41results about How to "Guaranteed dynamic stability" patented technology

An earthmoving machine including a control system is disclosed. The machine comprises first and second satellite navigation antennas mounted in a longitudinal direction on the earthmoving machine. A third satellite navigation antenna is mounted on a pole attached to an operational element of the earthmoving machine. In one embodiment, the earthmoving machine is a bulldozer and the operational element is a blade of the bulldozer. The machine further comprises a gravity reference sensor and a plurality of gyroscopes mounted on the machine. A computer processor generates control signals based on sensor data received from the various components. The disclosed system and method allows for dynamically stable operation of the earthmoving machine at relatively fast speeds without the development of unwanted oscillations.

An earthmoving machine including a control system is disclosed. The machine comprises first and second satellite navigation antennas mounted in a longitudinal direction on the earthmoving machine. A third satellite navigation antenna is mounted on a pole attached to an operational element of the earthmoving machine. In one embodiment, the earthmoving machine is a bulldozer and the operational element is a blade of the bulldozer. The machine further comprises a gravity reference sensor and a plurality of gyroscopes mounted on the machine. A computer processor generates control signals based on sensor data received from the various components. The disclosed system and method allows for dynamically stable operation of the earthmoving machine at relatively fast speeds without the development of unwanted oscillations.

The invention relates to a flexible biped robot, in particular to a pneumatic-electric combined driving flexible biped robot. The problems that linkage between joint flexibility and a dynamic response characteristic of existing flexible biped robots is poor, the walking efficiency of the robots is low and the dynamic stability of the robots is poor are solved. The pneumatic-electric combined driving flexible biped robot comprises a left leg, a right leg and a pelvis. The left leg and the right leg each comprise a thigh, a shank, a foot, a hip joint, a knee joint and an ankle joint. Each hip joint comprises a one-way series-connection elastic driver and a hip joint transmission mechanism. Each one-way series-connection elastic driver comprises a motor, a motor seat, a torsion spring, a first hub, a second hub, a first clamping ring, a second clamping ring and a hip joint driving shaft. Each hip joint transmission mechanism comprises a driving belt wheel, a driven belt wheel, a driving belt and a hip joint driven shaft. The driving belt wheels are mounted on the hip joint driving shafts correspondingly. Each knee joint comprises a knee joint driving mechanism and a knee joint transmission mechanism. The pneumatic-electric combined driving flexible biped robot belongs to the field of humanoid robots.

The invention discloses a compound for the stress absorbing layer of rubber asphalt and a preparation method and application thereof. In the invention, the method for preparing the compound for the stress absorbing layer of the rubber asphalt comprises the following steps: adding 17-20 parts of radial tyre rubber powder by weight, 2-6 parts of rubber processing oil by weight and 0.1-0.3 part of montmorillonite by weight into 75-80 parts of road petroleum asphalt, stirring and reacting for 45-120min at the temperature of 180-200 DEG C to obtain the rubber asphalt; heating 100 parts of mineral aggregate by weight to 160-200 DEG C, adding 9-11 parts of rubber asphalt by weight, and evenly stirring to obtain the finished product of the compound for the stress absorbing layer of the rubber asphalt. The compound for the stress absorbing layer of the rubber asphalt, which is prepared according to the method of the invention, is specially used as an intermediate layer when asphalt pavement is coated on the cement pavement, thus playing the role of preventing reflection cracks.

The embodiment of the invention discloses a humanoid robot gait planning method, a humanoid robot gait planning device and a humanoid robot. The method comprises the following steps: acquiring stressinformation of a swinging leg of the humanoid robot in a single-foot supporting period at present; judging whether the swinging legs fall to the ground or not according to the stress information, andacquiring biped stress information and waist poses of the humanoid robot after the humanoid robot enters a biped supporting period when it is judged that the swinging legs fall to the ground; controlling an original supporting leg according to the waist pose and the expected waist track in the biped supporting period, and controlling an original swinging leg according to the expected swinging legtrack; and judging whether a preset task switching condition is met or not according to the biped stress information and the biped supporting period transition duration, and switching the trajectory tracking tasks of the original supporting leg and the original swinging leg when the preset task switching condition is met. According to the technical scheme, smooth alternate switching of the supporting legs and the swinging legs can be achieved in the rapid walking process of the humanoid robot, and the dynamic stability and the like of the posture and the speed of the humanoid robot are guaranteed.

