GB2243927A

GB2243927A - A hydraulic elevator

Info

Publication number: GB2243927A
Application number: GB9105328A
Authority: GB
Inventors: Yoshio Sakai; Noboru Arabori
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1990-03-16
Filing date: 1991-03-13
Publication date: 1991-11-13
Also published as: CN1024338C; GB9105328D0; CN1054949A; KR910016602A; JPH03267279A; JPH0780644B2

Abstract

A hydraulic elevator has a cage 5 being moved upwardly and downwardly by a hydraulic cylinder 2, and an induction motor driven hydraulic pump 13 supplying pressured hydraulic oil to the cylinder 2 through a electromagnetic change-over valve 12. The induction motor speed is controlled on the basis of a output signals of a speed instruction generating circuit 33 and start compensation instruction circuit 34 which generates a compensation signal in response to the difference between the discharge pressure oil of the hydraulic pump 13 and oil pressure in the cylinder 2 so as to prevent jerky movement of cage 5 when the discharge pressure first exceeds the cylinder pressure and valve 12 becomes conductive. <IMAGE>

Description

A HYDRAULIC ELEVATOR This invention relates to a hydraulic elevator, and more particularly to a control apparatus of a hydraulic elevator by driving a hydraulic pump and moving a cage upward and downward by controlling its discharge flow rate.

A motor speed control system is known as a conventional hydraulic control system of a hydraulic elevator. When constant discharge type of pump for supplying a pressure oil to a cylinder for moving a cage upwardly and downwardly through an electromagnetic changeover valve which operates normally as a check valve and becomes conductive in an opposite direction when energized by an electromagnetic valve is driven by an induction motor, this system changes voltage and frequency so as to change the speed of the motor in a wide range and variably controls the oil discharge quantity of the pump so as to move the cage up and down.

Oil leakage exists in a hydraulic pump and for this reason, there is a range where the cage is not started even when the hydraulic pump is rotated. When the hydraulic pump is driven on the basis of a start instruction, start shock and a problem of discomfort o.ccur...

To solve this problem, a proposal has been made which discharges in advance the oil in a quantity corresponding to the oil leakage quantity or in other words, which superposes a bias pattern signal which operates the motor at such a low speed as not to start the cage and a pattern signal which travels the cage, and starts smoothly the cage.

Japanese Patent Publication No. 64-311(1989), Japanese Patent Laid-open Patent Publication No. 61-37678(1986), Japanese Laid-open Patent Publication No. 60-71474(1985) and Transaction papers of Japan Society of Mechanical Engineers papers No. 708(1990), disclose the superposition technique of both the bias pattern and travel pattern signals.

In accordance with the prior art technique, the oil leakage quantity under the actual operating state is determines by calculation from the load of the cage, the oil temperature of an oil tank and the oil leakage quantity of each hydraulic pump with those at non-load and at an oil temperature of OOC being the reference in order to reduce the start shock and to obtain a bias pattern.

The actual oil leakage in the hydraulic pump has variance due to variance in the production of the hydraulic pump,and changes gradually with time.

In other words, it is difficult to detect always correctly the oil leakage quantity for reducing the start shock and since the bias pattern is determined indirectly through calculation, there is the limit to the reduction of the start shock.

Having perceived these problems, we also perceive that it would be desirable to provide a hydraulic elevator which generates directly a bias pattern corresponding to the oil leakage quantity, to minimize the start shock.

In accordance with the present invention, we provide means for making start compensation in accordance with a bias pattern based on the pressure difference between the oil pressure of a cylinder for moving a cage and the output pressure of a hydraulic pump, such as, a bias pattern based on the pressure difference between the inlet and outlet of a check valve.

The pressure difference is detectable by comparing the outputs of pressure detectors for detecting the output pressures of the cylinder and hydraulic pump. Assuming that the pressure difference when the output pressure of the hydraulic pump is higher than the cylinder oil pressure has a positive sign, the check valve is open in this case. Under the positive pressure difference state, the pressure oil flows from the check valve to the cylinder and accordingly, the existence of the pressure difference is detectable by detecting its flow rate. As the pressure oil flows from the check valve to the cylinder, the cage moves up. Accordingly, the existence of the pressure difference is detected by detecting the speed and moving distance of the cage.

The pressure difference may be set to a negative code so long as it does not provide any sensible start shock to the human body. It may be set to zero.

The start compensation means makes start compensation in accordance with a bias pattern based on the pressure difference between the oil pressure of the cylinder and the output pressure of the hydraulic pump, that is, the pressure difference between the inlet and outlet of a check valve. The pressure difference is based on the actually measured value and is not affected by the fluctuation of the oil leakage quantity for each hydraulic pump.

