674results about How to "Realize the protection function" patented technology

The invention relates to a comprehensive automation integrated protecting method and a system which adopt an integrated IED to carry out automation functions such as protection, measurement and control, computation and the like of all bay units in a substation; state quantity, analog quantity and digital quantity which are output in interval by primary equipment on a process layer of the substation are respectively uploaded to the integrated IED through an ethernet switcher by a dual Ethernet (100mega / 1000mega), and the protection and automation function of the substation are realized by calculating and processing the state quantity, analog quantity and digital quantity which are output in interval respectively by the integrated IED, therefore, a spacing layer and a substation layer of the substation are unified into one layer according to IEC61850 standard, and a plurality of IEDs are integrated into one integrated protecting IED, and two same integrated IEDs are provided for hot spare for improving the reliability. The comprehensive automation integrated protecting system leads the substation integrated protecting functions to share a uniform information platform, and communication network is used for replacing control cables, thus improving the reliability of the signal transmission, further improving automation and management level and reducing comprehensive construction cost.

The invention discloses a method and a device for recovering mixed regenerative energy of an urban railway power supply system. The method comprises the steps of determining an energy feedback / absorption mode according to the AC power grid failure state, controlling an energy feedback converter to feed regenerative brake energy back to the AC power grid in the energy feedback mode, and converting regenerative brake energy into direct-current low-voltage electricity to be absorbed by an energy absorption component in the energy absorption mode. The device comprises a direct-current disconnecting switch unit, an energy feedback transformer, a converter control unit and at least one converter unit. Each of the at least one converter unit comprises the energy feedback converter, an energy feedback branch switch K1, an energy absorption branch switch K2 and three energy absorption components. By means of the method and the device, regenerative brake energy is absorbed by the energy absorption component during the failure of the AC power grid to maintain the stability of the DC power grid voltage, and the connection between the energy recovery device and the DC power grid is not needed to be cut off, so that the safe reliability of the energy recovery device is improved, the structure of a chopper can be omitted, and costs are saved.

The application discloses a rack end protection method of an electric power steering system. When a rack of a steering gear moves towards the end of the rack and enters a rack end protection area, an ECU (electronic control unit) of the electric power steering system takes a rotating angle of a steering wheel, the speed of the rotating angle and rotating torque as input to calculate a rack end protection gain value which serves as a multiplier during assisting torque calculation. The rack end protection gain value is the product of a basic gain coefficient, a rotating speed gain coefficient and a rotating torque gain coefficient. The basic gain coefficient decreases progressively as the absolute value of the rotating angle of the steering wheel increases. The rotating speed gain coefficient decreases progressively as the absolute value of the rotating angle of the steering wheel increases. The rotating torque gain coefficient increases progressively as the absolute value of the rotating angle of the steering wheel increases. According to the rack end protection method of the electric power steering system, during working conditions of rack ends, current output can be limited, temperature rise can be reduced and mechanical impact of the rack ends can be avoided.

The invention relates to a vector controller of an alternating current (AC) asynchronous motor. The vector controller comprises a control chip, a drive circuit, a three-phase inverter circuit, a Hallsensor and an amplifying and filtering circuit, and is characterized in that a PWM output hardware interlock circuit is connected between the control chip and the drive circuit, and the IGBT overflowing signal of the drive circuit is fed back to the PWM output hardware interlock circuit; a stator current overflowing signal generation circuit is connected with the output end of the amplifying and filtering circuit of a current sampling circuit in parallel, and a stator current overflowing signal is fed back to the PWM output hardware interlock circuit; and a temperature sensor is additionally arranged at the bottom of an IGBT module, a signal thereof is input to the A / D port of the control chip, and the general input / output ports of the control chip are utilized to control the operation of a radiator fan. The invention can effectively realize under-voltage protection and current overflowing protection on the IGBT module, and achieves the functions of IGBT soft turn-off and motor stator current overflowing protection.

