Abstract: A modulator mechanism for a rotary dobby, the input side of the modulator mechanism being connected to a drive which rotates at an essentially constant angular velocity and the output side thereof providing an output which is applied to a main shaft controlling heald shafts and which is temporally modulated inch a way that a delay of the movements of the heald shafts their maximum displacement positions is caused. To permit a sufficiently large shed rest angle for aft insertion in the case of fabrics having a very large width, a substantially enlarged shed rest angle is provided by a rotatable cam body, which is connected to the drive, and by at least one cam body follower in the form of an articulated lever, which, when the cam body rotates, carries out an oscillating pivoting movement modulated in accordance with the cam shape of the cam body, the pivoting movement being transmitted to the main shaft.