The invention discloses a self-adaptive robust control method and device for an under-actuated hydraulic single-leg power-assisted exoskeleton. The control method comprises the following steps of establishing a physical model; obtaining a reference displacement and an actual displacement; adopting the actual displacement and the reference displacement as input quantities, and adopting the output of a middle-layer position tracking controller as a virtual expected joint driving torque; and converting the expected joint torque into expected hydraulic cylinder output force, adopting the expected hydraulic cylinder output force and actual hydraulic cylinder output force as input quantities, converting flow into driving voltage of an electro-hydraulic servo valve, using the driving voltage to control the output force of a hydraulic cylinder, and driving all joints of the under-actuated single-leg power-assisted exoskeleton to rotate. According to the self-adaptive robust control method and device for the under-actuated hydraulic single-leg power-assisted exoskeleton provided by the invention, under the condition that the number of the hydraulic cylinders is smaller than the number of freedom degrees of motion of the exoskeleton, the influences of multi-joint strong coupling of the under-actuated hydraulic single-leg power-assisted exoskeleton, high-order nonlinearity of a hydraulic driver and model uncertainty are effectively overcome, and the good following and power-assisted effects of the hydraulic power-assisted exoskeleton on human motion are achieved.

The invention relates to a red mud-based asphalt mixture warm-mixing agent and a preparation method thereof, and belongs to the technical field of asphalt warm-mixing agents. The preparation method comprises the following steps: step 1) calcining red mud powder and then mixing with an active aluminum silicon source in proportion, and allocating the molar ratio of SiO2 / Al2O3 to obtain a geopolymerprecursor; step 2) adding the geopolymer precursor obtained in the step 1) into an alkaline activator solution, and stirring to obtain geopolymer mud; step 3) curing the geopolymer mud obtained in thestep 2) to obtain a geopolymer block, and preparing the geopolymer block into powder; and step 4) adding the geopolymer powder obtained in the step 3) into a surfactant solution, stirring uniformly,and then suction-filtering and drying the obtained slurry to obtain the red mud-based asphalt mixture warm-mixing agent. According to the invention, the asphalt mixture warm-mixing agent is prepared by surface modification of red mud-based geopolymer powder, thereby effectively ensuring mechanical properties of an asphalt mixture while significantly reducing a mixing temperature and a molding temperature of the asphalt mixture.

The invention discloses a combined steel box girder and a construction method thereof, belonging to the field of high-speed railway bridges. A steel box of the combined steel box girder comprises adjacent upper steel box and a lower steel box sharing one horizontal separating plate; a prefabricated prestressed concrete plate is glued to the inner of the lower steel box with structural glue. The prestressed concrete plate passes through the lower steel box and the peripheral gap is filled with structural glue. Since the girder is made of the steel box, a concrete top board and the prestressed concrete plate inside the lower steel box, the girder can be assembled on site, which is convenient for transportation and hoisting for construction and it is possible to build simply supported beams with larger span. Compared with present whole simple girders of the same span, the provided combined steel box girder has increased cross section rigidity of the steel box girder, the weight of girders is reduced and the span of girders is increased. The combined steel box girder of the invention has reasonable construction stress and is convenient to construct; the method is applied for building high speed railway beam bridges with larger span.

The invention discloses a self-adaptive three-step method-based truck formation driving following vehicle control method. A vehicle longitudinal dynamics equation is established according to a stresssituation of a vehicle in a running process; by using the vehicle longitudinal dynamics equation, taking expected vehicle distance deviation and speed deviation as state variables, and taking an expected output torque as a control variable, establishing a nonlinear state space equation; then establishing queue integral Lyapunov, and then based on this, establishing a form of a controller referenceinput signal; and based on a three-step method control theory, designing a controller, determining a parameter self-adaptation law of the three-step method controller, obtaining a control rate of thecontroller, determining an output control variable by the controller according to state information at each moment and in combination with an expression form of a control law, and applying the outputcontrol variable directly serving as a driving / braking torque signal to the controlled vehicle. A Lyapunov function method is used in a design process of a controller reference input, and the three-step method controller is used for adjusting the parameters of the controller in real time under the adjustment of the self-adaptive law.