The invention discloses a distributed generation-based grid connection transition operation mode coordination comprehensive protection method. When the DG capacity is continuously increased, the short-circuit current level is improved, the DG is changed from a "pure load" into a "small power supply", and a problem that conventional protection and switching breakpoints cannot meet the transition condition is solved. Based on the conventional protection and the switching breakpoints, the scheme provided by the invention performs continuous matching with a primary operation model and is continuously optimized, and the information and the state quantity are continuously exchanged to form a protection control interface adapted to a primary system, so that dual purposes of safe operation of a system and continuous power supplying are achieved. The fault isolation range is determined by collecting a new boundary which is determined by the switching breakpoints, and that whether the system sectionalizing and the island operation mode generated as a boundary point is determined is stable or not is comprehensively considered.

The invention discloses an intelligent electronic type voltage transformer. The intelligent electronic type voltage transformer comprises a far-end module, an amorphous iron core, an optical fiber composite insulator, an insulating oil layer, a resistance-capacitance voltage divider, an optical fiber and a combination unit. According to the intelligent electronic type voltage transformer, the iron core is made of amorphous materials, a resistance-capacitance voltage division principle is used as a design principle, and a transformer body is formed by pouring insulting silicone rubber on the amorphous iron core, a primary winding and a secondary winding. According to the intelligent electronic type voltage transformer, the iron core is made of amorphous alloy, so that the intelligent electronic type voltage transformer has high saturated magnetic induction and low loss, the weight and the size of the intelligent electronic type voltage transformer can be reduced greatly, and efficiency can be improved greatly. In addition, the intelligent electronic type voltage transformer has low noise, is easy and convenient to install and use, does not need maintaining in an operation process, is light in weight, high in accuracy, good in linearity and wide in measuring range, overcomes the defects that a conventional electromagnetic voltage transformer is narrow in frequency band, slow in response and the like, and has practical significance to transformation of and improvement to existing electrical equipment, and the ability to resist electromagnetic interference is enhanced.

The invention discloses an over-current protection circuit, including a switch control module, high and low level states, and software and hardware switch protection modules. An input end and an output end of the switch control module are respectively connected with a high level and a load, the software and hardware switch protection modules are connected with a control end of the switch control module, and the software switch protection module includes a constant current source module. In the over-current protection circuit provided by the invention, output turning-off of the switch control module can be controlled automatically either by the software switch protection module according to the practical running need of a device or by hardware through automatically detecting electric current flowing through a power driving tube. The two protection methods are integrated together, and protection will take effect if either condition is met at any time. The constant current source module will keep an output turning-off state if the load is short-circuited for a long time, and can return back to its normal state once external abnormalities are excluded. Therefore the device can be free of maintenance and manual intervention in operation, which reduces labor cost and greatly improves labor productivity.

The invention provides a fixing device for machining, comprising a base plate, an arc-shaped splint, a two-way screw, a moving seat, an electric telescopic rod, a mounting plate, a support rod, a suction cup and an electric telescopic cylinder. There is an electric telescopic rod, the electric telescopic rod is fixed on the inner end of the moving seat, the moving seat is installed on the two-way screw rod, the two-way screw rod is installed inside the base plate, and the lower end of the moving seat passes through the base plate and the two-way screw rod. The screw rods are connected, the design realizes the clamping function, and the distance between the electric telescopic rods can be adjusted at the same time. For the suction cup, an electric telescopic cylinder is installed on the right side of the support rod, and the design can adjust the angle to meet different processing requirements.

The invention discloses a conveying bent pipe, a concrete conveyer and a manufacturing method of the conveying bent pipe. The disclosed sequentially comprises an inner pipe, an outer pipe and a filling layer, and the outer pipe at least comprises two supporting pipes which are sequentially connected; the outer pipe of the conveying bent pipe has a split type structure and comprises two or more than two supporting pipes, thereby reducing the cost of the conveying bent pipe under the condition that the wearing resistance, the strength, the high toughness and the impact resistance are ensured. In an optimized technical scheme, the inner pipe and outer pipe are fixed by an adhesive layer to transfer the acting force of the inner pipe to the outer pipe, the supporting and protecting function of the inner pipe by the outer pipe is ensured, and safety of the conveying bent pipe can be increased. Because the inner pipe and the outer pipe can be mutually positioned by matching with an inner convex body and an inner notch, the manufacturing method of the conveying bent pipe not only can simplify a manufacturing technology in a conveying bent pipe manufacturing process, but also can reduce auxiliary mechanisms and reduce the manufacturing cost of the conveying bent pipe.

