Abstract: An operator and related method for adjusting an internal force setting for a motorized garage door operator is disclosed. The operator checks for the presence of a secondary entrapment safety feature and automatically increases a force threshold setting from a first value to a second value if the secondary entrapment safety feature is detected. If the safety feature is not detected or it is later disconnected, then the operator automatically sets the force threshold to a more sensitive value.

Abstract: A window lifter system and method coordinates closing of multiple windows by detecting when more than one window pane is approaching a fully closed position and moving one window pane to only an approximately closed position while the other window pane is moved to the fully closed position. By staggering the closure of window panes to the fully closed positions, the system and method provides the illusion that all of the window panes are being closed at the same time while avoiding voltage drops in the vehicle power supply caused by excessively high blocking currents generated when multiple window panes are moved to the fully closed position.

Abstract: An operating system which utilizes a multi-functional wall station for a motorized barrier includes an operator for controlling movement of a barrier between various positions. The operator may receive signals from a wireless or wired wall station transmitter, a wireless keyless entry device and/or a portable remote transmitter device. The multi-function wall station also provides for an operational selection wherein the door may be closed in a normal manner; by an auto-close/delay-open feature, wherein the door closes after a predetermined period of time; or a RF block mode, wherein the station prevents transmission of any remote radio frequency signals to the operating system. The delay-open feature is initiated by actuating a delay switch when the barrier is in a closed position. After a predetermined period of time the operator moves the barrier to an open position. The predetermined period of time is user adjustable.

Abstract: A control unit for a moveable barrier, such as a garage door, includes a microcontroller connected to a motor speed detector, motor current sensor or a sensor for determining forces exerted on or by the barrier. A user interface includes user actuatable switches for setting a first maximum force value to be exerted on or by the barrier when moving in one direction and the microcontroller automatically sets the value of a second maximum force to be exerted on or by the barrier when moving in the opposite direction. The second force value may be based on the force value set by the user or the second force value may be a preset value. Both force limits may be automatically set as a function of a maximum force exerted on said barrier during movement thereof, during a force learning operation.

Abstract: A power window driving apparatus includes a motor which drives a window by supplying a supply voltage of a power supply, a control circuit which controls the motor so as to stop or reverse a rotation of the motor when a motor current flowing to the motor is increased, a shunt resistance which detects the motor current as a voltage value, and is provided between the motor and a ground and a diode which is provided between a positive side of the power supply and the control circuit for protecting the control circuit.

Abstract: A current sensing circuit includes; a shunt resistor, on which a motor current is flown; a reference resistor which has a resistance value that is n times the shunt resistor; and a current following circuit. The current following circuit includes: a following current control circuit, which controls the following current and generates a first reference voltage; and a capacitor which generates a second reference voltage indicating an average value of the first reference voltage. A first comparator compares a third reference voltage higher than the first reference voltage with the second reference voltage, and outputs the current limitation control signal. A motor current sensing range expanding circuit expands a motor current sensing range by increasing a ratio of the current sensing circuit having the shunt resistor and the reference resistor.

Abstract: An improved drive circuit is provided for a DC motor. The drive circuit includes: a DC power source; a relay having a normally open contact and a normally closed contact; a DC motor electrically connected through the normally open contact of the relay to the power source; and a discharge circuit connected in parallel to the DC motor. More specifically, the discharge circuit is coupled to the normally closed contact of the relay and operable to inhibit current flow from the DC motor until the relay has settled in a closed position.

Abstract: A controller has a plurality of control units that are mutually connected by a communication line and are set at different places of an automobile, each corresponding to a different one of its power windows and serving to control its opening and closing. One of these control units is adapted to transmit a signal, in response to a switch operation, to another of the control units through the communication line to open or close the window corresponding to the latter control unit. When this control unit detects that it has submerged in water, it applies a constant voltage to an interface of the communication line. This prevents communications through the communication line and windows from moving in an unwanted manner.

Abstract: A controller is disclosed for a motor. The motor includes a first terminal and a second terminal. In a positive mode, the first terminal is connected with the positive electrode of a power supply, and the second terminal is connected with the negative electrode of the power supply. In a negative mode, the first terminal is connected with the negative electrode, and the second terminal is connected with the positive electrode. The controller includes a central conductive device comprising a first conductor connected with the positive electrode of the power supply, a second conductor connected with the first terminal, a third conductor connected with the negative electrode of the power supply and a fourth conductor connected with the second terminal. An upper conductive device includes a first conductor for contacting the first and second conductors of the central conductive device and a second conductor for contacting the third and fourth conductors of the central conductive device in the positive mode.

