Device for rolling up and unrolling a material web onto and from a shaft (1, 15), the device further comprising two tensioning ropes (3, 16) and having the following features: - the material web comprises a first fastening end, at which the material web can be directly or indirectly fastened to a holding structure; - the material web comprises a second fastening end which is opposite the first fastening end and which is fastened to the circumference of the shaft (1, 15) in such a way that the material web can be rolled up and unrolled on a central portion of the shaft (1, 15) by rotating the shaft (1, 15) about an axis of rotation; - the shaft (1, 15) comprises a rim portion in each of the two axial end regions thereof, a tensioning rope (3, 16) in each case being fastened to the respective circumferences of said rim portions, it being possible to roll up and unroll the tensioning ropes (3, 16) on the respective rim portions by rotating the shaft (1, 15); - by rotating the shaft (1, 15) in an unrolling direction, making the shaft (1, 15) move away from the holding structure, the material web is unrolled from the central portion of the shaft (1, 15) and the tensioning ropes (3, 16) are rolled up on the respective rim portions of the shaft; and - by rotating the shaft (1, 15) in a roll-up direction, making the shaft (1, 15) move towards the holding structure, the material web is rolled up onto the central portion of the shaft (1, 15) and the tensioning ropes (3, 16) are unrolled from the respective rim portions of the shaft, characterised in that a first radial distance assigned to any given roll-out length of the material web, between the material web and the axis of rotation, differs from a second radial distance assigned to this roll-out length, between the tensioning rope (3, 16) and the axis of rotation, in such a way that a first torque exerted on the shaft (1, 15) via the material web differs in direction and magnitude from a second torque exerted on the shaft (1, 15) via the tensioning ropes (3, 16), in such a way that the shaft (1, 15) is driven by a force transmitted via the tensioning ropes (3, 16) as a result of the torque difference between the first torque and the second torque. - the material web comprises a first fastening end, at which the material web can be directly or indirectly fastened to a holding structure; - the material web comprises a second fastening end which is opposite the first fastening end and which is fastened to the circumference of the shaft (1, 15) in such a way that the material web can be rolled up and unrolled on a central portion of the shaft (1, 15) by rotating the shaft (1, 15) about an axis of rotation; - the shaft (1, 15) comprises a rim portion in each of the two axial end regions thereof, a tensioning rope (3, 16) in each case being fastened to the respective circumferences of said rim portions, it being possible to roll up and unroll the tensioning ropes (3, 16) on the respective rim portions by rotating the shaft (1, 15); - by rotating the shaft (1, 15) in an unrolling direction, making the shaft (1, 15) move away from the holding structure, the material web is unrolled from the central portion of the shaft (1, 15) and the tensioning ropes (3, 16) are rolled up on the respective rim portions of the shaft; and - by rotating the shaft (1, 15) in a roll-up direction, making the shaft (1, 15) move towards the holding structure, the material web is rolled up onto the central portion of the shaft (1, 15) and the tensioning ropes (3, 16) are unrolled from the respective rim portions of the shaft,