elevator balance coefficient and detection
mathematical expressions elevator balance coefficient calculated as follows:
k level = (w1-w) / q
q: elevator rated load (kg);
w: car weight (kg);
w1: heavy weight (kg);
k ping: elevator balance coefficient;
professionals elevator balance coefficient is a parameter both familiar and unfamiliar. it is because we all know the familiar traction elevator counterweight configuration has a "balance factor", knows that there are provisions in the national standard "balance coefficient should be in the range of 40% to 50%," it is strange because in the end what role the equilibrium coefficient in the elevator? what size will affect its value? how should the value of the most appropriate? and in the end how the determination is accurate? many elevator installation, inspection personnel are not clear.
at present, around special equipment inspection and testing institutions in the elevator for acceptance testing, the most time-consuming, but also the most expensive human, material, and that is the detection of the elevator balance coefficient. according to inspection requirements: it must be hosted in the car were 30%, 40%, 45%, 50%, 60% rated load, measured elevator load - current curve, whichever, the load factor downstream of the intersection point of the curve, the ladder is balanced coefficient, intersection points within the range of 40% to 50% qualified. in order to determine this parameter, in addition to the two inspectors, workers also need to carry back and forth several law codes. because many factors affect the test, the results are credible to say nothing, even if the test results in the range of 40% to 50%, with certain qualified? if beyond this range, why it failed? what is the meaning "balance factor" is? what is the impact on the elevator? i do not know why, measured "equilibrium factor" would be meaningless.
1, "balance factor" in substance
to explore the essence of balance coefficient must start from the principle of traction elevator. vertical lift is to make the weight for vertical up and down movement of the lifting equipment. from a mechanical point of view, to make a weight remain stationary in the air, there must be a pull of gravity and the object q t equilibrium, namely t = q, then the object is at rest or in uniform motion state, called the force balance. this system is called balancing system. to make the object upward movement, the speed is changed, then the tension t in addition to overcome gravity q of the object, but also to provide an acceleration force generated f, namely t = q f = q ma (m - for the object quality; a- acceleration).
if the gravity of the object q is another balanced counterweight w, w = q, constitute a balanced system, then pull t will not have to overcome gravity q, while only providing an object to generate the required acceleration forces, namely t = f = ma this greatly reduces the tension t. this is the elevator on the use of "balance principle." this counterbalancing force is provided by the counterweight. we therefore call on the weight of gravity w, to the car and loads of gravity (p q) are equal.
but to really do this, in the practical application of the elevator is very difficult, or say then is still not figured out a way to achieve this. because the car load q is random variation, it may be 0 (no load) or 100% qh (full load) to any value within the range, so we can only choose an appropriate weight for weight.
that is to take w = p k qh --------------- (1)
this coefficient k, is the "balance factor." thus, in essence, it is to design the configuration equilibrium constant counterweight quality size. it will impact on the quality and lift heavy unbalanced loads. when the car with a load of p q, (where p- is the car's weight; q --- is the actual load of the car; qh --- car rated load), the car side and the counterweight side unbalanced load is:
△ t = (p q) - (p kqh) = q - kqh -------- (2)
2, the balance value of the coefficient k
(2) it can be seen from the above formula, q = kqh only when the system was in balance, therefore, no matter what value k, equilibrium is only relative, while the imbalance is absolute. we can only hope that the system as close to balance. a simple solution is to take the average car load change. because changes in car load is: 0 to 100%, so take k = about 50% is reasonable, it is difficult to say how many get better. elevator at the factory do not fully understand the actual runtime loads, in order to truly achieve the ideal balance, should use the elevator actual operation, the actual determination of the daily operation of load changes. for example, at present a large number of residential elevators the actual basic load changes from 0 to 60%, full load of very rare, so take k = 30% ~ 40% should be more appropriate. the passenger elevator is now generally exceeds 80% when the load goes straight ahead state, and therefore less true when fully loaded, and therefore take balance coefficient k = 40% ~ 50% is appropriate. on the contrary, some of the lifts, because the car over the area, which will load change from 0 to 105%, so the balance factor of k≥50% should be more appropriate. it must be noted here that the value k refers elevator designed to balance the value of the coefficient k, known as the design value, not a k value after the elevator installation or use of freely configurable.