Abstract: The control device includes a switch (12) controlling the power supply to the motor and an actuator which actuates this switch by rotatably reacting against the moving object being restrained so as to cause said switch to be opened and to cut off the power supply to the motor. This actuator consists of a bistable mechanical device (11) capable of taking up a first state in which the switch (12) is closed and a second state in which the switch is open. The actuating device also comprises exclusively manual means, such as a cable (17) for putting the actuating device into its first state, this device being brought into its second state by reacting against the moving object.

Abstract: A control device and method of used includes receiving a signal from a first sensor and receiving a signal from a second sensor after receiving the signal from the first sensor. In response to the received signals, the electronic device executes the function.

Abstract: In the method of controlling a process for moving a part (20) by an electric motor (12) against an end stop, pinching events are detected by monitoring a motor operating variable, such as a motor rpm, and if pinching is detected the motor (12) is stopped and/or reversed. The electric power triggering the motor (12) at the start of and during a startup phase while system slack is taken up is controlled so that it is constant and lower than the power triggering the motor in an ensuing operating phase (54) in which the part (20) moves. Preferably power during the startup phase is reduced to power values that are just barely enough to move the motor while system slack is taken up. In a preferred embodiment the applied motor voltage is reduced and controlled by a power end stage that includes a bipolar transistor or a field effect transistor.

Abstract: This invention discloses an electronic control system for an Industrial Motor Operator that uses standard steady state logic to improve reliability in rough service wet and dirty environments. It includes means of providing electronic snow limit to close limit sensing removing the need for two switches and radically improving its accuracy. A low voltage switch reverses the high voltage motor wires and at the same time reverses the open limit, close limit, and snow limit sensors mechanical positions. It discloses a system using lamps to indicate that the power wiring is connecting to three-phase motors in the correct sequence or that single-phase motors have their windings correctly phased.

Abstract: A power-window jamming preventing apparatus, includes a current sensing circuit, which senses a motor current flowing through a motor; a current limiting circuit, which increases and decreases the motor current based on a current-limitation control signal outputted from the current sensing circuit when an amount of increase of the motor current exceeds a predetermined vale; and a jamming determining circuit, which determines a jamming of a foreign matter in the window glass, and a potential difference generating circuit, which monitors a power source voltage supplied to the current sensing circuit and the power window motor, and which clamps a third reference voltage so as to drop a constant voltage from the third reference when the power source is low such that a potential difference between the second reference voltage and the third reference voltage is kept greater than a predetermined voltage.

Abstract: A power-window jamming preventing apparatus, includes a current sensing circuit, which senses a motor current flowing through a motor for driving a window glass; a current limiting circuit, which increases and decreases the motor current based on a current-limitation control signal outputted from the current sensing circuit when an amount of increase of the motor current exceeds a predetermined vale; a jamming determining circuit, which determines a jamming of a foreign matter in the window glass based on increase of the motor current to reverse a rotation of the motor; and a charge/discharge controlling circuit which monitors a voltage level of a charge/discharge controlling signal, and controls a charging/discharging circuit to keep a third reference voltage constant when the charge/discharge controlling signal having one of voltage levels is continuously outputted for a predetermined time.

Abstract: A window position detection and anti-pinch system and method for detecting the presence of an obstruction between a window and window frame of a door assembly of a vehicle is disclosed. The system includes at least one sensing device disposed adjacent the window detecting the position of the window in the window frame and generating an output representative of the detected position of the window. A controller responsive to the output generated by the at least one sensing device compares the window position signal output against predetermined values to determine window position and whether an obstruction exists between the window and window frame.

Abstract: An opening and closing device for an opening and closing member of a vehicle includes a driving motor, a feedback control unit for controlling an output duty to the driving motor so that a preset target speed of the driving motor can be achieved, a high-pass filter for filtering a frequency of an actual speed of the driving motor, and a pinching determination unit for determining a pinching of an object based on an output from the high-pass filter.

