Abstract: A tool interference checking method for checking whether a tool (TL) will interfere with a workpiece (WK) when the tool is transported relative to the workpiece to cut the workpiece on the basis of NC data comprising a number of blocks (B.sub.1 -B.sub.5), characterized by having steps of obtaining tool travelling directions (+X, -Y, +X, +Y, +X) indicated by the NC data in respective blocks, obtaining a tool offset path (TCP) using the tool diameter and NC data, obtaining tool travelling directions (+X, -Y, -X, +Y, +X) in respective blocks of the tool offset path, comparing, for each and every block, the tool travelling direction indicated by the NC data and the tool travelling direction indicated by the tool offset path, and rendering a decision to the effect that tool interference will occur if the tool travelling directions are in non-agreement in at least one block.

Abstract: In a system for controlling the motion of an industrial robot, a resultant translational velocity of a preselected point on the robot is calculated from a plurality of velocity values such as actual velocity values detected by sensors or target velocity values computed from a velocity reference value. Upon the exceeding of a predetermined maximum velocity by the calculated resultant velocity, all robot motion is terminated. Robot motion may also be stopped upon detecting an excessive difference between an actual angular velocity of one robot component and a respective desired or target angular velocity of that robot component, upon detecting an excessive translational acceleration of a predetermined point on the robot, or upon detecting a position of the robot part or point located more than a predetermined distance from a reference position.

Abstract: An overload protection device adapted to be secured between a robot arm and a tool, comprises a floating piston (20) within a cylinder (18). Hall effect sensors (124) are spaced around the cylinder wall and mating magnets (40) are spaced around the piston wall. The cylinder is pressurized to axially align the piston with the cylinder and to position each magnet in alignment with a sensor. When an overload occurs involving either the robot arm or the tool, the magnets are moved relative to the sensors causing the sensors to signal for depressurization of the cylinder. An electronic system (FIG. 27) responsive to the Hall effect sensor signals lights an "overload" LED D1 and triggers a timer circuit T1 which generates a timing pulse of fixed duration. During the duration of the timing pulse, the robot is de-energized. A red LED R is illuminated indicating the robot system is not ready to be operated. Also, a solenoid valve L1 is energized, cutting off the pressure to the cylinder.

Abstract: An amplifier system for energizing a d.c. motor from a power source in response to an error signal includes a bridge circuit including a first switching transistor pair for supplying a first current from the power source through the motor in one direction and a second switching transistor pair for supplying a second current from the power source through the motor in the opposite direction. A zero crossing detector determines the sign of the error signal and enables the first transistor pair when the error is positive and enables the second transistor pair when the error is negative. A current sensing resistor senses the first and second currents through the motor and provides a motor current signal representative thereof. An absolute value circuit provides an absolute value error signal representative of the magnitude of the error signal.

Abstract: The hoist, lifting apparatus or the like of our invention comprises at least one hoist motor, a protective controller for the hoist motor, and an overload safety device operating on the protective controller, wherein the overload safety device has a cable load force pick-up with a tension measuring bridge, an analyzer, and a mechanism for suppression of load peaks in periodic load fluctuations. The tension measuring bridge is connected with two connecting conductors to a bridge supply generator and has two output conductors for transmission of the output signal of the tension measuring bridge. The analyzer acts on the protective controller for the hoist motor. Between the analyzer and the tension measuring bridge is a frequency converter with associated frequency generator which changes the output signal of the measuring bridge into a periodic signal.

Abstract: In a control system for a robot having a servo motor driving an operation axis, position error detecting means, detects an error of the actual position with reference to a desired instantaneous position, and a drive circuit receives the position error for supplying a current to the servo motor to reduce the position error. The control system is characterized by means for limiting the current supplied from the drive circuit to the servo motor thereby to limit the torque of the servo motor when the servo motor is driving the operation axis in a first mode in which movement of the operation axis is subject to undesired obstruction.

