Intelligent safety door

Abstract

The present invention concerns a motorized door comprising an array of n detection cells distributed along the length of the leading edge, capable of detecting the presence and distance, x, from said detection cell of a body positioned between said detection cell and a distal transverse edge. The detection cells are coupled to a CPU which triggers different actions during the closing of the shutter, depending on the proportion, P=n1/n of the number, n1, of detection cells identifying the presence of a body at a same time located at a distance, xxs, wherein xs is a predefined safety distance. (a) if PPs, wherein Ps is a predefined safety proportion, the detected body is considered as an accidental obstacle and the CPU is programmed to instantly stop the movement of the shutter; (b) if P>Ps, the CPU considers that the detected body is a distal transverse edge defining the end of the closure run, and orders to decrease the closing speed of the shutter until the leading edge contacts the distal transverse edge.

Claims

1. A motorized door for closing an area, said area being defined by a first and second lateral edges which extend parallel to a longitudinal axis, X1, by a proximal transverse edge extending parallel to a transverse axis, X2, normal to the longitudinal axis, X1, and a distal transverse edge, transverse to the longitudinal axis, X1, wherein said motorized door comprises: (A) a shutter sized to close the area, and comprising a leading edge substantially parallel to the distal transverse edge of the area, (B) a motorized driving mechanism configured to move the leading edge of the shutter along the longitudinal axis, X1, between an open position, wherein the leading edge is adjacent to the proximal transverse edge and a closed position, wherein the leading edge contacts the distal transverse edge, in a first direction to close said area and in a second direction to open said area; (C) an array of n detection cells (s1, s2, . . . , sn), wherein n2, distributed along the leading edge of the shutter, each respective detection cell of said array of n detection cells being adapted to detect and communicate to a processing unit (CPU) a presence of a body and a distance, x, from said respective detection cell measured along the longitudinal axis, X1, to the body positioned between said respective detection cell and the distal transverse edge, (D) the processing unit (CPU) programmed to receive signals from each of the n detection cells and to trigger the following operations, in case a number n1 of the array of n detection cells, with n11, communicates to the CPU the detection of the presence of the body located at a distance, x, of less than or equal to a predefined safety distance, xs, from said detection cell, x<xs, during the moving in the first direction of the shutter at a service closing speed, v1, from the open position towards the closed position, (a) in case a proportion, P=n1/n, of respective detection cells of the array of n detection cells identifying the presence of the body at a same time located at the distance, xxs, is less than or equal to a predefined safety proportion, Ps, (PPs) the CPU is programmed to instantly stop the movement of the leading edge in the first direction, and optionally reverse said movement into the second direction; (b) in case the proportion, P, of respective detection cells of the array of n detection cells identifying the presence of the body at the same time located at the distance, xxs, is greater than the safety proportion, Ps, (P>Ps), the CPU is programmed to communicate a signal to progressively reduce the closing speed of the leading edge in the first direction, down to a stop upon contacting said body at x=0.

2. The motorized door according to claim 1, wherein the safety proportion, Ps, is from about 80% to about 100%.

3. The motorized door according to claim 1, wherein the array of n detection cells distributed along the leading edge of the shutter comprises at least 3 detection cells per metre of leading edge measured along the transverse direction, X2.

4. The motorized door according to claim 1, wherein the detection cells are selected among one or more of the following: ultrasonic sensors, optical sensors, capacitor sensors, radar sensors, and radio-frequency sensors.

5. The motorized door according to claim 1, wherein in case PPs, and all of the n1 detection cells of the array of n detection cells having detected the presence of the body communicate to the CPU that said body is located at a distance, x, greater than the predefined safety distance, xs, from each of said detection cells, x>xs, during the moving in the first direction of the shutter at the service closing speed, v1, from the open position towards the closed position, the CPU is programmed to trigger the following operations: (a) in case the distance, x greater than the predefined safety distance, xs, is greater than a precautionary distance, xp, which is predefined, keep closing the door at the service closing speed, v1, (b) in case the distance, x greater than the predefined safety distance, xs, is not greater than the precautionary distance, xp, reducing the closing speed to a reduced closing speed, v2<v1.

6. The motorized door according to claim 1, wherein the service closing speed, v1, is from about 0.25 to about 1 m/s.

7. The motorized door according to claim 5, wherein the reduced closing speed, v2, is from about 40% to about 80% of v1.

8. The motorized door according to claim 1, wherein the safety distance, xs=v1.Math.t.sub.imp, wherein t.sub.imp is a safety impact time required for the leading edge to cover the distance, xs, at the service closing speed, v1, and wherein t.sub.imp is from about 0.5 to about 3 s.

