EP2602221B1

EP2602221B1 - Comfort peak curve operation

Info

Publication number: EP2602221B1
Application number: EP12196299.7A
Authority: EP
Inventors: Holger Jürgen König
Original assignee: Nidec Control Techniques Ltd
Current assignee: Nidec Control Techniques Ltd
Priority date: 2011-12-09
Filing date: 2012-12-10
Publication date: 2015-09-30
Anticipated expiration: 2032-12-10
Also published as: GB2497362B; GB201121318D0; EP2602221A3; GB2497362A; ES2556812T3; EP2602221A2

Description

Field

The invention relates to a method for controlling movement of a physical load such as an elevator.

Background

There are many practical situations in which a system must decelerate a moving physical load such that the load arrives smoothly at a specified target point at zero speed. Examples of systems in which this smooth deceleration can be required include an elevator, a conveyor, a crane, a rollercoaster, a vehicle, a hoist, robotics and gunnery.
Looking at the example of an elevator (also known as a "lift" in the UK), one method for controlling deceleration is known as the creep speed "positioning method" and is normally based on deciding the point (or position) during an elevator's journey at which to decelerate the elevator to a "creep speed". The creep speed is generally much slower than the elevator's nominal speed and is adopted before the load reaches its target point, to ensure it will arrive accurately at a standstill at that target point. As will be known to the skilled reader, a creep speed drive which includes a frequency converter having two different set points can be used to obtain two different speeds on the same elevator shaft, with the lower speed typically being a small percentage such as 10% of the higher speed. A two speed motor can also be used, the motor having a high speed winding and a low speed winding wherein the turn speed of the low speed winding is much less than that of the high speed winding for the same frequency input.
Depending on the actual travel distance from the elevator's initial position to its target position (i.e. depending on the actual travel distance for a particular journey), one of a variety of different nominal speeds may be selected in order to optimise travel time under the creep speed positioning method. To ensure the elevator does not overshoot its target position, different deceleration distances are defined for different respective nominal speeds according to the positioning method.
In general terms, an elevator is part of a drive system including a drive unit for supplying electricity to drive a motor, a controller either within or connected to the drive unit, and a shaft rotatable by the motor in order to move the elevator by means of a pulley system. The controller will know the elevator start position and target end position before the journey begins. It also knows some preferred profile parameters for the elevator, such as limits on magnitude of acceleration and/or rate of change of acceleration. The profile parameters set will generally ensure smooth acceleration and deceleration of the elevator and minimise jerk, to increase safety and comfort for its passengers (or other load).
An elevator journey usually includes an accelerating phase and a decelerating phase and a transition from acceleration to deceleration, wherein the transition may include movement of the elevator at a constant speed for a period of time. Figure 1 shows traces of speed, acceleration and speed selection commands versus time for a relatively long elevator journey controlled using the creep speed positioning method.
Generally, the drive unit or motor moving an elevator will not know the target end position for an elevator journey. They therefore rely on commands from the elevator controller. The commands shown by the sloping lines in the speed selection trace in figure 1 are issued by the elevator controller to the drive unit (or directly to the motor) in order to control movement of the elevator. The first is a deceleration command to decelerate the elevator to the creep speed. The second is a stop command to decelerate the elevator to a standstill.
The journey shown in figure 1 is of a sufficiently long distance that the elevator accelerates towards a predetermined constant or "nominal" speed, stays at that nominal speed, decelerates to a creep speed as it approaches its target end point, and then decelerates to zero speed at the target end point. The deceleration command is a command from the controller that tells the drive unit to change from moving the elevator at nominal speed to moving it at creep speed - it is shown by the first vertically sloping line in the speed selection trace in figure 1. As can be seen therein, deceleration begins as soon as the deceleration command is issued under the positioning method. For a relatively long journey such as the one shown in figure 1, this does not present a significant problem and the elevator will reach the creep speed when the elevator is at a relatively short distance from the target end point.
Figure 2 shows the same three traces as figure 1, but for a short journey controlled using the creep speed positioning method. In figure 2 the deceleration command is given when the distance between the elevator and its target end position is equal to or less than the predefined deceleration distance which has been programmed into the elevator controller. Because the journey shown in figure 2 is short, the deceleration demand must be given before the acceleration of the elevator has reached its maximum possible value. Usually the evaluator controller will only be operable to look at positions and distances and will not consider speed. Therefore it is not sophisticated enough to issue the deceleration command later if the elevator is at a relatively low speed when its position is less than or equal to the deceleration distance away from the target end position. As described above in relation to figure 1, under the creep speed positioning method the deceleration begins as soon as the deceleration command is issued. As a result, the elevator reaches creep speed much too early. It therefore will creep for a relatively long time before reaching the target end point. This is inefficient and inconvenient for the user.
