Field of the Invention

[0001] The invention relates to a door system for a loading dock which is part of an industrial or commercial building such as, for example, a warehouse or storage facility, at which goods are loaded or unloaded from a road vehicle, such as, for example, a lorry. The invention also relates to a building comprising a door system.

Background to the Invention

[0002] Often, a building has a number loading docks in a row along one wall. Each loading dock typically comprises a door such as, for example, a vertical roller door. The door may be hydraulically operated, in which case it will have an hydraulic actuator which is controlled by a control unit.

[0003] Following loading or unloading of a vehicle, the door may be left open unnecessarily, typically because an operator forgets to close it, which results in loss of heat from the building.

Summary of the Invention

[0004] According to a first aspect, the invention provides a loading dock door system comprising: a door for an opening having an in direction in which, when the door is open, the people go through the opening from one side to the other, and an out direction in which, when the door is open, people go through the opening in a direction opposite to the in direction; a people sensor; and a control unit for operating the door; wherein the sensor senses the number of people going through the opening in the in direction and the number of people going through the opening in the out direction, and wherein, when the people in num- ber and the people out number are equal, the control unit responds by closing the door.

[0005] Aptly, the control unit comprises a timer unit which causes the control unit to delay closing the door until a time period after the people in number and the people out number are equal. The control unit may comprise a programmed logic controller (PLC) or a microcontroller.

[0006] Aptly, the system comprises an actuator and, in response to actuation of the actuator, the control unit opens the door.

[0007] Aptly, the system comprises a door sensor which detects when the door is closed and, in response, the control unit resets the sensor.

[0008] Aptly, the people sensor shines at least two beams of radiation across the opening, wherein the beams are horizontally spaced apart, wherein the sensor senses when each of the beams is broken, and wherein sensing a sequential breaking of the beams in the in direction is counted as a person going through the opening in the in direction and sensing a sequential breaking of the beams in the out direction is counted as a person going through the door in the out direction. Further aptly, the sensor comprises a laser emitter and detector unit, and a reflector unit, wherein the laser emitter and detector unit shines the at least two laser beams across the opening to the reflector unit, from where the at least two beams are reflected to the emitter and detector unit, which senses when a beam shone from the emitter and detector unit to the reflector unit and back again is broken.

[0009] The system may comprise an indicator lamp indicating whether the door is staying open or be closed, and an alarm warning that the door is to be closed.

[0010] According to a second aspect, the invention relates to a building comprising a loading dock door system according to the first aspect.

Brief Description of the Drawings

[0011] Figure 1 is a front view of a warehouse having three loading docks, each comprising a door system according to the invention;

[0012] Figure 2 is a front view of one of the loading docks shown in Figure 1 , with its door in the open position; [0013] Figure 3 is a cross sectional top view taken along the line Ill-Ill in Figure 2; and

[0014] Figure 4 is a schematic layout of a loading dock door system according to the invention. Detailed Description of the Illustrated Embodiment

[0015] With reference to Figure 1 , a warehouse indicated generally at 1 has a front wall 2 and a raised floor 4. The warehouse 1 also has three loading docks 6a, 6b, 6c along the wall 2. Each loading dock 6a, 6b, 6c comprises a vertical roller door 8a, 8b, 8c for a corresponding opening 10a, 10b, 10c in the wall 2.

[0016] With further reference to Figures 2, 3 and 4, the wall 2 has an inside surface 24. An hydraulic actuator 12, mounted above the door on the inside surface 24 of the wall 2, makes 8 the door move up and down. The hydraulic actuator 12 is controlled by a control unit 14 which comprises a PLC (not shown). Associated with the door is a switch 16. When it is desired to load or unload a vehicle (not shown), an operator (not shown) actuates switch 16, in response to which the control unit 14 controls the hydraulic actuator 12 to move the door 8 up to the open position.

[0017] The opening has right side surround 26 and left side surround 28. A people sensor 18 comprises a laser emitter and detector unit 20 and a reflector unit 22. The laser emitter and detector unit 20 is mounted on the inside surface 24 of the wall 2, adjacent one of the two side surrounds 26, 28 of the opening 10, and the reflector unit 22 is mounted on the inside surface 24 of the wall 2, adjacent the other of the two side surrounds 26, 28 of the opening 10. Both the emitter and detector unit 20 and the reflector unit 22 are mounted about 600mm off the ground. In other words, the emitter and detector 20 unit and the reflector unit 22 are mounted in an opposing, facing relationship.

[0018] The laser and detector unit 20 comprises first and second lasers 30a, 30b and first and second photo detectors 32a, 32b. The reflector unit comprises first and second reflectors 34a, 34b. A first laser beam 36a is shone from the first laser 30a to the first reflector 34a and back to the first detector 32a. A second laser beam 36b is shone from the second laser 30b to the second reflector 34b and back to the second detector 32b. The first and second lasers 30a, 30b, the first and second reflectors 34a, 34b and the first and second photo detectors are so arranged that the first and second laser beams 36a, 36b are horizontally spaced apart by about 300mm.

[0019] During loading and unloading, operators go in through the opening 10 from outside to inside in an in direction as indicated by the arrow A, and through the opening from inside to outside in an out direction as indicated by the arrow B. Each time an operator goes through the opening 10 in the in direction A, he sequentially breaks the laser beams 36b, 36a; first he breaks the second laser beam 36b, then he breaks first laser beam 36a. The second and first photo detectors 32b, 32a sense the sequential breaking of the second and first laser beams 36b, 36a and count it as a person going through the opening 10 in the in direction A. Similarly, the first and second detectors 32a, 32b sense the sequential breaking of the first and second laser beams 36a, 36b and count it as a person going through the opening 10 in the out direction B. Hence, the sensor 18 senses the number of people going through the opening 10 in the in direction A and the number of people going through the opening 10 in the out direction B. [0020] When loading or unloading has finished, everybody that came in through the opening 10 in the direction A should have gone out through the opening 10 in the out direction B. Consequently, the people in number sensed by the sensor 18 being equal to the people out number sensed by the sensor 18 is indicative of the loading or unloading being complete, and the control unit 14 controls the hydraulic actuator 12 to move the door 8 down into the closed position. The control unit 14 also comprises a timer unit 38, in response to which the control unit 14 will not close the door until a delay time has elapsed. A door sensor 40, at the bottom of the opening 10, detects when the door 8 is closed and in response the control unit 14 resets the sensor 18. A door indicator lamp 42 is green when the door 10 is being kept open and changes to red when the door 10 is about to be closed. An alarm 44 also sounds when the door is about to be closed. [0021] The door 8 is opened when operators are required to re-enter through the opening 10 from the outside by actuating a manually operated switch located on the exterior of the warehouse 1 . The switch signals to the control unit 14, which actuates the hydraulic actuator 12 to move the door 8 into the open posi- tion.