A tension adjustment and modulation system, device and method for stringed instruments based on screw drive.

Abstract

This invention discloses a tension adjustment and modulation system, device, and method for stringed instruments based on screw drive. The system includes at least one tension adjustment module, each module comprising: a screw drive mechanism that converts rotational motion into linear motion to adjust string tension; a tension sensor positioned in the force transmission path to detect tension values; a drive motor that drives the screw; and a control circuit including a microcontroller and a memory. This invention replaces the traditional rotary winding knob with linear screw drive, eliminating nonlinearity and backlash problems; and replaces audio frequency detection with direct tension measurement. The system supports: one-key recovery—storing the target tension value and adjusting it to the target value in a closed loop after triggering; continuous pitch maintenance—automatically monitoring and fine-tuning to correct drift while powered on; and active tension modulation—actively changing string tension in response to a trigger signal to achieve effects such as pitch bend, string bending, and vibrato. It is applicable to all stringed instruments that rely on string tension to determine pitch.

Description

Technical Field

[0001] This invention relates to the field of stringed instrument technology, specifically to a tension adjustment system and method that uses a transmission mechanism that converts rotational motion into linear motion to replace the traditional wound-wound string knobs, and has the functions of direct string tension detection, memory recovery, continuous holding and active modulation, applicable to stringed instruments. Background Technology

[0002] Traditional stringed instruments (such as guitars and violins) use wound-rotor tuning pegs (worm gear reduction for manual rotation of the tuning pins) to adjust string tension. This method has the following problems: 1. Insufficient precision: Manually rotating the tuning pegs makes it difficult to precisely control the rotation angle, which can easily lead to over-tuning or under-tuning during the tuning process, requiring repeated corrections; 2. Inefficient: Each tuning requires manual operation of each string. For example, a six-string guitar needs to be tuned six times in sequence, which is time-consuming. 3. Prone to pitch deviation and lack of continuous monitoring: The worm gear mechanism of traditional tuning pegs develops wear gaps after long-term use. Combined with temperature and humidity changes causing the strings and body materials to expand and contract, playing often requires interruption and retuning. More fundamentally, traditional stringed instruments cannot sense changes in string tension when the strings are not plucked—they must be plucked to produce sound before the pitch can be judged by sound, making real-time, continuous tension monitoring and automatic correction impossible. 4. High learning curve for non-professional users: For beginners or non-professional performers, judging pitch by ear and fine-tuning with manual knobs has a high learning curve. Furthermore, traditional stringed instruments suffer from a more fundamental physical limitation that has remained unresolved for centuries: once tuned, the string tension is fixed, and the performer cannot actively and precisely change the string tension to produce pitch variations during performance. Existing performance-based pitch modulation methods are extremely limited, and each method has its applicable boundaries, for example: (1) Finger string bending / vibrato - Although it is a mature playing technique, it is highly dependent on the player's skill. It is difficult to control the consistency of each string precisely, and it cannot be applied to stringed instruments such as piano and dulcimer. (2) Mechanical crank (tremolo arm) - changes the tension of all strings at the same time, cannot selectively act on a single string, and has the inherent defect of going out of tune after use; (3) For struck string instruments such as the piano and dulcimer, the pitch of each note is completely fixed after the string is struck, and the performer cannot apply any pitch changes (such as vibrato or bend) during the duration of the note. This limitation has never been overcome since the birth of such instruments. For plucked string instruments such as the guzheng, although a limited bend can be achieved through manual techniques, the precision and consistency are limited by human intervention, and there is a lack of precise and controllable electronic modulation methods. In other words, in traditional stringed instruments, string tension is a static parameter that is "set and locked," rather than an expressive dimension that can be dynamically controlled in real time during the performance.

[0003] Currently known automatic tuning schemes all use a motor to drive traditional tuning pegs. Essentially, they still rely on rotating the string to change the tension—that is, the motor's rotational motion is converted into a change in the number of turns of the string through the tuning peg. Its accuracy is limited by the non-linear relationship between the tuning peg rotation angle and the string tension (the radius of the string winding on the tuning peg changes with the number of turns), and it still retains the worm gear backlash problem of traditional tuning pegs.

[0004] Other patent documents disclose automatic tuning schemes based on force sensors or tension detection. These schemes use tension sensors to detect string tension, adjust the tuning pegs via a motor, and store the tension value at standard pitch. However, in these schemes, the tension sensor is located on the string rest (body end) rather than the headstock end, and the motor still drives the traditional tuning pegs, failing to change the basic "rotational winding" tuning method. Other stringed instrument tuning methods use thin-film stress sensors to detect force values ​​and control a stepper motor to drive the tension pegs via a reduction gear set, also relying on rotary tuning pegs. There are also tuning methods that use tension values ​​as a tuning reference, storing preset tension values ​​and automatically comparing and adjusting, but the actuator is still a servo motor driving a fixed knob. A high-speed closed-loop tension control guitar is also disclosed, which uses a displacement sensor to indirectly calculate tension through a nonlinear spring (rather than direct measurement) and uses a capstan or crank arm drive method. The aim is to achieve fretless playing through tension changes rather than maintaining the pitch after tuning. The aforementioned existing technologies have not deviated from the basic paradigm of "rotating tuning pins winding strings", and have inherent nonlinear accuracy problems and worm gear backlash problems.

[0005] Furthermore, existing automatic tuning schemes based on audio frequency detection (such as closed-loop schemes that collect sound through pickups or microphones, analyze frequencies, and control motors with feedback) have inherent drawbacks: they cannot work reliably in noisy environments; each tuning requires plucking each string, collecting data, and analyzing it, which is time-consuming; and the accuracy of frequency detection is affected by environmental noise, overtone interference, and harmonic richness. While schemes that use tension value as the tuning reference avoid the environmental dependence of audio detection, the actuators in existing schemes are still rotary tuning pins, with worm gear backlash in the transmission chain, and the tension detection point is not directly located at the most direct mechanical sensing position in the string tension transmission path.

[0006] Therefore, there is currently no string instrument tension adjustment system that uses a transmission mechanism to directly linearly adjust string tension by converting rotational motion into linear motion, places a tension sensor in the string tension transmission path to achieve direct tension measurement and memory recovery, and further transforms string tension from a static parameter that is "set and locked" into an expressive dimension that can be dynamically controlled in real time during performance. Summary of the Invention

[0007] Technical problems to be solved The technical problem to be solved by this invention is: (1) A high-precision tuning mechanism is provided to replace the traditional rotary tuning mechanism (such as wound-wound tuning pegs, tuning pins, etc.), eliminating the inherent nonlinear precision problem and worm gear backlash problem of the rotary winding method; (2) It realizes direct digital detection and memory storage of string tension, supports one-click restoration of calibrated tuning state, and does not rely on audio frequency detection, and works reliably in noisy environments. (3) Realize continuous real-time monitoring of string tension without plucking or audio acquisition, and automatically detect and correct pitch drift. Existing solutions based on audio frequency detection must wait for the string to be plucked to produce sound before they can determine the pitch, and cannot continuously perceive the pitch status during the performance interval. (4) Reduce the time cost and skill threshold of tuning operations, so that non-professional users can quickly complete accurate tuning; (5) Breaking the physical limitation of the traditional string tension of stringed instruments being "locked when tuned", making string tension an expressive dimension that can be dynamically controlled in real time during the performance, expanding and surpassing the ability boundaries of traditional mechanical cranks, finger string pushing / vibrato and other performance pitch modulation methods; (6) This invention enables various stringed instruments such as guitars, pianos, violins, and guzheng to benefit from its automated tuning capabilities (e.g., a piano can be precisely tuned with one click, replacing hours of manual tuning); it also provides striking string instruments such as pianos and yangqins, which traditionally cannot apply any pitch changes during the duration of a note, with entirely new pitch modulation capabilities; and for plucked string instruments that can achieve limited pitch bending through manual manipulation, it provides electronic pitch modulation with precision and consistency far exceeding that of manual tuning. The aforementioned technical problems are not limited to the listed instrument types, but are prevalent in all stringed instruments that rely on string tension to determine pitch. The solution of this invention is applicable to all such instruments. The technical solution of this invention is as follows: Screw drive mechanism: includes a screw and a screw nut that threadedly engages with the screw, the screw nut being capable of linear movement along the axial direction of the screw. The screw drive mechanism converts the rotational motion of the drive source into the linear motion of the screw nut, thereby directly and linearly changing the tension of the connected string. Types of screws include, but are not limited to, ball screws, trapezoidal screws, rectangular thread screws, sawtooth thread screws, and miniature linear actuators based on the thread principle. Different types of screws differ in their self-locking characteristics; specific selection should be based on product positioning and cost considerations, see the "Transmission-Self-Locking Relationship" section for details. String end fixing device: This device is installed on or connected to the lead screw nut and is used to fix one end of the string. For example, the string end fixing device can be a ball head groove—a groove slightly larger than the diameter of the string ball head is opened on the nut or module body, with a narrow slit at the top (the slit width is greater than the string diameter but less than the ball head diameter). After the ball head is placed in the groove, the string passes through the narrow slit. The greater the string tension, the more the ball head is pulled into the bottom of the groove, forming a natural self-locking mechanism. The string ball head can adopt various structural forms: a standard spherical ball head (common for traditional steel strings); a straight-line snap-fit ​​ball head—the end of the string is wrapped and fixed to a straight-line force-bearing component, with both ends of the force-bearing component spanning the two side walls of the narrow slit to form a snap-fit; a frustum-shaped ball head—the larger end faces the string direction, and under tension, the conical surface creates a wedging effect with the inner wall of the groove; if necessary, an anti-dislodgement pin or a bolt-type locking plate can be added to prevent the ball head from accidentally slipping out. Alternatively, the string end fixing device may be any one or a combination of screw clamping, pressure block locking, clamping block locking, wedge self-locking, and tortuous path friction locking. Tension sensor: Located on the force transmission path between the string end fixing device and the string, it is used to directly detect the current string tension value. Unlike methods that indirectly calculate tension through the displacement of an elastic body (such as through nonlinear displacement-force conversion of a function-spring), in this invention, the tension sensor is directly located in the tension transmission path, detecting the direct mechanical quantity of string tension. The specific location of the tension sensor in the force transmission path is not limited—it can be located on one side of the fixed end of the string (such as the headstock end), or on the other fixed end of the string (such as the bridge end, the string rest end), or simultaneously at both ends; as long as it is located in the force transmission path of string tension and can directly detect the string tension value, it falls within the protection scope of this invention. Drive motor: Connected to the lead screw via a transmission mechanism, used to drive the lead screw to rotate. The type of drive motor is not limited, such as stepper motor, servo motor, DC motor, brushless motor, etc. The transmission mechanism can be any one or a combination of direct-drive, gear reduction, worm gear drive, synchronous belt / belt drive, chain drive, friction wheel drive, and magnetic coupling drive. Control circuit: Electrically connected to the drive motor and the tension sensor, including a microcontroller and a memory (non-volatile memory). The memory stores at least one set of target tension values, each set corresponding to the target tension of each string under a tuning configuration. The control circuit is configured to: read the target tension value from the memory, compare the current tension value detected by the tension sensor with the target tension value, and based on the comparison result, control the drive motor to drive the lead screw to rotate, causing the lead screw nut to move axially to change the string tension until the current tension value matches the target tension value.