9. The motorized door according to claim 1, wherein in case the proportion, PPs, as defined in claim 1 (a), after instantly stopping the movement of the leading edge in the first direction, the CPU is programmed to reverse said movement into the second direction until the leading edge reaches a waiting position, Xw, where it stops for a waiting time, tw, before resuming its movement in the first direction as long as no body is detected by the detection cells.

10. The motorized door according to claim 9, wherein after instantly stopping N times the movement of the leading edge in the first direction, the CPU is programmed to reverse said movement into the second direction until the leading edge reaches the open position, wherein N is from 2 to 5 times.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) For a fuller understanding of the nature of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings in which:

(2) FIG. 1: shows a door according to the present invention, with (a) a front view and (b) a bottom view.

(3) FIG. 2: shows three embodiments of motorized doors according to the present invention.

(4) FIG. 3: shows a flow chart of the actions the CPU is programmed to trigger depending on the events according to an embodiment of the present invention.

(5) FIG. 4: shows (a) a door according to the present invention, wherein the leading edge approaches the floor forming the distal transverse end, and (b) the information received by the CPU from the various detection cells indicating that all detection cells identified a body at a distance <xs, construed by the CPU as being the distal transverse end.

(6) FIG. 5: shows (a) a door according to the present invention, wherein the leading edge approaches the floor forming the distal transverse end with a car parked underneath, and (b) the information received by the CPU from the various detection cells indicating that a proportion, P<Ps; of the detection cells identified a body at a distance >xs, construed by the CPU as an accidental obstacle located at a safe distance from the leading edge.

(7) FIG. 6: shows the car still parked underneath, and (b) the information received by the CPU from the various detection cells indicating that a proportion, P<Ps; of the detection cells identified a body at a distance <xs, construed by the CPU as an accidental obstacle located at a short distance from the leading edge and involving a risk of impact.

(8) FIG. 7: shows (a) a door according to the present invention, wherein the leading edge approaches the floor forming the distal transverse end with a raised deck of a lorry parked underneath, and (b) the information received by the CPU from the various detection cells indicating that a proportion, P>Ps; of the detection cells identified a body at a distance <xs, construed by the CPU as being a distal transverse end.

(9) FIG. 8: shows (a) a door according to the present invention, wherein the leading edge approaches the floor forming the distal transverse end with a person standing underneath, and (b) the information received by the CPU from the various detection cells indicating that a proportion, P<Ps; of the detection cells identified a body at a distance <xs, construed by the CPU as an accidental obstacle located at a short distance from the leading edge and involving a risk of impact.

(10) FIG. 9: shows a door according to the present invention with the shutter (a) open, and (b) closed.

(11) FIG. 10: shows a perspective view of a door according to the present invention.

(12) FIG. 11: shows an example according to the present invention of a leading edge provided with an array of detection cells and with resilient lips.

(13) FIG. 12: the time dependent movement of the shutter of a door according to the present invention in case (a) no accidental obstacle is identified (P>Ps) and (b) in case an accidental obstacle (a person) is identified, according to a preferred embodiment.

DETAILED DESCRIPTION OF THE INVENTION

(14) As illustrated in FIG. 1, a motorized door according to the present invention is for closing a quadrilateral area (20) defined by a first and second lateral edges (20L) which extend parallel to a longitudinal axis, X1, by a proximal transverse edge (20P) extending parallel to a transverse axis, X2, normal to the longitudinal axis, X1, and a distal transverse edge (20D), transverse to the longitudinal axis, X1. In most cases the distal transverse edge is parallel to the proximal transverse edge and to the transverse axis, X2, but this is not necessarily the case. The area comprises an opening to be closed with a shutter (1) of dimensions suitable for closing the area and the opening comprised therein. The shutter comprises a leading edge (1L) substantially parallel to the distal transverse edge (20D) of the area. The motorized door comprises a motorized driving mechanism (5) suitable for moving the leading edge (1L) of the shutter along the longitudinal axis, X1, over a distance x1=x1,0x1,1, between an open position (x1,1), wherein the leading edge is adjacent to the proximal transverse edge (cf. FIG. 9(a)) and a closed position (x1,0), wherein the leading edge contacts the distal transverse edge (cf. FIG. 9(b)). The leading edge can move in a first direction () to close said area and in a second direction () to open said area (cf. arrows & in FIGS. 1&2).

