Vibration damping device for rope type elevator

Abstract: A rope type elevator comprises a car vertically movably arranged in a hoistway, a sheave arranged in an upper portion of the hoistway, a rope passing around the sheave for drawing the car up and down, a suspension rod supported by the rope, a spring (15) interposed between the suspension rod and the car for cushioning vibration, a cylinder device (16) for attenuating vibration and having a flow control valve (22), a car position detector (24) for detecting a position of the car to calculate a length of the rope, a load detector (25) for detecting a load applied to the car, and a control circuit (23) for calculating a characteristic frequency f of the rope from the length of the rope, and calculating a characteristic frequency f N of the spring from the load of the car, then calculating a frequency ratio u (u = f/f N ) so that, when u = 1 or u ≒ 1, the flow control valve of said cylinder device is closed.

Description: The present invention relates to a rope type elevator which contributes to a reduction in the vibration produced when drawing a rope by a winding mechanism. A conventional rope type elevator is shown in Fig. 5. In this Figure, 101 is an elevator car vertically movably arranged in a hoistway, and having an upper portion to which a pair of car sheaves 104, 105 are mounted through a car frame 103. That is, the car sheaves 104, 105 are mounted on a support channel 106 to which a suspension rod 107 is mounted. The suspension rod 107 is engaged with the car frame 103 through a spring seat 108 and a plurality of coil springs 109. A plurality of ropes 110 pass around the car sheaves 104, 105, and also around a drive sheave 111 of the winding mechanism. DE 699265 shows one particular example of an elevator employing such suspension means. When the winding mechanism is driven to draw the ropes 110 by the drive sheave 111, a vibration is produced, which is attenuated by the spring 109 to avoid giving an unpleasant feeling to passengers when transmitted to the car 101. With such conventional rope type elevator, a vibration produced at the drive sheave 111 of the winding mechanism was transmitted to the car 101 through the ropes 110. When a frequency ratio u (u = f/f N ) of a characteristic frequency f of the ropes 110 to a characteristic frequency f N of the springs 109 is equal to 1 (u = 1), a resonance occurs. The problem arose that this resonance gives an unpleasant feeling to the passengers in the elevator car. The present invention aims to provide a rope type elevator wherein a resonance of the ropes and the spring, if produced, is restrained as low as possible. For achieving such object, the present invention is constructed so that it provides a car vertically movably arranged in a hoistway, a sheave arranged in an upper portion of the hoistway, a rope passing around the sheave for drawing said car up and down, a suspension rod supported by the rope, a spring interposed between the suspension rod and said car for cushioning vibrations, a cylinder device interposed between said suspension rod and said car for attenuating said vibrations and having a flow control valve for controlling the degree or attenuation of said vibration, a car position detector for detecting a position of the car to calculate a vibrating length of the rope, a load detector for detecting a load applied to the car, and a control circuit for calculating a characteristic frequency f of the rope from said length of the rope, and calculating a characteristic frequency f N of the spring from the load of the car, then calculating a frequency ratio u (u = f/f N ) so that, when u is substantially equal to 1, the flow control valve of said cylinder device is closed. An embodiment of the present invention will be described hereinafter by way of example only and with reference to the drawings. Brief Description of the Drawings Fig. 1 is a front view showing an embodiment of a rope type elevator according to the present invention. Fig. 2 is a schematic block diagram of the elevator suspension control. Fig. 3 is a flowchart showing the operation of the cylinder devices. Fig. 4 is a table showing the relationship between the frequency ratio and the vibration propagation rate. Fig. 5 is a front view of a conventional rope type elevator. In Fig. 1, a car 1 is vertically movably arranged in a hoistway of an elevator, and comprises a car frame 2 and a cab 3 supported by the car frame 2. Arranged above a crosshead channel 2a of the car frame 2 is a support channel 4 to which a pair of car sheaves 7, 8 are mounted through support pieces 5, 6. A suspension rod 9 is downwardly fixed to the support channel 4, and extends downwardly passing between a pair of C-shaped steels which constitute the crosshead channel 2a. A disc-shaped lower spring seat 10 is fixed to the suspension rod 9 at a lower end thereof by tightened double nuts 11. On the other hand, a disc-shaped upper spring seat 12 through which the suspension rod 9 is arranged is mounted to the crosshead channel 2a on a lower face thereof. A plurality of ropes 13 pass around the car sheaves 7, 8, and also around a drive sheave 14 of a winding mechanism. The rope 13 has one end fixed to a dead-end hitch beam (not shown) of a machine room, and another end fixed to a dead-end hitch beam in the same way as the rope on the car side, but via a counterweight (not shown) arranged to balance the car 1. A coil spring 15 and a plurality of cylinder devices 16 are interposed between the upper spring seat 12 and the lower spring seat 10. The cylinder devices 16 serve to carry out further attenuation of vibration produced at the drive sheave 14 and cushioned by the coil spring 15. The cylinder device 16 comprises, as shown in Fig. 2, a cylinder 17 interposed between the upper and lower spring seats 12, 10 and a piston 18 disposed in the cylinder 17, upper and lower chambers 19, 20 separated and defined by the piston 18 being filled with a working fluid. The upper and lower chambers 19, 20 communicate with each other by a duct 21 which functions as an orifice, and in the middle of which a flow control valve 22 is arranged. The flow control valve 22 serves to