Abstract: An industrial robot system for starting a robot moving to a predetermined location according to starting instructions is equipped with detecting devices operating when the location reached by the robot once started is within a predetermined range from the predetermined location. Accordingly, the system is capable of preventing accidents caused by the operation when the work origin has drifted due to an abnormality in the robot. Because the robot is only allowed to do its work after an output is given by the detecting devices operating only when the robot thus started is within the predetermined range from the predetermined location, the robot system is capable of not only preventing accidents caused by the presence of abnormalities, but also controlling the operation of the robot with little chance of trouble.

Abstract: A system and method for monitoring vibrations of a machine tool metal-cutting tool insert and interpreting them to promptly detect the initial touch to the workpiece and signal the tool to stop advancing before marring the surface. The signal generated by a sensor such as an accelerometer is preprocessed to eliminate lower frequency machine noise and detect the energy in a higher frequency band, then sampled and analyzed by digital circuitry. In order to avoid false alarms on high amplitude spiky noise pulses generated by traverse operation of the machine tool, the tool touch alarm is delayed longer than the maximum duration of the noise pulses. Two techniques are given to ignore the noise spikes while still detecting the tool touch signal.

Abstract: An industrial robot system comprising a robot disposed in an environment having peripheral equipment and operable under program control of a control unit to shift between a normal job mode of operation and an earthquake mode of operation, an earthquake detector which produces an output in accordance with an earth vibration exceeding a predetermined value, and earthquake mode controller disposed between the earthquake detector and the control unit for generating a control output in response to the output of the earthquake detector to interrupt the normal job mode of operation of the robot and shift the robot to the earthquake mode of operation, whereby on the basis of the output of the earthquake detector, the normal job mode of operation of the robot is suspended through the earthquake mode controller and an actuator of the robot is moved in a direction away from peripheral equipment of the robot.

Abstract: Life of a tool used in a machining center having various sorts of tools can be detected by steps that a tool selection code at every execution of NC program is detected and the current-use tool number is stored, the machining distance of each tool is calculated, the machining distance is accumulated per each tool, the cumulative machining distance is compared with predetermined machining life distance to indicate the life of each tool, and then the life of each tool is determined on the basis of a result obtained in the comparing step.

Abstract: In a numerical control system, a machine tool with an automatic tool changer is provided with an origin detector for generating an origin signal when an NC drive axis for effecting relative movement between a spindle head and a work table in an axial direction of a tool spindle is returned to a machine origin. A numerical controller is connected to the NC dirve axis, the tool changer and when operated in accordance with a numerical control program, controls them so that a series of machinings can be selectively performed on a workpiece on the work table. The numerical controller executes an emergency returning control program when a manual switch is depressed to instruct the returning of the NC drive axis to the machine origin.

Abstract: A numerical control machining method in which plural machining operations, such as drilling and tapping, are performed by a unified machining cycle command, which is unified from several separate rotation/positioning commands for the workpiece and machining cycle commands, such as for controlling drilling operations. Also, a safety route of the tool from a rest position to the position at which a machining operation is to be started is automatically created from a knowledge of the configuration of the workpiece, the rest position of the tool, and the position at which the machining operation is to be performed. Programming of a numerically controlled machine tool can be performed in accordance with the invention without the need of a high level of programming skill.

Abstract: The user of a remotely controlled, powered manipulator is provided with audible feedback signals which provide useful information relating to the force and speed of the motor. An audio tone is generated and is frequency modulated by a signal which corresponds to motor speed. The tone is amplitude modulated by a signal corresponding to motor force thus providing the user with an intuitively interpretable feedback signal having a speed-proportional pitch and force-proportional volume. In the case of an electric motor, voltage and current can be monitored to provide speed and force signals respectively. Additional modulation means are disclosed for introducing a force-proportional warble component to said tone.

Abstract: A brushless dc motor has switching transistors to be sequentially made conductive to cause sequential excitation of field windings from a dc power supply and hence to cause rotation of an armature. The switching transistors are provided with respective protection diodes connected in parallel therewith and in an opposite polarity. The field windings are further connected, via respective energy release diodes opposite in polarity to the protection diodes, to a common energy dissipating circuit comprising a capacitor and two transistors having their emitters grounded. The energy dissipating circuit can take up the electric energy produced in the field windings during the nonconducting periods of the switching transistors.