Figure 3 shows the same three traces as figure 1, for a different short journey controlled using the creep speed positioning method. In figure 3 the deceleration command is given when the acceleration of the elevator has reached its maximum possible value, has remained at that maximum value for a period of time, and has already begun to (or is just about to) decrease as the elevator approaches nominal speed. In this situation, the controller controls the drive unit to keep (or begin) decreasing the magnitude of the acceleration until it is zero when the elevator reaches nominal speed. It will then continue to decelerate the elevator over the predetermined deceleration distance for that nominal speed. The creep speed positioning method therefore doesn't take into account the fact that the elevator already covered some distance (d) between the time at which the deceleration command was issued and the time at which the elevator actually reached nominal speed. As a result, the elevator will overshoot by that distance (d). Therefore it will begin creeping too late, and may not be able to arrive at a standstill at the target end point.
Another known elevator control scheme is "profile optimisation", which is also known as "peak curve operation". Peak curve operation removes the need for complex control signals and wiring in an elevator system by allowing the use of one elevator nominal speed instead of many. It therefore simplifies elevator control signals significantly. Peak curve operation controls the speed and acceleration of an elevator by controlling the timing of issuance of the "deceleration command" from a controller to the drive unit driving movement of the elevator. The timing is controlled so that the "deceleration distance" between the deceleration point (i.e. the position of the elevator when a deceleration command is issued) and the position at which the elevator reaches the creep speed is the same for all the elevator's journeys. However the elevator does not necessarily begin decelerating immediately when the deceleration command is issued, under peak curve operation, as will be understood further from the discussion below.
The deceleration distance for peak curve operation is generally determined as being the distance that the elevator must travel in decelerating from its nominal speed to its creep speed comfortably, within the constraints of some predefined profile parameters. Those profile parameters include magnitude of acceleration and rate of change of acceleration. The deceleration distance can also take into account the maximum speed of the elevator and/or the values of the nominal and creep speeds.
For a relatively long journey such as the one shown in figure 1, when the elevator has time to reach nominal speed and continue moving at that nominal speed for a period of time before the deceleration command must be issued, the timing of the deceleration command and the speed, acceleration and speed selection traces shown for the creep speed positioning method in figure 1 will be exactly the same for peak curve operation. The shaded area underneath the decelerating portion of the speed trace is equal to the deceleration distance as defined for that elevator within a predetermined set of profile parameters.
Conventional peak curve operation was designed to optimise elevator travel and prevent the long periods of creeping which can be experienced using the creep speed positioning method. Figure 4 shows an example of conventional peak curve operation of an elevator for a journey comprising a short travel distance. In figure 4 the deceleration command for the elevator is given during constant or increasing acceleration of the elevator. As mentioned above, the deceleration command is given when the distance between the current elevator position and the position at which the elevator should have decelerated to the creep speed, in advance of the end point of the journey, is equal to the predetermined deceleration distance. Because the journey depicted in figure 4 herein is relatively short, the deceleration command is therefore given during increasing or constant acceleration of the elevator load. However, after issuance of the deceleration command, the elevator's acceleration initially remains constant or continues to increase up to a maximum magnitude of acceleration, before reducing to zero speed. As soon as it reaches zero acceleration, the elevator is decelerated to the creep speed and then further decelerated in order to arrive at the target position at zero speed. Therefore the prolonged creeping experienced in the creep speed positioning method, as shown in figure 2 herein, is avoided.
Looking at the speed trace in figure 4, the shaded area under the curve represents the distance travelled after the deceleration command has been given. This shaded area therefore represents the "deceleration distance". It is the same size as the deceleration distance shown in figure 1, even though the values of the speed and acceleration of the elevator over time for the journey in figure 1 is different to the speed and acceleration values in figure 4. By smoothly controlling acceleration and subsequent deceleration of the elevator to meet the predetermined deceleration distance, conventional peak curve operation ensures that, for the journey shown in figure 4, the elevator arrives at creep speed before the end target position and does not overshoot.