The pressure difference between the inlet and outlet of the check valve is not the value which is determined indirectly by calculation of the oil leakage quantity in the hydraulic pump but is measured actually. Therefore, start compensation performs accurately.

Embodiments of the invention are now described by way of example, with reference to the accompanying drawings in which: Fig. 1 is an overall construction diagram of a hydraulic elevator in accordance with one embodiment of the present invention; Fig. 2 is a view showing the schematic construction of the speed control apparatus of Fig. 1; Fig. 3 is a detailed view of the speed control apparatus of Fig. 1; Figs. 4a to 5g are explanatory views explaining the UP and DOWN operation of the hydraulic elevator shown in Fig. 1; Figs. 6a to 6e are explanatory views explaining a start compensation instruction generation circuit in accordance with the present invention; Fig. 7 is a sequence circuit diagram of the hydraulic elevator shown in Fig. 1; Figs. 8a and 8b are views showing the disposition construction of the hydraulic pump and the induction motor in Fig. 1;; Figs. 9a and 9b are views showing a cut detector of a belt connecting the hydraulic pump and the induction motor shown in Fig. 1; and Figs. 10a and 10b are views showing other embodiment of the present invention and correspond to Fig. 6c.

In Fig. 1, a hydraulic elevator has an elevator shaft 1, a cylinder 2 buried in the pit of this elevator shaft 1, a pressure oil 3 charged into this cylinder 2, a plunger 4 supported by this pressure oil 3, a cage 5 fixed to the top of the plunger 4, and an induction type position detector 6 disposed on the cage 5. This detector 6 detects a door zone and a stop position when it opposes shield plates 7, 8 arranged at each floor. A pulse encoder 11 is coupled directly to a pulley 9 disposed at the lower part of the elevator shaft 1 and detects cage speed and position. The pulley 9 rotates in synchronism with the movement of the cage 5 owing to pulley 10 and a line lla fixed to the cage 5. An electromagnetic changeover valve 12 functions normally as a check valve and is switched to make an opposite direction conductive, too, when an electromagnetic coil is energized.A pipe 12a is connected between the cylinder 2 and the electromagnetic change-over valve 12 and sends the pressure oil 3 to the cylinder 2. A hydraulic pump 13 rotates reversibly and sends or receives the pressure oil 3 to or from the electromagnetic change-over valve 12 through a pipe 13a.

Pressure detectors 14 and 15 detect the pressure of the cylinder 2 and the output pressure of the hydraulic pump 13. An electromagnetic brake 16 is directly coupled to the hydraulic pump 13. An oil tank 17 holds oil 3 sent to or received fron the hydraulic pump 13 through a pipe 17a. A three-phase induction motor 21 drives the hydraulic pump 13 through pulleys 18, 19 and a belt 20. A pulse encoder 22 detects the rotating speed of this three-phase induction motor 21. A convertor 25 converts an A.C. three-phase power source R, S and T to D.C. and vice versa. Through a smoothing capacitor 24, an inverter 23 for subjecting the D.C. to pulse width control and generating a three-phase A.C. having a variable voltage and variable frequency is coupled to the convertor 25.

A speed control apparatus 26 has signal input lla from the pulse encoder ll,for Cage position and speed, also inputs for the signal 6a of the induction type position detector 6 for detecting the stop position of each floor, the speed feedback signal 22a of the pulse encoder 22 for detecting the rotating speed of the three-phase induction motor 21, the signals 14a, 15a of the pressure detectors 14, 15 and normally-open and normally closed contacts 43awl 43bl of the operation instruction relay 43 from the start instruction till the stop instruction are inputted, respectively.This apparatus outputs the signal 23a to ontrol the inverter 23, outputs the signal 16a to control the electromagnetic brake 16 and outputs the signal l2b to control the electromagnetic change-over valve 12.

The outline of the construction of the speed control apparatus 26 is shown in Fig. 2. The components or portions which are not closely related with the speed control among those shown in Fig. 1 are omitted from Fig.

2 for the purpose of simplification, and like reference numerals are used as in Fig. 1 to identify the same or like parts.

In Fig. 2, a current control circuit 30 receives the output i* of a vector control circuit 31 and outputs the control signal 23a of the inverter 23. The vector control circuit 31 receives the output of the pulse encoder 22, that is, the rotating speed WrM of the induction motor 21 and the output of the speed control circuit (ASR) 32, that is, the torque instruction T*. The ASR circuit 32 receives the output of the speed instruction generation circuit 33, i.e. the speed instruction war*, the output of the pulse encoder 11, that is, the speed r of the cage 5, and the start compensation instruction T (reference start compensation instruction T0) as the output of the start compensation instruction generation circuit 34.