3, affect the balance of the value of the coefficient k for the elevator
has been described above, regardless of how the value of balance coefficient k to a constant k value should be changing the load q is impossible, so the imbalance in the car and on the weight of the system is absolute, from a design point of view the size of k value first influence on both sides of the wheel traction imbalance moment, if the maximum load is overloaded load 110% qh, k value by 40% to 50%, the no-load unbalanced load of : (0.4 ~ 0.5) qh, unbalanced load overloading is: (1.1-k) qh = (0.6 ~ 0.7) qh, if the most severe load 125% qh acceptance tests in accordance with the elevator, the unbalanced load of 1.25 k = (0.75 ~ 0.85) qh, which is the maximum possible lift unbalanced load (of static load), which is the minimum force static traction elevator has to offer.
this first affect the choice of host motor power p. main motor power p is determined by: pα (1-k) qh vh. if the motor power supporting the use of the elevator is large enough, then k choice will affect the size of energy consumption when the elevator is running, if the choice of motor power margin is small, the balance may result in inappropriate coefficient start after the elevator appeared to pull back occurrence or hoisting slip car accident.
affect the balance of the value of the coefficient of unbalanced load size, but also affect the traction sheave rope tension on both sides, the size of this tension will affect the hoisting rope rope than the pressure in the tank, the greater the tension than the pressure also the larger the capacity of the hoisting rope traction provided stronger. thus the value of balance unbalanced load factor of both decisions, will also affect the elevator hoisting capacity. when the maximum unbalanced load is greater than the maximum traction force of lift, hoisting rope in the rope groove to be slipping, sliding the car accident occurred. in the elevator designed to balance the coefficient k is necessary to consider the choice of motor power to the host, but also consider the impact on the hoisting capacity.
balance coefficient k will also affect the car, the counterweight system's total mass:
m = p q w y = (p q) (p k qh) y (y- traction device quality wire rope, etc.), it can easily be ignored. the car, on the total mass of the weight of the system will affect the safety factor of the elevator, the impact of the hoisting rope, sheave rope grooves and other parts of the parameter choices. at the same time also affects the size of the total mass of the elevator running plays, plus braking and deceleration. influence the choice of elevator safety gear used, buffers and other safety components. when the elevator installation, in order to cope with acceptance testing, reducing the unbalanced load acceptance when the installer tend to achieve greater balance coefficient k is configured to nearly 50 percent, increase balance coefficient is to increase the quality of heavy, will bring the elevator kai, brake reduce acceleration and braking as well as difficulties. therefore, the balance coefficient k is a ratio of the surface, in fact it with the car, the counterweight of quality are closely related. it is one of the important parameters of the overall design of the elevator, leaving aside the rated load, weight and other parameters of the car, pure balance coefficient is meaningless.
so balance coefficient k is determined to be in the elevator design, combined with traction sheave, considering the rope groove shape, hoisting rope, the weight of the car as well as supporting the hoisting machine motor, brakes, safety gear, buffers and the like. their mutual relations had another paper in my "elevator parameters and their mutual relations" mentioned in, i will not dwell on. that is why the elevator installation when balancing factor should be the reason 40% to 50% of design value configuration. it is worth mentioning that some of the recent re-decoration with the elevator car, the car's weight increases, then in order to maintain equilibrium coefficient k value remains unchanged, the method adopted to increase the weight of the overall quality of the system greatly increased this is very wrong, when the balance factor has lost its original meaning. lift the safety factor is reduced, starting and braking deceleration decreases, the elevator will cause serious safety hazards.
so balance coefficient k value, not as long as the installation or acceptance tests when measured in 40% to 50% range, were found to comply with the requirements. if the value deviates from the design value is not met, or it is in line with the value of the design value, but its rated load or car weight p qh are changed, the same is not met. check in hoisting gb7588-2003 appendix d of this description: "you should check whether the balance coefficient as the installer says," where "the installer says," actually refers to design values, not arbitrary personnel installation results. this requires the elevator balance coefficient factory business will lift design, installation and construction personnel informed, installation and construction personnel must comply with the design value of the configuration of heavy equipment, and not free to change the weight of the car. it must determine its actual value is consistent with design values, and check whether unauthorized changes when the car weight and other parameters for acceptance testing organizations test. this should draw attention to the industry.
4 determination of equilibrium coefficient k value
(1) direct weighing p and w
balance coefficient k parameter is not mysterious. in the final analysis it is the configuration of the heavy mass size, so the determination of equilibrium coefficient k, the most direct and simplest way is to direct the overall quality weighing heavy w and the overall quality of the car p, the equilibrium coefficient k = (w- p) / qh. once focusing on the car and the shaft were assembled outside, and all other components assembled individually weighed, which according to the design value of balance coefficient to configure the weights. this method is cumbersome to operate, and other parts of weighing difficult to be exhaustive, generally does not apply.