(15) As shown in FIG. 2(a) the shutter can be a flexible shutter in the form of a flexible fabric or curtain, and the motorized driving mechanism (5) drives the rotation of a drum (2) to move the leading edge (1L) in the first direction () to close the area by unwinding the flexible shutter from said drum, and to move it in the second direction () to open said area by winding the flexible shutter about said drum.

(16) FIG. 2(b) illustrates a deformable shutter comprising rigid panels (1P) hinged to one another parallel to the transverse axis, X2, wherein the motorized driving mechanism (5) drives the rotation of an axle about which the hinged panels rotate and change direction. For example, radial pins or teeth in the axle may cooperate with openings within the hinges between panels to ensure a slip-free movement of the deformable shutter. Alternatively, cables or chains can be used to drive the movement of the shutter.

(17) FIG. 2(c) shows a third type of shutter in the form of a rigid shutter, wherein the motorized driving mechanism (5) drives the rotation of an axle which moves the rigid shutter in the plane of said area in the first and second directions &. A gear system is illustrated in FIG. 2(c), but any means known to a person skilled in the art for moving up and down a rigid shutter, such as cables or chains can be used without affecting the present invention.

(18) In case of a vertical area (20) as illustrated in FIGS. 1&10, a shutter is a surface defined by a leading edge (1L) moving up () and down (), said leading edge bridging two lateral edges parallel to one another. Regardless of the type of shutter used, the lateral edges are preferably engaged in guiding rails (47) suitable for guiding the shutter in its trajectory when opening or closing the area (20). An example of an automatic door comprising lateral edges of a shutter coupled to guiding rails is given e.g., in EP0587586 or WO2008155292, the contents of which are herein incorporated by reference.

(19) A motorized door according to the present invention must also comprise an array of n detection cells (s1, s2, . . . , sn), wherein n2, distributed along the leading edge of the shutter. Each detection cell is suitable for detecting and communicating to a processing unit (CPU) the presence and distance, x, from said detection cell measured along the longitudinal axis, X1, of a body positioned between said detection cell and the distal transverse edge.

(20) The gist of the present invention is the control system, driven by a processing unit (CPU) which is programmed to receive signals from each of the n detection cells, either continuously, or at regular intervals. Energy can be saved by activating the detection cells only when the leading edge is moving in the closing direction, a. For high speed doors, a continuous communication between detection cells and CPU is preferred or, in case of intermittent communication, the frequency of emitted signals should be high, preferably greater than 1 signal per second. When, during the moving in the first direction () of the shutter at a service closing speed, v1, from the open position (x1,1) towards the closed position (x1,0), a number n1 of the n detection cells, with n11, communicates to the CPU the detection of the presence of a body located at a distance, x, of not more than a predefined safety distance, xs, from said detection cell, x<xs, the CPU is programmed to trigger the following operations depending on the proportion, P=n1/n, of detection cells having detected a body.

(21) In case the proportion, P=n1/n, of detection cells identifying the presence of a body at a same time is not more than a predefined safety proportion, Ps, (PPs) the CPU is programmed to instantly stop the movement of the leading edge in the first direction (). The CPU may optionally be programmed to then reverse said movement into the second direction () to drive the leading edge away from the identified body. This optional reversal of the shutter movement depends inter alia on the value of the safety distance, xs: for high values of xs, a reversal may not be necessary; for short safety distances, xs, a reversal may be advisable.

(22) In case, however, the proportion, P=n1/n, of detection cells identifying the presence of a body at a same time is greater than the safety proportion, Ps, (P>Ps), the CPU is programmed to communicate a signal to progressively reduce the closing speed of the leading edge in the first direction (), down to a stop upon contacting said body at x=0 of the detection cell located closest to said body (cf. FIG. 12(a)).

(23) By considering the proportion, P=n1/n, of detection cells identifying the presence of a body at a same time, the CPU is able to distinguish between: an actual accidental body, such as a person as illustrated in FIG. 8 or an object like an automobile (as illustrated in FIGS. 5&6, which contact with the leading edge of the shutter should be avoided, and a distal transverse edge (20D) defining the end of the run of the shutter for closing the area (20), as illustrated in FIGS. 4&7, the latter showing a provisional raised deck formed by the platform of the trailer of a lorry.

