WO2018002241A1

WO2018002241A1 - Elevator ride quality enhancement by drive cycle optimization

Info

Publication number: WO2018002241A1
Application number: PCT/EP2017/066166
Authority: WO
Inventors: Timo HILSDORF
Original assignee: Inventio Ag
Priority date: 2016-06-30
Filing date: 2017-06-29
Publication date: 2018-01-04

Abstract

A motion profile (20) for controlling the movement of an elevator through an acceleration phase (Δt_acc) and a deceleration phase (Δt_dec) of an elevator trip wherein the motion profile (20) is continuously differentiable. The use of a continuously differentiable motion profile frees the velocity response (R4) from free vibrations.

Description

Elevator Ride Quality Enhancement By Drive Cycle Optimization

The present invention relates to a method and system to enhance elevator ride quality by reducing transient vertical vibration acting on and resultant noise generated within an elevator car.

A common problem associated with most elevators is that of low frequency vertical vibration of the elevator car. This phenomenon is principally due to the inherent elasticity of the main drive system used to propel and support the car within the hoistway; for example the compressibility of the working fluid used in hydraulic elevators and the elasticity of the rope used in traction elevators. Accordingly, any fluctuation in the force acting on the car will cause transient vertical vibration about a steady-state displacement of the car. The predominant frequency of these vibrations is that of the fundamental mode of vibration which is dependent on the travel height of the elevator and, for a traction elevator, the type of rope used. For a traction elevator having a travel path of 400m and using steel ropes the fundamental frequency can be less than 1 Hz. Vibrations at such low frequencies are easily perceptible to passengers, undermining passenger confidence in the safety of the elevator and generally leading to deterioration in perceived ride quality. Even with elevators exhibiting higher fundamental frequencies, vibration generated within the cabin can result in disturbing and unwanted noise at the natural frequency and harmonics thereof.

One of the sources of vibration while the car is travelling is jerk phases in a travel profile sent by an elevator controller to the drive. Fig. 1 illustrates typical and conventional travel profiles sent to the elevator drive system to run an elevator car on a journey from an initial starting floor to a selected destination floor within the elevator hoistway, wherein the generally square-wave shaped plot a depicts jerk values during the elevator journey, the trapezoidal shaped plot a depicts acceleration and the velocity is shown in plot v. There are three discrete phases performed by the drive during an elevator journey from the initial floor to the final destination floor, namely an acceleration phase (depicted by time interval At_acc in Fig. 1) during which the drive accelerates the car up to rated velocity, a constant speed phase (between times ti and X2 in Fig. 1) and a deceleration phase (time interval Atd_ec in Fig. 1) whereby the drive slows the car down to stop at the intended destination floor. In this example, at the start of the elevator run at time t₀, the acceleration phase At_acc commences and the jerk value instantaneously transitions from zero to a maximum where it remains until the acceleration a of the elevator car ramps up to its constant, rated level at which point the jerk a is instantaneously transitioned back down to zero and the acceleration remains at its constant, rated level. Subsequently, as the velocity v approaches its rated value, the motion profile ramps down the acceleration a to zero with an accompanying negative step transition in the jerk a.

The constant speed phase then begins at time ti during which the acceleration and jerk values are both zero while the elevator car runs at constant, rated speed.

As the elevator car continues to move and the distance remaining to the intended destination floor decreases, it is necessary to initiate a stopping sequence at time ti by commencing the deceleration phase Atd_ec. The deceleration phase Atd_ec effectively adopts the inverse sequence as that described above for the acceleration phase At_acc. At commencement at time X2, there is an instantaneous negative step transition in the jerk a, which in turn causes the acceleration a to begin to decrease from zero. When the deceleration reaches its rated value rate, jerk a is transitioned again to zero. As the car approaches its intended destination floor, there is an instantaneous positive step transition in the jerk a, accompanied by a decrease in the deceleration and velocity of the car until the car reaches its destination at time t3.

When a typical velocity or acceleration command generated by the elevator controller from a profile stored therein, as shown in Fig. 1, is fed directly into the elevator drive, there tends to be some overshoot in the car's response producing jerk and unwanted noise and vibrations as illustrated by the first response curve Rl in Fig. 2. An actual elevator system response to the travel profile is presented in Fig. 3 which shows the graphical representations of the sound levels recorded in the car and acceleration as measured by an accelerometer mounted on the car. Large fluctuations are present in the acceleration response during both the acceleration phase and the deceleration phase, as highlighted by the circles in the figure. These fluctuations excite vibrations of the elevator car particularly at its natural frequencies, which stimulate sound intensity level spikes, indicated by the arrows in the figure. A conventional method of reducing the vibrations in the response is to compensate by reducing acceleration and increasing the flight time to round off the jerk as shown by travel curve trajectory R2. As shown in the Figure, the flight time increases from approximately 26s to 29s. However, this compensation of the response always increases travel time and therefore reduces the performance and the transport capacity of the elevator.

