Method for determining a fully extended position of a screening body of a screening device

A method for determining a fully extended position of a screening body of a screening device adapted for mounting on a frame structure with frame members comprising top and bottom members as well as side members and lining an opening in a building, in particular a door or a window, the screening device (12) comprising:

• a top element (13), the top element comprising a roller tube (15), a screening body (14) attached to the roller tube, a first end section (16) comprising a first spring element (164) and a second end section (17) comprising a second spring element (174),
• a bottom element (19) attached to the screening body,
• an end stop (23) adapted for abutment with the bottom element in a fully extended position of the screening body, in which all of the screening body is rolled off of the roller tube,
• an electric motor (18) connected to and adapted for rotating the roller tube, the first spring element and the second spring element such as to drive the screening body between a fully retracted position, in which all of the screening body is rolled onto the roller tube and the fully extended position of the screening body while tensioning or relaxing the first spring element and the second spring element, the electric motor comprising a tachometer (181), and
• a control unit adapted for controlling the electric motor, the control unit comprising a data storage device,
• the method comprising the following steps:
• a) rotating (100), by means of the electric motor, the roller tube such as to drive the screening body and the bottom element from the fully retracted position to the fully extended position of the screening body, in which the first spring element and the second spring element are tensioned to a first tension level, T1, and the bottom element abuts the end stop,
• b) stopping (101) the electric motor when the current drawn by the electric motor reaches a breaking current corresponding to a predetermined current level above the current level needed to drive the screening device, at which point the first spring element and the second spring element are tensioned to a second tension level, T2, above the first tension level, T1,
• c) measuring (102), by means of the tachometer, the number of revolutions, Rd, of the roller tube necessary to drive the screening body and the bottom element from the fully retracted position to the position of the screening body at which the motor is stopped in step b),
• d) storing (103) the measured number of revolutions, Rd, in the data storage device,
• e) measuring (104) by means of the tachometer the number of revolutions, Rb, of the roller tube, that a release of a tension of the first spring element and the second spring element corresponding to the difference, ΔT, between the first tension level, T1, and the second tension level, T2, will cause the roller tube to move back towards the fully retracted position,
• f) storing (105) the measured number of revolutions, Rb, in the data storage device, and
• g) calculating and storing (106) in the data storage device a value R=Rd−Rb.