TIME CONSUMED WHEN STOPPING (ts)

The parameter ts involves evaluation of flight and door times. The time consumed when stopping is given by Definition 4.22 as

(5.23) which can be expressed in terms of Equation (4.14) as:

(4.14)

The lift performance time (T) has the most significant effect on the round trip time. It is defined as the period of time between the instant (when a stationary) lift starts to close its doors and the instant when its doors are open by 800 mm at the next adjacent floor (Definition 4.23). The time to transit two

adjacent floors at rated speed (tv) was dealt with in the previous section.

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5.8.1 Cycle Time (Definition 4.24) and Other Times

There can be some confusion regarding the meaning of flight time, performance time and cycle time and also when door opening time is considered to be finished.

Figure 5.3(a) is the usual operating cycle, without advanced door opening. This begins with passengers transferring into the car, the doors closing, the interlocks making up and the car moving (brake to brake time). When the car stops moving the doors open and the passengers transfer out of the car and some passengers may transfer into the car.

Figure 5.3(b) illustrates what happens when the lift is supplied with the advance door opening feature. Here some of the time of the door opening is shared with the levelling operation. That is the doors open BEFORE the lift has finished moving. This feature can reduce the cycle and performance times by

between 0.5 s to 1.7 s.

The cycle time is measured from some consistent point in the cycle, ie: when the doors are closed, or when the doors are just opening. The measurement of cycle time is made with no passengers entering or leaving the car. The cycle time thus includes any car/landing door dwell times, see Section 5.11. Figure 5.3(c) shows the operating cycle for a lift responding to a car call and Figure 5.3(d) shows the operating cycle for a lift responding to a landing call. Cycle time therefore includes time which might be wasted if a car call is registered in error and when the lift stops no one leaves; or when a landing call is registered and when the lift stops no one enters.

Performance time is the most important variable, as this can be controlled and predicted. The

components of the performance time must be carefully selected to achieve the correct handling capacity for the lift installation. The lift maker should be contracted at the tender stage to provide them at the specified values and the maintenance contractor should be required to keep them at the rated values throughout the life of the installation. Failure to do so will invalidate any traffic design. The equation for the performance time is given by:

(5.24) 5.8.2. The Single Floor Flight Time

The single floor flight time tf(1) is the time taken from the instant the car doors close to the instant the car is level with the next adjacent floor (Definition 4.20). It is dependent on the rated speed, the

acceleration value and the jerk value. Jerk, sometimes called “shock” is the rate of change of

acceleration (units in m/s3). The relationships between distance travelled, velocity, acceleration and jerk are complex and are given in detail in Chapter 7 and Appendix 1. Flight times need to be obtained for any distance or number of floors travelled.

Fortunately for designers of lift drives there are limits on the maximum values of both acceleration and jerk. These constraints are imposed by human physiology, as described in Chapter 4. Passengers are uncomfortable when subjected to acceleration values greater than about one sixth of the acceleration due to gravity (ie: about 1.5 m/s2). Similarly, the maximum value of jerk commonly used in calculations is about 2.2 m/s3, although there is no drive control on this variable.

As a result of these limits there is little or no difference in single floor flight times for rated speeds in excess of about 5.0 m/s, as the maximum possible values of acceleration and jerk have been reached. Below 5.0 m/s, the flight times are dependent on the type of drive and drive controller, mainly owing to variations in levelling times and non-ideal acceleration deceleration profiles.

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Figure 5.3 Illustration of lift system timings

Table 5.3 indicates the likely range of acceleration values and single floor flight times. The single floor flight times are slightly larger than a theoretical calculation would give to allow for start-up delays. Different manufacturers and drive systems will result in small variations in the values given. Naturally the flight times also depend on the interfloor distance. Where the higher speeds have the most effect is where a lift serves a high zone in a building and has to pass non-stop through a number of lower floors. 5.8.3 Door Operating Times

5.8.3.1 General

Door operating times comprise opening and closing times, and door dwell times. The dynamic operating (opening and closing) times are dependent on a number of factors: door panel velocity, panel

arrangement, width and control.

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There is a limit to door panel velocity commensurate with passenger safety. The European and US Standards require that the energy present in a moving door should not exceed 9.5 J (joules) and 10.0 J (respectively). This restriction applies mainly to closing doors. The restriction has the effect of limiting the maximum door velocities during closing to about 300 mm/s. Doors can operate faster if they are not allowed to touch a passenger. However, this involves the use of complex (and sometimes expensive) passenger detection and door control systems.

There are two basic door types: side opening and centre opening. Side opening doors have to open the whole width of the doorway, which takes more time. Here the width is taken as the clear opening width ignoring any returns or architraves. Centre opening doors open and close more quickly and the

symmetrical reaction against the car frame will reduce car sway.

