HYDRAULIC ACTIVE GUIDE ROLLER SYSTEM FOR HIGH-SPEED ELEVATOR BASED ON FUZZY CONTROLLER.doc

hydraulic active guide roller system for high-speed elevator based on fuzzy controllerabstract: increase of elevator speed brings about amplified vibrations of high-speed elevator. in order to reduce the horizontal vibrations of high-speed elevator, a new type of hydraulic active guide roller system based on fuzzy logic controller is developed. first the working principle of the hydraulic guide system is introduced, then the dynamic model of the horizontal vibrations for elevator cage with active guide roller system and the mathematical model of the hydraulic system are given. a fuzzy logic controller for the hydraulic system is designed to control the hydraulic actuator. to improve the control performance, preview compensation for the controller is provided. finally, simulation and experiments are executed to verify the hydraulic active guide roller system and the control strategy. both the simulation and experimental results indicate that the hydraulic active guide roller system can reduce the horizontal vibrations of the elevator effectively and has better effects than the passive one, and the fuzzy logic controller with preview compensation can give superior control performance. key words: high-speed elevator horizontal vibmions hydraulic /mt glide roller system fuzzy logic control0 introductionhorizontal vibration is ens of the main problems affecting ride comfort in elevators. there are many reasons contributing to the horizontal vibrations of elevators, such as the irregularity of the guide rails, the abnormity of the guide rollers, the running speed of elevators, the offset load of passengers, the wind buffeting, etc. research indicates that these horizontal vibrations are mainly generated by the irregularity of the guide rails1 and are in proportion to the running speed of elevators23 to meet the need of high and super-high buildings, elevator speed is now becoming higher and higher, which results in serious horizontal vibrations. suppression method of horizontal vibrations is necessary for high-speed elevator. the conventional horizontal vibration reduction techniques include structure changes and passive guide roller system using stiff spring. these passive suppression methods need no power supply and have the advantages of simple structure, low price and high reliability and can work well when the elevator speed is low. but they cannot do with the increasing elevator speed because of such disadvantages as limited frequency band width and low working force. active vibration reduction techniques can flexibly cope with the new situations and have good effects and have been used widely. accordingly, studies on the active suppression method of horizontal vibrations for high-speed elevators have been advanced. now mitsubishi co. and others have already developed their active guide roller device to alleviate horizontal vibrations of high-speed elevators based on magnetic effect451. and they have acquried patent protection for that61. accordingly, we propose in this paper a new type of active guide roller system based on hydraulic actuator which can reduce the horizontal vibrations of high-speed elevators. first, the structure and the working principle of the hydraulic active guide roller system are analyzed. then the mathematical model of the system is given. and the fuzzy logic controller with preview compensation is designed to control the active guide system. last, computer simulation and experimental tests are performed to verify the effectiveness of the hydraulic device and the controller.1 active control model of horizontal vibrations for elevator cagethe elevator system is a kind of complex multi-body structure. elevator cage is the part loading the passengers. fig. 1 is the configuration of a.i elevator cage. it includes a car body, a frame and four passive guide roller systems. the car body is supported by the frame and the guide system is fixed on the frame. the three rollers of the conventional guide systems are contacted with the t type rails tightly by the stiff spring damper. the elevator goes up and down when the guide roller runs along the rail. the unevenness of the guide rails is transmitted to the elevator cage through the guide roller system and brings about horizontal vibrations of the elevator. this problem can be overcome by the active guide roller system.considering the horizontal vibrations in the direction parallel to the elevator door, the dynamic model of the horizontal vibrations for elevator cage with active guide roller system is developed as shown in fig. 2. here the car body and the frame are supposed to be a whole rigid symmetrical body, the rollers are modeled as mass-spring-damper units with same structure and parameters71, the elevator runs at the constant velocity v, and only the rail disturbance is taken into account. the motion equations of the elevator cage in the horizontal direction are given as2 hydraulic active guide roller system2.1 system configuration and working principlethe configuration of the hydraulic active guide roller