Figure 5 shows another example of conventional peak curve operation for a short journey. In this case the deceleration command is given by the controller when the magnitude of the acceleration has peaked, plateaued and is already beginning to decrease as the elevator approaches it nominal speed. According to conventional peak curve operation, when the deceleration command is issued in this situation the rate at which the acceleration is reducing will not be changed and deceleration will begin immediately once acceleration has reached zero (i.e. the elevator has reached constant speed). This enables a smooth transition from acceleration to deceleration. However it has a disadvantage in that, if the elevator decelerated at the same rate at which it had accelerated, hence giving a substantially symmetrical profile of speed versus time for the journey, the area under the curve from the time at which the deceleration command was given to the time at which elevator reaches creep speed, and hence the distance travelled by the elevator after the deceleration command was issued, would exceed the predetermined deceleration distance. This means that the elevator would overshoot and therefore exceed its target position. To overcome this overshooting problem with conventional peak curve operation, known algorithms have been designed to adapt the deceleration profile and jerk for the elevator in order for it to reach the target position at zero speed. However, the application of such an algorithm will increase jerk and will also make the acceleration/deceleration curve more steep as can be seen in figure 5, wherein the deceleration magnitude increases so as to be "off the scale" in order for the elevator to reduce down to its creep speed in advance of the target end position. Therefore the elevator journey will be less comfortable and potentially less safe for its passengers.
EP 1273547 A1 discloses a variable speed apparatus capable of equalising a moving distance at the time of deceleration from deceleration start to deceleration completion in the case that a deceleration stop command is inputted during acceleration to a moving distance at the time of deceleration from deceleration start to deceleration completion in the case that a deceleration stop command is inputted during operation at an adjustable speed reference frequency even when the deceleration stop command is inputted during acceleration.
An invention is set out in the claims.
According to an aspect, a method of controlling movement of a load from a known start position to a known target position is provided, as stipulated in claim 1.
The nominal speed may be a maximum speed for the load or may be any other selected speed for which a deceleration distance has been defined. The creep speed is preferably a relatively low speed which movement of the load must reach in advance of the known target position, for example it may be 10% of the nominal speed.
Issuance of the deceleration command by the controller to the drive means may prompt the drive means to control the load, and/or to control a motor driving the load, to decelerate instantly, or to continue at a constant speed before decelerating, or to continue accelerating before reducing its magnitude of acceleration to zero and subsequently decelerating, after the deceleration command has been issued.
The drive means may drive movement of the load so that it will be moving at the creep speed before it reaches it target position. Movement of the load may be further controlled so that creep speed is reached at a predetermined creep distance, before the load reaches its target position.
The controller may issue an additional stop command after the deceleration command, to decelerate the load from its creep speed to zero speed at the known target position.
The load can be any load which is position controlled by an external controller, for example it may be an elevator, a crane hoist or a stage hoist.
According to an aspect a drive system is provided for controlling movement of a load from a known start position to a known target position as stipulated in claim 12.
According to an aspect a method of controlling movement of a load using comfort peak curve operation is provided. The method comprises using a controller to control movement of a load from a start position to a target position by issuance of a deceleration command to reduce the speed of the load to a creep speed and subsequently by issuance of a stop command to reduce the speed of the load to zero. The timing of the deceleration command is calculated by the same method regardless of the distance between the start and target positions for the load's journey. The deceleration command is issued when the distance between the load's current position and a "creep position", at which the load should be travelling at a creep speed, is equal to a combined distance that comprises an acceleration-reduction distance, over which the load must travel during reduction of the magnitude of its acceleration from maximum to zero, plus a deceleration distance which is the distance over which the load must travel in order to reduce its speed from a preselected speed to zero.
Optionally, the creep speed and stop command may be omitted and instead the deceleration command will decelerate the load directly to zero speed.