decrease or increase the flow of working fluid in the duct 21 in accordance with an instruction from the control circuit in the control panel 23. Input to the control panel 23 are a signal from a rotary encoder 24 (car position detector) mounted on a speed governor or the like for detecting a position of the car, and a signal from a load sensor 25 (load detector) arranged on a floor surface of the cab 3 for detecting the load of passengers therein. The control panel 23 may include a microprocessor arranged to follow a program according to the flowchart of Fig. 3. Next, referring to the flowchart as shown in Fig. 3, the operation of the cylinder devices 16 will be described. When the car 1 having the passengers therein is started towards a target floor, the load of the passengers is detected by the load sensor 25 (step S 1 ). By detecting the load of the passengers in the car 1, a weight W (Kgf) of the entirety of the car 1 is known. Since a characteristic frequency f N (Hz) is expressed by f N = 1 2Π Kg W (where K is the spring constant (Kgf/cm); and g gravitational acceleration (980 cm/sec 2 )), the characteristic frequency f N of the spring 15 is calculated in the control panel 23 (step S 2 ). Next, the position of the car 1 is detected by the rotary encoder 24 (step S 3 ). By detecting the position of the car 1, the length of the ropes 13 between the drive sheave 14 of the winding mechanism and the car sheave 8 is known. A characteristic frequency f (Hz) of the ropes 13 between these two is expressed by f = n 2 L S P (where L is the length of the ropes (m); S is the tension of the ropes 13 (N); P is the mass (Kg/m) per unit length of the ropes 13; and n the order of the vibration). Here, the tension S (N) of the ropes 13 is known from the driving force of the winding mechanism. Thus, the characteristic frequency f of the ropes 13 between said two is calculated in the control panel 23 (step S 4 ). Next, a frequency ratio u = f/f N is calculated from the characteristic frequency f N of the spring 15 and characteristic frequency f of the ropes 13 (step S 5 ). Here, Fig. 4 shows how the relationship between the frequency ratio u and a vibration propagation rate is varied by the flow control valves 22 of the cylinder devices 16. When the flow control valves 22 of the cylinder devices 16 are maximally opened, a crest of the vibration propagation rate (resonance point between the ropes 13 and the spring 15) becomes the highest in the vicinity of the frequency ratio [1], whereas, when the frequency ratio exceeds [√2], the vibration propagation rate rapidly lowers tracing a sharp curve. As the flow control valve 22 is reduced, the crest of the vibration propagation rate becomes gradually lower in the vicinity of the frequency ratio [1], whereas, when the frequency ratio exceeds [√2], the vibration propagation rate is not so lowered. Therefore, when the frequency ratio is [1], closing the flow control valve 22 makes the crest of the vibration propagation rate to be lowered. On the other hand, when the frequency ratio is not [1], opening the flow control valve 22 makes the vibration propagation rate lower. Thus, it is judged whether or not the frequency ratio u is equal to 1 (u = 1) (step S 6 ). When the frequency ratio u is equal to 1 (u = 1), the flow control valve 22 is maximally closed (step S 7 ). Then, the crest of the vibration propagation rate is lowered, so that a resonance of the ropes 13 and the spring 15 can be kept low. On the other hand, when the frequency ratio u is not equal to 1 (u ≠ 1), the flow control valve 22 is opened (step S 8 ). Then, the vibration propagation rate can be lowered. The control valve 22 can be closed when u equals 1 or is approximately equal to 1, or when u is within a predetermined range around 1. And in any of these cases the valve can be opened when u has other values. The valve may be closed when u is between 1 and √2 and opened when u is above √2. Therefore, a vibration transmitted from the drive sheave 14 of the winding mechanism to the car 1 through the ropes 13 is kept as low as possible even with a resonance of the ropes 13 and the spring 15, and it can be kept lower with no resonance. As described above, since the present invention is constructed to calculate the characteristic frequency f of the rope from the length of the rope, and calculate the characteristic frequency f N of the spring from the entire load of the car, then calculate the frequency ratio u (u = f/f N ) so that, when u equals 1 or is approximately equal to 1 (u = 1 or u ≒ 1), the flow control valve of said cylinder device is closed, a vibration transmitted from the sheave to the car through the rope can be kept as low as possible even with a resonance of the rope and the spring, and it can be kept lower with no resonance, thus avoiding giving an unpleasant feeling to the passengers in the car.

Claims: A rope type elevator, comprising a car (3) vertically movably arranged in a hoistway, a sheave (14) arranged in an upper portion of the hoistway, a rope (13) passing around the sheave for drawing said car up and down, a suspension rod (9) supported by the rope, a spring (15) interposed between the suspension rod and said car for cushioning vibration and a cylinder device (16) interposed between said suspension rod and said car for attenuating said vibration, characterised by said cylinder device (16) having a flow control valve (22) for controlling the degree of attenuation of said vibration, and further by a car position detector (24) for detecting a position of the car to calculate a length of the rope, a load detector (25) for detecting a load applied to the car, and a control circuit (23) for calculating a characteristic frequency f of the rope from said length of the rope, and calculating a characteristic frequency f N of the spring from the load of the car, then calculating a frequency ratio u = f/f N so that, when u is substantially equal to 1, the flow control valve of said cylinder device is closed.

Inventors: IWAKIRI ATSUSHI, MIYAHARA NOBUYUKI, IWAKIRI, ATSUSHI, MIYAHARA, NOBUYUKI
Applicants: OTIS ELEVATOR CO, OTIS ELEVATOR COMPANY
Application year: 1996
Main classification: B66B7
IPC codes: B66B7, B66B11