[0008] Furthermore, the system may also include one or more of the following auxiliary components: Auxiliary sensing units include frequency / vibration sensors (such as pickups, piezoelectric sensors, microphones, etc.) for detecting string vibration frequencies to assist in pitch calibration; and / or position / displacement sensors (such as encoders, Hall sensors, photoelectric sensors, etc.) for detecting the lead screw rotation angle or lead screw nut position to achieve travel limit protection or position memory. It should be noted that the frequency / vibration sensor is only used for initial pitch confirmation during calibration; routine one-click tuning recovery is entirely based on tension value comparison using a tension sensor and does not rely on audio frequency detection. The above sensor types are exemplary examples; any sensor capable of performing the corresponding detection function falls within the scope of this invention. Communication module: Used for wired or wireless data interaction with external terminal devices (such as smartphones, tablets, personal computers, cloud servers, etc.). Communication methods include, but are not limited to: Bluetooth (including BLE), Wi-Fi, 2.4GHz proprietary protocol, NFC, UWB, Zigbee, LoRa, Sub-GHz wireless, infrared, ultrasonic communication, visible light communication (Li-Fi), and wired interfaces such as USB, UART, I2C, and MIDI. Any currently known or future communication technology or protocol capable of enabling data interaction between the control circuit and external devices falls within the protection scope of this invention. Display unit: Used to display at least one of the following information: tuning status, string tension values, target tension value, pitch deviation, battery level, current tuning mode, communication connection status, etc. The display unit includes, but is not limited to: OLED display, LCD display, e-ink screen, LED digital tube, LED indicator array, touch screen, and external displays connected via interfaces such as HDMI / VGA / DisplayPort; Power supply module: The power supply method is not limited, such as: a battery installed inside each tension adjustment module; a centralized power supply connected to the body of the instrument; an external power supply introduced through a wired interface (such as USB power supply, power adapter); wireless power supply; or any combination of the above methods. The key inventive points of the present invention will be described in detail below.

[0009] Invention Point 1: Linear Screw Drive Replaces Rotary Winding String This invention replaces the traditional wound-winding type of knob (rotational motion → rotational winding) with a lead screw drive mechanism (converting rotational motion into linear motion), fundamentally eliminating the nonlinearity problem of the rotational winding method. The lead screw has a fixed pitch, and the distance the nut advances per revolution of the motor is precisely controllable. Taking a fine-pitch lead screw paired with a stepper motor as an example, the nut displacement for each step can be controlled at the micrometer level, enabling extremely precise tension adjustment with an accuracy far exceeding the smallest discernible pitch difference. Simultaneously, the lead screw drive chain eliminates the worm gear backlash of traditional knobs, eliminating the backlash and nonlinearity caused by it. It should be emphasized that the term "screw drive mechanism" in this invention should be interpreted broadly, encompassing any transmission mechanism that converts rotary motion into linear motion through threaded engagement, including but not limited to: ball screws (rolling friction, high efficiency), trapezoidal screws (sliding friction, natural self-locking), rectangular thread screws, sawtooth thread screws, and miniature linear actuators based on the thread principle. For example, when using a trapezoidal lead screw, its thread self-locking characteristic can be used to maintain tension even when power is off, while also being naturally compatible with manual tuning (the self-locking is directional, and the lead screw can still rotate in the forward direction to drive the nut). For details on the self-locking characteristics of lead screw types, please refer to the "Transmission-Self-Locking Relationship" section.

[0010] Invention Point Two: Direct Measurement of Tensile Force and Recovery of Tension Memory In this invention, the tension sensor is placed in the string tension transmission path to directly measure the actual mechanical quantity of the string tension, which differs from: (a) the indirect detection method of collecting audio / vibration frequencies through a pickup or microphone—this method is unreliable in noisy environments and requires re-plucking the string every time it is tuned; (b) the method of indirectly calculating the tension through the displacement of an elastic body—this method suffers from nonlinear errors in displacement-force conversion and calibration drift. The tuning reference is the tension value directly measured by the tension sensor, not the audio / vibration frequency. After the initial calibration, the target tension value is stored in non-volatile memory. During daily use, the user triggers a one-key recovery, and the control circuit directly reads the stored target tension value, adjusting the current tension value in a closed-loop manner until it matches the target tension value. The entire process requires no string plucking, no audio acquisition, and is unaffected by environmental noise. For example, when each string is equipped with an independent drive motor and tension sensor, multiple strings can be adjusted in parallel during daily one-button recovery, and the tuning time for the whole instrument is comparable to the tuning time for a single string.

[0011] Invention Point Three: Continuous Pitch Preservation – "Instant Pitch When Powered On" This invention incorporates a tension sensor within the string tension transmission path, enabling the system to continuously sense real-time changes in string tension while powered on, without waiting for the strings to be plucked. This feature overcomes the fundamental limitation of existing technologies that require string plucking to determine pitch, achieving the ability to continuously monitor pitch without string plucking or audio acquisition. Pitch drift caused by slow factors such as temperature, humidity, string plastic elongation, and wood deformation is automatically detected and corrected with micron-level precision before the user notices it, ensuring the instrument is always at the standard pitch as long as it is powered on. In contrast, existing audio frequency detection-based solutions require string plucking and sound production to determine pitch, making it impossible to detect pitch changes during performance breaks. Traditional mechanical tuning peg systems (including those using motors to rotate traditional pegs) lack the physical conditions for continuous automatic fine-tuning due to worm gear backlash and nonlinearity. This invention relies on the synergy between the micron-level displacement precision of the lead screw (making minute tension correction possible) and the direct mechanical sensing of the tension sensor (obtaining real-time tension values ​​without string plucking).

[0012] Invention Point Four: Active Tension Modulation – Transforming String Tension into a Dimension of Performance Expression This invention further expands the drive motor and lead screw transmission mechanism from "behind-the-scenes tools for maintaining pitch" to "performance components for creating music." By responding to any form of modulation trigger signal, the system can actively change the tension of a specified string to produce a pitch modulation effect, transforming string tension from a static parameter that is "locked in once set" to an expressive dimension that can be dynamically controlled in real time during performance. The core value of this invention lies in the independent controllability of each string, thereby deriving new capabilities that are completely impossible to achieve by traditional methods: (i) Single string pitch bend, other strings unaffected: Only the target string is pitch modulated, while the pitch of other strings remains unchanged—this is the core difference that traditional mechanical cranks (which change the tension of all strings at the same time) cannot physically achieve; (ii) Instant simplification of complex chord fingering: During performance, the pitch of a string can be temporarily raised or lowered, which can simplify complex chords that originally required a large range of fingering to conventional fingering. The performer triggers complex harmonic effects with simple fingering, and the chords automatically return to their normal positions after the performance is completed. (iii) Precise and controllable pitch: The modulation amplitude of effects such as pitch bend and string bending can be precisely calibrated digitally, and the pedal travel can be calibrated to a specific pitch. The pitch accuracy and consistency far exceed those of manual operation; after modulation, it automatically and accurately returns to the original position, and there is no problem of pitch drift after using a traditional crank. (iv) Imbuing new instrument categories with expressive dimensions: This invention grants entirely new expressive capabilities to struck string instruments like the piano, which traditionally cannot exert any pitch variation during the duration of a note—a limitation that has remained unchallenged for centuries since their inception. For plucked string instruments like the guzheng, which can achieve limited pitch bend through manual manipulation, this invention transforms manual operation into precise and controllable electronic modulation, achieving a consistency and programmability far exceeding that of manual operation. The systematic capabilities of lead screw precision transmission, tension sensor closed loop, and digital control enable the active tension modulation of this invention to functionally expand the capabilities of traditional methods such as mechanical cranks and finger string bending / vibrato, and create a new performance dimension that is completely impossible with traditional methods.

