatus for the numerical control of a roll grinding machine comprises a flaw detecting means for scanning the entire surface of a roll (11), provided with an ultrasonic detecting head (23) for detecting flaws formed in the surface of the roll (11), a command generating means for generating cross-feed commands to repair detected flaws on the basis of flaw information about the positions and levels of the detected flaws, a control means for executing a first shaft position control operation on the basis of the cross-feed command to position the grinding wheel at a position with respect to a Z-axis corresponding to the position of the flaw by moving the wheel spindle stock in parallel to the axis of the roll and a second shaft positioning control operation to cross-feed the grinding wheel in parallel to an X-axis, and a decision means for deciding whether or not the flaw has been completely repaired and invoking the next cross-feed command if the flaw has been completely repaired.

Abstract: Master and slave servo control circuits 2a and 2b are configured with servo controllers 3a, 3b, servo amplifiers 4a, 4b, servo motors 5a, 5b, feedback detectors 6a, 6b and error detectors 7a, 7b, and the servo motors 5a, 5b are mechanically interlocked and connected to a load. At a location upstream from the servo amplifier 4b, a torque command value selector 21 is provided; when the error detector 7a does not detect an error in the servo control circuit 2a, the selector switches so that the servo amplifier 4a and the servo amplifier 4b both receive a torque command value from the servo controller 3a, and when the error detecter 7a detects an error in the servo control circuit 2a, the selector switches so that the servo amplifier 4b receives a torque command value from the servo controller 3b.

Abstract: The invention regards an electric circuit (200; 300; 400; 500) comprising a first electronic control circuit (201; 301) controlling the operation of a first electric load (102) to operate alternatively in a push mode or in a pull mode. To reduce the costs an electric circuit is proposed wherein said first electronic control circuit (201; 301) controls the driving of a second electric load (203) in cooperation with a second electronic control circuit (202; 302).

Abstract: A retractor device for the LCD unit of an on-board entertainment unit is disclosed. The retractor device uses capacitors as storage device to provide electrical energy to drive the retractor motor in the reverse direction in the event of power outage. Under normal operating conditions, the deployment and retraction of the LCD is performed by the motor, with its polarity switched by a relay. At the same time, a storage capacitor is charged up. In the event of power outage while the LCD is in a deployed mode, the energy stored by the capacitor is discharged to drive the motor's retraction mechanism. Blocking diodes may be used on the discharge path to ensure that the discharge path goes toward the motor.

Abstract: An apparatus and method for providing redundant power and redundant fan speed control to a plurality of fans is provided. A first power supply input is electrically connected to a second power supply input to provide a combined power supply input. First and second fan speed controllers each having an input and an output are provided, along with first and second power converters each having an input and an output. The combined power supply input is electrically connected to the input of the first fan speed controller and the input of the first power converter. The combined power supply input is also electrically connected to the input of the second fan speed controller and the input of the second power converter. The output of the first fan speed controller is electrically combined with the output of the second fan speed controller to provide a combined fan speed control signal. The combined fan speed control signal is electrically connected to the plurality of fans.

Abstract: The present invention provides a processing machine having the function of sensitively detect collisions or other abnormalities to prevent the machine from being operated under abnormal conditions. Means 22 is provided for detecting a load on a drive source 1 for driving a movable member 2. Abnormality determining means 23 is provided for determining the load is abnormal if the lead as detected by the abnormality means 22 exceeds an abnormality determination level (Lb). The abnormality determining means 23 sets the abnormality determination level (Lb) on the basis of the load as measured during the preceding driving operation of the movable member 2 or the average of loads as measured during several past driving operations that are temporally close to the current one.

Abstract: A capacitor powered electronic emergency device retracts and parks an actuator into a resistive parking position with a crash stop barrier. Due to variations of the kinetic status of the actuator at the begin of the retraction, the actuator reaches the resistive parking position with different velocities, which can be at a level that causes the actuator to bounce off the crash stop barrier. A modulating pulsing of the energy flow extends the discharge time of the capacitor long enough to provide sufficient energy to compensate an eventual bounce-off. The use of transistors in the device keeps the internal energy consumption low. An increase of the pulsing frequency in dependence on the capacitor voltage results in a high average current flow.

Abstract: A microcomputer receives a position detection signal from a throttle angle sensor, and produces drive command signals to a drive circuit to control the position of a throttle valve to a target position through a motor. The current supplied to the motor is limited to less than a maximum value in a current variation zone in a normal motor operation range, when the throttle valve cannot be controlled to the target position, that is, when it is locked to the same position. The microcomputer produces a signal to cancel the current limitation to the motor, when it detects from the position detection signal of the throttle angle sensor that the throttle valve undergoes a predetermined change under the current limitation condition.

Abstract: A control device, disposed in or on a vehicle seat, which has a pickup for detecting seat occupation, a pickup for detecting a position of the vehicle seat, a common control circuit, and an energy supply for the control circuit. The pickup for detecting seat occupation and the pickup for detecting the position of the vehicle seat are connected electrically conductively with the common control circuit.

Abstract: A servo control apparatus for performing a feedback control to an analog controlled system, includes an error generating device that generates a digital error corresponding to a difference between a desired value and a feedback value corresponding to a controlled variable of the analog controlled system, a control device that generates a digital manipulated variable, and a digital-to-analog converting device that converts the digital manipulated variable into an analog manipulated variable for driving the analog controlled system. The control device includes a disturbance estimating device that estimates a disturbance applied to the analog controlled system by carrying out a digital estimating process by using the digital manipulated variable and the digital error and generates a digital compensated variable corresponding to the estimated disturbance, and a manipulated variable generating device that generates the digital manipulated variable by using the digital error and the digital compensated variable.

Abstract: The information processing device includes a first device (31) supplied with power and a second device (32) supplied with power from the first device (31) when connected to the first device (31). The information processing device includes a detection portion (121-1, 121-n, 221-1, 221-n) detecting the attachment/detachment of the second device (32) and a supply portion (121-2, 221-2) supplying power to the second device (32), and the first device (31) includes a control portion (151) controlling the supply of the power by the supply portion (121-2, 221-2) according to the result of detection by the detection portion (121-1, 121-n, 221-1, 221-n). As the supply of the power by the supply portion (121-2, 221-2) is controlled according to the result of the detection by the detection portion (121-1, 121-n, 221-1, 221-n), the electric shock on an internal circuit of the second device (32) at the time of attachment/detachment of second device (32) can be prevented.

Abstract: A movable barrier or garage door operator has a barrier drive for moving the movable barrier or garage door between open and closed positions. Motion of the barrier is detected by a tachometer connected to the barrier drive or by upper and lower barrier travel limit switches. A test is made to determine if the barrier has been commanded to be in a closed state and to determine if a preselected time interval has elapsed following closure of the barrier. When both of those conditions are present and the door is moved upward without authorization an alarm signal is generated and can signal the barrier drive to apply a closing force. The timer prevents the barrier from being closed on a person or obstacle during normal operation and prevents injury. An obstacle detector also prevents unwanted closure on an obstacle.