Abstract: A field effect transistor is provided between the ground and an H bridge circuit for rotating a motor in forward and reverse directions in a manner that the drain of the transistor is grounded and the gate thereof is coupled to a DC power source such as a battery serving as a bias source which supplies electric power to the H bridge circuit. Thus, when the DC power source such as a battery is reversely connected, the field effect transistor normally in an on state is turned off. A controller monitors the source voltage of the field effect transistor, and when the controller detects an excess current, the controller outputs a control signal to the high-side driver to prevent the supply of electric power to the motor.

Abstract: An antipinch circuit prevents the motor driven closure of an automotive window if a soft obstacle is compressed between the window and the top of the door frame, and the window is opened in response to the sensing of the obstacle. The circuit measures the motor torque (by measuring motor current) and the motor shaft speed (by measuring motor back EMF). The torque and motor speed are compared to “signatures” of these values in the case of the window closing normally against the top of the door frame, or against an obstacle, and either stopping or reversing the motor rotation accordingly.

Abstract: A system and method to simulate and evaluate management algorithms of a panel or mobile window, activated by an electric motor, with anti-crushing security and a program for its execution. It includes a modular structure integrating a series of models representative of the electric parameters of the electric motor, mobile panel performance, incidence of a possible obstacle and an activation and control methodology implemented by means of a sequential state machine related to starting, stopping and/or motor displacement direction according to position and panel displacement direction and a module to evaluate an algorithm to be validated on introducing the current supplied to the motor and its angular speed and which analyzes said values and its temporary evolution and combinations between some or other values. Said models and modules are implemented in a high level programming language.

Abstract: A method for controlling an electric drive motor (10) of a motor vehicle adjusting drive by means of applying a variable voltage to it should be improved so that an EMV interference suppression can be inexpensively executed. To this end, a controllable resistor (12, 18, 20, 22) is used, which supplies the voltage applied to the drive motor (10).

Abstract: When abnormal current due to jamming is detected through motor current (ID), the motor current (ID) performs an operation in which an ON/OFF operation and a continuous ON operation are repeated, so that increment of the motor current (ID) is restrained. At this time, determination of jamming is performed based on the ON/OFF operation and the continuous ON operation. When the jamming is determined, the motor current (ID) is stopped, and the motor is reversed.

Abstract: A method for determining the position of an element driven by the drive shaft of a commutated direct current (DC) motor includes counting current ripples detected in an armature current signal as the motor rotatably drives the shaft. A frequency spectral analysis of the armature current signal is performed to determine frequency components of the armature current signal. The frequency components are analyzed to determine which of the frequency components is indicative of the current ripple frequency. The current ripple frequency is monitored for changes over time while the motor drives the shaft. The number of counted ripples is modified upon a change in the current ripple frequency in a time interval if the current ripple frequency change deviates from the current ripple frequency more than a threshold deviation for the time interval. The rotational position of the shaft is determined based on the modified number of counted ripples.

Abstract: A motor driving circuit includes a window opening switch, a window closing switch, an auto switch, a motor which opens and closes a window by driving rotating operation, a charging circuit which charges one capacitance element by a first CR time constant upon operating the window opening switch, and a discharging circuit which sharply charges another capacitance element upon operating the auto switch and which discharges a discharging voltage charged to the other capacitance element by a second CR time constant upon stopping operation of the auto switch. Driving operation of the motor stops when a voltage of the one capacitance element in the charging circuit is higher than a first reference voltage or a voltage of the other capacitance element in the discharging circuit is lower than a second reference voltage during driving the motor.

Abstract: Methods and apparatus for controlling an automatic barrier movement system, particularly for beginning movement of a barrier which has been stopped between an open and closed position of the barrier. The receipt of a barrier movement command will generally start movement of the barrier toward the open position, however, when predetermined conditions are met the barrier may be started in a direction determined by a preprogrammed algorithm. The predetermined conditions may include that the barrier has been stopped for less than 5 minutes and/or that the barrier was stopped in response to an obstruction during travel toward the open position. The preprogrammed algorithm may be to move the barrier toward the closed position or move the barrier in a direction determined from other sensed conditions.