The invention relates to a method for planning and tracking a local obstacle avoidance path of an autonomous vehicle. The method comprises the following steps: acquiring a global reference path; planning a local path of the autonomous vehicle through an RRT local path planner; and stably and effectively tracking an ideal local obstacle avoidance path by adopting a personified T-S fuzzy path tracking strategy. According to the invention, a vehicle dynamics model is fused into an RRT algorithm, and the personified driver behavior dynamics model and the fuzzy algorithm are fused in path tracking control so that the autonomous vehicle can effectively track an ideal obstacle avoidance path in a high-dynamic road environment, and meanwhile, the dynamics stability of the vehicle can be well ensured; and a theoretical basis preparation is made for path planning and tracking of the autonomous vehicle applied to urban road vehicle driving with dense pedestrians, field environment engineering vehicle obstacle avoidance driving and even battlefield military vehicle actual obstacle avoidance driving for avoiding enemy firepower in the future.

The invention provides a method for designing a multi-balance point nonlinear system for dynamic stability control. The method comprises the following steps of: 1) establishing a synchronous unit model, and determining a gradient-like definition; 2) judging the gradient-like performance of the synchronous unit model, and if the synchronous unit model is chaotic, executing the step 3); 3) performing controller design on the synchronous unit model in the step 1); and 4) performing dynamic stability analysis and control on a power system by using a controller in the step 3), so the dynamic stability of the whole power system is ensured. According to a dynamic stability control method which is employed in the invention, the linearization of the conventional like methods is eliminated, so accumulated errors which are generated in the method are greatly reduced, and a future practical engineering guiding function is realized.

The invention discloses a method for simultaneously identifying loads and mutual inductance of a multi-load wireless power transmission system, which comprises the following steps of: firstly, enabling a multi-load system to be equivalent to single-load systems with different working time sequences through a time division multiplexing method; voltage overshoot and instable voltage occurring in a time division operation identification algorithm are prevented through double filter capacitors and bus voltage adjustment; and then introducing a particle swarm algorithm, establishing a system steady-state circuit model, establishing a fitness function through a difference value between a sampling output voltage and a prediction output voltage, converting a parameter identification problem into an algorithm optimization problem, and carrying out optimal solution search on a to-be-identified parameter to replace a traditional calculation method, so that errors generated by a traditional equation are avoided. According to the method, only input and output voltages need to be sampled, the communication data volume is reduced, the circuit complexity is reduced, and the system size is reduced. According to the method, the load and mutual inductance of the multi-load wireless charging system can be identified in real time, and the working range of the wireless charging system is expanded.

The invention discloses a control system suitable for an unmanned articulated train set. The control system comprises n longitudinally-arranged vehicle bodies, n is larger than or equal to 2, the vehicle bodies comprise two types including a traction vehicle body and a following vehicle body, traction is divided into two types including a main traction vehicle body and an auxiliary traction vehicle body, the vehicle bodies comprise the main traction vehicle body arranged at the foremost end of the vehicle set, an auxiliary traction vehicle body arranged at the backmost end of the vehicle set, and a following vehicle body at the middle part between the main traction vehicle body and the auxiliary traction vehicle body. The main traction vehicle body and the auxiliary traction vehicle body are not in a traction state at the same time, the articulated vehicle achieves stable starting through power-assisted traction of an articulated rod and the following vehicle body, and then steering is achieved by segmenting a preset path into a plurality of straight line segments. And the following driving of the following vehicle body is realized on the basis of the driving path of the traction vehicle body and the traction vehicle train, the dynamic stability of the whole train train is ensured, and the stability of the vehicle is monitored from multiple angles in the driving process of the train train to ensure the safety of the train train.

The invention discloses a preparation method of a surface abrasion-resistant coating of a floating clamping jaw of a numerical control punching machine. Firstly, chromium oxide ceramic particles and alow-melting-point additive are weighed according to the proportion of the coating and are evenly mixed; and then the high-performance abrasion-resistant coating is prepared on the surface of the clamping jaw after sand blasting through an atmospheric plasma spraying technology. The method solves the problem that a dovetail groove structure is used in a traditional floating clamping jaw of the numerical control punching machine and accordingly a plate is locally deformed in the clamping process. The low-melting-point glass powder additive in the mixed powder is of a unique spherical structure,so that the fluidity is better, the repose angle formed due to stacking is smaller, and material mixing is more uniform; a base material and a filler can be sufficiently dense, the density of the prepared coating is greatly improved, and problems of the pure chromium oxide coating in the using process are effectively solved, so that the tribology performance of the coating is better, the servicelife is longer, and the preparation cost is lower; and the thermal influence of the spraying process on the floating clamping jaw of the numerical control punching machine is small, and the structureand shape of a base body are not changed.