It would be useful to be able to control an elevator travel profile in a way that provides a desired level of ride quality without sacrificing performance such as by reducing acceleration and increasing flight time as in the conventional solution as outlined above.

Patent document EP-A1 - 1705147 proposes a way to reduce vertical vibrations of an elevator car. The elevator comprises a car arranged to travel along guide rails within a hoistway, a main drive to propel the car. A sensor mounted on the car measures a vertical travel parameter of the car, and a comparator is provided to compare the sensed car travel parameter with a reference value derived from the drive. An error signal output from the comparator is used by an auxiliary motor mounted on the car to exert a vertical force on at least one of the guide rails in response. Accordingly, any undesired vertical vibrations of an elevator car while it is stationary at a landing or travelling through the hoistway will produce an error signal from the comparator and the auxiliary motor is driven to exert a vertical frictional or electromagnetic force on the guide rail to counteract the vibrations.

Alternatively, JP2003-160281 discloses vibration suppression within an elevator system by using a closed-loop feedback of an acceleration signal from an accelerometer mounted to the elevator car to the drive.

Furthermore, WO-A1-2010/016826 describes a device for controlling an elevator car motion profile and includes a controller that is programmed to cause an associated elevator car to move with a motion profile that includes a plurality of jerk values. The controller is programmed to cause at least one transition between two of the jerk values to be at a non- instantaneous transition rate.

Accordingly, the objective of the present invention is to reduce vertical vibrations of an elevator car. This objective is achieved by providing an elevator control unit comprising a computing unit adapted to control the movement of an elevator according to a motion profile wherein the motion profile is continuously differentiable.

The primary advantages of using a continuously and infinitely differentiable motion profile according to the invention are that the velocity, acceleration and the jerk responses during the elevator trip will be continuous and smooth and therefore the any vibrations or oscillations, particularly at the end of the acceleration and deceleration phases, will be greatly reduced. Accordingly, the elevator ride quality is enhanced by reducing transient vertical vibration acting on and resultant noise generated within an elevator car.

As a consequence of the reduction in vibrations and oscillations, a further advantage of present invention is that the overall stress on the system can be reduced and in particular the stresses associated with the drive system including the motor, suspension ropes/belts etc. Preferably, the times for the acceleration phase and the deceleration phase of the elevator trip are equal.

Preferably, to ensure that the motion profile is continuously and infinitely differentiableO it can be defined by the Gauss error function or error function.

The motion profile can be a velocity profile.

Typically, during the acceleration phase of the elevator trip the velocity can be defined by the equation

where c is a variable, to is the time at the start of the acceleration phase and VKN is a rated car speed.

During the deceleration phase of the elevator trip the velocity may be defined by the equation v(t) =

where c is a variable, t2 is the time at the start of the deceleration phase and VKN is a rated car speed.

The variable c can be defined by the equation

5

^{C ~} VKN AK

AK AKT where AK is rated acceleration and AKT is maximum car jerk.

Typically for any elevator, the rated car speed and acceleration are defined by the original design specification for the drive and motor. Maximum car jerk is conventionally defined in the relevant codes and standards governing the elevator industry in a particular country or region. Alternatively, in the interest of passenger comfort, the commissioning elevator company may reduce the maximum jerk value below the levels defined in the codes and standards.

Depending on the length of the elevator trip, the motion profile may include a constant speed phase between the acceleration phase and the deceleration phase of an elevator trip.

Alternatively, the motion profile can be an acceleration profile.

The invention also provides an elevator comprising a car arranged to travel along a hoistway, a drive to propel the car and an elevator control unit to control the drive wherein the control unit contains a motion profile previously explained above.

Preferably, the elevator includes a sensor to measure a travel parameter. Typically, the travel parameter will be indicative of either a speed or an acceleration of the elevator.

Furthermore, a comparator can be used to compare the sensed travel parameter with a reference value derived from the motion profile. The result from the comparator can be used the drive to ensure that the movement of the elevator approaches that defined by the motion profile. The comparator may be housed within the drive or alternatively within the control unit.

The invention also provides a method for reducing vibrations exerted an elevator car comprising the steps of providing a drive to propel the car along a hoistway, measuring a vertical travel parameter, comparing the measured travel parameter with a reference value derived from the aforementioned motion profile and controlling the drive in accordance with a result from the comparison.