(2) according to the known value of k, the adjustment counterweight
know the essence of balance coefficient k, when the car is loaded kqh equivalent load, traction wheel should be balanced on both sides of the static moment. if the value of the equilibrium coefficient of known design, provided in full by kqh load load, and then verify that the balance can be. the easiest way is to verify on the host, the brake is released the brake, torque balance with human feeling on both sides of the traction sheave or not on hand disks, thereby appropriately increase or decrease depending on the weight. this approach seems more "earth", but has many advantages: 1) elevator at rest, to avoid the resistance movement of the car caused due to torque error. 2) ensures that the car and the counterweight at the same horizontal position. 3) the test is simple, quick, rapid adjustment, saving manpower and material resources. 4) human error is to force the feeling in a few kilograms, and its high reliability. 5) more importantly, with the established design value of load balancing factor directly verify or adjust the counterweight to meet the requirements, to avoid blindness, to ensure compliance with the design requirements of the k value.
in the elevator installation and construction also often use this approach to configure the weights. i think there can be placed a special weighing device instead of human feeling, to make detection more precise on the traction sheave.
(3) according to the existing counterweight, find the value of k
recommended national standard traction motor current measurement methods fall into this category. the basic principle is: when the elevator constant speed operation, the traction motor shaft output torque t2 as: t2 = t0 ± △ t --------- (3)
t0 ---- converted to the motor shaft, the elevator mechanical transmission rebellious resistance torque (referred to as drag torque)
△ t --- converted to the motor shaft, unbalanced load torque. ± representatives with load unbalanced load torque change direction will change. (referred to as unbalanced load)
when the car with a load of gravity (p q) and the counterweight of gravity (p kqh) are equal (ie, a state of equilibrium), then △ t = (p q) - (p kqh) = 0
then q = kqh balance coefficient: k = q / qh
the key is to use the current method of measuring current to determine whether the balance, the equilibrium state:
△ t = 0, assuming that the resistance of the car when the uplink and downlink torque t0 is the same, then, the output torque of the motor when the downlink is the same as t2, t2 = t0, then the measured motor currents should be equal. above, to determine the balance of the down currents are equal, (note: not the current minimum), which is the principle of the current law.
to measure the current to determine the torque, which is an indirect measurement method. the relationship between current and torque is obtained directly from the power balance on the motor.
motor output mechanical power p2 = t2 ω (ω --- motor angular velocity), which electromagnetic power between the pm motor and there is: pm = pcu p2 (pcu ----- motor rotor copper losses),
as ignore rotor copper losses, there are: pm = p2
for ac induction motor, electromagnetic power pm = (mp / 2πf1) · (i22 r / s) ---- (4) when the constant motor speed, frequency, electromagnetic power pm and the rotor current i22 proportional. ac induction motor rotor current can not be measured, can only measure the stator current i1
i1 = i0 (- i2,) (i0 ---- excitation current of the motor),
as ignore excitation current i0, there i1 = (- i2,)
for dc motors, electromagnetic power pm = ct φis when the air gap flux φ is constant, the electromagnetic power pm and armature current is proportional. air-gap flux φ and voltage.
therefore, when using current measurement, the ac motor will have to keep the speed, frequency constant. for dc motors will have to keep the voltage constant.
seen from the above analysis, the current method by measuring the motor stator current i1 to determine load imbalance motor shaft △ t = 0, after a joint string conversion relationship:
i1 → i2 → pm → p2 → t2 → △ t
each step conversion must have certain conditions, were: i0 unchanged; f1 unchanged; constant voltage u1; pcu unchanged; n constant speed; down the line t0 equal, and factors that affect these quantities are complex, such as elevator on, downlink, different car air resistance, resistance down the line would be difficult to set up the torque t0 equal, especially in the high speed. also affecting the measurement process of human factors, such as: how to hold the car and run to the same level of weight measurement of the current position; on how to ensure this position, the downstream speed is the same; there are current measuring instruments used; position measuring current, etc., will result in large errors. also plotted curve, since there is no load of the measuring point within the 40% to 50% range, curve drawing contains a lot of human factors. these all affect the accuracy of the determination of the coefficient k value of the current balance method.
in summary, for the elevator balance coefficient, the first should correctly understand the significance of its value, and the impact of changing the value of the elevator. second it is practical to take the right measurement method