[0013] Transmission-Self-Locking Relationship Whether a lead screw drive system can maintain string tension and prevent it from slipping after a power outage (i.e., "self-locking") depends on the combination of the lead screw type and the drive method: - Trapezoidal lead screw + direct drive / gear reduction type: The trapezoidal lead screw has natural self-locking due to thread friction, requiring no additional mechanism. The self-locking is directional—string tension cannot push the nut in the opposite direction to rotate the lead screw (preventing loosening), but the lead screw can be driven by a motor to rotate in the forward direction to push the nut (regardless of whether the string is tightened or loosened), and the automatic adjustment function is not affected in any way; - Ball screw + direct drive / gear reduction type: Ball screws are highly efficient (90%+), with minimal rolling friction. The string tension is sufficient to reverse the drive of the screw nut, causing it to loosen ("pulley"), and it does not self-lock. If power-off self-locking is required, a power-off locking electromagnetic brake, one-way bearing (wedge clutch), miniature ratchet mechanism, or worm gear reducer can be added to achieve self-locking. - Any screw type + worm gear drive: When the worm lead angle is less than the friction angle (usually requiring a single-start worm and a sufficiently large reduction ratio), the worm gear drive itself has self-locking characteristics and can be applied to any screw type. However, under vibration conditions, the worm self-locking may experience slow slippage; it is recommended to use a trapezoidal screw or electromagnetic brake for double protection. Alternatively or additionally, the following self-locking / anti-reverse mechanisms may be employed: a power-off brake (where a spring presses the brake pads to lock the shaft when power is off, and the electromagnet releases when power is on); a one-way bearing or wedge clutch (allowing only rotation in the tightening direction and preventing reverse rotation in the loosening direction); a miniature ratchet mechanism (allowing free rotation in the tightening direction and preventing reverse rotation in the loosening direction); and any combination thereof. It should be noted that the aforementioned self-locking / anti-reverse measures are all optional configurations and not necessary conditions for realizing this invention. Any type of lead screw can be used independently without configuring any self-locking or anti-reverse device (for example, a ball screw can be used for a fixed device that is always plugged in without a brake; self-locking can be deliberately omitted in scenarios where it is expected that the strings will automatically loosen after a power outage). During system power-on, all functions such as one-key recovery, continuous pitch maintenance, and active tension modulation operate normally—these functions rely on the lead screw transmission accuracy, the closed-loop tension sensor, and the motor drive, and are unrelated to whether the lead screw is self-locking.

[0014] Transmission variant The transmission connection from the drive motor to the lead screw can be any one of the following or a combination thereof: (a) Direct connection type: The motor output shaft is coaxially connected with the lead screw, which has the simplest structure and the smallest axial dimension; (b) Gear reduction type: The motor drives the lead screw (including spur gear, helical gear, planetary gear, harmonic gear, etc.) through a reduction gear set to provide speed reduction and torque increase, which is suitable for small torque high-speed motors; (c) Worm drive type: The motor drives the worm wheel at the end of the lead screw through the worm. The motor axis and the lead screw axis form a 90-degree angle, which saves the axial space of the module (especially suitable for installation positions with limited thickness), and the worm drive itself has a natural self-locking characteristic. (d) Synchronous belt / belt drive type: The motor drives the lead screw through the synchronous pulley and synchronous belt, which can flexibly arrange the position of the motor and buffer vibration and impact; (e) Chain drive type: The motor drives the lead screw through sprockets and chain; (f) Friction wheel drive type: The motor drives the lead screw directly or indirectly through the friction wheel; (g) Magnetic coupling drive type: The motor drives the lead screw in a non-contact manner through a magnetic coupling, realizing physical isolation between the motor and the lead screw and reducing vibration transmission. All the aforementioned variations of the transmission method fall within the protection scope of this invention. In product implementation, they can be flexibly selected or combined according to cost, accuracy, space layout, and self-locking requirements.

[0015] Variations in string end fixing method In scenarios where the ball head slot is unavailable or inapplicable (such as classical guitar nylon strings, violin strings, or other strings without a ball head, or in cases where the bridge ball head is retained in a modification kit), the string end fixing device can also be any one or a combination of the following: (a) Screw tightening: A screw presses directly onto the string from the side or top, with the end face of the screw in contact with the string; (b) Pressure block locking: A screw drives a pressure block, and the flat or curved surface of the pressure block presses against the string, which reduces damage to the string surface compared to the screw pressing the string directly; (c) Clamping block locking: Two slotted clamping blocks are joined together to clamp the strings, and the two clamping blocks are locked with screws; (d) Wedge-shaped self-locking: The base has a V-shaped groove, with the narrow opening facing the direction of string tension and the wide opening facing the opposite direction. A wedge-shaped locking block is located inside the V-shaped groove, with a through hole for the string to pass through. The string enters through the narrow opening of the V-shaped groove, passes through the through hole in the wedge-shaped locking block, loops back, and exits through the narrow opening again—that is, the string enters and exits through the same opening, following a U-shaped path inside the wedge. When the string is pulled towards the narrow opening by tension, the wedge-shaped locking block is dragged towards the narrow opening of the V-shaped groove. As the distance between the two sides of the V-shape gradually narrows at the narrow opening, the wedge-shaped locking block is squeezed by the two sides, pressing the two ends of the string tightly against the two sides of the V-shaped groove. The greater the string tension, the more the wedge moves towards the narrow opening, and the greater the clamping force, creating a "tighter the tighter" self-locking effect. To release the string, simply push the wedge-shaped locking block from the wide opening direction to release it. This method requires no screws, no tools, and the strings come with built-in ball heads, making it suitable for any type of string; (e) Twisted Path Friction Locking: Two or more staggered string holes are set on the lead screw nut or tension adjustment module body, with the axes of the holes not collinear along the string threading direction, forming at least one S-shaped or Z-shaped bending path. After the string passes through each hole in sequence, it is subject to frictional constraints at multiple points of change along the zigzag path—with each bend, the normal force and frictional force between the string and the edge of the hole multiply (winch effect superposition). To further increase the locking force, a transverse pressure block (driven by a hand-tightening screw or a lever-type eccentric cam) can be added between two of the string holes to apply additional positive pressure to the string in the middle section of the path. After locking, the direction of string tension and the direction of frictional force in each segment of the zigzag path form multi-level resistance, making it extremely difficult for the string to slip even if the string surface is smooth. This method is suitable for ballless strings (including bare steel strings, nylon strings, etc.) and does not rely on any pretreatment of the string ends. In addition, in the scheme of using screw clamping or pressure block locking, a self-tightening linkage string locking mechanism can be further configured (see self-tightening linkage string locking mechanism below) so that the string clamping force automatically increases during the tuning process.

[0016] Self-tightening linkage locking mechanism When the strings are secured using screws or clamping blocks, the rotation of the lead screw can be used to drive the string-locking device via a transmission mechanism, automatically increasing the string-locking clamping force during tuning. One exemplary solution involves a lead screw shaft connected to a small worm gear or threaded rod via a one-way clutch (such as a one-way bearing or ratchet). The rotation of this worm gear / threaded rod drives the clamping block to rise perpendicular to the strings, pressing the strings against the fixed surface from below. The one-way clutch only allows torque transmission in the "clamping direction," increasing the clamping force synchronously when tightening the strings, and slipping during tuning without reducing the clamping force. A relief groove or smooth rod area at the end of the threaded section forms a travel limit, preventing excessive clamping and damage to the strings. This solution achieves mechanical linkage between tuning and string-locking actions, eliminating the need for additional electrical or manual operation.

[0017] Group-driven scheme As a compromise or supplement to the independent motor per string approach, the number of drive motors, M, can be equal to or less than the number of strings. When M equals the number of strings, each string is driven independently, allowing multiple strings to be adjusted in parallel, and the tuning time for the entire guitar is comparable to that for a single string. When M is less than the number of strings (e.g., a six-string guitar with 1 to 5 motors), at least one drive motor selectively drives the corresponding lead screws of a group of strings via an electromagnetic clutch assembly; the clutches are selectively engaged by the control circuit according to the string that needs adjustment; strings within the same motor assembly are tuned sequentially, and different motor assemblies can be tuned in parallel. This approach allows for flexible trade-offs between cost, weight, and tuning speed: more motors result in higher parallelism and faster tuning, but also increased cost and weight. In the extreme case, M=1, meaning a single motor drives all strings, resulting in the lowest cost but completely sacrificing parallelism. Similarly, the number of tension sensors can be equal to or less than the number of strings (for example, by using a time-division multiplexing circuit or a mechanical switching device to allow the same sensor to detect the tension values ​​of different strings at different times).

[0018] Manual tuning backup When the battery is depleted or the electronic system malfunctions, the user can manually rotate the lead screw to adjust the string tension, ensuring the instrument can still be tuned and played even without power. The form of the manual operation interface is not limited (e.g., a knob at the end of the lead screw; a connection to existing tuning pegs via a transmission mechanism for traditional tactile operation; or acceptance of manual rotation input via other mechanical interfaces). For trapezoidal lead screw designs, manual operation is naturally compatible (the self-locking mechanism is directional, allowing the lead screw to rotate forward to drive the nut); for designs using electromagnetic brakes, a mechanical release mechanism (such as a lever or button) can be added to the brake, temporarily releasing the lock when manually pressed and automatically re-locking upon release.