The present invention is herein described by way of specific examples with reference to the accompanying drawings of which:

Figure 1 is a diagrammatic overview of conventional elevator motion profiles according to the prior art;

Figure 2 is a diagrammatic overview of the conventional travel curve responses of an elevator car to the motion profiles of Fig. 1 ;

Figure 3 is a graphical representation of the resultant sound intensity levels and acceleration experienced within an elevator car;

Figure 4 is a schematic representation of an elevator according to an embodiment of the present invention implementing a method according to the invention;

Figure 5a is a representation of a velocity profile according to one embodiment of the present invention;

Figure 5b is a representation of an acceleration profile according to an embodiment of the present invention;

Figure 6 is a series of graphical illustrations of a set of results obtained from simulation; and

Figure 7 is an exploded section of the velocity response illustrated in Fig. 6.

To avoid unnecessary repetition within the description, features that are common to more than one embodiment have been designated with the same reference numerals. Furthermore, within the figures certain graphical characteristics may be exaggerated in order to clearly demonstrate the effectiveness of the present invention.

Figure 4 illustrates an elevator according to the present invention. The elevator contains an elevator car 1 which is arranged to travel upwards and downwards within a hoistway 8 of a building by means of an electric drive 5 which in turn is controlled in accordance with values V_r or A_r derived from a motion profile 20 stored within a computing unit 19 of an elevator control unit 18. As illustrated in Figure 5a the motion profile 20 can be either a velocity profile v(t) or alternatively, as shown in Figure 5b, the profile 20 could be acceleration based a(t). The drive 5 comprises a frequency converter 12 to supply current from a commercial a.c. electrical power supply 10 within the building to an a.c. motor 14.

The elevator car 1 comprises a passenger cabin 2 supported in a frame 4. A traction rope or belt 52 interconnects the car 1 with a counterweight 50 and this rope 52 is driven by a traction sheave 54 located above or in an upper region of the hoistway 8. The traction sheave 54 is mechanically coupled to the motor 14 and driven concurrently therewith. An encoder 16 or other sensor is arranged in conjunction with the traction sheave 54 or a drive shaft of the motor 14 to provide a signal V_c or A_c representative of the actual speed or acceleration, respectively to the frequency converter 12 and/or to the elevator control unit 18.

In high-rise elevators the weight of the traction rope 52 is significant and a compensation rope 60 is generally provided to counteract any imbalance of the rope 52 weight as the car 1 travels along the hoistway 8. The compensation rope 60 is suspended from the counterweight 50 and the car 1 and is tensioned by a tensioning pulley 62 mounted in a lower region of the hoistway 8. As clearly shown in the drawing, there is a degree of elasticity and damping associated the traction rope 52, the compensation rope 60, the mounting of the traction sheave 54, the mounting of the tensioning pulley 62 and the mounting of the passenger cabin 2 within the car frame 4, respectively.

In operation, the computing unit 19 of the elevator control unit 18 sends the values V_r or A_r derived from the motion profile 20 to the frequency converter 12 via a data transfer bus between the elevator control unit 18 and the frequency converter 12. The frequency converter 12 measures the actual speed V_c or acceleration A_c of the elevator motor 11 with the encoder 16 or other sensor and has a comparator 13 to compare this actual value with that derived from the motion profile 20. Depending on this comparison, the frequency converter 12 adjusts the current running in the elevator motor 14 such that the movement of the motor, and thereby the movement of the elevator car 1 , approaches the aforementioned movement profile 20.

It has been shown experimentally and by simulations, for example as illustrated in FIGS. 1-3, that the conventional driving cycle causes ride quality issues.

It is proposed that the large fluctuations present in the acceleration response during both the acceleration phase At_acc and the deceleration phase Atd_ec and the associated vibrations and noise experienced within the elevator car 1 can be greatly reduce by ensuring that the motion profile 20 is continuously or infinitely differentiable in its derivatives. One example for achieving this objective is to apply the Gauss error function or error function erf to the motion profile 20. The error function erf is defined in equation 1 below:

EQN. 1

In the demonstrative example that follows the motion profile 20 is a velocity motion profile v(t) and the error function erf is applied as follows in the discrete travel phases.

The velocity profile v(t) in the acceleration period At_acc between discrete times to and ti is defined in equation 2 below:

EQN. 2

Subsequently, the velocity profile v(t) in the constant speed phase of travel between times ti and ti is defined by equation 3 : v(t_!_₂) = VKN

EQN. 3 Finally, in the deceleration phase Atd_ec whereby the drive slows the car down to stop at the intended destination floor, the velocity profile v(t) between times ti and t3 is defined by equation 4 below:

EQN. 4

The variable c controls the maximum acceleration. If the same acceleration time period is used as before, to ensure that the flight time remains the same, it is recommended to set:

5

^{C ~} VKN AK

AK ⁺ AKT

EQN. 5

In the above equations the term VKN is the rated car speed (m/s), AK is the rated acceleration (m/s²), and AKT is maximum car jerk (m/s³).