A satellite antenna kinetic control system comprises a system setting circuit, a main control unit, a drive and power circuit, a current sensing circuit, a angular position sensing circuit, a rotate speed sensing circuit and a actuator. The main control unit mainly includes a DSP chip and a FPGA chip. The utility model effectively improves the pointing accuracy and the dynamic tracking performance and decreases the cubic capacity and the power consumption of the control system, so as to provide the significant value for the application in the field of the satellite antenna pointing control system.

The invention relates to a protective circuit of a control and protection switch. The circuit comprises: a microprocessor circuit, a signal acquiring circuit, a power supply circuit, an input circuit, a drive circuit, an output control circuit, a human-computer interface circuit and a communication circuit. The circuit has a plurality of protection functions such as overload, phase failure, underload, imbalance and the like, as well as the display function of nixie tubes and the communication function of field buses, and can form a digital control and protection switch capable of communicating together with the main body of the control and protection switch. The protective circuit of the control and protection switch adopts few elements, effectively realizes the protection, control, measurement and display functions of the control and protection switch by reasonable connection, and has communication function. The circuit is simple in connection and high in anti-interference performance, and has the advantages of small volume and high reliability when used in the control and protection switch.

The invention provides a protective composite material, which comprises a protective layer, a functional layer and a comfort layer stacked in order; from the end of the protective layer, the functional layer includes a nuclear radiation shielding layer, an electromagnetic shielding functional layer and a textile substrate which are sequentially stacked, or, the functional layer includes the nuclear radiation shielding layer and the textile substrate which are sequentially stacked; and from a fabric substrate end, the comfort layer includes a neutron protective coating and a polypropylene high-molecular substrate which are sequentially stacked. The invention also provides a preparation method of the protective composite material. The protective composite material has multiple functions of flame retardation, static prevention, anti-ionization / electromagnetic radiation and neutron protection, and can be used for processing nuclear radiation protective clothing and protective tents, flexible protective screens and the like.

The invention discloses a photovoltaic power station system with low voltage ride through and anti-islanding protection functions. The photovoltaic power station system comprises a photovoltaic power generation system array, a first breaker, a three-phase inverter, a filter, a parameter detecting module, a loader, a second breaker, a transformer, a power grid and a controller. The output current of the photovoltaic power generation system array sequentially passes through the first breaker, the three-phase inverter and the filter to be input into the input end of the parameter detecting module, one path of the parameter detecting module is connected with the loader, the other path of the parameter detecting module is connected with the power grid through the transformer and the second breaker, the parameter detecting module can detect switch signals of the second breaker and the voltage V and the frequency f of the coupled point between the parameter detecting module and the loader and input the switch signals, the voltage V and the frequency f to the input end of the controller, one path of the output end of the controller is connected with the inverter to provide PWM signals to the inverter, and the other path of the output end of the controller is connected with the first breaker. The photovoltaic power station system combines the low voltage ride through function and the anti-islanding protection function, so that the purpose of improving the stability and the safety of the photovoltaic power station system is achieved.

A method for the monitoring, control and optimization of filling equipment for foods and beverages, such as, for beverage bottles. The abstract of the disclosure is submitted herewith as required by 37 C.F.R. §1.72(b). As stated in 37 C.F.R. §1.72(b): A brief abstract of the technical disclosure in the specification must commence on a separate sheet, preferably following the claims, under the heading “Abstract of the Disclosure.” The purpose of the abstract is to enable the Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure. The abstract shall not be used for interpreting the scope of the claims. Therefore, any statements made relating to the abstract are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.

The invention relates to an unattended central heat supply monitoring station. The station is characterized by mainly comprising a plate heat exchanger, a variable frequency water replenishing pump, a circulating pump, an electric adjusting valve, a ball valve, a controller and a control cabinet, wherein an inlet and a return port of the plate heat exchanger are connected with a primary heat supply pipeline and a primary water return pipeline respectively; the electric adjusting valve is arranged between the primary heat supply pipeline and the plate heat exchanger; a water outlet and a water return port of the plate heat exchanger are connected with a secondary heat supply pipeline and a secondary water return pipeline respectively; the controller is connected with an outdoor temperature sensor, a temperature sensor and a pressure sensor; and the temperature sensor and the pressure sensor are connected with the primary heat supply pipeline and the secondary heat supply pipeline respectively. The unattended central heat supply monitoring station has the advantage of realizing remote transmission and remote control by using a fully automatic unattended operating mode. The system has over-temperature, over-voltage and under-voltage chain protection and alarm function; and through the controller, the temperature of the water supplied by the pipe network can be adjusted according to the outdoor temperature variation so as to ensure the indoor heat supply temperature.