[0019] Workflow Initial calibration procedure: The purpose of the initial calibration is to establish a "target tension value" for each string and store it in non-volatile memory for subsequent one-click recovery. The initial calibration supports the following three paths, which can be used independently or in combination: Path A (manual calibration, no power required or only sensor circuit power required): (1) The user manually rotates the manual operation part at the end of the lead screw to adjust the string tension to the target pitch; pitch judgment can rely on the user's own hearing, an external independent tuner, or a mobile phone tuning APP; (2) After the user confirms that the string has been tuned to the target pitch, the "memory" operation is triggered (such as a physical button on the module, or a storage command is sent through the APP); (3) The control circuit reads the tension value measured by the tension sensor at this time and writes it as the target tension value of the string into the non-volatile memory; (4) Repeat the above steps for each string until all are completed; Path B (electric assisted calibration, power required): (1) The user manually plucks the string, and the tension sensor collects the current string tension value in real time; (2) At the same time, the system detects the actual vibration frequency of the string through the built-in pickup or vibration sensor to determine whether the pitch meets the standard; (3) The control circuit drives the motor to rotate the screw, and the nut moves along the axis to automatically adjust the string tension until the target pitch (frequency) matches the target tension value at the same time; (4) Each string can be calibrated one by one, or multiple strings can be calibrated simultaneously in parallel. After all the strings are calibrated, the control circuit stores the target tension value corresponding to each string in a non-volatile memory; Path C (APP-assisted calibration, requires power and connection to a smart device): (1) The smartphone connects to the control circuit via Bluetooth or Wi-Fi to establish a two-way real-time data channel; (2) When the user plucks the string, the mobile APP collects the string audio through the mobile phone microphone or the system's built-in pickup and analyzes the current pitch; at the same time, the control circuit pushes the current tension value collected in real time by the tension sensor to the APP for display; (3) The APP interface displays the deviation (cents) between the current pitch and the target pitch, the current tension value and the target tension value. The user can choose to manually rotate the physical knob to tune, remotely control the motor to tune via the virtual knob on the APP, or have the APP control the motor to automatically tune to the target value; (4) After the tuning is up to standard, the APP sends a storage command, and the control circuit writes the tension value measured by the current tension sensor into the non-volatile memory. Three paths can be flexibly selected according to the actual use scenario: use path A in the absence of power; use path B when rapid batch calibration is required; use path C when an intuitive and visual operation interface is required. Path A is the most basic calibration method, ensuring manual calibration even under completely power-free conditions.

[0020] One-click recovery process (daily use): (1) The user triggers one-click recovery (such as a physical button on the module, or operation via APP, or other preset triggering methods); (2) The control circuit reads the stored target tension values ​​of each string from the non-volatile memory; (3) Perform the following on each string: The tension sensor reads the current tension value in real time, compares it with the target tension value, and drives the motor to adjust the screw until the current tension value matches the target tension value (allowing preset tolerance range); Each string can be adjusted sequentially, or multiple strings can be adjusted in parallel (when each string is equipped with an independent drive motor and tension sensor); (4) After all strings are adjusted, the system issues a confirmation signal (such as LED indication, display change or buzzer).

[0021] It is particularly important to emphasize that the tuning benchmark for daily one-click recovery is the tension value directly measured by the tension sensor. The entire process requires no string plucking, no pickup or microphone to collect audio, and no frequency analysis. This feature allows the invention to work reliably in noisy environments (such as performance venues, rehearsal rooms, and outdoors), and the tuning speed is significantly better than closed-loop solutions based on audio frequency detection—the latter requires plucking each string, collecting data, waiting for the frequency to stabilize, analyzing, and then adjusting the feedback for each tuning session.

[0022] APP / Cloud Control Process: A two-way real-time data channel (wired or wireless) is established between the APP and the control circuit to achieve the following functions: - Real-time data transmission: The control circuit pushes information such as the current tension value of each string, battery level, and tuning status to the APP in real time, which is then displayed in a visual manner on the APP; - APP manual remote control tuning: Users can send motor control commands (including rotation direction, speed, number of steps / angle) to the control circuit through the virtual knob, slider or directional button on the APP interface, so as to achieve remote control operation of "tuning the volume without taking your hands off the mobile phone"; - Preset modes and automatic tuning: Users can select preset tuning modes (such as standard tuning, half-tone lowering, Open G, DADGAD, etc.) or customize tension parameters in the APP, and choose one-click automatic tuning or manual fine-tuning; - Cloud synchronization and OTA upgrade: Users can upload their custom tuning schemes to the cloud and download and synchronize them on other devices; the control circuit can receive firmware upgrade packages wirelessly to complete OTA upgrades.

[0023] Continuous pitch hold mode Unlike passively triggered one-key recovery, this invention also provides a continuous pitch-maintaining mode: when the system is powered on, the control circuit (50) continuously reads the current tension value of each tension sensor (30) at a preset frequency and compares it with the corresponding target tension value in the memory. When the deviation between the current tension value and the target tension value of a string exceeds a preset threshold (which can be set to correspond to a tension change of, for example, 1 to 5 cents) and the duration exceeds a preset time window (to exclude instantaneous interference and playing actions), the control circuit (50) automatically controls the corresponding drive motor (40) to perform fine-tuning correction, so that the current tension value is restored to the tolerance range of the target tension value. The entire process does not require user triggering.

[0024] The key to the continuous pitch-keeping mode is that the tension sensor (30) is placed in the string tension transmission path, so that the system can obtain the current real-time tension value regardless of whether the string is plucked or the environment is noisy. This is fundamentally different from the scheme that relies on audio frequency detection - the latter must wait for the string to be plucked and produce a sound in order to determine the pitch, and cannot continuously monitor during the performance interval, let alone perceive the tension change in real time during the playing process. In the continuous pitch-keeping mode, pitch drift caused by slow factors such as temperature changes, plastic elongation of the string, and deformation of the wood of the instrument is automatically corrected before the user notices it, achieving the effect of "as long as the power is on, the instrument is always at the standard pitch".

[0025] Furthermore, the system can distinguish between "natural string drift" and "tension changes caused by playing actions" (such as string bending, vibrato—rapid, large-amplitude, or periodic) based on the rate and / or direction of tension change characteristics, automatically correcting only the former to avoid interfering with the performance expression. Distinction rules may include: a rate of change below a preset threshold is considered natural drift, while a rate above the threshold is considered a playing action; periodic repetitive changes are considered vibrato; and the direction of tension change aligning with the direction of finger position change is considered a glissando (when the system is equipped with finger position detection).

[0026] The continuous pitch retention mode can coexist with the one-key recovery mode: the system defaults to continuous retention mode (retains pitch when powered on), but users can still manually trigger a one-key full recovery when needed (such as after changing strings or after a significant temperature change).

[0027] Active tension modulation – electric performance modulation mode This invention further expands the drive motor (40) and lead screw transmission mechanism (10) from "behind-the-scenes tools for maintaining pitch" to "performance components for creating music": utilizing their precise tension adjustment capabilities, they actively change the string tension during performance to achieve pitch modulation effects, functionally expanding the capability boundaries of traditional mechanical tremolo arms.

[0028] In this mode, the control circuit (50) receives modulation instructions from at least one control input device (hereinafter referred to as "controller"), and controls the drive motor (40) to actively change the tension of a specified string to produce real-time pitch changes according to the instructions. The controller can be any one or a combination of the following: a foot pedal (continuous variable controller), a foot switch (discrete trigger), a button / switch mounted on the instrument body, an external MIDI controller, or a smart terminal device running control software (sending modulation instructions via wired or wireless means). The control method is not limited, and any input device or communication method capable of sending tension modulation instructions to the control circuit falls within the protection scope of this invention.