The output signals 14a, 15a of the pressure detectors 14, 15, or in other words, the cylinder oil pressure and the output pressure of the hydraulic pump 13, are inputted to the start compensation instruction generation circuit 34, The detailed construction of the speed control apparatus 26 is shown in Fig. 3.

The speed control of the cage 5 by this speed control apparatus 26 will be described later. Here, the outline of elevation of the cage 5 and start compensation will be explained.

Firstly, the UP operation will be explained with reference to Fig. 4.

The electromagnetic brake 16 is opened at a time to by a operation instruction relay 43 (See Fig. 7) so as to raise gently the start compensation instruction T . In this case, the DOWN motion of the cage 5 does not occur even when the electromagnetic brake 16 is opened, because the check valve of the electromagnetic change-over valve 12 is closed. The inverter 23 is controlled by the output signal 23a in accordance with the start compensation instruction T through the ASR circuit 32, the vector control circuit 31 and the current control circuit 30 and the induction motor 21 is rotated at a low speed.The speed is raised until the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15, becomes higher than the pressure of the cylinder, that is, the signal 14a of the pressure detector 14, and then the check valve of the electromagnetic valve 12 is opened. The start compensation instruction T is increased till the cage rises at a low speed and is held at the time tl. Next, the speed instruction wr* rises at the time t2, and acceleration is made till time t3. A start compensation instruction output control relay 41 (described later - Fig. 7) is turned ON at the time t2, tllat the normally-closed contact 41b between the start compensation instruction generation circuit 34 and the ASR circuit 32 is open and the start compensation instruction becomes zero. Traveling is effected at a rated speed till the time t4.When the elevator approaches to a target floor, deceleration is started by use of the position signal lla of the cage and the speed is lowered near to the stop position and reaches the landing speed at the time t5. Next, the operation instruction relay (43) is turned OFF at the time t6 by the stop position signal 6a to stop the elevator. The electromagnetic brake 16 is closed at the time t8 and the start compensation instruction output relay 41 is turned OFF at the time tg. In this manner the operation is completed.

Next, the start compensation in this embodiment will be described further in detail with reference to Fig. 6.

The normally-open contact 43a1 and normally-closed contact 43b1 of the operation instruction relay (see Fig.

7), the oil pressure of the cylinder, that is, the signal 14a of the pressure detector 14, and the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15, are inputted as the input signals of the start compensation generation circuit 34 shown in Fig. 61,- and this circuit outputs the reference start compensation instruction To.

Fig. 6b shows the output circuit of the reference start compensation instruction To, Fig. 6c shows the driving circuit of the relay 61 for keeping the reference start compensation instruction 10 constant, Fig. 6d shows the sequence circuit used for the output circuit of the reference start compensation instruction TO and Fig. 6e shows the output pattern of the reference start compensation instruction To, that is, the bias pattern based on the pressure difference between the output pressure of the hydraulic pump 13 and the oil pressure of the cylinder.

In Figs. 6b to 6d, the output circuits comprise amplifiers OP1 to OP3, resistors R1 to Rll and a capacitor C.

When the normally-open contact 43a1 of the operation instruction relay shown in Fig. 6d is turned ON, the relay 64 is turned ON through the normally-closed contact 61b of the relay 61 shown in Fig. 6c and the normally-closed contact 62b of the relay 62. In Fig. 6b, since the normally-closed contact 43b1 of the operation instruction relay is open, the output circuit of the reference start compensation instruction To becomes an integration circuit. Since the normally-open contact 64al of the relay 64 is closed, the reference start compensation instruction To rises with the inclination such as shown in Fig.'Se with the power source voltage E1 being the reference voltage. The output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15, enters the input of OP2 shown in Fig. 6c and the polarity is inversed. The power source voltage E2 is set to the bias reference voltage for the cage 5 to rise at a low speed. The relay 61 is turned ON when the value obtained by subtracting the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15, from the sum of the pressure of te cylinder 3, that is, the signal 14a of the pressure detector 14a, and the bias reference voltage E2 for the cage 5 to rise at a low speed, becomes negative. When this normallyopen contact 61a is closed, the relay 62 is turned ON and the normally-open contact 62a is closed and makes selfholding.The normally-open contact 61b and the normallyclosed contact 62b are open and the relay 64 is turned OFF. The normally-open contact 64a1 is open and the output in the output circuit in Fig. 6b, that is, the reference start compensation instruction Tot is kept at a constant value at the time T1 as shown in Fig. 6e. The reason why the normally-closed contact 62b is inserted in the circuit of the relay 64 in Fig. 6d is to prevent the normally-closed contact 61b from closing and the relay 64 from being turned ON if the hydraulic pump 13 is driven by the speed instruction after the time Tl shown in Fig.