The invention relates to a quick network electric power relay protection system and belongs to the technical field of electric power relay protection. The quick network electric power relay protection system comprises intelligent terminals arranged on power distribution equipments, an optical fiber communication network, a network protection device and a network protection server, wherein the optical fiber communication network respectively connects the intelligent terminal with the network protection device, and connects the network protection device with the network protection server, and the intelligent terminal collects analog quantity and switching quantity operating condition data of the power distribution equipment and uploads the data to the network protection device; the network protection device gathers the data uploaded by the intelligent terminals, performs wide-area differential protection calculation and uploads the calculation results to the network protection server; and the network protection server displays the data uploaded by the network protection device, finishes intelligent setting and intelligent control according to the real-time change of network topology, and transmits the data to the network protection device. With the quick network electric power relay protection system, the number of secondary equipments is reduced, the management workload on the operation and maintenance of secondary equipments is relieved, and the benefit maximization of the power system is realized.

A motor vehicle, includes a drive motor for driving the motor vehicle, at least one additional motor and at least one differential for distributing a torque generated by the drive motor and transmitted by a drive shaft to a driven differential element of the differential to two output shafts. The motor vehicle includes a coupling device which can be controlled by a control device, and in a first coupling state directly or indirectly couples the additional motor with an output shaft, thereby rendering the distribution of the drive torque to the output shafts dependent on an additional torque exerted by the additional motor, and in a second coupling state directly or indirectly couples the additional motor with the driven differential element.

The invention discloses a method for controlling a rotor position angle of a permanent magnet synchronous motor and a control method. The control method is to establish a sliding mode model and obtaina position angle estimation equation. By collecting the stator current signal of the permanent magnet synchronous motor, the rotor position can be calculated effectively, and the sensorless setting can be realized. Moreover, the current and the voltage are collected and input into the protection circuit, and additional protection is realized by using hardware, wherein a protection circuit 10 is electrically connected to a controller or a protection signal is directly input into a PWM driving module 9, and a PWM signal is enabled to be enabled under control. Once a fault signal occurs, the PWMsignal is directly blocked to implement the hardware protection function, and the direct driving mode is adopted to reduce the possibility of interruption due to the control panel fault interference.

The invention relates to a wiper device (10) for cleaning a vehicle windscreen, with a wiper blade (15), which is fastened exchangeably on a wiper arm (11), wherein along the wiper blade (15) an elongatedly constructed spray device (40) having several nozzle openings (50) is arranged for applying a washing fluid to the vehicle windscreen, which is constructed as a separate component from the wiper blade (15). It is provided according to the invention that the wiper arm (11) has a hood-shaped cover (20) for the wiper blade (15), which covers the wiper blade (15) over its entire length, and that the spray device (40) is arranged in the area of the cover (20).

The invention provides a relay protection device of a variable pitch blade system of a wind driven generator. The device comprises a power source, a variable pitch blade motor relay, a brake relay, a relay control circuit and a control power source, wherein the power source is used for supplying power to the variable pitch blade motor and a brake thereof; the variable pitch blade motor relay is used for controlling power-on or power-down of the variable pitch blade motor; the brake relay is used for controlling the power-on or power-down of the brake; the relay control circuit is used for controlling the power-on or power-down of the variable pitch blade motor relay and the brake relay; the control power source is used for supplying power for the relay control circuit; and the relay control circuit is a digital circuit. The device has the advantages of realizing digital protection of a single blade, improving the action feature and the performance of the relay protection, occupying small space and volume of a shaft control cabinet and greatly reducing the power consumption, along with high correctness, stability, reliability and self-examination and polling capacity, friendly man-machine interface, superior technical structural conditions, remarkable economic benefit and obvious technical improvement, and is flexible and convenient to use, and easy to use on a large scale and popularize.

