Yamaha MX-1, Product Handbook

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I-31
Typical Key Sensors and Their Structures
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1-beam ON/OFF sensor
Used on models up to the MarkIIXG.
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2-beams 4-points sensor
Used on silent pianos (uprights and grands), etc.
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1-beam continuous sensor
The continuous sensor was introduced on the GranTouch GT1, and has thereafter been used on the GT2, GT7,
DGPS, PRO, MPX70, GT15, GT20, MARKIII, and others. Although all of these sensors operate according to the
same principle, the sensor implementation varies somewhat according to the Disklavier model. Specifically, the
method for setting the displacement points (K1 to K4) varies by model.
Features
1. The optical beam passes through a lens that changes the beam shape from a point
to a strip. When the key is at rest position, the shutter blocks the top of the strip.
As the key moves down, the shutter gradually blocks more and more of the strip.
The sensor detects key movement continuously over the full range by measuring
the amount of unblocked light at each instant.
2. Whereas previous sensors required a separate beam (a separate emitting fiber and receiving fiber) for
each key, the continuous system uses a prism to divide the beam so that it covers two adjacent keys. As a
result, models that use the continuous sensor require only 1/4 as many fibers as those using the earlier 2-
beams sensor.
3. The sensor implementation integrates key-emission and key-receive logic on the same sheet.
(Point Settings: K1 to K4)
Although light quantity is measured continuously, four specific displacement points (K1 to K4) are used to repre-
sent key positions during performance. The light quantity corresponding to each of these points is set based on the
continuous data as follows.
GT1, etc. Light quantity for each point K1 to K4 is a preset percentage of the light quantity that passes when the
key is at rest. The at-rest quantity is measured separately for each of the 88 keys each time the power
comes on, and the K1 to K4 values for each key are set as fixed percentages of this at-rest value. (The
percentages themselves apply in common to all keys.)
PRO The PRO uses a servo system to move keys at precise speed. K1 to K4 points are automatically set by
means of calibration.
OFF ON
Rest K1 K2 K3 K4
shutter
beam