[0029] Active tension modulation supports at least one of the following modulation modes: (a) Single / Multi-String Bend: The user operates the continuous variable controller (e.g., pressing the expression pedal), and the control circuit maps the position / angle of the controller to the target tension offset, driving the motor (40) of the corresponding string to adjust the position of the lead screw nut (12) in real time to change the string tension, producing a continuous pitch bend effect. A bend range of at least ±2 semitones can be achieved on a typical steel-string guitar. Compared with traditional mechanical tremolo arms, this invention supports: (i) applying bend only to selected strings, rather than all strings changing synchronously; (ii) the intonation of the remaining strings is not affected during the bend; (iii) the target pitch of the bend is precisely controllable (the pedal travel can be calibrated to a specific pitch); (iv) automatic and precise return to the original position after bend, without the common problem of out-of-tune notes after tremolo arm use. (b) One-button string bending: When the user triggers the discrete controller (e.g., by pressing the foot switch or the button on the instrument body), the control circuit (50) automatically controls the drive motor (40) to perform a complete string bending-returning action according to the preset string bending parameters—including the target pitch offset (e.g., major second, minor third), pitch bend rate, and pitch bend curve (linear, exponential, S-curve, etc.). The user does not need to master the finger string bending technique, and the pitch accuracy and consistency of the string bending far exceed those of human finger control. Moreover, the string automatically and accurately returns to its original position after the button is released. (c) Pre-programmed tension modulation sequence: The user pre-programs a tension modulation sequence via an external terminal device—applying a specified amplitude and curve of tension change to a specified string at a specified time node. The modulation sequence can be synchronized with the music timeline and is automatically executed by the control circuit (50) according to the pre-programmed timing instructions. The user triggers the start / stop and segment switching of the sequence through the controller. This mode realizes automated microtone playing and programmable pitch bend effects; (d) One-click tuning switch: The user triggers the controller to select a preset number, and the control circuit (50) reads the corresponding set of target tension values ​​from the memory, driving the motors (40) of each string to adjust all strings in parallel to the new tuning configuration. For example, during a performance, the player can switch from standard tuning (EADGBE) to open G tuning (DGDGBD) with one click, and switch back with one click after finishing the piece. The switching time depends on the required tension change, and can be completed within a few seconds for adjacent tuning configurations. This mode eliminates the need for the player to carry multiple guitars with different tunings or manually retun them on stage; (e) Virtual capo: The user triggers the controller to select the target pitch shift by a semitone (positive value increases, negative value decreases), and the control circuit (50) controls the drive motor (40) of each string to synchronously adjust the strings, so that the tension of each string changes proportionally to produce a uniform pitch shift effect. When the pitch is increased, the effect is the same as using a physical capo, but the physical pressure of the capo on the strings (causing a brighter tone and shorter sustain) and the pitch disturbance caused by uneven clamping force on each string are avoided; when the pitch is decreased, a uniform pitch drop below the standard tuning (such as tuning a semitone down) can be achieved without manually retuning each string. (f) Tension vibrato: The control circuit (50) periodically controls the drive motor (40) to reciprocate the position of the lead screw nut (12) at a preset frequency and amplitude, so that the string tension fluctuates periodically in a controlled manner near the target value, producing vibrato / string vibrato effect. Compared with traditional finger vibrato (which depends on the player's skill and the consistency of vibrato on each string is difficult to guarantee) and tremolo (all strings vibrate synchronously and the amplitude cannot be adjusted independently), the tension vibrato of this invention supports: (i) independent vibrato frequency, amplitude and waveform (sine wave, triangle wave, square wave, etc.) for each string; (ii) pre-programmed vibrato parameters or real-time control by a continuous variable controller; (iii) giving a new dimension of performance expression to stringed instruments such as pianos that originally could not apply any pitch changes during the duration of a note - taking the piano as an example, the player can trigger the tension change by pressing the pedal or key, and apply a controllable vibrato or pitch bend effect to the sustained note after the hammer strikes the string, realizing the pitch modulation expression ability that the acoustic piano could not achieve for hundreds of years. For plucked string instruments such as the guzheng, which can achieve limited pitch bend through manipulation, tension vibrato provides a more precise, consistent, and programmable alternative. In all the above active tension modulation modes, the system always maintains real-time closed-loop monitoring of the tension sensor (30). During the modulation process, the tension is precisely controlled in a closed-loop manner, and the target state is automatically maintained after the modulation is completed. The tension change caused by the active modulation command has preset characteristics in terms of rate, amplitude and / or curve, which is completely different from the slow unidirectional characteristics of the natural drift of the string. The two are clearly distinguished by the control logic.

[0030] It is important to note that the active tension modulation mode of this invention does not simulate pitch changes through audio signal processing (DSP)—DSP pitch bend alters the audio signal rather than the physical vibration of the strings, resulting in unrealistic timbre and overtone structure. This invention, however, directly changes the physical tension of the strings through a lead screw mechanism, providing realistic and physical pitch changes that preserve all the tonal characteristics and overtone structure of acoustic instruments. This is the fundamental difference between this invention and digital audio effects processors.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. High tuning accuracy: The lead screw drive mechanism precisely converts rotary motion into linear displacement with a fixed pitch. The nut displacement corresponding to each step of the motor can be accurate to the micrometer level, and the tuning accuracy far exceeds the smallest discernible pitch difference of the human ear. At the same time, there is no worm gear backlash in the transmission chain, eliminating backlash and nonlinear errors caused by backlash. 2. One-click quick recovery: Closed-loop control based on stored tension values ​​significantly outperforms solutions based on audio frequency detection—no string plucking, no waiting for frequency stabilization, and no frequency analysis required. Especially in noisy environments, it is completely unaffected by ambient noise. When each string is equipped with an independent drive motor and tension sensor, multiple strings can be adjusted in parallel, and the tuning time for the entire instrument is comparable to that for a single string. 3. Purely Mechanical Self-Locking Retention: When using a trapezoidal lead screw (especially a fine-pitch trapezoidal lead screw), natural self-locking is achieved through thread friction, ensuring the string tension remains completely intact even after power is cut off. Combined with a backlash-free nut and friction retaining ring, multiple purely mechanical safeguards ensure the instrument stays in tune for extended periods of playing, completely independent of electricity. The trapezoidal lead screw's self-locking is directional, naturally compatible with manual tuning operations. 4. Flexible modification: The tension adjustment module can be installed as an independent accessory on the string fixing end of existing instruments (such as the headstock, bridge, pinblock, etc.) without irreversible modification to the instrument itself; it can also be used as an integrated component of the whole instrument, with centralized power supply for the whole instrument; 5. Supports custom tuning: Users can freely set and save any tuning scheme via the app to meet the needs of different musical pieces and performance styles. Cloud synchronization allows sharing tuning configurations across multiple devices. 6. Beginner-friendly: No tuning skills required; restore standard pitch with a single click. The app's visual interface provides intuitive tuning guidance. 7. Flexible transmission solutions: such as direct drive, gear reduction, worm gear drive, synchronous belt drive, chain drive, friction wheel drive, magnetic coupling drive and other transmission methods. Screw types include but are not limited to ball screws, trapezoidal screws, rectangular thread screws, sawtooth thread screws and miniature linear actuators based on thread principle, which can be flexibly selected for different product positioning. 8. Multiple string end fixing methods: ball head slot, screw tightening, pressure block locking, clamp block locking, wedge self-locking, zigzag path friction locking and other fixing methods, which can be adapted to different types of strings (steel strings / nylon strings / ballless strings, etc.) and different usage scenarios; 9. Continuous Pitch Preservation – “Instant Pitch When Powered On”: Unlike trigger-based one-button recovery, this invention uses a tension sensor positioned in the string force transmission path, continuously sensing real-time changes in string tension while powered on. Pitch drift caused by slow factors such as temperature, humidity, string plastic elongation, and wood deformation is automatically detected and finely corrected before the user notices, achieving “the instrument is always in standard pitch as long as it is powered on.” This effect relies on the micron-level displacement accuracy of the lead screw and the direct mechanical sensing of the tension sensor – a function that traditional rotating tuning pin solutions (which have gaps and nonlinearities) and audio frequency detection solutions (which cannot be detected without plucking the strings) cannot achieve. 10. Electric Performance Modulation – Independently Controllable Pitch Modulation Capability for Each String: This invention uses the tuning actuator as a performance expression tool. Through any control input device capable of sending modulation trigger signals, the tension of a specified string can be actively changed during performance, achieving effects such as independent pitch bending of single / multi-strings, one-click string bending, pre-programmed tension modulation sequences, one-click tuning switching, virtual capo, and tension vibrato (string bending). Its core advantage lies in the independent controllability of each string – selectively applying pitch modulation only to a specified string, while the pitch of the other strings remains unaffected. This capability transcends the physical limitations of traditional mechanical cranks (which simultaneously change the tension of all strings) and finger-based string bending / vibrato (which relies on the performer's skill and is difficult to guarantee consistency), creating new possibilities that traditional methods cannot achieve: (i) Instant simplification of complex chord fingerings—temporarily changing the pitch of a string during performance simplifies large-span chords into conventional fingerings, with simple fingerings triggering complex harmonies, and automatically returning to their original positions after performance; (ii) Single-string bending does not affect other strings—only the target string experiences pitch changes; (iii) Precise and controllable pitch bend intervals—the modulation amplitude can be calibrated to a specific interval, with precision and consistency far exceeding manual operation; (iv) Automatic and precise return to the original position after bending, eliminating the problem of pitch deviation associated with traditional cranks; (v) Support for pre-programming—tension changes can be automatically executed according to a preset sequence; (vi) Support for independent tension vibrato for each string—frequency, amplitude, and waveform can be set independently, enabling entirely new performance expressions on struck string instruments such as the piano, which originally could not apply any pitch changes during the duration of a note, or providing electronic modulation with precision far exceeding that of manual operation on plucked string instruments such as the guzheng. This effect is a direct reflection of the system performance of precision lead screw transmission + closed-loop force sensor + digital control; 11. Platform-based Expansion Capability: The core architecture of this invention—linear lead screw transmission + closed-loop tension sensor + digital control—constitutes an open platform. New control modes (such as the aforementioned continuous hold, active modulation, and other modes that may be developed in the future) can be implemented through software / firmware upgrades without changing the hardware structure. The control input device can be any device capable of sending commands to the control circuit (foot pedal, handheld, wearable, voice control, eye tracking, etc.), and the control logic and interaction method are software-defined, not limited to the factory-preset functions. This "hardware platformization + software-defined functions" architecture means that the scope of protection of this invention is not limited to the specific application scenario described here, but covers all tension control functions that this hardware architecture can achieve. Attached Figure Description

[0032] Figure 1: Schematic diagram of each part, showing the relationship between the strings, string end fixing device, tension sensor, lead screw transmission mechanism, drive motor and control circuit board in the form of mechanical line drawing.