Abstract: An opening and closing control device of opening and closing member for a vehicle includes a motor for actuating the opening and closing member, and a control unit for driving the motor so as to become a predetermined target speed and for driving the motor in reverse direction as a detection of entrapped obstacles when the actual speed of the motor reaches to an entrapment judgment speed which is set lower than the target speed. The control unit sets a threshold speed which is higher than the target speed and outputs an output duty to the motor for achieving the target speed by feedback control. The control unit switches the output duty after the actual speed of the motor becomes higher than the threshold speed to an output by feedforward control based on the target speed.

Abstract: The present invention relates to a contact-disk system including a control unit, a rotatable contact disk and a plurality of contact elements, the contact disk having a plurality of paths and each contact element being associated with one path. The paths have electrically conductive segments and electrically insulating segments, logical states being encoded by the electrically conductive segments and the electrically insulating segments. The contact disk has n paths with n≧2, and N logic states are encoded by the n paths and by the sequence of the electrically conductive segments and the electrically insulating segments, with N>2n. The present invention also relates to a method for controlling a windshield-wiper motor and a windshield-wiper motor having a contact-disk system according to the present invention.

Abstract: A method for determining the position of an element drivable by a motor within a travel segment between first and second positions. The method includes energizing a motor to drive the element along the travel segment. Current ripples contained in an armature current signal of the motor are counted as the motor drives the element. The position of the element along the travel segment is determined as a function of the counted current ripples. The motor is de-energized once the position of the element is within a certain distance of the first position if the element is to be driven into the first position. The motor is then re-energized to drive the element into the first position. The counted current ripples is set to a reset value after the element has been driven into the first position such that the reset value corresponds to the first position.

Abstract: A vehicle power window and power door lock system includes a vehicle pillar adapted for use between openable and closable vehicle doors and a single lock actuation assembly in the pillar adapted for engagement with a front door lock latch assembly on a front door and a rear door lock latch assembly on a rear door for locking and unlocking the doors. The vehicle power window and power door lock system further includes a single reversible electric motor in the pillar adapted for selective engagement with a front window on an adjacent front door and a rear window on an adjacent rear door for driving the windows up and down. A vehicle side door assembly includes a door lock latch assembly, a latch rod operatively connected to the latch assembly, a window, and a driven gear operatively connected to the window. The latch rod is operably connectable to a lock actuation assembly located in a body pillar adjacent to the door when the door is positioned against the body pillar.

Abstract: An abnormality detector for motor drive system easily detects, using a CPU, abnormality such as short circuit or disconnection in magnetic field coils of a motor, wiring, an open/close element, etc., which are controlled by a microprocessor (CPU). The open/close elements conducting an open/close operation sequentially in response to pulse outputs P1, P2 generated by the CPU, drive the magnetic field coils. Surge voltages generated upon interrupting the mentioned open/close elements are OR connected through a diode, and input to a temporary storage circuit. Then the CPU reads out, stores and resets the surge voltages using pulse edges of the pulse output P1 or P2. When any generation of the surge voltage is not stored in the temporary storage circuit, the CPU operates an abnormality alarm display.

Abstract: A three phase motor starting system is provided to reduce the in-rush current to the motor in order to obtain a soft start of the motor. The soft start of the motor equates to reduced impact forces on motor parts and device components connected to the motor during startup of the motor, especially a startup resulting from a reversal of the direction of rotation of the motor. The system uses an impedance load in series with the motor windings of the motor to reduce the in-rush current to the motor windings, which results in a reduced acceleration of the motor shaft and a soft start to the motor. The impedance loads used by the system can be a resistive load, a capacitive load or an inductive load, depending on the type of impedance load that is desired for the soft start of the motor.

Abstract: 1. Method for operating the electric window openers of a motor vehicle.

Abstract: A control and motor arrangement for use in a model train includes a control arrangement integrally constructed with a motor. The control arrangement receives rotational speed and positional information from the motor and uses this information to determine how much power to supply to the motor, thus controlling the rotational speed of the motor. In this way, the control arrangement maintains a constant motor speed, if desired. In addition, the speed and positional information is optionally provided to a sound control arrangement for use in selecting appropriate sound effects.

Abstract: A closure system including a closure moveable for substantially closing an aperture in use, and an actuator for at least closing the closure, the actuator being mounted by mounting means, the mounting means including one or more measurement cells for measuring, in use, parameters of the closure systems, in use the system being subjected to movement and being arranged such that it is possible to at least partially distinguish trap forces applied to the closure from acceleration forces applied to the closure as a result of the movement of the closure system by consideration of the measured parameters.