(24) This system is highly advantageous, because it requires no metering system capable of determining the instant position of the leading edge. Such systems can be unreliable, for example if counting the number of revolutions of a drum (2) carrying a flexible shutter wound around it, or not readily available or easy to install in existing doors, in case for example of optical sensors counting markers distributed along an edge of the shutter. Furthermore, a metering system is not capable of taking account of a provisional raised deck as illustrated in FIG. 7, which may be formed by a ramp or by the platform of a trailer parked across the plane of the area (20).

(25) By distinguishing between accidental obstacles and distal transverse edges (even if not at a fixed position), by means of the proportion, P=n1/n, of detection cells identifying the presence of a body at a same time, and by considering the closest distance, x, of said body from a detection cell with respect to a safety distance, xs, a motorized door according to the present invention can be run with a high level of security, in accordance with the requirements of EN12453 and, at the same time smoothly closing an area, contacting the distal transverse edge (20D) at nearly zero velocity. The detection of an obstacle and its identification by the CPU allows for the use of motors of lower power, since quick starts and stops are operations driving motor size and therefore also cost (of the motor and its power consumption), and said operations can be avoided with the present invention.

(26) The safety proportion, Ps, of detection cells identifying the presence of a body at a same time used to trigger the sudden stopping of the shutter (if PPs), or the slowing down of the closing velocity of the shutter (if P>Ps) depends on the number, n, of detection cells, and their position along the leading edge of the shutter. The safety proportion, Ps, is generally comprised between 80% and 100%, preferably between 90% and 100%. If Ps=100%, a body detected by (some of) the detection cells (si) will be considered as the distal transverse edge only in case all the detection cells identify the presence of said body at a same time. In case of a vertical shutter as illustrated in FIGS. 1&4, the distal transverse edge is usually formed by the floor, which will necessarily be identified by all the detection cells together. A lower value of Ps, between 80 and less than 100% makes sense in case the position of the distal transverse edge may vary with time. It could be formed by a raised deck such as a ramp or the platform of the trailer of a lorry, as illustrated in FIG. 7. In this case, the detection cells located closest to the lateral edges (20L) of the area (20) may not identify the presence of a raised deck, and yet the stopping of the shutter may not be desirable, since the leading edge of the shutter should continue its movement until it reaches the level of the raised deck.

(27) Although two detection cells (n=2) are theoretically sufficient to carry out the present invention, it is preferred to have a higher number of detection cells distributed along the leading edge of the shutter For example, the array of n detection cells distributed along the leading edge of the shutter preferably comprises at least 3, preferably at least 4, more preferably at least 5 detection cells per metre of leading edge measured along the transverse direction, X2. A higher number of detection cells allows a safer distinction by the CPU between an accidental obstacle and a distal transverse edge. On the other hand, a higher number of detection cells increases the cost of the door. By increasing the angle of the area covered by each detection cell, it is possible to cover the whole area below the door's leading edge. This, however, is at the expenses of a lower accuracy of the definition of the shape of an object detected within the trajectory of the leading edge. A good balance between the requirements and cost of the door must be found in each particular case, a task which is well within the skills of a person of the art.

(28) To further increase the security of the door in case of PPs (i.e., detection of a body considered by the CPU as an accidental obstacle), the CPU may also consider the case wherein all of the n1 detection cells having detected the presence of a body communicate to the CPU that said body is located at a distance, x, greater than the predefined safety distance, xs, from each of said detection cells, x>xs, during the moving in the first direction () of the shutter at the service closing speed, v1, from the open position (x1,1) towards the closed position (x1,0). If such situation happens, the CPU can thus be programmed to trigger the following operations: (a) In case the distance, x, is greater than a precautionary distance, xp, keep closing the door at the service closing speed, v1, (b) In case the distance, x, is not greater than the precautionary distance, xp, reducing the closing speed to a reduced closing speed, v2<v1, as illustrated in FIG. 12(b). The reduced closing speed, v2, can typically be comprised between 40% and 80% of v1, preferably between 50% and 75% of v1.