Abstract: A device for driving a motor-operated closure part for an opening, especially on a motor vehicle, having a protective circuit for interrupting the closing movement when there is an indication that an object may be obstructing closure of the opening. A speed transmitting means exists that detects the adjusting speed of the closing part on at least one range of the adjusting path of the closure part that is critical with respect to the engagement of an obstruction. In addition, an evaluating stage is provided that responds to the speed signal and/or its rate of change with respect to time, for producing an obstruction signal that activates a control means of the circuit to interrupt the closing movement.

Abstract: In a feed control system, a feed controller controls a servomotor in such a manner as to reduce the difference between an objective position and a present position of a movable body. An interference detection circuit coupled to the feed controller detects the occurrence of an interference between the movable body and an obstruction when feed movement of the movable body is discontinued nevertheless the difference between the objection and present positions does not reach zero. A digital computer is coupled to an objective position counter provided in the feed controller to selectively set therein objective positions to which the movable body is to be positioned successively. The digital computer, when receiving a signal from the interference detection circuit, sets the objective position counter with data for moving the movable body a predetermined amount in a direction opposite to that wherein the movable body was moved before the occurrence of an interference.

Abstract: A safety system for a machine tool, e.g. an EDM machine, having a multiplicity of different items of setting procedure to be attended to manually and inspected by the operator before the machine is actuated for performing a given machining operation, employs a loudspeaker associated with the machine. A control unit is used to produce a preselected sequence of multiple, time-spaced electrical signals corresponding to multiple verbal instructions prescribed for alerting the different setting items, respectively, and to apply these signals in that sequence to an electromechanical transducer in the loudspeaker. The transducer responsive to each of the electrical signals produces through the loudspeaker a corresponding unit of the multiple verbal instructions audible to the operator for a corresponding item of the setting procedure.

Abstract: A system for reversing the direction of an electric discharge machine in response to a short-circuit signal. A controller responds to the short circuit signal by generating a command signal with a magnitude greater than a stored error between a commanded value and a number of feedback pulses produced by rotation of a motor which drives the electrode. The sign of the generated command signal is opposite to that of the stored error so that the stored error is converted into a value capable of reversing the direction of the electrode without delay.

Abstract: The invention relates to a mechanism wherein a relative rotary angle of a driving motor is detected by use of an encoder, and, if an error occurs in a servo control action when the driving motor is servo-controlled in accordance with a deviation value of the relative rotary angle from a desired rotary angle of the driving motor, then the servo control action is brought to an emergency stop. A potentiometer for detecting an absolute rotary angle of the driving motor is connected to a rotary shaft of the driving motor and said emergency stop is effected when a difference between said absolute rotary angle and said relative rotary angle exceeds a preset tolerance value, so that an error in the servo control action can be reliably prevented.

Abstract: A synchro system having a microprocessor control element emulating a synchro transmitter. Current sensing circuits measure current developed in a synchro receiver responsive to drive signals generated by the microprocessor control element; the microprocessor control element alters the drive signals to maintain control of current dissipated in the synchro receiver within predetermined limits.

Abstract: By using the fly-wheel current effectively, the d.c. servo motor current can be rapidly decreased when the circuit becomes non-driving state or the driving polarity is changed, and the inexpensive circuit of the high performance driving circuit, in which the form factor of the driving signal is improved, can be obtained.

Abstract: A numerical controller for a machining center comprising a microprocessor connected to a data input device, a CRT display device and a data storage device. The microprocessor prepares an NC program for a workpiece to be machined, based upon machining information manually input by the use of the data input device and stored in the data storage device. The debugging of the prepared NC program is then executed, wherein the microprocessor obtains by calculation a workpiece interference space defined outwardly from the outer periphery of the workpiece, based upon workpiece blank shape and dimension data and workpiece mounting position data stored in the data storage device. The microprocessor further calculates, based upon the NC program, a tool path along which a tool spindle of the machining center would be moved relative to a work table in accordance with the NC program.