Abstract: The invention concerns a method for controlling a motor vehicle wiper motor comprising steps which consist in: determining at least a range related to an operating parameter of the motor and capable of having several non null values; comparing said range with a predetermined threshold (high LS, low; HS, high INT, low LS, low INT); and controlling the motor on the basis of the result of the comparison. The range is determined when the rotor of the motor occupies a determining position corresponding to a predetermined point on a trajectory of a blade driven by the motor.

Abstract: A vehicle with a tailgate (5) or the like, the vehicle being defined in that the tailgate (5) has a sensor for sensing objects at least during the opening operation.

Abstract: An improved window covering and lighting system for a window in a room includes a plurality of cornices, each cornice including a window covering supported by the cornice and movable between an open position and a closed position, an actuator supported by the cornice for moving the window covering between the open position and the closed position, a lighting system mounted to the cornice, and a programmable logic unit for operating at least one of the actuator and the lighting system independently from one another upon demand. The system also includes a remote control unit providing a signal selectively to the programmable logic unit to operate at least one of the plurality of cornices. Each of the plurality of cornices further includes a light sensor for sensing ambient light conditions in the room, and a motion detector for detecting occupance of the room. The programmable logic control unit is responsive to the sensed ambient light conditions and the detected occupance.

Abstract: A method of operation for a motor-driven worm gear actuator coupled to a load device energizes the motor in a series of pulses during an initial period of motor operation when reversal of the motor is commanded. The pulsed energization produces a slow initial axial movement of the motor armature without moving the load device, minimizing the contact force between the armature shaft and a mechanical end stop of the motor. Rotation of the motor is determined by identifying and counting motor current pulses due to commutation, and the pulse count is adjusted at each reversal of motor rotation to compensate for motor current pulses due to the pulsed energization.

Abstract: The invention relates to a process for adjusting a motor vehicle part between at least two positions, the motor vehicle part being driven by an electric motor, pulse signals being generated according to the rotary motion of the electric motor and being supplied to a control unit for controlling the electric motor, in the first computation (50) with a first parameter set the first value for the instantaneous force acting on the motor vehicle part is determined from the acquired pulse signals at certain first instants. Parallel to the first computation, in at least the second computation (52) with a second parameter set which differs from the first parameter set the second value for the instantaneous force acting on the motor vehicle part is determined from the acquired pulse signals at certain second instants, the two values being considered for the instantaneous action of the force in order to decide whether the electric motor is turned off or reversed or not.

Abstract: A method and a device for incrementally determining the actual reversal of a rotary drive that rotates on slightly even after a preceding signal switching the rotational direction is applied. A sequence of pulse signals (N; S; SL) that are proportional to the rotational speed, with an intermittent reference signal (SL) that is different from said pulse signals, is output by an asymmetric transmitter wheel (1) and received by a single sensor (3) located on the stator. A pulse signal correction value for determining the pulse signal count value corresponding to the actual reversal (U) of the rotary drive is defined, based on the number of pulse signals that are measured between two reference signals following a switch of direction.

Abstract: A wiper control device in which an abnormal condition of a FET is detected by distinguishing an action of an overheat-cutting protective function normally difficult to be detected with measuring the drain voltage of the FET and by which the control of the pertinent FET is restrained upon the detection of abnormality so as to prevent a short circuit in the wiper control device from occurring. When an FETB (Qb) is set on, whether or not a drain voltage Vd is lower than Vpe ({fraction (l/2)}VG) is judged (step S5), and if lower, it is judged that the drain and ground is short-circuited, that is, an overheat-cutting protective function is acted, and “1” is added to the number of times of short circuit detection Perror (step S7). It is judged whether or not the added value of the number of times of short circuit detection Perror reaches a reference value (step S11).

Abstract: The invention relates to a process for adjusting a motor vehicle part between at least two positions and a drive device for executing this process. The motor vehicle part is driven by an electric motor, and a pulse signal is generated according to the rotary motion of the electric motor which is supplied to a control unit for controlling the electric motor, in which at certain instants the value for the current force acting on the motor vehicle part is determined from the pulse signal. This value of the force is used as the criteria in the decision whether the electric motor is to be turned off or reversed [or not]. Before connection of the electric motor to the motor vehicle part measurements are taken on the electric motor for determining the individual motor characteristics, the measured values determined in this way are used in the determination of the value of the action of force.