6e, the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15 and the oil pressure of the cylinder 3 or in other words, the signal 14a of the pressure detector 14, change and thus the condition occurs in which the relay 61 is turned OFF.

When the operation instruction relay 43 is turned OFF, the normally-closed contact 43b1 is closed and discharges the charge of the capacitor C through the resistor R3, thereby returning the operation state to the initial state.

As described above, the amplifier OP3 in Fig. 6c is disposed in order to generate the bias pattern shown in Fig. 6e on the basis of the difference between the signals 14a and 15a corresponding to the output pressure of the hydraulic pump and the oil pressure of the cylinder, respectively, or in other words, on the basis of the pressure difference before and after the check valve in the electromagnetic change-over valve 12.

Next, the UP operation shown in Fig. 4 will be explained with reference to Figs. 6 and 7.

In Fig. 7, (+) and (-) represent the positive and negative terminals of the D.C. power source. The relay 60 is the one for confirming safety. Reference numeral 45b represents a normally-closed contact of a safety device, not shown in the drawing, and 49b is a normallyclosed contact of a relay 49 of a belt cut detector which will appear later. Reference numeral 43 represents an operation instruction relay; 60a1 is a normally-open contact of the safety confirmation relay 60; and 10a is a normally-open contact of the operation generation instruction relay 10 not shown in the drawing. Symbol TON represents a ON-delay timer, which is belatedly turned ON after the normally-closed contact 62a2 is closed.

The inputs of the speed instruction generation circuit 33 include a normally-open contact UPa for instructing the UP instruction, which is not shown in the drawing, and a normally-open contact DNal of a relay DN for instructing the DOWN operation, which is not shown in the drawing. When the normally-open contact UPa is closed, the UP operation speed instruction is generated and when the normally-open contact DNal is closed, the DOWN operation speed instruction is generated. Reference numeral 41 represents the start compensation instruction output control relay. TOFF, TOFF2 and TOFF3 are OFFdelay timers, which are turned OFF belatedly after the normally-open contact of the input is open. The delay sequence is set to be TOFF, TOFF2 and TOFF3. Reference numeral 63 represents a relay for controlling the electromagnetic change-over valve 12.When this relay 63 is turned ON, it opens the electromagnetic change-over valve 12 and when OFF, it closes the latter. Reference numeral 46 represents a relay for controlling the electromagnetic brake 16. When this relay 46 is turned ON, it opens the electromagnetic brake 16 and when OFF, it closes the latter.

o; when the normally-open contact lOa of the operation generation instruction relay 10 is closed, the operation instruction relay 43 is turned ON because the normally-open contact 60a1 of the safety confirmation relay is closed. When the operation instruction relay 43 is turned ON, the reference start compensation instruction To rises with the inclination as shown in Fig. 6e as has already been explained with reference to Fig. 6. At the same time, the normally-open contact 43a3 is closed and TOFF2 and TOFF3 are turned ON.

Since the operation is the UP operation, the DOWN operation instruction relay DN is OFF and TOFF1 is not turned ON. Since the normally-open contact 60a3 of the safety confirmation relay 60 is closed, the control relay 46 is turned ON and opens the electromagnetic brake 16 when TOFF2a is closed. The time T1 in Fig. 6e is in conformity with the time tl in Fig. 4. The start compensation instruction T (reference start compensation instruction T0) becomes constant at the time tl. The relay 62 shown in Fig. Sd is turned ON at the time tl.

The normally-open contact 62a2 is closed and the ON-delay timer TON is turned ON belatedly at the time t2. The normally-open contact TONal, TONa2 are closed at the time t2. Since the UP operation instruction relay UP is turned ON, the speed instruction generation circuit 33 is caused to generate the UP operation speed instruction through the normally-open contacts 43a2r TONal. The start compensation instruction output control relay 41 is turned ON at the time t2 through the normally-open contact TONa2 and through TOFF3a. Acceleration is made by the instruction of the speed instruction wr* till the time t3 and thereafter the operation becomes the steady speed operation. Deceleration is started at the time t4 and the floor reaching speed is attained at the time t5.The normally-open contact 10a of the operation generation instruction shown in Fig. 7 is open at the time t5 and the operation instruction relay 43 is turned OFF. When the operation instruction relay 43 is turned OFF, the normally-closed contact 43b1 of Fig. 6b is closed and discharges the charge of the capacitor C. The normallyopen contact 43a1 of Fig. 6d is open, the relay 62 is turned OFF and the operation state returns to the initial state. The normally-open contact 43a3 is open and the OFF-delay timers TOFF2 and TOFF3 are turned OFF sequentially and belatedly.

