Servo Gain Adjustment for Soft Pedal Stability in Player Pianos

Solution Overview

Problem

Automatic player pianos face instability in tone production when the soft pedal is depressed, leading to unintended double strikes and misstouches due to oscillations in key movements, caused by the rearward movement of the hammer rail reducing the load on keys and the subsequent cyclic change in duty ratio of driving signals.

Innovation Solution

The solution involves reducing gains in the servo control system when the soft pedal is depressed, using separate gain tables for pedal-on and pedal-off states to manage the key stroke and hammer movement, ensuring stable and accurate reproduction of musical performances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the soft pedal is depressed to reduce hammer stroke and soften tone, then the loudness of tones is reduced, but the key movements become unstable causing oscillations, double strikes, and misstouches

Engineering Contradiction:

Improvetone production accuracyVSAvoidkey movement stability

Core Design Contradiction:

Manufacturing precisionVSReliability

Solution Approach 1:

The patent applies dynamics by making the gain values in the servo control system variable based on the pedal state. When the soft pedal is depressed, the system dynamically switches to a different gain table with reduced gain values, allowing the control system to adapt to the changed mechanical conditions and maintain stable key movements despite the reduced hammer stroke

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the control parameter (gain values) based on the pedal state. By switching between different gain tables depending on whether the soft pedal is depressed or not, the system adjusts its control characteristics to match the mechanical conditions, thereby maintaining reliability across different operating states

Inventive Principle:

Principle #35Parameter changes

2Length of moving object

If the hammer rail moves rearward to reduce hammer stroke, then the distance between hammer and string is reduced for softer tones, but the load on keys is reduced causing cyclic changes in duty ratio

Engineering Contradiction:

Improvehammer strokeVSAvoidkey movement consistency

Core Design Contradiction:

Length of moving objectVSStability of the object's composition

Solution Approach 1:

The patent changes the control parameter (gain values) based on the pedal state. By switching between different gain tables depending on whether the soft pedal is depressed or not, the system adjusts its control characteristics to match the mechanical conditions, thereby maintaining reliability across different operating states

Inventive Principle:

Principle #35Parameter changes

3Reliability

If separate gain tables are used for pedal-on and pedal-off states, then key movement stability is improved, but the device complexity increases

Engineering Contradiction:

Improvekey movement stabilityVSAvoidcontrol system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies dynamics by making the gain values in the servo control system variable based on the pedal state. When the soft pedal is depressed, the system dynamically switches to a different gain table with reduced gain values, allowing the control system to adapt to the changed mechanical conditions and maintain stable key movements despite the reduced hammer stroke

Inventive Principle:

Principle #15Dynamics

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 stabilizes key movements, preventing double strikes and ensuring high-fidelity performances by adjusting the gain values based on the pedal state, thus maintaining optimal tone production and reducing oscillations.

Implementation Method 1

The prior art automatic playing system includes sensors, which monitor the plungers of solenoid-operated key actuators

Methodology Applied

Scientific EffectSolenoid: Solenoid

Implementation Method 2

the prior art servo controller multiplies the difference by a gain, and determines a duty ratio of the driving signal through the multiplication

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS7960629B2Automatic player piano equipped with soft pedal, automatic playing system and method used therein

Publication Date: 2011.06.14 YAMAHA CORP

AI summary

An upright piano is equipped with a soft pedal, and a player makes the hammer stroke shorter by depressing the soft pedal; while a user is reproducing a music tune by means of an automatic player piano fabricated on the basis of the upright piano, the keys are servo controlled on the basis of a position difference of keys between target values and actual values and a key velocity difference, and the duty ratio of driving signal, which is supplied to solenoid-operated key actuators for the keys, are determined on the basis of multiplications between the position difference/key velocity difference and a position gain and a velocity gain; the value of position gain is reduced on the condition that the soft pedal is depressed for preventing the playback from an unintentional loud tone or tones.