Abstract: A mobile robot system includes a RF module that is under the control of a controlling computer. The mobile robot system includes a running device for moving the mobile robot about a room, an obstacle detecting device for detecting the presence of an obstacle in the mobile robot's path, a location recognizing device, a first transceiver for transmitting and receiving a signal to control the various devices, and a controlling computer for data processing the signal from the first transceiver and transmitting a control command to the mobile robot. The controlling computer includes a second transceiver for transmitting and receiving a signal to and from the first transceiver, an image board for processing image data from the obstacle detecting device and the location recognizing device, and connecting means for connecting to the Internet. The mobile robot is compact and sized and can be remotely controlled via the Internet.

Abstract: A seat adjusting system having a motor assembly with an integrated sensor and control electronics assembly for adjusting a vehicle seat. The integrated electronics assembly performs electronic memory seat module functions. The integrated electronics assembly includes a multiplex link for communicating data between the integrated sensor and control electronics assembly and an external switch. The integrated electronics assembly further includes motor control relays positioned between the motors of the motor assembly for controlling the motors to adjust the seat. The integrated electronics assembly also includes seat position sensors for monitoring the position of the seat. In contrast to typical seat adjusting systems having an external electronic memory seat module, the seat adjusting system needs only a minimal set of wires connecting the seat adjusting system to an external switch as the integrated electronics assembly performs electronic memory seat module functions.

Abstract: A string drawing electrical device for a racquet has a casing, a string holder, an actuating device and a control unit. The string holder is rotatably attached to a panel of the casing. The actuating device is mounted in the casing and provides two functions, feeding and reversing, to the string holder. The control unit is mounted in the casing for controlling the actuating device to act. Accordingly, the string drawing electrical device can tighten and loosen the string, and the tensile force of the string of the racquet can be accurately controlled.

Abstract: A capacitor is placed in series with a solenoid to bear a substantial portion of the voltage so that a reduced voltage energizes the solenoid. The solenoid may operate a brake on a motor. Applying voltage to operate the motor, energizes the solenoid which retracts the brake.

Abstract: In a power window device an MCU detects motor torque values one by one when a window is opened and closed, compares the detected motor torque values with base values set to the travel regions and stops or reverses a motor determining that an object is pinched in the window when the former values exceed the latter values.

Abstract: A process for displacing a motor vehicle part between at least two positions and a drive device for executing this process in which the motor vehicle part is driven by an electric motor (10), a pulse signal is generated according to the rotary motion of the electric motor (10) and is supplied to a control unit (24) for controlling the electric motor (10), and the instant of input of each signal on the control unit (24) is acquired. Furthermore, at certain instants, a respective for the change of motor rpm is determined from at least some of these previously measured instants, from each value of the rpm change a force change value (&Dgr;F*[k]) is computed and at least some of the previously determined values of the force change are added up with weighting in order to determine the value for the instantaneous force acting on the moveable motor vehicle part. This value is used as the criterion in deciding whether or not the electric motor (10) is turned off or reversed.

Abstract: A movable barrier operator includes a wall control switch module having a learn switch thereon. The switch module is connectable to a control unit positioned in a head of a garage movable barrier operator. The head unit also contains an electric motor which is connected to a transmission for opening and closing a movable barrier such as a garage door. The switch module includes a plurality of switches coupled to capacitors which, when closed, have varying charge and discharge times to enable which switch has been closed. The control unit includes an automatic force incrementing system for adjusting the maximal opening and closing force to be placed upon the movable barrier during a learn operation. Likewise, end of travel limits can also be set during a learn operation upon installation of the unit.

Abstract: A lift type tailgate on a passenger van type vehicle body is operated by an electric motor powered actuator with an electronic control circuit utilizing a microprocessor operating under program control to respond to user-initiated opening and closing signals to move the tailgate in the selected direction. In the control circuit, feedback information to the microprocessor indicative of tailgate position is provided by a potentiometer coupled with the actuator motor and the microprocessor is programmed to operate with this information to stop the tailgate at a wide open position, a partially closed position and a fully closed position. Obstruction detection is performed by the microprocessor using an obstruction detection circuit and additionally by monitoring the position signal input from the potentiometer to stop the tailgate on encountering an obstacle.