(29) FIG. 3 shows a flow chart illustrating various steps triggered by the CPU depending on the situation. Starting from an open door, the leading edge is moved along the longitudinal axis, X1, at a service closing speed, v1, as long as no body is detected by any detection cell (si). If a body is detected at a distance, xxs, the CPU considers the proportion, P=n1/n, of detection cells identifying the presence of a body at a same time. If the proportion, P, is smaller than or equal to the safety proportion, Ps, (PPs) the CPU considers that the detected body is an accidental obstacle and stops the movement of the shutter. If, on the other hand, the proportion, P, is larger than the safety proportion, Ps, (P>Ps) the CPU considers that the leading edge is approaching the distal transverse end and reduces the speed of the leading edge, until it reaches the distal transverse edge at which point the leading edge is stopped, as illustrated in FIG. 12(a).

(30) According to a preferred embodiment described above, in case PPs, but none of the detection cells has identified an object at a distance less than xs, (x>xs for all of the n1 detection cells), the CPU considers a predefined precautionary distance, xp>xs, above which the leading edge continues its run at the service closing speed, v1, and below which the leading edge slows down to a closing speed, v2<v1, as illustrated in FIG. 12(b).

(31) According to another embodiment of the present invention indicated in FIG. 3 and illustrated with the dashed lines in FIG. 12(b), in case the proportion, PPs, i.e., a detected body is considered as an accidental obstacle, after instantly stopping the movement of the leading edge in the first direction (), the CPU is programmed to reverse said movement into the second direction () until the leading edge reaches a waiting position, Xw, where it stops for a waiting time, tw, before resuming its movement in the first direction () as long as no body is detected by the detection cells. The waiting position can be defined as a fixed position along the longitudinal axis, X1, or, alternatively, can vary with the position of impact, such as Xw=X.sub.stop+Xw, wherein X.sub.stop is the position where the leading edge stopped, and Xw is a clearance distance. If the cell detectors fail to identify the presence of the body, as illustrated in FIG. 12(b) with the shaded and crossed out figure, who simply walked out of the door, the leading edge continues its run until it reaches the distal transverse edge (as shown in FIG. 12(a)). On the other hand, if after instantly stopping N times the movement of the leading edge in the first direction (), because the identified body is still detected at its original location, the CPU is programmed to reverse said movement into the second direction (), until the leading edge reaches the proximal transverse edge and stops there in an open position, as shown in the lower boxes of the flow chart of FIG. 3. The number, N, of repetitions before the shutter opens definitely is preferably comprised between 2 and 5 times.

(32) The value of the predefined safety distance, xs, depends very much on the service closing speed, v1, of the shutter, as it determines the time required for stopping the leading edge before impact. The safety distance can therefore be defined as, xs=v1.Math.t.sub.imp, wherein t.sub.imp is a safety impact time required for the leading edge to cover the distance, xs, at the service closing speed, v1. To be on the safe side, t.sub.imp is preferably comprised between 0.5 and 3 s, preferably, between 0.8 and 2 s. Service closing speeds, v1, comprised between 0.25 and 1 m/s, preferably between 0.5 and 0.8 m/s, are representative of fast doors. With a service closing speed of 0.75 m/s, and a safety impact time of the order of 1 s, yields a safety distance, xs=0.751=0.75 m, whilst with a service closing speed of 0.5 m/s, and a safety impact time of the order of 0.8 s, yields a safety distance, xs=0.50.8=0.4 m.

(33) The detection cells (si) are preferably selected among one or more of the following: ultrasonic sensors, optical sensors, capacitor sensors, radar sensors, radio-frequency sensors, and the like. As illustrated in FIG. 11, the leading edge of the shutter is preferably provided with resilient lips with locations for the fixing of the detection cells (si). Such resilient lips have multiple advantages. First they absorb part of the impact force in case an impact between the leading edge and a body should happen. Second they protect the detection cells when the leading edge contacts the distal transverse edge. Third, they focus the radiation emitted by the detection cells to a more specific area. As illustrated in FIG. 11, the resilient lips can be formed by a first and second lips extending parallel to one another along the transverse direction, X2. Partition wall coupling one lip with the other (not shown in FIG. 11) can be provided to (a) stiffen the resilient lip structure, and (b) to further focus the radiation emitted by the detection cells in all directions.

(34) FIGS. 4 to 8 show different situations managed by a motorized door according to the present invention. In these examples, a shutter comprising an array of n=11 detection cells (s1-s11) is illustrated, with a preset value of the safety proportion set at 80%, Ps=80%. In FIGS. 4(a) to 8(a) are represented the same motorized door with different bodies identified by the detection cells (s1-s11). In FIGS. 4(b) to 8(b) are represented the distances, xi, separating each detection cell (si) from the identified body. The safety distance, xs, is illustrated with a horizontal dashed line in the graphs (b) of FIGS. 4 to 8. The value of P=n1/11 of detection cells identifying the presence of a body at a same time located at a distance, xxs, is indicated in each Figure.