The invention relates to a design method of a protection function of a centralized protection device of a transformer substation. The method comprises the following steps: (1), designing basic function modules; (2), combining the basic function modules into a protection module; (3), forming a logic equipment protection module; and (4), carrying out layered structure combination. According to the method, on the basis of the visual logic development environment, the modularized and structural protection function design is realized; the protection function realization is simplified; the work intensity is also reduced in the large-scale application; the protection transportability is high; and the reliability is also substantially enhanced.

The invention discloses a position feedback and protection device of a sub-span super wind tunnel diffuser adjustment sheet. The position feedback and protection device comprises a framework, a strokesensor, adjustment sheets, a simulation adjustment sheet, a limit switch and a wind tunnel body, wherein the adjustment sheets in a wind tunnel body cavity are symmetrically arranged at two sides ofthe central axis of the wind tunnel body, upstream ends of upstream adjustment sheets are attached to an inner wall surface of the wind tunnel body through an upstream stretching rod perpendicular toa wall surface of the wind tunnel body, downstream ends of the upstream adjustment sheets are hinged with one end of a throat stretching rod perpendicular to the wall surface of the wind tunnel body,the two symmetric upstream adjustment sheets form a required airflow channel, an airflow throat is formed at the narrowest point of the adjustment pieces, the downstream may have no adjustment sheet or is hinged with at least one downstream adjustment sheet segment through a downstream stretching rod perpendicular to the wall surface of the wind tunnel body, a tail end of the downstream adjustmentsheet is attached to an inner wall surface of the wind tunnel body, and the simulation adjustment sheet is in hinge connection with an outer side of the wind tunnel body through an upstream stretching rod, a throat stretching rod and a downstream stretching rod.

The invention discloses a compact type insulated gate bipolar transistor (IGBT) module driving unit. The compact type IGBT module driving unit comprises a power board, a driving core board and a driving adaptive board, wherein a control protection circuit is arranged on the driving core board, a driving circuit is arranged on the driving adaptive board, and the power board, the driving core board and the driving adaptive board are connected in sequence through a cable or connecting terminals. According to the compact type IGBT module driving unit, a power module is independently arranged, core circuits of control protection and the like of an IGBT module are placed in the driving core board, the driving circuit is placed in the adaptive board, and only a corresponding module adaptive board needs to be changed so as to correspond to IGBT modules of different manufacturers and different model numbers. The core board can be connected with module adaptive boards of various model numbers, so that the aim of being in common use is achieved. A temperature measurement circuit, an electric current measurement circuit and a control protection circuit are designed to be in the same driving core board, wherein the temperature measurement circuit, the electric current measurement circuit and the control protection circuit are arranged in a dispersed mode, so that compactibility is achieved. Optional functions such as overheating protection, short pulse suppression and weak light protection are arranged, so that flexible smart configuration is achieved.

The invention relates to a renewing and transforming method for oasis protection forest in drought regions. The method is characterized by comprising the following steps of: in front of wind sand, carrying out row alternated cutting mode on an original Populus bolleana forest belt, (namely retaining one row of Populus bolleana and cutting one row of Populus bolleana, then retaining one row of Populus bolleana and cutting one row of Populus bolleana, and the like), and separately planting Populus bolleana seedlings and russian olive seedlings in the cut rows in the forest belt in an inter-plant mixing mode; carrying out early-stage protection on the seedlings by utilizing the retained Populus bolleana to guarantee the survival and growth of the Populus bolleana seedlings and russian olive seedlings; and cutting the retained Populus bolleana after newly planted Populus bolleana and russian olive have a certain protection effect, and renewing the oasis protection forest by the same method. By the adoption of the method provided by the invention, healthy growth and protection function of the oasis protection forest can be achieved and fine circulation of wood can be provided.

Being installed on bus of transformer substation, dedicated integrated protection relay (IR) is connected to current transformer and voltage transformer on all outgoing wires of bus. Combining with new development in traditional protection and protection of power distribution, IR makes up of new protection including three phases: first phase is instantaneous trip unit; second phase is acceleration trip unit implemented by using directional comparison technique of communication channel or technique of non channel; in third phase, based on collected information of fault and direction sent from IR through network, integrated network protection unit sends out corresponding trip command directly. The invention provides quick protection for single sect of wire, as well as integrated protection function for whole system of power distribution. The invention possesses wide foreground of application along with development of measurement, communication, and process etc. techniques.