designed is shown in fig. 3. the hydraulic cylinder fixed between the roller level and the cylinder bracket is the actuator. it replaces the conventional spring damper. two high-speed on/off valves(hsv) are linked to a piece of hydraulic cylinder, one taking charge for the oil supply is called in-oil-valve(lhsv), the other for the oil return is called out-oil-valve(ohsv). the hydraulic pressure in the cylinder is controlled by these two valves. when the guide roller runs along ideal even rail, both valves are off. the cubage of the cylinder is an airtight space. the hydraulic pressure remains the initial setting value p0. the guide roller is pressed to the guide rail tightly by the prestressing force. the elevator keeps balanced without horizontal vibrations. when the guide roller comes across the convex surface of the rail, the roller moves to the elevator and the oil pressure increases. the 1hsv is turned off and the ohsv is turned on. the oil in the cylinder is reduced and the pressure value falls down to po- on the contrary, if the guide roller meets with the concave surface, the valves will take converse actions to keep the pressure value constant. there fore, with proper control method the pressure value of the hydraulic actuator can be maintained constant. the hydraulic active guide roller system would isolate the elevator body from the rail disturbance for the sake of the passengers comfort and at the same time maintain a firm contact between the rail and the roller. each cylinder is connected with an accumulator to absorb the pressure pulsation. 2.2 mathematical modelsthe equations of pressure and fluid flow of the hydraulic cylinder are shown as compressible fluid flow between the accumulator and the cylinder so the active control force produced by the hydraulic actuator can be expressed as follows where the sign in eq. (6) is positive when i is equal to 1 or 3, and is negative wheni is equal to 2 or 4.the fluid flow equations of the high-speed on/off valves are shown asthe compressible fluid flow between the accumulator and the cylinder is modeled as equation3 controller designthe nonlinearities of the hydraulic active guide roller system make it difficult to design the controller using linear control theory. since the fuzzy logic system has no requirements for linearity assumptions and has good robustness, fuzzy logic strategy is employed to control the hydraulic system. furthermore, as any hydraulic system has time delay in nature, and the guide rail disturbance in ahead of the roller is easy to get61, preview compensation is introduced to improve the control performance. that is, the controller consists of fuzzy logic controller(flc) and the preview controller(pc). fig. 4 is the block diagram of the controller. the sum of up and uf is converted into the duty ratio of pwm signal r, and r for hsv according to the rules as follows3.1 fuzzy logic controllerthe fuzzy logic controller is a feedback loop. it is composed of a fuzzification interface, fuzzy rule base, decision making logic and defuzzification interface. fuzzification is the process which transforms input signal into fuzzy sets. the input signal of the flc is the oil pressure of actuator p and its derivative p . the output signal uf means the duty ratio of pwm signal for hsv. when f is positive, ihsv will be on and the ohsv will be off. when wf is negative, the ihsv will be off and the ohsv will be on. when u( is zero, both valves will be off. the input signal p, p and the output signal uf vary in the interval 0, pm, -&pm, apj and -1, 1, respectively. their universe of discourse are defined as 0, 1, -1, 1 and -1, 1. the linguistic variables of the input and output signals are defined as pb, pm, ps, ze, ns, nm and nb. triangular and trapezoid membership functions are used for the fuzzy variables, which are shown in fig. 5. the objective of control is contained in the fuzzy rule base in the form of the linguistic variables using the fuzzy conditional statement. it is summarized in table 1. the construction rule is as follows: when the error between p and po is big, the error should be minimized as quickly as possible; when the error between p and po is small, the overshoot should be avoided to keep the system stable. the most widely used center of gravity method is applied here to defuzzify the output.3.2 preview controllerthe preview controller is a feedforward loop. it is just a compensation for the flc. as the rail disturbance varies at all time, the preview control up is assumed to bewhere a is a negative constant, t is the width of the preview time window which depends on the delay time of the hydraulic system, k is the weight of the disturbance displacement xw it increases when the distance between the sampling place and the roller location decreases and should satisfy the following equationas computer-aided control in reality is digital control, rewrite eq. (13) and eq. (14) in discrete form81where m is the number of preview steps, j represents the current sampling time and a/ is the sampling cycle. supposewhere p is a positive constant. eq. (17) can be normalized as.4 simulation studybased