[0033] Figure 2: System circuit block diagram, showing the electrical connection between the control circuit board, tension sensor, and drive motor.

[0034] The arrangement and relative positions of the components in Figure 1 are for illustrative purposes only and do not constitute a limitation on the actual structure of the product. In particular, the front-to-back arrangement of the string end fixing device (20) and the tension sensor (30) in Figure 1 is only an exemplary representation. In actual implementation, the tension sensor (30) can be placed on either side of the string end fixing device (20) along the force transmission direction, or integrated with the string end fixing device (i.e., the string end fixing device itself constitutes the force-bearing structural component of the tension sensor), as long as the tension sensor is in the force transmission path of the string tension.

[0035] The same reference numerals in the figures indicate the same or similar parts. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," "outer," "axial," and "radial," etc., indicate the orientation or positional relationship based on the orientation or positional relationship of the musical instrument in its normal playing posture (headstock facing up, body facing down). They are only used for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0038] Example 1: Trapezoidal lead screw scheme (independent module for each chord) Referring to Figures 1 and 2, this embodiment provides a guitar tension adjustment system based on trapezoidal lead screw transmission and tension memory. The guitar is a six-string guitar, with six independent tension adjustment modules 100 installed on the headstock. The six modules are arranged in a 3×2 staggered pattern on the headstock to fully utilize the headstock space and maintain a clean appearance. Each tension adjustment module 100 includes: A lead screw transmission mechanism 10 includes a lead screw 11 and a lead screw nut 12 that mates with the lead screw thread. The lead angle of the lead screw 11 is much smaller than the thread friction angle, satisfying the self-locking condition. The lead screw nut 12 adopts a backlash-free nut structure—consisting of two half-nuts offset relative to each other along the axial direction by elastic elements. The two half-nuts abut against both sides of the lead screw thread, eliminating thread backlash. The two ends of the lead screw 11 are supported within the module housing by bearings. A string end fixing device 20 is provided at the end of the lead screw nut 12. In this embodiment, the string end fixing device is a ball head groove: a groove is opened on the extension arm of the nut 12, and a narrow slit is opened at the top of the groove. The width of the narrow slit is greater than the diameter of the string and smaller than the diameter of the ball head. After the ball head of the string 90 is put into the groove, the string passes through the narrow slit, and the string tension pulls the ball head towards the bottom of the groove; A tension sensor 30 is positioned on the force transmission path between the lead screw nut 12 and the ball head slot. Specifically, one end (the force-bearing end) of the tension sensor 30 is fixedly connected to the lead screw nut 12, and the other end (the measuring end) is fixedly connected to the extension arm where the ball head slot is located. When the string 90 is under tension, the tension is transmitted through the path of ball head → ball head slot → tension sensor 30 → lead screw nut 12 → lead screw 11 → bearing → module housing → headstock. The tension sensor 30 is positioned in this path to directly measure the actual value of the string tension. A drive motor (40) is fixed inside the module housing, and its output shaft is coaxially connected to one end of the lead screw (11); A control circuit board (50), installed inside or outside the module housing, includes a microcontroller (MCU) and non-volatile memory, a motor drive chip, a signal conditioning circuit (for analog signal amplification and analog-to-digital conversion of the tension sensor (30), and integrates a communication module. The control circuit board (50) is electrically connected to the tension sensor (30) and the drive motor (40); A physical button is located on the outer surface of the module housing to trigger a one-key recovery operation; An LED indicator light is provided to indicate the completion status of the tuning process; One power supply module: Each tension adjustment module 100 has a built-in battery.

[0039] The lead screw 11 has a manual operating part (such as an internal hexagonal socket or a protruding knob) at the end away from the motor. The user can manually adjust the tone by directly rotating the lead screw with a tool (or fingers) when there is no power.

[0040] The lead screw (11) is provided with a friction retaining ring at its shaft end—a spring-compressed friction ring that fits tightly against the bearing end face or a dedicated friction surface to provide constant friction torque, serving as a second line of defense against accidental reverse rotation of the lead screw.

[0041] Initial Calibration (Path B – Electric Assisted Calibration): The user connects to each tension adjustment module 100 via the APP and selects the "Standard Tuning" mode. For each string, the following steps are performed sequentially: The string 90 is manually plucked. The built-in piezoelectric sensor (not shown separately in the diagram, but integrated into the module housing at the string contact point) or the phone microphone collects the string's vibration frequency. The APP analyzes the current pitch and displays the deviation from the target pitch (in centimeters). Simultaneously, the tension sensor 30 detects the current tension value in real time and displays it on the APP. The user selects "Automatic Calibration of this String." The microcontroller controls the stepper motor 40 to drive the lead screw 11 to rotate, and the lead screw nut 12 moves axially, stretching or loosening the string 90 until the vibration frequency matches the target pitch and the tension value stabilizes. At this point, the microcontroller writes the string's current tension value into non-volatile memory as the target tension value for that string in "Standard Tuning" mode. The above steps are performed sequentially (or simultaneously, as each module operates independently) for all six strings to complete the initial calibration.

[0042] One-click recovery: During daily use, the user presses the physical button on any module (or triggers all modules with one click via the APP). The microcontroller reads the target tension values ​​of the six strings from the non-volatile memory. For each string, the microcontroller reads the current tension value from the tension sensor 30, compares it with the target tension value, and controls the stepper motor 40 to rotate forward or backward to adjust the position of the lead screw nut 12 until the deviation between the current tension value and the target tension value falls within the preset tolerance range. The adjustment of all six strings can be performed simultaneously. After all strings have been adjusted, the LED indicator turns green (or emits a buzzer signal) to indicate that the tuning is complete. The entire one-click recovery process requires no string plucking or audio acquisition and works reliably even in noisy environments.

[0043] Example 2: Ball screw combined with electromagnetic brake scheme This embodiment is basically the same as Embodiment 1, except that: - The lead screw drive mechanism 10 uses a ball screw (high precision grade, fine pitch) instead of a trapezoidal lead screw. The ball screw has an efficiency of about 90% or more and very low rolling friction, which can further reduce motor power consumption and improve response speed, but it does not have self-locking capability - the tension of the string is sufficient to reverse drive the lead screw nut to loosen the tension; - A power-off locking electromagnetic brake is added to the shaft end of the lead screw 11 (on the side near the motor 40). When the power is off, the electromagnetic brake presses the brake pads with an internal spring, locking the lead screw 11 to prevent reverse rotation; when energized (when the system is working normally), the electromagnet overcomes the spring force to release the brake pads, and the lead screw 11 can rotate freely; - The control line of the electromagnetic brake is electrically connected to the control circuit board 50. After the system is powered on, the microcontroller first energizes the electromagnetic brake to release the brake, and then performs the tuning operation. After tuning is completed, the microcontroller can choose to keep the brake energized (continuously consuming a small amount of power) or de-energize and lock it (consuming no power at all). Before one-key recovery, the microcontroller first energizes and releases the brake, and then performs tension adjustment; - A manual release lever is added to the electromagnetic brake. When the battery is completely depleted, the user can manually release the brake pads by moving the lever, temporarily unlocking them, and then manually tune the brake by rotating the lead screw (11) through the manual operating part using a tool. After releasing the lever, it automatically resets, and the brake pads lock again. - Because the ball screw is not self-locking, manual tuning requires first moving the release lever, which is less convenient than the trapezoidal screw solution in Example 1. Therefore, this embodiment is suitable for products that prioritize electric adjustment efficiency and precision but accept slightly more complex manual operation (such as high-end performance pianos). As an alternative or additional solution, a one-way bearing (wedge clutch) can be used instead of an electromagnetic brake, allowing the screw to rotate only in the tightening direction while preventing the string from reversing in the loosening direction. However, the string loosening (lowering pitch) operation under the one-way bearing solution requires an additional release mechanism.

[0044] Example 3: Simplified Scheme Without Self-Locking This embodiment is basically the same as embodiment one, except that: the lead screw transmission mechanism (10) uses a lead screw type that does not have self-locking characteristics (such as a ball screw), and is not equipped with any self-locking or anti-reverse device—no electromagnetic brake, no one-way bearing, no ratchet mechanism, and no worm gear reducer. During system power-on, all functions such as one-key recovery, continuous pitch maintenance, and active tension modulation operate normally. The realization of these functions depends on the lead screw transmission accuracy, the closed loop of the tension sensor, and the motor drive, and is unrelated to whether the lead screw is self-locking. After power-off, the string tension is naturally released, and the string returns to a relaxed state.

[0045] This solution has the simplest structure and lowest manufacturing cost, making it suitable for applications such as: permanently plugged-in equipment (e.g., fixed-installation performance instruments, recording studio instruments); products where the strings are expected to automatically release after power failure to protect the strings and instrument body from long-term static stress; or any application where maintaining tension after power failure is not required. It should be noted that the screw type in this embodiment is not limited to ball screws—any screw type that does not possess self-locking characteristics is applicable; the ball screw is merely an example.

[0046] Example 4: Compact Layout Scheme for Worm Gear Drive In this embodiment, the drive motor 40 and the lead screw 11 are connected by a worm gear transmission. The motor 40 is arranged laterally (its axis forms a 90-degree angle with the lead screw axis), the worm is mounted on the motor output shaft, and a worm wheel is mounted on the end of the lead screw 11. The worm and the worm wheel mesh.