For the purpose of demonstration, the intervals for the acceleration period At_acc and the deceleration phase Atd_ec were kept equal.

The performance of the system using the velocity profile v(t) was evaluated using the elevator schematically illustrated in Fig. 4. A detailed analysis of the results obtained showing car 1 velocity and associated acceleration of the conventional system against that recorded for a the system according to the invention using the modified motion profile 20 is shown in the graphical representations of Figures 6 and 7, wherein R3 refers to the response of the conventional system and R4 is the response according to the present invention.

The results clearly illustrate that the modified motion profile according to the invention does not excite free vibrations because it is continuously differentiable. It is important also to note that the flight time for the trip remains the same. Accordingly, the modified elevator travel profile provides a desired level of ride quality without sacrificing performance by increasing flight time.

It will be appreciated that the invention can equally be applied to an elevator wherein the motion profile 20 is an acceleration profile a(t). In the embodiment described above the comparator 13 is housed within the frequency converter 12 of the drive 5. In an alternative embodiment, the comparator 13 could be housed within the control unit 18. In such an arrangement, the actual speed V_c or acceleration A_c of the elevator motor 11 would be measured with the encoder 16 or other sensor and send to the control unit 18. The control unit 18 would then, using its internal comparator 13, compare this actual value with that derived from the motion profile 20. Depending on this comparison, it can send a signal to the frequency converter 12 adjusting the current running in the elevator motor 14 such that the movement of the motor, and thereby the movement of the elevator car 1, approaches the aforementioned movement profile 20.

Although the invention has been described in relation to and is particularly beneficial for traction elevators incorporating traction ropes 52 or belts, it will be appreciated that the invention can also be employed in hydraulic elevators. In such an arrangement the main drive comprises an elevator controller and a pump to regulate the amount of working fluid between a cylinder and ramp to propel and support the elevator car 1 within the hoistway 8.

Having illustrated and described the principles of the disclosed technologies, it will be apparent to those skilled in the art that the disclosed embodiments can be modified in arrangement and detail without departing from such principles. In view of the many possible embodiments to which the principles of the disclosed technologies can be applied, it should be recognized that the illustrated embodiments are only examples of the technologies and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims and their equivalents.

Claims

1. An elevator control unit (18) comprising a computing unit (19) adapted to control the movement of an elevator according to a motion profile (20) wherein the motion profile (20) is continuously differentiable.

An elevator control unit (18) according to claim 1 , wherein times for acceleration phase (At_acc) and a deceleration phase (Atd_ec) of the elevator trip equal.

An elevator control unit (18) according to claim 1 or claim 2, wherein the motion profile is defined by the error function (erf).

An elevator control unit (18) according to any preceding claim, wherein the motion profile is a velocity profile (v(t)).

An elevator control unit (18) according to any preceding claim, wherein during an acceleration phase (At_acc) of the elevator trip the velocity is defined by the equation

6. An elevator control unit (18) according to any preceding claim, wherein during a deceleration phase (Atd_ec) of the elevator trip the velocity is defined by the equation

7. An elevator control unit (18) according to claim 5 or claim 6, wherein c is defined by the equation 5

c =

VKN AK

AK + AKT

where AK is rated acceleration and AKT is maximum car jerk.

8. An elevator control unit (18) according to any preceding claim, further comprising a constant speed phase (ti-t2) between an acceleration phase (At_acc) and an deceleration phase (Atd_ec) of an elevator trip.

9. An elevator control unit (18) according to any one of claims 1 to 3, wherein the motion profile is an acceleration profile ( (t)).

10. An elevator comprising a car (1) arranged to travel along a hoistway (8), a drive (5) to propel the car (1) and an elevator control unit (18) according to any of claims 1 to 9.

1 1. An elevator according to claim 10, further comprising a sensor (16) to measure a travel parameter (V_c;Ac).

12. An elevator according to claim 1 1 , further comprising a comparator (13) to compare the sensed travel parameter (V_C;A_C) with a reference value (V_r;A_r) derived from the motion profile (20).

13. An elevator according to claim 12, wherein the comparator (13) is within the drive (5).

14. An elevator according to claim 12, wherein the comparator (13) is within the control unit (18).

15. A method for reducing vibrations exerted on an elevator car (1) comprising the steps of providing a drive (5) to propel the car (1) along a hoistway (8), measuring a vertical travel parameter (V_C;A_C), comparing the measured travel parameter (V_C;A_C) with a reference value (V_r;A_r) derived from a motion profile (20) derived from an elevator control unit (18) according to any of claims 1 to 9 and controlling the drive (5) in accordance with a result from the comparison.