There are several standard widths. Narrow doors of 800 mm width are usually fitted to cars with a rated car capacity of up to 12 persons. Wider doors of 1100 mm width are fitted to lifts with a rated car

capacity of over 12 persons. Doors of 1300 mm width or larger are fitted to goods lifts and hospital lifts. Obviously, the narrower the door, the faster the operation.

The control of the door operator can significantly affect door timings in respect of start-up, slow down and safety. There are a number of types usually rated according to their operating speed and method of control of the door operator (open or closed loop). The speeds are not well defined and in broad brush terms are defined as: low (about 300 mm/s), medium (about 450 mm/s) or high speed (about 750 mm/s). Generally a low speed operator will be found on a low speed lift and obviously cost less than a high speed operator. Low speed operators are often characterised by delivering the same opening and closing times.

5.8.3.2 Door closing time (tc)

Door closing always takes place whilst the lift is stationary, and typical door closing times are given in Table 5.5. The door closing time (tc) is the time taken from the instant the car doors start to close to the time they are locked up. Remember the energy constraints of the previous section.

5.8.3.3 Door opening time (t0)

Door opening time is not subject to the energy constraints found in door closing and can be much faster. The doors can operate at any speed provided the trapping hazard for fingers, etc. against the door architrave or door lining is negligible. However, as the same door operator will be used for both directions of movement, opening times may not be much improved. There are two cases of door opening to be considered: with and without advanced door opening.

Where the advanced door opening time feature is not installed, the door opening time is considered to have ceased, when the passenger transfer may begin. This usually can occur when the doors are open by approximately 800 mm. Thus in this case the door opening time is taken to be the time from the instant the doors start to open until the instant the doors are open to a width of 800 mm.

Time can also be saved by advanced door opening. Once the car has entered the door zone some 200 mm from a landing, the doors can be unlocked and opened. Then an improvement in opening times can be achieved by overlapping the levelling operation with the first part of the opening of the doors called advanced door opening, or

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pre-opening. This is possible within the door zone, provided that the tripping hazard is negligible. The door opening value to be used in this case in the evaluation of the parameter ts is the time from the moment the lift is level at the landing, until the doors are open by 800 mm. This time will be less than the measured door opening time for lifts without advanced opening, viz: t0−tad, where tad is the time saved by opening the doors during levelling.

Typical door opening times are given in Table 5.6 for normal and advanced opening. The table gives representative values for two door types, two door sizes, and with and without advanced door opening. These values may be used where specific values are not available.

Table 5.6 Typical door closing and opening times (s) for stated door width (mm)

Door operation Opening (advanced) Opening (normal) Closing

Door type 800 1100 800 1100 800 1100

Side 1.0 1.5 2.5 3.0 3.0 4.0

Centre 0.5 0.8 2.0 2.5 2.0 3.0

5.8.3.4 Door weight

The weight1 of the door is determined by many factors, such as fire resistance, height, width, configuration, etc. A moving door gathers considerable kinetic energy. To protect passengers from injury, the standards require the maximum energy to be limited to 10 J, provided the safety edge is operative. If the safety edge is inoperative then the energy value must not exceed 4 J. The maximum values of energy acquisition limit the maximum door speed when closing. Typically a 150 kg door has a maximum speed of 0.23 m/s and a 500 kg door has a maximum speed of 0.13 m/s. For a particular door weight (M), the maximum speed (s) at which the doors may move to meet the energy value requirements are given in Table 5.7.

Table 5.7 Maximum door movement speeds for different weight of doors

Total door weight (kg) Maximum speed for 10 J (m/s) Maximum speed for 4.0 J (m/s)

150 0.36 0.23 200 0.31 0.20 250 0.28 0.18 300 0.25 0.16 350 0.23 0.15 400 0.22 0.14 450 0.21 0.13 500 0.20 0.13

Where the weight of a door is not known, the weight can be approximately estimated by assuming: A painted hoistway door weighs 35 kg/m2

Painted car doors weigh 24 kg/m2 Hangers per door weigh 10 kg

Other hardware (vanes, operating arms, safe edges, etc.) per system weigh 5 kg 1Purists will say mass.

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5.8.3.5 Example 5.4

A 1100 mm single panel side opening door has an area of 2.5 m2. Calculate the door closing time.

Hoistway door weighs 87.5 kg

Car door weighs 60.0 kg

Hangers weigh 20.0 kg

Other hardware weighs 5.0 kg

172.5 kg From Table 5.7 (by interpolation) the maximum door speed is 0.34 m/s.

It is the practice to measure door closing times from a point 50 mm from the open and closing jambs. This allows for the acceleration and deceleration time periods at the extremes of travel. Thus the door will move the 1.0 m in 2.94 s.

The actual door closing time will be longer than this to allow for the acceleration and deceleration of the door panels. Add 1.0 s to account for this giving a door closing time of some 4.0 s.