Figures

Embodiments will now be described by way of example with reference to the figures of which:

Figure 1 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under the creep speed positioning method or conventional peak curve operation for a long journey when a deceleration command is given during constant speed movement of the elevator;
Figure 2 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under the creep speed positioning method for a short journey when a deceleration command is given during increasing acceleration of the elevator;
Figure 3 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under the creep speed positioning method for a short journey when a deceleration command is given during constant acceleration of the elevator;
Figure 4 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under conventional peak curve operation for a short journey when a deceleration command is given during increasing acceleration of the elevator;
Figure 5 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under conventional peak curve operation for a short journey when a deceleration command is given during constant acceleration of the elevator;
Figure 6 is a schematic representation of an elevator system;
Figure 7 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under "comfort" peak curve operation for a long journey when a deceleration command is given during constant speed of the elevator;
Figure 8 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under "comfort" peak curve operation for a short journey when a deceleration command is given when acceleration of the elevator has just reached a maximum level; and
Figure 9 shows profiles of speed, acceleration and speed selection commands versus time for an elevator under "comfort" peak curve operation for a short journey when a deceleration command is given when acceleration of the elevator has reached (and stayed at) a maximum level.

Overview

In overview an improved control method is provided for controlling operation of a moving physical load such as an elevator.
The improved control method, referred to herein as "comfort peak curve operation", enables a moving physical load such as an elevator to be decelerated smoothly in order to arrive at a target position at zero speed. The method can be applied for both long distance travel and short distance travel and works well regardless of whether a deceleration command is issued to a motor (telling it to decelerate the elevator to a creep speed) during movement of the elevator at a constant speed, during constant acceleration of the elevator, during increasing acceleration of the elevator or during decreasing acceleration of the elevator.
The improved control method enables smooth acceleration and deceleration and accurate arrival at a target position without the need for any correction of profile parameters for the elevator during operation. The acceleration or rate of change of acceleration does not have to change steeply during the elevator journey. As a result, the journey is safer and more comfortable. Furthermore, the improved control method avoids excessive creeping. Therefore it is efficient, enabling the elevator to reach its target end position in as short a time as possible, within predefined profile parameters.
The improved control method improves the timing of the issuance of the deceleration command for an elevator journey. This improvement is based on a recognition that the controller for an elevator should take into account a distance for decreasing the magnitude of the elevator's acceleration from maximum to zero, as which point the elevator would reach a constant (nominal) speed, as well as a deceleration distance for decelerating the elevator from that constant speed to a creep speed. By accounting for both these aspects of distance from the outset, the issuance of the deceleration command from the controller can be timed to ensure that elevator arrives smoothly at its target destination at zero speed, regardless of the length (i.e. total distance) of the journey. This is achieved without having to amend the predefined profile parameters for the elevator. Furthermore, it ensures that the target position is not exceeded, without the need to apply a correction or algorithm that would increase the jerk or otherwise make the journey less comfortable or less safe. And the elevator will not creep for an excessive period of time. Therefore it will reach its destination in as short a time as possible, but in a smooth and accurate manner.
The improved control method can be implemented using existing controllers and drive systems. Therefore it is efficient and cost effective to implement as well as giving accurate results.