The invention discloses a method based on current waveform recognition for preventing failure protection maloperation of a circuit breaker. The method can recognize tripping-off state of a switch of the circuit breaker quickly, so as to prevent maloperation of failure protection of the circuit breaker due to a tail current generated after the switch is tripped off. The recognition process takes short time, the problem of maloperation of failure protection of the circuit breaker caused by the tail current generated after the switch of the circuit breaker is tripped off under the condition of short action delay is solved, a blocking signal as a circuit breaker tripping-off recognition mark is added into the original failure logic, a deduction that the circuit breaker is tripped off is made through recognizing the tail current quickly, the failure protection logic is blocked quickly so as to prevent maloperation of the failure protection caused by the tail current; and since the recognition of the tail current logic takes short time, the inherent action delay of failure protection can be further shortened when conditions permit, the method is of positive significance in maintaining dynamic stability of power system operation, and has good application prospect.

The present invention relates to the application field of zero-moment point (ZMP) dynamic stability control in mobile robots, and in particular discloses a dynamic adaptive stability control system for mobile robots, including a mobile platform, which can be connected to the torso of the robot The connecting device can be stretched out along the edge of the mobile platform, thereby enhancing the stability of the mobile platform to support the stretching device and the control unit connecting the mobile platform and the stretching device; the control unit includes real-time calculation of the mobile platform. Stability ZMP calculation module, vehicle body motion and navigation control module, and a control box connected to the torso of the robot; the control box is connected to the ZMP calculation module, vehicle body motion and navigation control module, mobile platform and stretching device. The invention can calculate the zero-moment point of the robot in real time, judge the dynamic stability of the mobile platform, automatically adjust the torso of the robot or the mobile extension device, and ensure the dynamic stability of the robot.

The invention provides a 3d (three-dimensional) visual movable composite robot. Four wheels of the movable robot are respectively connected to a body of the movable robot through a telescopic rod, a motor drives the four wheels to rotate, a radar detector is used for detecting barriers with a certain distances away from the front and the rear of the movable robot and acquiring distance data among the movable robot and the barriers, a gyroscope is used for acquiring inclination angles of the movable robot, a GPS (global positioning system) positioning module is used for acquiring position data of the movable robot, a control module is used for controlling the telescopic rods of the four wheels to expand and contract, a stepping motor controls the telescopic rods to expand and contract, a hand-held control terminal is used for transmitting instructions to the control module, and the control module controls the telescopic rods of the four wheels of the movable robot and the motor. The 3d visual movable composite robot can effectively control postures and directions of the robot, and dynamic stability of the robot is ensured.

The invention provides an iterative local search method for solving a power grid splitting problem. The iterative local search method is mainly used for solving an island problem of a power system, and mainly comprises three parts, namely a two-stage method, a local search method and a disturbance method. The two-stage method is used for randomly generating a feasible initial solution; the local search method is used for improving an existing solution; and the disturbance method is used for jumping out of a local optimum trap. According to the iterative local search method, after the feasibleinitial solution is generated, local search and disturbance optimization are continuously executed on the current solution until the deadline is up, and the algorithm is ended. Under the condition that connectivity constraints of power grid islands, generator coherence constraints and power transmission capacity constraints are met, power grid splitting of thousands of power nodes can be achievedin a short time, and the defect that an existing algorithm can only be used for a small-scale power grid is overcome to a certain extent. The iterative local search method has the advantages of high calculation speed, high solving quality and practicability, and can solve the island problem of the power system effectively.