The invention discloses a single-arm robot stamping and carrying apparatus. The single-arm robot stamping and carrying apparatus comprise a machine table; a linear lifting platform is arranged in themiddle part of the machine table; a liftable robot carrying apparatus is arranged at one end, positioned on the linear lifting platform, of the machine table; an isolation paper placement plate and anisolation paper carrying apparatus for carrying isolation paper to a finished product placement plate one by one are arranged at the other end, positioned on the linear lifting platform, of the machine table; the finished product placement plate is positioned on the linear lifting platform; and the linear lifting platform is also provided with a supplied material plate structure with a compensating and lifting function. The single-arm robot stamping and carrying apparatus is mainly specific to flexible FPC board stamping and carrying. The apparatus is a four-axis robot with a liftable base; the Z axis of the robot is positioned on the base, so that the robot can walk in the narrow space of upper and lower modules of a punch conveniently; a suction cup is arranged at the tail end of the robot, and a product protection function is added at the suction cup adsorption position; the suction cup is rotatable, so that a secondary stamping function of the symmetrical products can be realizedconveniently; and the four-axis robot with the liftable base is mainly used for material carrying.

The invention discloses an underground refuge corridor smoke prevention, protection and cold source system based on artificial intelligence. The system comprises an underground refuge corridor, a first fireproof compartment and a second fireproof compartment. A first refuge corridor smoke prevention front chamber is arranged between the first fireproof compartment and the underground refuge corridor, a second refuge corridor smoke prevention front chamber is arranged between the second fireproof compartment and the underground refuge corridor, the first fireproof compartment corresponds to thefirst refuge corridor smoke prevention front chamber, the second fireproof compartment corresponds to the second refuge corridor smoke prevention front chamber, a smoke prevention front chamber pressurization air supply well is arranged between the first refuge corridor smoke prevention front chamber and the second refuge corridor smoke prevention front chamber, an air cooling unit outdoor unit is arranged in the smoke prevention front chamber pressurization air supply well, and communicating air openings are formed among the first refuge corridor smoke prevention front chamber, the first fireproof compartment and the underground refuge corridor and among the second refuge corridor smoke prevention front chamber, the second fireproof compartment and the underground refuge corridor. The intelligence degree is high, fire prediction is accurate, underground space is saved, and the energy saving effect is good.

The invention belongs to the technical field of electric power system fault recognition, and particularly relates to an interstation protection fault recognition system and method based on information fusion. The interstation protection fault recognition system based on information fusion is characterized by comprising a protection information uploading module, an interstation information interaction module and an information fusion action module which are connected in sequence; the protection information uploading module extracts distance protection and zero sequence current protection action messages on the basis of protection line interval output results; the interstation information interaction module calculates and sends interstation interaction information on the basis of the action messages uploaded by the information uploading module; the information fusion action module recognizes interstation faults according to the interstation interaction information and local protection action information. Accurate judgment results can be obtained for faults of various types, the protection performance is sensitive and reliable, the backup protection action time is shortened, and meanwhile the problem that protection fixed value setting is hard is successfully solved.

The invention provides an after-current circuit breaker operation mechanism which comprises a handle and a transmission mechanism which are arranged in a rotating mode, a tripping fastening assembly, a releasing piece and a free releasing mechanism. The transmission mechanism comprises a first connection rod connected with a handle and a second connection rod in pivoting connection with the first connection rod. The second connection rod is in transmission connection with a movable contact. The tripping fastening assembly comprises a tripping fastening piece, a locking fastening piece, a tripping fastening spring and a locking fastening spring. The releasing piece drives the locking fastening piece to move to enable the tripping fastening piece to be separated from the locking fastening piece. The free releasing mechanism enables the movable contact to move when the handle does not rotate. The free releasing mechanism comprises a cam arranged in a rotating mode and a third connection rod, a protruding portion of the cam contacts the tripping fastening piece in an abutting mode, one end of the third connection rod is in pivoting connection with the cam, and the other end of the third connection rod is in pivoting connection with the connection position of the second connection rod and the first connection rod. When the stripping fastening piece is separated from the locking fastening piece, the cam drives the tripping fastening piece to rotate to drive the third connection rod to drive the second connection rod to move to drive the movable contact to move. The mechanism is simple in structure and capable of achieving a free releasing function without the aid of external force.