[0047] Worm gear drives inherently possess self-locking characteristics (when the worm lead angle is less than the friction angle, typically a single-start worm with a sufficiently large reduction ratio), thus achieving self-locking upon power failure regardless of whether the screw type is a trapezoidal screw or a ball screw. Furthermore, the reduction ratio of a worm gear drive can replace a separate reduction gear set, achieving a large reduction ratio within a smaller space.

[0048] The motor 40 is arranged laterally on the side of the lead screw 11, rather than extending axially, which significantly reduces the total axial length of the module (saving the space occupied by the motor axially). This is particularly suitable for instruments with limited space for the headstock thickness (such as violins and ukuleles).

[0049] The self-locking reliability of worm gear drives may not be as good as that of trapezoidal lead screws under continuous vibration environments (worm gear drives may experience slow slippage). Therefore, in this embodiment, trapezoidal lead screws are preferred to be used to form a double self-locking system of "worm gear self-locking + trapezoidal lead screw thread self-locking". In addition, a friction retaining ring or a miniature electromagnetic brake can be added to the worm shaft as a third line of defense.

[0050] Example 5: Single motor + electromagnetic clutch multi-string solution This embodiment provides a drive motor 40 that selectively drives the lead screw corresponding to different strings via an electromagnetic clutch assembly. Specifically: - A drive motor 40 is fixed in the center of the headstock; - A drive gear is installed on the motor output shaft; - The driven gear and electromagnetic clutch are respectively installed at the ends of the lead screw 11 corresponding to each of the six strings; - Each electromagnetic clutch is in a disengaged state when power is off, and the lead screw does not rotate with the driving gear; When a string needs to be tuned, the control circuit board 50 energizes the electromagnetic clutch corresponding to that string to engage it. The rotational power of the motor 40 is transmitted through the driving gear → the driven gear of the string → the electromagnetic clutch of the string → the lead screw of the string, driving the lead screw nut to move.

[0051] This solution replaces six independent motors with a single motor and clutch assembly, reducing the number of motors and overall weight, thus lowering costs. The trade-off is the sacrifice of multi-string parallel adjustment capability—tuning can only be done string by string, and the total tuning time equals the single-string tuning time multiplied by the number of strings. Simultaneously, the electromagnetic clutch system increases electrical control complexity and potential points of failure. It is suitable for cost-sensitive products or small musical instruments with extremely limited space (such as the ukulele). This embodiment can be used in combination with any lead screw type and self-locking scheme in Embodiments 1, 2 or 3.

[0052] Example 6: Multiple methods for fixing string ends Depending on the type of string and the application scenario, the string end fixing device 20 can be any of the following: (a) Ball head slot (refer to Figure 1): As detailed in Example 1, it is suitable for steel strings with a built-in ball head. The preferred installation direction of the ball head slot is: the ball head end faces the headstock (tension adjustment module end), and the string 90 extends from the narrow slit through the nut to the bridge. For standard single-ball head steel strings, the factory-installed ball head end can be used for the headstock tuning end, and the bridge end can be clamped separately; (b) Screw tightening: A string hole is made on the extension arm of the lead screw nut 12. After the string 90 passes through the string hole, a tightening screw is screwed in vertically from above, with the end face of the screw directly pressing against the string. This is suitable for strings without ball heads or when the end of the string has been cut off. (c) Clamping Block Locking: Two clamping blocks with semi-circular grooves fit together to form a complete string clamping hole. The string passes through the string clamping hole at a 90° angle, and the two clamping blocks are locked together by screws. The grooves of the clamping blocks may have fine textures to increase friction. Compared to screws directly pressing the string, clamping block locking causes less local stress on the string surface; (d) Wedge-shaped self-locking: A V-shaped groove is provided on the base, with the narrow opening of the V-shaped groove facing the direction of string tension and the wide opening facing the opposite direction. A wedge-shaped locking block is provided inside the V-shaped groove, with the wedge angle matching the included angle of the V-shaped groove. A through hole is opened on the wedge-shaped locking block for the string to pass through. The string 90 enters from the narrow opening of the V-shaped groove, passes through the through hole on the wedge-shaped locking block, loops back, and then exits from the same narrow opening of the V-shaped groove (traveling a U-shaped path inside the wedge). When the string is pulled towards the bridge under tension, the wedge-shaped locking block is dragged towards the narrow opening of the V-shaped groove, and the two side walls of the V-shape squeeze the wedge-shaped locking block, causing it to press the two ends of the string into and out of the V-shaped groove tightly against the two side walls of the V-shaped groove. The greater the string tension, the deeper the wedge is pulled into the narrow opening, the greater the squeezing force, and the greater the clamping force—creating a "tightening as it is pulled" self-locking effect. To release the string, use your fingers or a tool to push the wedge-shaped locking block outwards from the wide opening (the wide opening side of the V-groove) to disengage it. This method requires no screws, no tools, and is not dependent on whether the string ends have a ball. It is suitable for any type of string, including nylon strings, bare steel strings, and ballless violin strings. (e) Twisted Path Friction Locking: At least two staggered string holes are provided on the lead screw nut 12 or the tension adjustment module body. The holes are not coaxial along the string threading direction. After the string 90 passes through each hole in sequence, it forms an S-shaped bending path. Each bend increases the normal force between the string and the edge of the hole (winch effect) due to the change in string direction. The tension at the end of the path is gradually reduced at each bend. After locking, the string is extremely difficult to slip out. A pressure block driven by an eccentric cam can be optionally added between the two string holes. Pressing down the cam handle can further increase the friction locking force, and lifting the handle can release it.

[0053] Example 7: Self-tightening linkage locking mechanism When the string end fixing device 20 adopts a screw clamping or pressure block locking method, a self-tightening linkage string locking mechanism can be further configured to enhance ease of use and reliability. An exemplary solution for a self-tightening linkage locking mechanism is as follows: - The end (or extension) of the lead screw 11 is connected to a small worm gear via a one-way clutch (such as a one-way needle roller bearing); - The worm gear meshes with a threaded post (or the threaded post directly engages with a nut), and the rotation of the threaded post drives a pressure block to rise / fall in a direction perpendicular to the string at 90 degrees. - The transmission direction of the one-way clutch is set as follows: When the lead screw 11 rotates in the direction of tightening the string, the torque is transmitted through the one-way clutch to the worm gear → threaded column → pressure block rises, pressing the string 90 against the fixed surface from below, and the clamping force increases synchronously. When the lead screw 11 rotates in the direction of loosening the string, the one-way clutch slips, the torque is not transmitted to the worm gear, the pressure block remains in place—the clamping force does not decrease; - The end of the threaded post is provided with a relief groove or a smooth rod area to form a mechanical travel limit. After the threaded post rotates to the limit position, it automatically disengages from the thread engagement and enters the smooth rod area to idle, preventing excessive clamping and damage to the strings. When it is necessary to loosen or change strings, the user first rotates the screw 11 in the reverse direction to release the string tension (at this time, the pressure block remains pressed due to the slippage of the one-way clutch), and then uses a tool to rotate the threaded column in the reverse direction (to overcome the friction of the worm gear or to design the worm gear to be driven in reverse), causing the pressure block to descend and loosen the strings. This solution achieves a mechanical linkage of "automatic string locking upon tuning and tightening", combining the three-step operation of "string loading - tuning - string locking" into one, eliminating the need for separate string locking steps and tools.

[0054] Example 8: A Complete Solution for APP Control and Cloud Synchronization This embodiment, based on the hardware of Embodiment 1, fully describes the functions of the APP and the cloud. APP functional modules: - Device Discovery and Connection: The app scans for nearby tension adjustment modules via wired / wireless connection, displays a list of devices and signal strength, and allows users to connect by clicking. Multiple modules can be connected simultaneously (six modules in total for a six-string guitar). - Dashboard Homepage: Displays the current tension values ​​(numerical value + progress bar) of the six strings in a graphical way. The target tension value of each string is marked on the progress bar as the "bullseye". The deviation between the current value and the target value is distinguished by color (green = met, yellow = slightly off, red = needs adjustment). - Tuning mode selection: Provides a list of preset tuning modes (Standard EADGBE, Half-tone Lower, Whole-tone Lower, Open G, Open D, DADGAD, Drop D, etc.), and users can create custom modes and name them; - One-click tuning: Clicking the "One-click tuning" button sends a recovery command to all connected modules. Each module independently performs tension comparison and adjustment, with progress updated in real-time on the app. The app sends a completion notification once all strings are tuned. - Manual Remote Control: Select a string to enter the "Manual Remote Control" interface. The interface features a large virtual knob (rotatable and touch-sensitive) in the center, with "+" and "-" fine-tuning buttons on the left and right sides (each press increments the motor rotation by a small step), and the bottom displays the current tension value in real time. Users can operate their mobile phone while plucking the string, remotely controlling the motor at the headstock from their playing position. - Custom tension scheme: After the user tunes the string to a satisfactory state in manual remote control mode, click "Save Current Tension", enter the scheme name, and the tension value will be saved to the APP's local storage and cloud account; - Cloud Synchronization: After logging into their personal account, all custom tuning schemes are automatically uploaded to the cloud server. When users change devices, phones, or use the same model guitar, they can download the saved tuning schemes from the cloud.