on the mathematical model in this paper, simulation study is carried out using matlab. table 2 shows part modelparameters. set the objective pressure value as 2.5 mpa. permitted error range of 0.1 mpa is allowed. take the measured rail disturbance as the input signal. fig. 6 shows the curve of the guide rail unevenness. fig. 7 shows the simulation results. fig. 7a is the acceleration response with passive guide roller. from the simulation results we can see that the maximal value is 0.278 7 m s2, the root mean square value is 0.090 1 m s2. the maximal value is head and shoulders above the boundary 0.15 m s2 specified by china elevator standards gb/t 10058-1997 and the ride comfort can be affected seriously. fig. 7b and fig. 7e are the acceleration curve and the pressure curve with the hydraulic active guide roller system based on the fuzzy logic controller, respectively. the acceleration response is reduced effectively with amplitude of 0.141 9m* s2and the root mean square value is 0.045 6 m s2, while the pressure value of the hydraulic actuator exceeds permitted error range. fig. 7c and fig. 7f are the acceleration curve and the pressure curve with the hydraulic active guide roller system based on the fuzzy logic controller with preview compensation. a fuzzy logic controller with preview compensation brings about ideal results. the maximal value of the acceleration response is 0.129 3 m s2 and the root mean square value is 0.032 4 m s2, and the hydraulic pressure are constrained between 2.4 mpa and 2.6 mpa. the preview compensation utilizes the future information in advance and can counteract the time delay of the hydraulic system in some degree. fig. 7d shows :ie power spectry.l unsity(psd) curves of the horizontal vibrations acceleration. the curve of the passive guide roller is displayed in the solid lines. the curve of the hydraulic active guide roller system based on the fuzzy logic controller is displayed in the dashed lines. the curve of the hydraulic active guide roller system based on the fuzzy logic controller with preview compensation is displayed in the dot-dashed lines. from fig. 7d we can conclude that the active guide roller system attenuates the vibrations in the low frequency area effectively, especially the vibrations of the main resonant frequencies. the fuzzy logic controller with preview compensation exhibits better control effects.from the simulation results we can get the following conclusions: so long as the oil pressure be kept the objective value with permitted error range, the horizontal vibrations of the elevator would be suppressed effectively by using the hydraulic active guide roller system. besides, a fuzzy logic controller with preview compensation can improve the system performance.5 experiment verification5.1 rig testto examine the effectiveness of the hydraulic unit and the control system, rig tests are carried out in the lab. fig. 8 shows the configuration of the test rig and the testing method. the guide rail simulator is taken on by an eccentric wheel. it is driven by a motor and produces sinusoidal wave displacement signal to imitate the uneveness of the guide rail. the hardware of controller is a single-chip-microcomputer based system. the 16-bit single-chip micro-controller sak-c167cr-lm of infineon family is chosen as the mcu chip. experimental results are sent to pc by can communication. the photo of the test rig is presented in fig. 9. set the objective pressure value as 2.5 mpa with permitted error range of 0.1 mpa, and the sinusoidal wave signal frequency is l.s hz. experimental results are shown in fig. 10 fig. 10a is the pressure response of hydraulic cylinder by fuzzy control. under the fuzzy control, the pressure value fluctuates heavily between 2.1 mpa and 2.8 mpa. the result is unsatisfied. fig. 10b is the pressure curve by fuzzy control with preview compensation. we can see that the curve has only lighter undulations confined in the permitted range. the hydraulic unit and the control system can work properly.5.2 real elevator testreal elevator tests are executed in an elevator experimental tower. as the lower guide roller system of the elevator has greater effect on the horizontal vibrations than the upper one3,91, only the lower passive guide rollers are replaced by the active guide rollers. the running speed of the elevator is 3.8 m s and the sampling frequency is 100 hz. the experimental results are shown in fig. 11.fig. 1 la is the acceleration response with passive guide roller. the maximal value of the acceleration is 0.046 1 m s2 and the root mean square value is 0.014 7 m s2. fig. lib is the acceleration curve with the hydraulic active guide roller system based on the fuzzy logic controller. the maximal value of the acceleration is 0.036 4 m s2, which is reduced by 21%. the root mean square value of the acceleration is 0.010 3 m *s , which is reduced by 29.9%. fig. lie is the acceleration curve with the hydraulic active guide roller system based on the fuzzy logic controller with preview compensation. the maximal value of the acceleration is 0.025 3 m s2 and a 45.1% reduction is made when compared wi