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 spatially movable device 1 is disclosed which is provided with actuators 7a-7f in such a manner that the system consists of a manual unit 2 with a process control unit 5 and a input unit 6 as well as a monitor 8. The manual unit 2 is operated in such a manner that the control elements 3a-3f are controlled by an operator's hand which through individual fingers controls the selection of various position parameters. A slider 4 is provided which controls the direction and speed of the selected parameter change with the slider being accessible to the thumb of the operator in order to provide complete operation by one hand and simultaneously setting and controlling the parameter values which are displayed on the monitor 8.

Abstract: A numerical control device for controlling a machine tool automatically selects the tool of the specified kind from among a plurality of tools of the same kind disposed in the magazine locations or holders. The numerical control device includes registers for storing the kinds and the lives of the tools disposed in respective magazine locations. Thus, when a tool select command specifying a tool kind is inputted, the magazine location in which the tool of the specified kind having a remaining life is selected by studying the contents of the registers in sequential order. The device further includes registers for storing adjustment values of the tools in the magazine locations, and thus can automatically effect the adjustment operation of the newly selected tool. Preferably, the device includes a tool damage detector and automatically changes the tool in use when it is damaged or reaches the end of its life in the middle of the machining operation.

Abstract: An arrangement to preclude false starting and stopping of a motor driving a loom in accordance with start and stop control signals from a microprocessor control unit susceptible to noise. The motor is connected to start only upon coincidence between the control unit start signal and energization of a manually operated start switch; and to stop in response to either the control unit stop signal or energization of a manually operated stop switch.

Abstract: A safety system and method for industrial robots includes a detection arrangement having a detection field covering the area of reach or operation of the robot. Detection data obtained through the detecting arrangement in each of predetermined operation positions of the robot is compared with the detection data indicative of the normal or correct detection field in the same operation position. The movement of the robot to the next operation position is prohibited when a difference of a level exceeding a predetermined level is obtained during the comparison.

Abstract: There is disclosed a control system for stopping a punch press and comprising first and second proximity sensor-amplifier combinations responsive to the cyclical movements of respective parts of the press to generate respective cyclical signals having respective recurrent digital waveforms which remain invariable while the press and such combinations operate normally. A device responds to a misfeed in the stock strip to change the waveform of the first signal. The two signals are fed to logic circuits which respond either to a change in waveform indicative of such fault or to a change in waveform indicative of malfunction of either combination to produce a signal for stopping the machine.

Abstract: A system for restoring a numerically controlled machine tool to its former condition after a power interruption, the numerical control system being of the type in which a position sensor senses the current position of a movable member or of a drive motor of the machine tool and generates a current position signal in accordance with said current position, the movable member being positioned on the basis of a commanded position signal and the current position signal. The positional control information which prevails immediately prior to an interruption in the electric power which is applied to the machine tool and to the numerical control device is stored in a non-volatile memory before the power interruption occurs.

Abstract: A control method and apparatus for a metal-forming machine such as a cold heading machine are described. The described method and apparatus monitor machine operation during production and permit relatively large deviations from a prescribed norm over a short term without shutting down the machine, while ensuring longer term compliance to relatively small tolerances from the norm. The described controller first determines an average of a measured parameter such as the hit energy applied to a group of workpieces resulting in acceptable metal-forming during a training mode and then stores this average as a target value. The controller then establishes a set of tolerance windows to be used to control forming operations in a production mode.

Abstract: A servomechanism avoids load-damaging conditions by being shut down whenever a power-amplifier saturation detector fails to detect a change in the saturation state of the power amplifier in response to the periodic and momentary replacement of the demand signal by one or other of two test signals, which of the two test signals is selected being dependent upon the expected direction of possible saturation of the power amplifier and the polarity of both test signals being the same as the polarity of the applied demand signal.

