Non-intrusive measurement of the pitch of a blade

1. A blade pitch measuring device of an un-ducted fan of a turbomachine, the fan comprising:

a. a hub,

b. at least one platform rotatable with respect to the hub and

c. at least one blade mounted on the platform,

wherein:

at least one first visual marker attached to the platform,

at least one second visual marker attached to the hub, the first and the second visual marker forming a pattern which evolves depending on the pitch of the blade and

at least one optical acquisition device, the optical acquisition device being configured to capture an image of the pattern so as to deduce the pitch of the blade from the image of the pattern,

wherein the device also includes a processing module including a memory, a processor and a communication device, the communication device being configured to communicate the images captured by the optical acquisition device to the processor, the memory including instructions, the processor being configured to implement the instructions of the memory so as to detect the pattern in the image and to deduce the pitch of the blade from the pattern, and

wherein the blade pitch measuring device further comprises:

a motor configured to rotatable drive the hub, and

a device for acquiring an angular position of the hub configured to deliver a signal depending on the angular position of the hub,

the processor being configured to cause the triggering of the optical acquisition device depending on the signal.

2. The blade pitch measuring device according to claim 1 , also including at least one light source directed toward a zone including the pattern, so as to increase the light intensity in the zone.

3. The blade pitch measuring device according to claim 1 , wherein the optical acquisition device is mounted on a movable support comprising at least one actuator allowing an adjustment of an orientation and/or of a position of the optical acquisition device with respect to the hub.

4. The blade pitch measuring device according to claim 3 , also comprising a sensor configured to determine a rotation speed of the hub and a control system configured to obtain servo control of the position of the optical acquisition device depending on the rotation speed of the hub.

5. The device according to claim 1 , wherein the optical acquisition device comprises a video camera.

6. The device according to claim 1 , wherein the turbomachine comprises two fans and the device comprises at least one optical acquisition device per fan.

7. A method for measuring the pitch of a blade with a blade pitch measuring device according to claim 1 , including the steps of:

a. acquiring an image of a pattern with the optical acquisition device,

b. detecting the pattern in the acquired image,

c. analyzing the detected pattern so as to deduce a value of the pitch of the blade from the pattern.

8. The method for measuring the pitch of a blade according to claim 7 , also comprising a calibration step during which the fan and the device are digitally simulated so as to simulate the position of a blade for at least one pitch value, thus forming a configuration of the pattern corresponding to the simulated pitch value, so as to assign a reference pitch value for the simulated configuration of the pattern.