(35) In FIG. 4, all the detection cells identified a body located at a distance, xxs=constant. With a proportion, P=100%, of detection cells identifying the presence of a body at a same time located at a distance, xxs, the CPU concludes that no accidental obstacle was detected by the detection cells (si), and that the detected body can only be the distal transverse edge. Consequently, as illustrated in FIG. 12(a), the CPU orders the command system to reduce the closing speed until the leading edge (1L) contacts the distal transverse edge (20D).

(36) In FIG. 5, a car is parked through the door. The detection cells have identified the presence of the car but it is still remote from the leading edge, with no detection cell identifying a distance xxs. Two detection cells, s8 and s9, however, are located closer than the precautionary distance, x8&x9xp. According to a preferred embodiment of the present invention, the CPU may therefore order the command system to reduce the closing speed from v1 to v2<v1, as shown with the solid line in FIG. 12(b).

(37) In FIG. 6, the leading edge keeps moving in the first direction () getting closer to the car which has not moved. Three detection cells now identify the presence of the car at a distance xxs. The proportion, P=3/11=27% is smaller than the safety proportion, Ps=80%. The CPU therefore considers the detected car as an accidental obstacle and stops the movement of the leading edge. In case, as illustrated in FIG. 12(b), the leading edge was moving at a reduced closing speed, v2, the stopping of the leading edge can be completed very rapidly.

(38) In FIG. 7 the trailer of a truck is parked across the door. The flat platform of the trailer forms a raised deck occupying almost the whole width (in the transverse direction, X2) of the door opening. All the detection cells si, but s1 and s11, detected the presence of the platform at a distance xxs. The proportion, P=9/11=82%, which is higher than the safety proportion, Ps=80%. Consequently, the CPU considers the raised platform as a distal transverse edge (20D) and orders the command control to reduce the speed until the leading edge contacts the platform, as illustrated in FIG. 12(a).

(39) FIG. 8 is quite similar to FIG. 6, but the detected body is a human body, with more serious consequences in case of impact with the leading edge. Two detection cells only, s6&s7, detected the presence of the human body located at a distance xxs. The proportion P=2/11=18%<Ps=80%. As illustrated in FIG. 12(b), solid line) the CPU therefore considers the detected human body as an accidental obstacle and stops the movement of the leading edge.

(40) Unlike the motorized doors of the prior art, a motorized door according to the present invention can distinguish whether an identified body is a distal transverse edge, including a non-permanent raised deck, or an accidental obstacle, and triggers different control procedure of the closing of the shutter accordingly. With a better prediction of the possible stopping of the shutter, a smaller motor can be used. Furthermore, the detection cells can be mounted very easily on the leading edge of existing doors, and coupled to a CPU either by cable or by wave (e.g., Bluetooth). The control of the detection cells can be coupled to the existing CPU originally controlling the movements of the door. Safety and closure efficacy are both enhanced with a motorized door according to the present invention.

(41) TABLE-US-00001 REF DESCRIPTION 1 shutter 1B shutter bead 1L leading edge of shutter 1P rigid panel of an articulated shutter 2 rotating drum 4 guiding rails 5 motor 20 area to be closed and opened 20D distal transverse edge of area 20L first and second longitudinal edges of area 20P proximal transverse edge of area 30 wall surrounding the area first direction of leading edge displacement to close the area second direction of leading edge displacement to open the area CPU processing unit n number of detection cells at the leading edge n1 number of detection cells having detected an object P proportion, n1/n, of detection cells having detected an object Ps safety proportion s1, detection cells 1 to n . . . sn t.sub.imp safety impact time, t.sub.imp = xs/v1 tw waiting time at Xw before closing the door again v1 service closing speed v2 reduced closing speed X1 longitudinal axis X2 transverse axis, normal to X1 x1 instant distance of the leading edge from the distal transverse edge 20D x1,0 position of leading edge when the area is closed by shutter x1.1 position of leading edge when the area is open Xstop stop position of the leading edge Xw waiting position after reversing the door movement x actual distance between a detection cell and a body measured along X1 xp precautionary distance between a detection cell and a body measured along X1 xs safety distance between a detection cell and a body measured along X1 Xw clearance distance from stop position