Adaptive Servo-Control for Piano Key Motion Stability
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Solution Overview
Problem
Automatic player pianos face challenges in producing high-fidelity music due to issues with key motion control, particularly during half-stroke movements, resulting in inconsistent tone loudness and stability problems.
Innovation Solution
The system categorizes key motions into full-stroke and half-stroke types and adjusts the servo-control loop's gain components to maintain stability, using a controller that optimizes the loop gain and fundamental components based on the type of motion to ensure accurate key trajectory following and consistent tone production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the key velocity is low to produce soft tones, then the tone loudness is reduced, but the time required for key motion increases causing instability and missed notes
Solution Approach 1:
The patent applies dynamics by making the key trajectory adaptive rather than fixed. The system dynamically adjusts the key trajectory based on the target loudness level, creating different trajectories for soft and loud tones. This allows the key motion to be optimized for each condition: slower and more stable for soft tones, faster for loud tones, thereby resolving the contradiction between tone loudness and motion stability
Solution Approach 2:
The patent changes the parameter of key trajectory based on the target loudness. By selecting different trajectories from a plurality of predetermined trajectories according to the target loudness level, the system adjusts the temporal and spatial parameters of key motion. This parameter adaptation ensures that soft tones are produced with sufficient time for stable key motion, while loud tones maintain appropriate speed
2Device complexity
If the key trajectory is fixed for all tones, then the control system is simple, but the fidelity of music reproduction deteriorates due to inability to handle half-strokes and varying loudness requirements
Solution Approach 1:
The patent segments the key trajectories into multiple predetermined trajectories, each optimized for specific playing conditions such as half-strokes and different loudness levels. Instead of using a single fixed trajectory, the system divides the trajectory space into multiple segments and selects the appropriate one based on the musical context. This segmentation enables high-fidelity reproduction of complex piano techniques while maintaining manageable system complexity through automated selection
Solution Approach 2:
The system makes the key trajectory dynamic by selecting from multiple predetermined trajectories based on the target loudness and playing style requirements. This dynamic selection allows the control system to adapt to different musical passages, producing authentic half-strokes and varying loudness levels without requiring overly complex real-time trajectory generation
3Ease of manufacture
If the servo-control loop uses fixed gain values, then the control implementation is straightforward, but the key motion accuracy deteriorates during half-strokes and rapid key changes
Solution Approach 1:
The patent applies dynamics to the control parameters by making the gain values adaptive rather than fixed. The system dynamically adjusts the gain values in the servo-control loop based on the current playing context, such as whether a half-stroke is being performed or how rapid the key changes are. This dynamic parameter adjustment maintains high key motion accuracy during challenging passages while keeping the control implementation manageable through automated adaptation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the fidelity of automatic music playback by stabilizing key motion and maintaining target loudness, reducing issues like double strikes and missing tones, thereby providing a more accurate reproduction of musical performances.
Implementation Method 1
The black and white keys are selectively pushed by the solenoid-operated key actuators 6 in response to driving signals ui supplied from a controller 302
Implementation Method 2
The black and white keys 1a/1b are monitored with key sensors 7 implemented by optical transducers
Implementation Method 3
the hammers 3 are brought into collision with the strings 4 at the end of the rotation. Then, the strings 4 start to vibrate, and the vibrations give rise to the piano tones
Data Source
AI summary
An automatic player piano includes key sensors, solenoid-operated key actuators and a controller, which form a servo-control loop, and the key motion is reproduced under the control of the servo-control loop; the servo-control loop adjusts the driving pulse signal to a target duty ratio or mean current so as to force the black and white keys to travel on reference key trajectories; the controller categorizes the key motion in half-stroke or full-stroke, and determines the target duty ratio on the basis of a deviation between the target key position and the actual key position, a deviation between the target key velocity and the actual key velocity and the sort of key motion so as to make the key motion stable.