The normally-open contact TOFF2a is open, the relay 46 for controlling the electromagnetic brake is turned OFF at the time t8 and the electromagnetic brake 16 is closed. The normally-open contact TOFF3a is open at the time tg and the start compensation instruction output control relay 41 is turned OFF. Thus, the operation is completed.

Since the description given above deals with the case of the UP operation, the difference of the DOWN operation from the UP operation will be first explained with reference to Fig. 5.

The start compensation instruction T is gradually raised at the time TO and the induction motor 21 is rotated at a low speed. The speed is increased until the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15, becomes higher than the oil pressure of the cylinder 3, that is, the signal 14a of the pressure detector 14, and the start compensation instruction T is increased until the cage rises at a low speed, and is then held at that level at the time tl. The electromagnetic coil is energized by the signal 12a at the time tl and the electromagnetic valve 12 makes the opposite direction conductive. The speed instruction Wr* is raised at the time t2 and acceleration is made till the time t3.Deceleration is started at the time t5, the landing speed is attained at the time t6, the operation instruction relay 43 is turned OFF at the time t6 and the coil of the electromagnetic change-over valve 12 is de-energized at the time t7. Thus the valve function returns to the function of the check valve.

The DOWN operation will be explained in detail with reference to Figs. 5, 6 and 7.

The operation instruction relay 43 is turned ON at the time to. The contact 43a1 shown in Figs. 6 and 7d is closed and the relay 64 is turned ON. The normally-closed contact 43b1 of Fig. 6(b) is open and the normally-open contact 64a1 is closed, so that the reference start compensation instruction 10 rises with the inclination as shown in Fig. 6e. The time T1 is in conformity with the time tl of Fig. 5 and the start compensation instruction T (reference start compensation instruction 10) becomes constant at the time t1. When the normally-open contact 43a3 is closed, the OFF-delay timers TOFF2 and TOFF3 are turned ON.When the normally-open contact 43a3 is closed at the time to, the OFF-delay timer TOFF2 is turned ON, the normally-open contact TOFF2a is closed, the electromagnetic brake control relay 46 is turned ON and the electromagnetic brake 16 is open. The relay 62 is turned ON at the time tl. The delay timer TOFF1 is turned ON because the normally-open contact 43air the normallyopen contact DN a2 of the DOWN operation instruction relay and the normally-open contact 62a4 are closed. The electromagnetic change-over valve control relay 63 is turned ON as the normally-open contact 60a2 of the safety confirmation relay, the normally-open contact DNa3 of the DOWN operation instruction relay and the normally-open contact 62a4 are closed, and makes the electromagnetic change-over valve 12 conductive in the opposite direction by the signal 12a.When the normally-open contact 62a2 is closed, the ON-delay timer TON is turned ON belatedly.

The normally-open contact TONal of the ON-delay timer TON is closed at the time t2 and lets the speed instruction generation circuit 33 generate the DOWN operation speed instruction through the normally-open contact DNal of the DOWN operation instruction relay DN. The normally-open contact TONa2 is closed at the time tl and the start compensation instruction output control relay 41 is turned ON. The cage 5 is accelerated till the time t3 and then reaches the steady operation. When the cage approaches to a target floor, deceleration is made at the time t4 and the landing speed is attained at the time t5.

The normally-open contact 10a of the operation generation relay 10 is open at the time t6 and the operation instruction relay 43 is turned OFF. The OFF-delay time TOFF1 is turned OFF at the time t7, the normally-open contact TOFFla is open, the electromagnetic change-over valve control relay 63 is turned OFF and the electromagnetic change-over valve 12 resumes the function of the check valve by the signal 12a. The OFF-delay timer TOFF3 is turned OFF at the time tg, the normally-open contact OFF3a is open, the start compensation instruction output control relay 41 is turned OFF and the operation is thus complete.

Here, the induction motor 21 is rotated at a low speed and the speed is increased until the output pressure of the hydraulic pump 13, that is, the signal 15a of the pressure detector 15 becomes higher than the oil pressure of the cylinder 3, that is, the signal 14a of the pressure detector 14, and the start compensation instruction T is increased until the cage rises at a low speed and is held at the time tl. Next, the speed instruction wr* is raised at the time t2 as will be explained now.

The reduction of the start shock resulting from the oil leakage can be accomplished by supplementing the leakage of the hydraulic pump 13.

In the hydraulic system, however, friction is great between the cylinder and the plunger and the difference between static friction and dynamic friction is great.

Therefore, in the present system, the reduction of the start shock is further accomplished by detecting the oil pressure of the cylinder 3 and the output pressure of the hydraulic pump 13, increasing the speed of the induction motor until the output pressure of the hydraulic pump 13 becomes higher than the cylinder oil pressure and thus making the shift from the static friction to the dynamic friction smooth.