Detailed Description

Figure 6 shows a conventional elevator system including a geared motor. The elevator system comprises an elevator controller 10, a drive unit 12, a feedback device 14, a motor 16, a gear (or set of gears) 18, a rotatable motor shaft 20 extending from the motor 16, via the gear 18, and a traction sheave 22 mounted to the gear or motor shaft 20. Ropes 24 run over the traction sheave 22. A weight such as an elevator cabin (not shown) can be connected to the ropes 24 in order to be moved by the elevator system.
The gear 18 is provided mounted on the motor shaft 20, between the motor 16 and the traction sheave 22. Therefore the gear 18 can be used to amend the speed of rotation of the motor shaft 20 for a particular torque applied to the motor 16. The motor shaft 20 will rotate with a rotor inside the motor 16, at a speed determined by the drive 12. The motor shaft 20 can therefore drive rotation of the traction sheave 22, to cause the ropes 24 to move therearound. The ropes 24 can therefore elevator a load such as an elevator cabin and, if used, a counterweight.
The feedback device 14 in figure 6 can comprise an encoder. The encoder 14 is provided mounted on an end the motor shaft 20, distal to the gear 18. It rotates with the rotor during operation of the motor 16. The encoder 14 can provide feedback to the drive unit 12 in order for it to control operation of the elevator system by controlling the supply of current to the motor 10. The drive unit 12 is supplied with electricity from a grid supply and can use the speed and position information from the encoder 14 to control the current supply to the motor. The drive unit 12 may itself contain a control means and/or it can be controlled by an external controller such as the elevator controller 10 in figure 6. The elevator controller 10 can control aspects of the operation of the system such as the set speed.
Figure 7 shows traces of speed, acceleration and speed selection commands for a system such as the one shown in figure 6. The traces in figure 7 are for a relatively long elevator journey similar to the journey depicted in figure 1 for the positioning method and conventional peak curve operation. However in figure 7 the system is operating under the improved control method, referred to herein as "comfort peak curve operation". As mentioned in the background section above, before operation of the elevator the elevator controller 10 will know the start and end points for the journey. It will also know the deceleration distance from a selected speed (such as the nominal speed) to the target position for the elevator. The drive unit 12 will not know the actual position of the elevator, and so must rely on the commands from the controller 10 in order to accurately control the elevator's movement. The drive unit will usually include storage means for storing profile parameters for the elevator such as a limit on magnitude of acceleration and/or a limit on rate of change of acceleration.
There are three distances shown by shaded regions under the speed versus time trace in figure 7. The first distance 70 is the area under the speed curve at the end of the acceleration phase, during the time period when acceleration of the elevator is changing from maximum acceleration down to zero acceleration (i.e. constant "nominal" speed). The second distance 72 is substantially identical to the first distance 70, and is a distance initially travelled by the elevator at nominal speed after the deceleration command has been given, before the elevator begins decelerating from its nominal speed down to the creep speed. The third distance 74 in figure 7 is the distance travelled during deceleration of the elevator from its nominal speed down to its creep speed. This third distance 74 is the same as the deceleration distance that would be defined for the elevator under conventional peak curve operation, as depicted in figure 1 herein, in order to decelerate the elevator comfortably from nominal speed down to creep speed.
The improved control method therefore makes use of a composite deceleration distance, which combines the deceleration distance 74 - which is determined during elevator set-up and is used for conventional peak curve operation - with a second distance 72 equal to the distance over which the magnitude of acceleration of the elevator previously changed from maximum to zero. It prompts issuance of the deceleration command from the elevator controller to the motor when the distance between the elevator's current position and the position at which it should reach its creep speed is equal to that combined deceleration distance. The controller can thus ensure that movement of the elevator from its start position to its target end position is smooth and accurate, regardless of whether the magnitude of the acceleration of the elevator at the time at which the deceleration command is issued is increasing, decreasing, constant or zero.
