Method for aligning bi-directional images in a mirror display
A mirror display system comprising a multiplicity of scan lines that are combined to generate an image. The multiplicity of scan lines are orthogonally positioned in response to a slow speed cyclic drive signal (for example, sinusoidal or repetitive triangular shape). To increase the brightness of the display, and unlike a typical raster scan display, scan lines are generated during both the positive going portion and the negative going portion of the cyclic drive signal.
1. In a display system comprising an oscillating high frequency mirror for generating scan lines for an image frame and an oscillating low frequency mirror for positioning said scan lines of said image frame, a method of generating at least two frames of images for each cycle of said oscillating low frequency mirror, comprising the steps of:
providing a cyclic drive signal having positive and negative going portions to said low speed mirror for positioning said scan lines;
generating a first initiate signal during said cyclic drive signal;
generating a first arming signal after a first selected time delay and in response to said first initiate signal;
generating a second arming signal after a second selected time delay;
generating said scan lines as said low frequency mirror travels in a first direction, and in response to said first arming signal; and
generating said scan lines as said low frequency mirror travels in a second direction opposite said first direction and in response to said second arming signal.
2. The method of claim 1 further comprising the step of generating a second initiate or interrupt signal and wherein said step of generating said second arming signal is in response to said second initiate or interrupt signal.
3. The method of claim 2 wherein said step of generating first and second initiate signals comprises selecting first and second points on said cyclic drive signal and generating said first and second initiate signals when said cyclic drive signal corresponds to said first and second selected points.
4. The method of claim 3 wherein said first selected point is at a zero voltage crossing point during said positive going portion of said cyclic drive signal and said selected point is at the zero voltage crossing point during said negative going point of said cyclic drive signal.
5. The method of claim 3 wherein said first and second points are selected so that said first and second time delays are equal.
6. The method of claim 2 wherein said first initiate signal is generated by the receipt of signals comprising said first image frame and said second initiate signal is generated by the receipt of the signals comprising the next or second image frame.
7. The method of claim 4 wherein said cyclic signal is monitored with a circuit that changes its output state each time said cyclic slow speed signal crosses the zero voltage point and generates said first and second initiate signals in response to said output changing state.
8. The method of claim 1 wherein both said first and second time delays are started in response to said first interrupt or initiate signal.
9. The method of claim 1 wherein said first arming signal also starts or initiates said second time delay.