If the difference between the static friction and the dynamic friction is not very great or the shock is not so great as to be sensible as a start shock to the human body, the bias reference voltage E2 shown in Fig. 6c can be set to zero or to a negative value. Even if it is a negative voltage, it does not exceed the difference between the output signals 14a and 15a of the pressure detectors 14, and is smaller as much as possible than the absolute value of the difference of both output signals 14a, 15a (signal 14a - signal 15alp 1E21) |E2| ) and is a value near zero in the sense of the reduction of the start shock.

Fig. 3 shows the speed control apparatus 26 shown in Fig. 2 in further detail.

This block diagram shows an example of the basic circuit of the slip frequency type vector control.

Reference numeral 32 represents the ASR circuit; 31 is the vector control circuit; and 30 is the current control circuit. The input signals of the ASR circuit 32 are the speed instruction wr* of the speed instruction generation circuit, the cage speed signal Wr and the start compensation instruction T of the start compensation instruction generation circuit 34. The ASR circuit 32 comprises a proportional integration constant Ki, Z-1 of the Z function of a sample value control, a proportional constant Kp, a torque limiter and an addition-subtractor.

When the operation instruction relay 43 is ON, the start compensation instruction I (reference start compensation instruction 10) is generated from the start compensation instruction generation circuit 34 and becomes the instruction value T* of the vector control circuit 31 through the normally-closed contact 41b and the torque limiter. Since the normally-open contact 41a is open at this time, the integration function does not operate and the start compensation instruction T becomes as such the instruction value T* of the vector control circuit 31.

At this time, the speed instruction Wr* = 0 and the cage speed xr = 0.

Incidentally, the start compensation instruction may be a bias pattern which rotates the induction motor 21 at a low speed within the range where the cage 5 is not started or in other words, within the range where the start shock due to the oil leakage is reduced.

The input signals of the vector control circuit 31 are the torque instruction T* of the ASR circuit 32 and the signal 22a of the pulse encoder 22 coupled directly to the induction motor 21, that is, the rotating speed WrM of the induction motor 21. The vector control circuit 31 comprises proportional constants K1, K2, the flux component Im of the induction motor 21, a function

a function tan-l (It/im) and an adder.The instruction i* of the current control circuit 30 comprises a frequency instruction Wi and a current value, instruction Ii and a phase instruction e. The frequency instruction wl multiplies the torque instruction l* by the proportional constant K1 and obtains the slip frequency 5. Next, it adds the rotating speed tsrM to the slip frequency 5 and obtains the frequency instruction w1. The current instruction Ii and the phase instruction e are obtained by multiplying the torque instruction T* by the proportional constant K2 to determine the torque component It of the induction motor 21 and calculating them from the functions jIm2 + It2 and tan'l (It/im) from this torque component It and the flux component Im, respectively.

The current control circuit 30 obtains the control signals iu, iv, iw of the three-phase alternating current from the current instruction i*, controls the inverter 23 and rotates the induction motor 21.

The operation which switches from the start compensation instruction to the speed instruction and accelerates the elevator will be explained.

At the same time as the speed instruction Wr* rises at the time t2 shown in Figs. 4 and 5 in the speed instruction generation circuit, the normally-open contact 41a is closed and the integration function operates.

Since the normally-closed contact is open, the start compensation instruction T becomes zero. As a result, the ASR circuit 32 becomes a proportional integration circuit using the cage speed Wr as a feedback signal, controls the induction motor 21 so that the cage speed Wr follows up the speed instruction Wr*, and rotates the hydraulic pump 13.

When such a system configuration is employed, the speed feedback control circuit inclusive of the cage speed can be accomplished and speed control performance canoe improved. As a result, the landing speed can be reduced from the conventional value of 5 m/min to 2 m/min . Since the landing speed is lower than in the conventional apparatus, the stop shock can be reduced, comfort to drive becomes better and the speed control from the start till landing can be made smoothly.

Since the cage speed is used for the speed feedback signal, the landing speed does not change in accordance with the load and the oil temperature. Accordingly, the operation time of the landing speed or in other words, so-called "snail-slow operation time" can be shortened and the operation time from the start till stop can be shortened.

Furthermore, since the start compensation T is inputted to the latter stage of the ASR circuit and the speed feedback is effected by comparing the speed instruction Wr* and the cage speed Wr, the start compensation instruction I does not become a disturbance factor in speed feedback and speed feedback having fidelity to the speed instruction (ssr* can be accomplished.

Fig. 8a shows the construction for rotating the hydraulic pump by the induction motor 21 through pulleys 18, 19 and the belt 20.

When the belt 20 is cut during the DOWN operation, the speed of the cage is accelerated in the DOWN direction due to the own weight of the cage.