As can be seen in figure 7, making use of the improved control method for a long journey - during which the elevator has time to increase to nominal speed, stay at that nominal speed for a period of time and then decelerate - does not alter the trace of speed versus time for the elevator as compared to using the creep speed positioning method or conventional peak curve operation as depicted in figure 1. However, it does change the point in time at which the deceleration command is issued. Whereas in figure 1 the deceleration command is given immediately before deceleration must begin, in figure 7 the deceleration command is given during constant speed and before the elevator actually needs to begin decelerating. The drive 12 controls the motor 16 and so controls movement of the elevator after the deceleration command has been issued. The drive 12 measures or counts the distance travelled by the elevator after the deceleration command has been issued and so can control the motor 16 to begin decelerating when the distance travelled after issuance of the deceleration command is equal to the distance represented by the first distance 70 in figure 7, over which acceleration of the elevator reduced from maximum down to zero.
Figure 8 shows traces of speed, acceleration and speed selection commands versus time for the same elevator with the same profile parameters as figure 7, but for an elevator journey comprising a relatively short distance. Again, the elevator is controlled by comfort peak curve operation. In this example, comfort peak curve operation determines that the deceleration command is given during the acceleration phase, when acceleration has just reached a maximum. The acceleration is allowed to continue at the maximum value after the deceleration command has been issued and then reduce to zero before the elevator begins to decelerate. The point at time at which the magnitude of acceleration will begin to reduce in the journey shown in figure 8 is selected so that the total distance travelled by the elevator from the time at which the deceleration command is given to the time at which creep speed is achieved is equal to the combined deceleration distance as defined with respect to figure 7 above. Because that combined deceleration distance is known, along with the target end position and "creep distance", at which the elevator should have decelerated down to creep speed, it can issue the deceleration command at an appropriate time to ensure the elevator meets its target position comfortably and smoothly.
Furthermore, the improved control method ensures that the elevator travels the required distance between its start and end positions in the shortest possible time within the predetermined profile parameters, to enable a smooth, jerk-free journey.
Figure 9 shows traces of speed, acceleration and speed selection commands versus time for the same elevator with the same profile parameters as figures 7 & 8, for a different relatively short elevator journey, controlled according to comfort peak curve operation. In this example the deceleration command is given when the magnitude of the acceleration has already been at a maximum for a period of time. Once the deceleration command is issued, the magnitude of the acceleration begins to decrease. The acceleration then stays at zero for a short period of time, before the elevator begins decelerating down to the creep speed.
As for the journeys depicted in figures 7 and 8, the timing of the deceleration command for the journey shown in figure 9 is chosen so that the distance travelled by the elevator after issuance of that command and until the elevator reaches its creep speed is equal to the combined deceleration distance defined above with respect of figure 7. Because the combined deceleration distance for the journey comprises the distance that must be travelled in order for the elevator to reduce from maximum acceleration to zero acceleration at nominal speed plus the distance required for deceleration from nominal speed to creep speed, the comfort peak curve operation described herein enables the elevator to arrive at its creep speed position comfortably and thus to arrive at its target position at zero speed without overshooting. Furthermore, it does not require any adjustment of the profile parameters to ensure that the journey can be comfortable and safe. The elevator will approach its target position in as comfortable a manner as if it had been travelling at constant speed when the deceleration command was issued.
The improved control method or "comfort peak curve operation" described herein works when an elevator controller only knows and takes into account positions and distances during operation of the elevator. The controller need not consider speed of the elevator at any time during its journey in order to control its movement accurately between its start position and target end position. During set up of an elevator system, a deceleration distance will be defined for decelerating to creep speed from one or more selected elevator speeds. The improved control method described herein can be used successfully for an elevator system wherein only one selected or "nominal" speed is available and a deceleration distance is predetermined for that one nominal speed. Alternatively, the elevator system may be set up to be more complex, with two or more different speeds defined at which the elevator travel can plateau, with different respective deceleration distances defined for each. As long as the controller knows which speed will be used for a particular journey, it can use the respective deceleration distance and implement the improved control method described herein. Under the improved control method, as described in detail above, the controller will issue the deceleration command under consideration of the deceleration distance of the elevator before its target end position, and the creep position or creep distance in advance of that target end position at which the elevator should have decelerated to its relatively slow creep speed.