The invention discloses a self-adaptive robust force control method and device for an under-actuated supporting leg assisting exoskeleton. The control method comprises the steps that a physical modelis established and converted into a state equation, wherein the physical model comprises a man-machine interface model, a motion model and a complete constraint model; the reference displacement of the under-actuated supporting leg assisting exoskeleton is obtained; the actual angle value of the exoskeleton and the actual displacement of the back contact portion are obtained; the actual displacement and the reference displacement are taken as input quantities, and the output of a lower-layer position tracking controller is taken as motor driving torque; and the motor driving torque is converted into output torque of control current control motors, and all joints of the under-actuated supporting leg assisting exoskeleton are driven to rotate. Under the condition that the number of the motors is smaller than the number of freedom degrees of exoskeleton movement, the influence of multi-joint strong coupling and model uncertainty of the under-actuated supporting leg assisting exoskeleton is effectively overcome, the good following and assisting effect of the assisting exoskeleton on human movement is achieved, and high application value is achieved.

The invention relates to a red mud-based asphalt mixture warm mix agent and a preparation method thereof, belonging to the technical field of asphalt warm mix agents. The method comprises: 1) calcining the red mud powder and mixing it with an active aluminum silicon source in proportion, and preparing SiO 2 / Al 2 o 3 mol ratio to obtain the geopolymer precursor; 2) the geopolymer precursor obtained in step 1) is added to the alkaline activator solution, and the geopolymer slurry is obtained after stirring; 3) the geopolymer slurry obtained in step 2) is Solidify the material slurry to obtain a geopolymer block, and then make the geopolymer block into powder; 4) add the geopolymer powder obtained in step 3) into the surfactant solution, stir the obtained slurry Suction filtration, drying, that is. The invention prepares the asphalt mixture warm mix agent by modifying the surface of the red mud base polymer powder, which effectively ensures the mechanical properties of the asphalt mixture while significantly reducing the mixing temperature and molding temperature of the asphalt mixture.

The invention discloses a combined steel box girder and a construction method thereof, belonging to the field of high-speed railway bridges. A steel box of the combined steel box girder comprises adjacent upper steel box and a lower steel box sharing one horizontal separating plate; a prefabricated prestressed concrete plate is glued to the inner of the lower steel box with structural glue. The prestressed concrete plate passes through the lower steel box and the peripheral gap is filled with structural glue. Since the girder is made of the steel box, a concrete top board and the prestressed concrete plate inside the lower steel box, the girder can be assembled on site, which is convenient for transportation and hoisting for construction and it is possible to build simply supported beams with larger span. Compared with present whole simple girders of the same span, the provided combined steel box girder has increased cross section rigidity of the steel box girder, the weight of girders is reduced and the span of girders is increased. The combined steel box girder of the invention has reasonable construction stress and is convenient to construct; the method is applied for building high speed railway beam bridges with larger span.

The invention relates to a robust control method and device for an under-actuated double-leg supporting hydraulic power-assisted exoskeleton. The control method comprises the following steps: initializing a sampling period of the real-time controller; the motion states of the left leg foot and the right leg foot of the exoskeleton are judged; establishing a physical model of the exoskeleton and converting the physical model into a state equation; the back acting force is obtained, and reference displacement is obtained in an upper-layer controller; an expected driving torque is obtained in a middle-layer controller according to the reference displacement; the expected flow of the electro-hydraulic servo valve is obtained in a lower-layer controller according to the expected driving torque; generating a current signal according to the expected flow; according to the current signals, all joints of the exoskeleton are driven to rotate, and tracking motion of the exoskeleton is achieved. The human-computer interaction exoskeleton following motion model is established by integrating multiple factors, the closed-chain dynamics problem of the exoskeleton is effectively solved, the influence of various interferences and uncertainties on the exoskeleton following motion is eliminated to a great extent, and the robustness of exoskeleton control is enhanced.

The invention provides a split internal-expansion switch angle valve. The split internal-expansion switch angle valve comprises a valve seat, a valve element, a valve rod, an angle type valve body andan upper cover, wherein the upper cover is arranged on the angle type valve body, the angle type valve body is arranged on the valve seat, and the valve element is arranged in an inlet flow channel of the angle type valve body. The lower end of the valve rod is connected with the valve element through a clamping nut, and the upper end of the valve rod penetrates out of the upper cover. The outerperipheral surface of the valve element comprises a positive conical surface located at the upper end of the outer peripheral surface of the valve element, a guide surface located under the positive conical surface and a sealing surface positioned under the guide surface; a flushing hole is formed in the angle type valve body, and a flushing plug is arranged in the flushing hole. The switch anglevalve has the advantages of being small in flow resistance coefficient, high in flowing capacity, reliable in sealing, convenient to disassemble and assemble and the like.