Abstract: A logic circuit (34) is provided for preventing the application of energizing voltage to a positioning motor in the case of a circuit failure in the drivers stage of a control system. An equality gate provides a signal to each AND gate corresponding to a failure detection criterion whenever signals of the same level are present at the respective transistors controlling operation of the motor into opposite directions. At one AND gate a signal is provided if either of the transistors is conducting, indicating a failure if there is no control signal. At the other AND gate a signal is provided if either terminal of the motor is connected to energizing potential, likewise indicating a failure if no control signal at a transistor input is present. If either AND gate responds the equivalent of a control signal is applied to a pair of diodes to both of the transistor inputs, thereby blocking the motor.

Abstract: Safety apparatus for an electrohydraulic servovalve. The safety apparatus includes a digital programmable switch (14) which is programmed to make switching decisions on the basis of whether or not the electrohydraulic servovalve is subjected to an external error and whether or not the electrohydraulic servovalve is free from internal error. Logic inputs that supply this information are provided to the programmable switch (14) by a logic device (16). On the basis of the logic inputs, the programmable switch (14) is programmed to interconnect, in a sequential manner, the analog electrohydraulic servovalve to one of four different analog drive systems. One of the drive systems is employed for the case whether there is no external or internal error, so that the electrohydraulic servovalve is in a normal mode of operation. Two of the drive systems are employed to quickly and safely de-energize the electrohydraulic servovalve upon the occurrence of an external error.

Abstract: To compensate for drops in the amplitude of signals read from magnetic records, in particular servo signals, a complementary correction signal is produced from the signal drops by rectifying, low-pass filtering, differentiating, integrating and forming the absolute value. This complementary correction signal is added to the defective signal to obtain a signal which has roughly been corrected to the original magnitude prior to evaluating and forming the position error signal (PES).

Abstract: A remote control system for controlling the movement of manually operable mechanisms such as hydraulic control valves for hydraulically operating the various cylinders on equipment such as cranes, or the like. A remote control unit includes a deadman switch and one or more potentiometers that provide control signals to a corresponding number of servo circuits. Each servo circuit drives a motor and a motor position sensing potentiometer that generates an error signal back to the servo. The motor rotation provides linear movement to the hydraulic control valve through a solenoid operated mechanical coupling. The servo circuit includes safety circuitry that detects open or shorted circuits in the cable to the remote unit and releases the solenoid coupling and returns the motor to a neutral position.

Abstract: There is disclosed a protective system for preventing damages to a tool and a work or tool changing mechanism component parts due to any interference between the tool and the work during the tool changing operation by an automatic tool changing apparatus in a numerical control machine tool such as a machining center.The protective system monitors the load current of a driving motor for the automatic tool changing apparatus, whereby when the load current reaches an abnormally high current value during the operating period excluding the motor starting period, the operation of the automatic tool changing apparatus is reversed and then stopped.

Abstract: This invention relates to a control circuit for a motor for use in driving an electrically controlled door such as an air mixing door, inner and outer surrounding air ventilation door, and mode change-over door etc. or an electro-magnetic solenoid for operating an injection pump applied in a Diesel engine or another motor for use in opening or closing a window pane etc. and protects the transistors forming the control circuit.

Abstract: A system for controlling the rotation of a spindle includes a motor, a speed detecting circuit for detecting the speed of the motor and for producing a signal indicative of the actual speed thereof, a speed control circuit for controlling the motor so as to narrow to zero a deviation between the actual speed thereof and a commanded speed, a spindle driven by the motor, and a position control circuit for producing a position deviation signal on the basis of a commanded stopping position and the rotational position of the spindle. The spindle is rotated at a commanded speed by the speed control circuit and is rotationally controlled by an orientation command signal so as to make the position deviation signal zero.

Abstract: A valve position monitoring and control system incorporates a proximity sensor positioned near a movable valve element to detect the operational position of the valve and includes circuit means coupled to a valve actuating solenoid for deactivating the solenoid in the event the valve fails to respond to command signals for positioning the valve in a predetermined position. In one embodiment, the system incorporates a pair of series connected valves used in presses which valves in turn are operated by solenoid actuated pilot valves. In the event either one of the valves do not operate either by opening within a predetermined time after actuation or closing within a predetermined time after their deactuation, the system of the present invention will not permit further operation of the valves until the system has been manually reset.