Therefore, the electromagnetic brake 16 is fitted to the shaft 13b which connects the pulley 18 and the hydraulic pump 13 to stop the acceleration of the cage at the time of cut of the belt 20 as shown in Fig. 8b.

The fitting position of the electromagnetic brake 16 is on the opposite side to the pulley 18. This brake may be of the drum type but is preferably a disc brake in consideration of a compact size and light weight.

Fig. 9 shows a belt cut detector inside the speed control apparatus 26.

The inputs of the belt cut detector 50 shown in Fig.

9(a) are the rotating speed WrM of the induction motor and the cage speed Wr. When the difference between the rotating speed WrM and the cage speed Wr is above a predetermined value (e.g. above 10% of the rated speed) the belt cut detector 50 operates, energizes the relay 49, opens the normally-closed contact 49b of Fig. 7 and turns OFF the safety confirmation relay 60. Accordingly, when the normally-open contacts 60air 60a3 are open, the control relay 46 of the electromagnetic brake 16 is turned OFF, the normally-open contact 46a shown in Fig. 9b is open and the electromagnetic brake 16 is closed. At the same time, the electromagnetic change-over valve control relay 63 is turned OFF and the electromagnetic changeover valve 12 is returned to the function of the check valve.

The operation of the belt cut detector 50 will be explained with reference to Fig. 9b.

The cage speed Wr is inputted to 0P3 and the polarity is inversed. OP4 compares the rotating speed w, of the induction motor with the cage speed Wr to determine the difference and its polarity is made positive by the absolute circuit 51. For example, the value of the power source voltage E3 is set to 10% of the rated speed. OP5 compares the value of the power source voltage E3 with the output value of the absolute circuit 51 and when this value becomes positive, the relay 49 is turned ON.

The function of the belt cut detector 50 described above can minimize the speed increase at the time of belt cut.

Next, another embodiment of the present invention will be explained.

Figs. 10a and lOb correspond to Fig. 6c.

In Fig. 10(a), reference numeral 14A represents the output voltage of a flow meter which is used in place of the pressure detector 14 shown in Fig. 1. As is obvious from the comparison with Fig. 6c, the output signal 15a of the pressure detector 15 is not used. In other words, this embodiment omits the pressure detector 15 shown in Fig. 1.

In Fig. 10b, a pulse counter PC is used in place of OP3 shown in Fig. 10a and the output lla of the pulse encoder (E2) 11 shown in Fig. 1 is used as its input.

In Fig. 1, when the output pressure P2 of the hydraulic pump 13 becomes greater than the oil pressure P1 of the cylinder due to the start compensation, the check valve 12 is open and the pressure oil starts flowing inside the oil feed pipe 12a. In this case, the output of the flow meter, that has so far been zero, exhibits a certain value 14A due to the detection of the flow of the oil pressure. The relay 61 is turned ON when the output 14A of the flow meter exceeds the bias reference voltage E2.

In Fig. 1, the check valve 12 opens similarly and the oil pressure starts flowing inside the oil feed pipe 12a. Then, the cage 5 rises at a low speed. Since this slow speed ascension is detected by the pulse encoder 11, the relay 61 is turned ON when the UP distance or the number of pulses corresponding to the converted speed exceeds the pulse set value Ep corresponding to the bias reference voltage E2.

In these examples, too, the bias pattern of the start compensation becomes the form of Fig. 6e.

In Figs. 10a and 10b, turn-ON of the relay 61 is grasped by detecting the pressure difference between the oil pressure of the cylinder and the output pressure of the hydraulic pump in the form of the output of the flow meter and the pulse encoder output.

In both embodiments, the set values E2, Ep can be set to the state where the cylinder oil pressure and the hydraulic pump output pressure are equal to each other.

Next, the forms of the embodiments of the present invention will be explained.

(1) The current control circuit 30, the vector control circuit 31, the ASR circuit 32, the speed instruction generation circuit 33 and the start compensation instruction circuit 34 of the speed control apparatus in the embodiments have been described as the separate circuits from one another. However, this is for the explanation of the functions and when a microcomputer is used, the functions described above can be put together because a software configuration is used.

(2) In Fig. 3, the start compensation instruction To may be compared with the output Wr of the pulse encoder (E2) 11 in the addition form with the speed instruction war*.

(3) In Fig. 4, the speed instruction Wr* rises from zero at the time t2. When the start compensation instruction T and the speed instruction xr* switch over at the time t2, the force for stopping the cage acts if the cage is rising at a low speed because the speed instruction is zero in the speed feedback system. Therefore, the switch to the speed instruction xr* may be made smooth by adding the low speed rise of the case is added and outputted as the rise of the speed instruction wr*.