During operation of an elevator system the speed and acceleration of the elevator may be changed on a continuous basis to improve passenger comfort. Profile parameters will normally be set to ensure smooth transitions between, for example, acceleration and deceleration or between travel at constant speed and either deceleration or acceleration. Furthermore, it will be understood that if an elevator is accelerating at a point in time it cannot instantly begin to decelerate. Instead the movement of the elevator must be controlled to reduce the acceleration down to zero before deceleration can begin. The improved control method described herein ensures that the requirements for smooth transitioning and changing from acceleration to deceleration are met, whilst at the same time providing a straightforward and accurate way of timing deceleration commands to ensure accurate arrival of an elevator at a target end position in the shortest time possible, regardless of the distance to be travelled by the elevator between its start and end points.
The improved control method described herein can be implemented for any length of elevator journey and for any appropriate nominal or selected elevator speed(s) with associated deceleration distance(s). By way of example, for a nominal elevator speed of 1 m/s the deceleration distance may be in the region of 1.3 m to 1.5 m. The acceleration distance, for accelerating the elevator from zero speed to its nominal speed of 1 m/s, would be approximately the same. Therefore, referring to the examples described in detail above with respect to the figures, a relatively long elevator journey in this context would be one that is greater than 3 m whereas a relatively short journey would be between around 1.5 m and 3 m.
The improved control method described herein can be implemented for any suitable elevator system. Whilst the example system shown in figure 6 herein includes a gear, the elevator system may instead be gearless. The controller and drive are shown as separate units in figure 6 whereas it is possible for them to be implemented within a single unit. They may each have their own storage means or a combined storage means may be provided. The pulley system for the elevator may include any suitable number and arrangement of sheaves and ropes. There may be more than one elevator cabin or other load within the pulley system. There may also be a counterweight included in the elevator system.
In practice, operation of the elevator system and other means cooperating therewith can be run and controlled using any suitable hardware or software means. Instructions for controlling the operation may be recorded in a digital or analogue record carrier or computer readable medium. The record carrier may comprise optical storage means such as a readable disc or maybe in a form of a signal such as a focussed laser beam. A magnetic record carrier such as a computer hard drive may also be used for storage of instructions for controlling the elevator system described herein. Alternatively, solid state storage or any suitable signal recording may be employed.
The controller may include a computer or other suitable processing means, for example a CPU, and may be programmed to execute instructions for controlling operation of the elevator system. The processing means may also be used for controlling operation of other components of a system within which the elevator is comprised or with which it is associated. The processing means may also be used for recording and/or storing data relating to the elevator and/or other components.
A computer program may be provided for use in a controller or other processing means in order to implement the control of the elevator system. Such computer implementation may be used to provide automated control of the elevator system. Alternatively or additionally, operation and control of the elevator system may be carried out using any suitable combination of computer and user implemented steps.
Although the examples described in detail herein refer to elevator control, the improved control method can also be applied to other systems wherein a load is distance-controlled by a controller. For example the load could be an elevator, a stage hoist, a crane hoist or any other load that is controlled in this manner.
Although specific examples have been described herein and shown in the figures these are not intended to be limiting. In particular, the numerical values depicted in these figures are not limiting.