An automobile transmission shaft torsional shock absorber, which is used to solve the problems of the existing torsional shock absorber that the elastic connectors are easily damaged and the overall life is short, including an inner skeleton, an inertia ring, an outer ring, a centering and limiting element, and a rubber block , the inner frame is connected with the flange of the transmission shaft through a bolt assembly, rubber blocks are uniformly distributed on the outer wall of the inner frame, one side of the rubber block is vulcanized and fixed on the outer wall of the inner frame, and the other side is vulcanized and fixed on the inner wall of the outer ring , the outer ring is fitted on the outside of the inner frame, and inertia rings are press-fitted on the inner walls at both ends of the outer ring, and the centering and limiting elements are evenly distributed in the cavity between the outer ring and the inner frame. The invention has the characteristics of few parts, simple structure and reliable performance, can not only improve the driving comfort of the vehicle, but also prolong the service life of the torsion damper of the transmission shaft of the vehicle.

The invention discloses a control method for following vehicles in formation driving of trucks based on an adaptive three-step method. According to the force situation of the vehicles during driving, the longitudinal dynamic equation of the vehicle is established; And the speed deviation as the state quantity, and the expected output torque as the control quantity, establish the nonlinear state space equation; then establish the queue as a whole Lyapunov, and establish the form of the controller reference input signal accordingly; based on the three-step control theory, design The controller determines the parameter adaptive law of the three-step controller to obtain the control rate of the controller. The controller determines the output control amount according to the state information at each moment and combined with the expression of the control law, which is directly used as the driving / braking torque signal Act on the charged vehicle. The Lyapunov function method is used in the design process of the controller reference input, and the three-step controller adjusts the controller parameters in real time under the adjustment of the adaptive law.

The invention provides a method for designing a multi-balance point nonlinear system for dynamic stability control. The method comprises the following steps of: 1) establishing a synchronous unit model, and determining a gradient-like definition; 2) judging the gradient-like performance of the synchronous unit model, and if the synchronous unit model is chaotic, executing the step 3); 3) performing controller design on the synchronous unit model in the step 1); and 4) performing dynamic stability analysis and control on a power system by using a controller in the step 3), so the dynamic stability of the whole power system is ensured. According to a dynamic stability control method which is employed in the invention, the linearization of the conventional like methods is eliminated, so accumulated errors which are generated in the method are greatly reduced, and a future practical engineering guiding function is realized.

The embodiment of the invention provides a motor grid-connected operation control method and device and a grid-connected operation control system.The method comprises the steps that when a first switch, a second switch and a third switch are all in an off state, if a starting-up instruction sent by instruction sending equipment is received, the second switch and the third switch are controlled to be switched on; the method comprises the following steps of: connecting an asynchronous starting permanent magnet synchronous motor and a power grid with a frequency converter; controlling the third switch to be switched off and the first switch to be switched on when the maximum voltage deviation between the power grid and the frequency converter is determined to be smaller than a preset voltage threshold value after the operation frequency of the asynchronous starting permanent magnet synchronous motor is controlled to be the target frequency carried in the rotating speed control instruction based on the frequency converter; and the asynchronous starting permanent magnet synchronous motor is connected into a power grid for operation. According to the invention, grid-connected operation of the motor can be realized through the frequency converter, so that the problems of difficulty in direct grid-connected starting of the motor and unsafety caused by over-torque and low voltage during operation are solved.

The invention relates to a bituminous mixture with physically modified red mud replacing mineral powder and a preparation method of the bituminous mixture, and belongs to the technical fields of roadengineering materials and preparation. The method comprises the following steps: firstly, mixing a modified material and water according to a certain ratio, so as to form a water solution; secondly, adding crushed and dried red mud into the water solution obtained in the first step according to a certain ratio, and stirring, so as to form mixed slurry; thirdly, ensuring that the mixed slurry obtained in the second step is subjected to suction filtration, drying and crushing processes, so as to obtain physically modified red mud powder used for preparing the bituminous mixture; fourthly, preparing the bituminous mixture through the physically modified red mud powder obtained in the third step replacing mineral powder. The bituminous mixture is prepared from the physically modified red mud replacing mineral powder, can effectively improve the high-and-low temperature performance and water damage resistance, and effectively guarantees the property.