(4) In Fig. 1, the cage is directly driven by the plunger but indirect system driving may be employed by disposing a pulley on the plunger, winding a rope whose one end is fixed to the cage with the other end kept fixed and moving the plunger up and down, so as to move up and and down the cage through the rope.

(5) Though the hydraulic pump is driven by the induction motor through the belt in Fig. 1, a shaft direct coupling system or a gear coupling system may be employed, too.

(5) In the electromagnetic valve shown in Fig. 1, the check valve and the valve for establishing conduction in the opposite direction are separate but the oil feed pipes 12a and 13a may be communicated through both valves.

In accordance with the construction described above, the hydraulic elevator having a small start shock can be obtained by generating directly and accurately the bias pattern corresponding to the oil leakage quantity in the hydraulic pump.

Claims

Claims:

1. A hydraulic elevator comprising: a cage capable of moving upward and downward along an elevator shaft; a cylinder for moving said cage; a motor; a hydraulic pump driven by said motor and producing a pressured oil; a change-over valve normally operating as a check valve and supplying the discharged pressured oil from said hydraulic pump to said cylinder, the cage speed being controlled by regulating the discharge flow rate of said hydraulic pump; a speed instruction generating circuit for controlling said hydraulic pump; and a start compensation instruction generating circuit for generating a compensation signal in response to the difference between the discharge oil pressure of said hydraulic pump and the oil pressure in said cylinder, the discharge flow rate of said hydraulic pump being controlled on the basis of output signals of said speed instruction generating circuit and said start compensation instruction generating circuit.

2. A hydraulic elevator according to claim 1, comprising pressure sensors for detecting the discharge pressure of said hydraulic pump and the oil pressure in said cylinder, said start compensation instruction generating circuit generating the compensation signal so as to maintain the difference between the discharge oil pressure of said hydraulic pump and the oil pressure in said cylinder at predetermined pressure.

3. A hydraulic elevator according to claim 1, wherein said change-over valve is an electromagnetic change-over valve which operates as a check valve and is rendered conductive in an opposite direction when energized by an electromagnetic coil and the electromagnetic coil is energized after said cage moves up at a low speed.

4. A hydraulic elevator comprising: a cage capable of moving upward and downward along an elevator shaft; a cylinder for moving said cage; an induction motor; a hydraulic pump driven by said induction motor and producing a pressured oil; an electromagnetic change-over valve which normally operates as a check valve and is rendered conductinve in an opposite direction when energized by an electromagnetic coil and supplies the discharged pressured oil from said hydraulic pump to said cylinder, the cage speed being controlled by regulating the discharge flow rate of said hydraulic pump; a cage speed instruction generating circuit; a speed control circuit for converting the output of said generation circuit to torque instruction; a slip frequency type vector control circuit for converting said torque instruction to a current instruction;; a current instruction circuit for driving a power converter on the basis of said current instruction and rotating said induction motor; and a start compensation instruction generating circuit for generating' a compensation signal in response to the difference between the discharge oil pressure of said hydraulic pump and the oil pressure in said cylinder, the discharge flow rate of said hydraulic pump being controlled on the basis of output signals of said speed instruction generating circuit and said start compensation instruction generating circuit, said vector control circuit ruses said start compensation instruction as a torque instruction.

5. A hydraulic elevator according to claim 4, wherein the speed of said cage is used as a speed feedback signal to said speed control circuit.

6. A hydraulic elevator according to claim 4, wherein the speed of said induction motor is used as a speed feedback signal to said vector control circuit.

7. A hydraulic elevator comprising: a cage capable of moving upward and downward along an elevator shaft; a cylinder for moving said cage; a motor; a hydraulic pump driven by said motor and producing a pressured oil; a change-over valve normally operating as a check valve and supplying the discharged pressured oil from said hydraulic pump to said cylinder, the cage speed being controlled by regulating the discharge flow rate of said hydraulic pump; a speed instruction generating circuit for controlling said hydraulic pump; and a start compensation instruction generating circuit for generating a compensation signal in response to the difference between the outlet and inlet pressures of said change-over valve, the discharge flow rate of said hydraulic pump being controlled on the basis of output signals of said speed instruction generating circuit and said start compensation instruction generating circuit.

8. A start control system for reducing start shock in a hydraulic elevator having a cage moveable in an elevator shaft by a hydraulic cylinder supplied with pressurised oil from a hydraulic pump by way of a check valve, the system comprising start compensation means responsive to actual detected relative pressure between the sides of said check valve to cause an appropriate start compensation flow of pressurised oil before a faster flow corresponding to movement of the cage.

9. A hydraulic elevator, or start control system, substantially as described and shown herein with reference to the accompanying drawings.