Abstract: Signals from a rudder position setting control and from a rudder position sensor constitute the only electrical information sources needed for operating a monitoring system for a rudder control that produces an alarm when the rudder control does not function effectively. The difference between the desired rudder setting and the actual rudder position, generated by a differential amplifier, is fed to a bi-directional limit circuit and a differentiating circuit is used to generate a signal corresponding to the rate of change of rudder position, which signal is likewise provided to a bi-directional limit circuit.

Abstract: In order to attain a more suitable control of a robot unit which serves a machine tool in accordance with various conditions of the operations of the machine tool and the robot unit, the number of the kinds of signals produced in the machine tool is increased and a predetermined control of the robot unit is attained in response to each of the increased kinds of signals.

Abstract: An electronic anti-skid controller system employing a plurality of anti-skid controllers is adapted to develop state signals representative of the operational states of the individual anti-skid controllers in the form of binary signals "1" and "0". When specific combinations of the controller state signals occur indicating a tendency of the vehicle to encounter a dangerous condition, the individual controllers are respectively activated or disabled in accordance with the nature of the instantaneous combination of the state signals in order to ensure safety of the vehicle. To this end, a central control unit is provided to be responsive to the specific combination of the binary state signals.

Abstract: An aircraft spoiler control system wherein each of a plurality of spoilers is driven by an electrically responsive actuator. Sense signals representative of the aircraft's control wheel rotation, speedbrake lever deflection, flap position and air/ground status are processed by logic which produces a corresponding control signal for each actuator. Fault detection circuitry switches in a back-up actuator control signal if a fault occurs in the active control circuit.

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 solid state electronic circuit for controlling a reversible direct curr motor from a voltage source such that it may be rotated in either direction. The reversible direct current motor is connected into a bridge circuit with semiconductor switching elements which provide that the full supply voltage is available for starting in either direction. A pair of comparators receives input signals from a triangular wave generator and a signal source and in conjunction with a cross-fire protection circuit generates the drive pulses which control the semiconductor switching elements.

Abstract: In a servo system for manipulating a displaceble member in response to movement of a control through corresponding changes of position, which operates by comparing an electrical signal representative of the position of the control with an electrical signal representative of the position of the displaceable member to provide error signals which can drive the displaceable member in either of two opposite directions, a safety interlock circuit is provided which detects the presence of an error signal in either direction immediately after the application of operating voltage or immediately after the switching of the machinery into a different mode of operation and locks the displaceable member in position if an error signal initially appears until the error signal is cancelled by bringing the manual control into a position corresponding with that of the displaceable member. Unexpected sudden movements that may endanger personnel are thereby prevented.

Abstract: An industrial robot for spray painting workpieces carried by a conveyor is provided with a control to allow the programmed robot sequence to proceed synchronously with conveyor movement so long as the conveyor maintains a normal speed. When, however, the conveyor stops, the control maintains robot operation until the spray gun is moved to a safe stopping place to avoid excessive paint application to a portion of a workpiece. Upon conveyor start-up, the robot remains stationary until the workpiece approaches normal speed and moves into a position synchronous with the robot position.

Abstract: An apparatus is described for controlling the sequences of operations executed at the various work stations. At each work station there is provided detecting means arranged for detecting the correct completion of an operation, e.g. the correct positioning of a part in a support such as a case for making a cartridge, and generating a fault signal when the operation is not correctly completed. The fault signal is written into shift register means and shifted in response to a timed control signal, the successive states of this shift register means being compared with a reference signal representing the number of steps along the path between that work station and the next. When the state of the shift register means is coincident with the reference signal, an inhibit signal is produced for inhibiting the operation at at least one next work station.

Abstract: Gyrocompass heading step-by-step repeater amplifier channels are provided with protection from damage by accidental short-circuits occurring in one or more compass step-by-step data repeaters or in the cables extending to such repeaters. Total shut-down of the affected channel or channels is effected by fast-acting thyristor pulse control circuits and the channels are automatically reset when the fault is removed. A cooperative latching short-circuit alarm is provided.