Claims

A method of controlling movement of a load from a known start position to a known target position, wherein the movement will comprise at least an acceleration phase and a subsequent deceleration phase;
said load being connected to a drive means, which is controlled by a controller;
said load having a predetermined movement profile including a nominal speed and a creep speed; said method comprising:
obtaining a first distance d₁ which is the distance that, according to the predetermined movement profile, the load must travel during its acceleration phase in order to reduce its magnitude of acceleration from maximum to zero, wherein at zero acceleration the load would be travelling at its nominal speed;

obtaining a second distance d₂ which is the distance that, according to the predetermined movement profile, the load must travel during its deceleration phase in order to reduce its speed from its nominal speed to its creep speed; and

issuing a deceleration command from the controller to the drive means during movement of the load when the distance D between the load's current position and a position at which it should be at creep speed is equal to the first distance d₁ plus the second distance d₂,
characterised in that,
in response to the deceleration command, regardless of whether the magnitude of the acceleration of the load at the time at which the deceleration command is issued is increasing, decresing, constant or zero, the drive means causes the load to be in a state of zero acceleration when the load has travelled the first distance d₁ after issuance of the deceleration command, and, after the load has travelled the first distance d₁, the drive means causes the load to decelerate according to the predetermined movement profile such that the load reaches the creep speed upon travelling the second distance d₂.
A method as claimed in claim 1 wherein the nominal speed is a maximum speed for the load, preferably wherein the creep speed is a relatively low speed that movement of the load must reach in advance of the known target position.
A method as claimed in any preceding claim wherein the movement profile for the load further comprises a predetermined limit on magnitude of acceleration and/or a predetermined limit on rate of change acceleration for the load.
A method as claimed in any preceding claim wherein the load would be travelling only instantaneously at the nominal speed at the end of the first distance d₁, before beginning to decelerate.
A method as claimed in any preceding claim wherein the load is allowed to continue accelerating at its current magnitude after issuance of the deceleration command if the load has not yet reached nominal speed.
A method as claimed in any preceding claim wherein the load is allowed to continue at nominal speed before beginning to decelerate if it had already reached nominal speed when the deceleration command is issued.
A method as claimed in any preceding claim wherein the load is allowed to continue accelerating and the magnitude of acceleration is allowed to continue to increase if it has reached not yet reached maximum acceleration and also not yet reached nominal speed when the deceleration command is issued.
A method as claimed in any preceding claim wherein the load is any of: an elevator, a crane hoist or a stage hoist.
A method as claimed in any preceding claim wherein, after issuance of the deceleration command, the drive means drives movement of the load so that it will be moving at the creep speed before reaching its known target position.
A method as claimed in any preceding claim comprising the step of controlling movement of the load so that it reaches its creep speed at a predetermined creep distance, before reaching its known target position.
A method as claimed in any preceding claim further comprising the step of issuing a stop command by the controller to the drive means after the deceleration command, to decelerate the load from its creep speed to zero speed at the known target position.
A drive system for controlling movement of a load from a known start position to a known target position, wherein the movement will comprise at least an acceleration phase and a subsequent deceleration phase;
said drive system comprising a load connected to a drive means and a controller arranged to issue control signals to the drive means;
said system further comprising a storage means for storing position and speed information for the load; wherein said controller is arranged to control movement of the load by:
obtaining a first distance d₁ which is the distance that, according to the stored position and speed information the load must travel during its acceleration phase in order to reduce its magnitude of acceleration from maximum to zero, wherein at zero acceleration the load would be travelling at its nominal speed;

obtaining a second distance d₂ which is the distance that, according to the stored position and speed information the load must travel during its deceleration phase in order to reduce its speed from its nominal speed to its creep speed; and

issuing a deceleration command to the drive means during movement of the load when the distance D between the load's current position and a position at which it should be at creep speed is equal to the first distance d₁ plus the second distance d₂, characterised in that, in response to the deceleration command, regardless of whether the magniude of the acceleration of the load at the time at which the deceleration command is issued is increasing, decresing, constant or zero, the drive means causes the load to be in a state of zero acceleration when the load has travelled the first distance d₁ after issuance of the deceleration command, and, after the load has travelled the first distance d₁, the drive means causes the load to decelerate according to the predetermined movement profile such that the load reaches the creep speed upon travelling the second distance d₂.
A drive system as claimed in claim 12 wherein the position and speed and information includes any of: a start position, a target position, a nominal speed or a creep speed for the load.
A drive system as claimed in claim 12 or claim 13 wherein the drive means includes a memory for storing profile information for the load such as a limit on the magnitude of acceleration and/or a limit on the rate of change of acceleration for the load.
A computer readable medium having computer-executable instructions configured to cause a computer system to perform a method of claims 1 to 11.