[0055] Control circuit firmware functions: - OTA Upgrade: When the app detects a new firmware version available on the control circuit, it prompts the user to upgrade. After user confirmation, the app wirelessly sends the firmware package in packets to the control circuit. The control circuit writes the firmware to its internal Flash memory and reboots to the new firmware after successful verification. If the upgrade process is interrupted, the control circuit can roll back to the previous version.

[0056] Example 9: Continuous Pitch Holding Mode This embodiment describes the operation of the continuous pitch-holding mode based on the hardware of Embodiment 1. After the system is powered on, the control circuit board (50) defaults to continuous pitch holding mode. The microcontroller polls the current tension value of each tension sensor (30) at a preset frequency (e.g., 10 to 100 times per second) and compares it with the target tension value of each string stored in the memory one by one. For each string, the microcontroller maintains a "drift counter": when the deviation between the current tension value and the target tension value exceeds the preset threshold (the threshold corresponds to the tension change of, for example, 2 cents) in N consecutive samplings (N is a preset value, for example, N=5 to 50 is configurable), and the deviation direction is consistent (both are too high or both are too low), it is determined that the string has experienced pitch drift, and a fine-tuning correction is automatically triggered - the microcontroller controls the corresponding drive motor (40) to drive the lead screw (11) in a low-speed microstep manner, and after each correction of a minimum step, the value of the tension sensor (30) is reread and compared until the deviation falls back to the tolerance range. The logic for distinguishing between "natural drift" and "playing action" is as follows: If the rate of change of tension (the amount of tension change per unit time) exceeds a preset rate threshold—this threshold is set to be greater than the maximum rate of change caused by natural factors such as temperature drift and plastic elongation of the string, but less than the typical rate of change for playing actions such as string bending and vibrato—it is judged as a playing action, and the system does not intervene. If the rate of change is lower than the rate threshold, the direction is consistent, and the duration exceeds a preset window, it is judged as natural drift, and correction is performed. This logic ensures that the system will not mistakenly trigger "correction" when the player is bending or vibratoing the string. To address potential ambiguities in extremely slow string bending scenarios (such as slow microtone bends) when using rate-of-change differentiation, the following methods can enhance the differentiation capability: If the system is equipped with finger position detection (e.g., a finger position sensor on the fingerboard to detect the fret the player is currently pressing), then combining finger position change information—when the finger position change and tension change are in the same direction and the proportion matches the physical characteristics of the string at that fret—is it determined to be a glissando or playing action; when there is no finger position change but the tension slowly drifts in one direction, it is determined to be natural drift. When the system is not equipped with finger position detection, differentiation relies on a rate-of-change threshold and a duration window. In most practical scenarios—the timescale of natural drift is from minutes to hours, while playing actions are from seconds to milliseconds—the rate difference between the two is sufficient for reliable differentiation. The continuous pitch hold mode and the one-key recovery mode coexist in an overlapping manner: continuous pitch hold handles minor daily pitch maintenance (usually within a few cents), while one-key recovery handles larger-scale batch recalibrations (such as after replacing strings). Users can disable / enable continuous pitch hold mode at any time via a physical button or the app.

[0057] Example 10: Active Performance Modulation Mode This embodiment, based on the hardware of Embodiment 1, describes the specific implementation of active tension modulation (electrical performance modulation). Input method: The control circuit board (50) can receive modulation commands in any way, including but not limited to: wireless reception via the wireless communication module (such as BLE, Wi-Fi) integrated into the control circuit board (50); wired reception via the wired interface (such as 6.35mm TRS, USB, UART) led out from the control circuit board (50); or generation of modulation commands via input components directly integrated into the system body (tension adjustment module housing or piano body). The physical form of the input component is not limited - it can be a physical button, touch screen, knob, touch sensing strip, pressure sensor, etc., all of which are essentially sending modulation trigger signals to the control circuit (50). The connection method, communication protocol and control signal format between the controller and the system do not constitute a limitation on the scope of protection of this invention.

[0058] Controller Input Processing: The microcontroller continuously reads the controller's input values. For continuous variable controllers (such as expression pedals), the microcontroller maps analog voltage or digital position values ​​(0-127 standard MIDI range or higher precision) to a target tension offset. The mapping can be linear (pedal position proportional to cent offset) or a custom curve (e.g., small offset for the first half of the pedal travel, large offset for the second half). For discrete controllers (such as foot switches), the microcontroller detects edge triggering (press / release) and executes the corresponding preset action.

[0059] The workflow of the pitch bend mode: When the user presses the expression pedal, the microcontroller detects the change in pedal position and calculates the target tension value corresponding to the current pedal position based on the currently selected pitch bend configuration (including the target string number, maximum pitch bend amplitude, and mapping curve). The microcontroller controls the drive motor (40) of the string to drive the lead screw (11) at a speed suitable for musical expression—rather than at the maximum speed of the tuning mode—to adjust the tension to the target value. The tension sensor (30) provides closed-loop feedback throughout the process. When the user releases the pedal, the motor reverses at a preset return speed, and the string tension returns to the original target value. The return speed can be set independently (such as fast return or gradual return) to adapt to different musical expression needs.

[0060] The workflow of the one-button string bending mode: When the user presses the foot switch (or the button on the instrument body), the microcontroller detects the trigger signal and reads the preset string bending parameters corresponding to the switch—including the target string, the string bending interval (e.g., a major second = 200 cents, a minor third = 300 cents), the rise time (e.g., 100ms, 200ms, 500ms, etc.), and the pitch bend curve (linear / exponential / S-curve). The microcontroller generates a tension-time trajectory based on these parameters and controls the drive motor (40) to drive the lead screw nut (12) to move according to the trajectory to change the string tension. At the same time, the tension sensor (30) provides real-time feedback to ensure the accuracy of the trajectory. After the rise phase is completed, if the user continues to press the switch, the system maintains the pitch bend state (during the continuous hold mode, the drift detection of the string is paused because the tension deviation from the target value is the result of active modulation). After the user releases the switch, the motor reverses and returns to its original position at the preset return speed. If the user wants to continue to add pitch bend during the string bending hold (e.g., using the pedal to further bend the pitch after the string is bent), the system supports the collaborative input of multiple controllers.

[0061] The workflow of the pre-programmed sequence mode: Users pre-create tension modulation sequences via an APP or computer software. The sequence is based on a timeline, and each event includes: trigger time (milliseconds relative to the start of the sequence), target string number, target tension offset, transition curve type and transition duration, hold duration, return curve type and return duration. The sequence can be transferred to the memory of the control board (50) via the APP. During performance, the user triggers the sequence start via a foot switch, and the microcontroller reads the preset sequence and executes it event by event based on the internal clock reference. The user can terminate the sequence early or jump to the next paragraph via another foot switch. For scenarios requiring synchronization with the band / accompaniment, the sequence can be synchronized via an external MIDI clock signal.

[0062] The one-click string switching workflow: The user cycles through preset string tuning mode numbers via a foot switch (or selects directly via the APP). After confirmation, the microcontroller reads a set of target tension values ​​corresponding to the tuning mode from the memory and loads the new target tension value as the current valid target value. The microcontroller controls the drive motors (40) of each string in parallel to adjust synchronously—each string moves independently to its own new target tension value at a preset switching speed. During the switching process, the tension sensor (30) provides real-time feedback on the current tension value of each string. After all strings are in position, the system issues a confirmation signal (LED / display). The switching speed can be set in the APP (fast switching vs. silent gradual switching).

[0063] The virtual capo's workflow: The user selects the number of semitones to change the pitch (e.g., +1, +2, +3... or -1, -2, -3..., positive values ​​increase and negative values ​​decrease). The microcontroller calculates the new target tension value based on the current target tension value of each string and the selected semitone (the relationship between the tension change and the semitone can be obtained through theoretical calculation or actual calibration based on the physical characteristics of the strings). The microcontroller controls the drive motors (40) of each string to simultaneously tighten or loosen the strings to the new target value. After the user switches back to 0 semitones or turns off the virtual capo function, the original target tension value is restored.

[0064] The working process of tension vibrato: The control circuit (50) periodically controls the drive motor (40) to adjust the position of the lead screw nut (12) slightly back and forth near the target tension value using preset vibrato parameters—including vibrato frequency (such as the typical vibrato frequency range of 3Hz to 8Hz), vibrato amplitude (corresponding to the target cent offset, such as ±5 to ±30 cents), and vibrato waveform (sine wave, triangle wave, square wave, etc.). For guitars, tension vibrato can be used as an auxiliary or alternative to traditional finger vibrato to achieve an independent and precise vibrato effect for each string. For pianos, when the player presses the sustain pedal and presses the key, the tension vibrato of the corresponding string is triggered—during the sustained phase after the hammer strikes the string, the string tension is periodically finely adjusted in a controlled manner, adding unprecedented pitch modulation expression capabilities to the acoustic piano. Vibrato parameters can be adjusted in real time by a continuous variable controller (such as the expression pedal or the pressure sensitivity after pressing the key), or can be pre-programmed into a fixed parameter group and switched by a discrete controller. In vibrato mode, drift detection distinguishes between normal vibrato modulation and genuine pitch drift based on the periodic characteristics of the vibrato waveform (preset frequency and amplitude range).

[0065] Synergy with sustained hold and drift detection: In active modulation mode, the system avoids misjudging modulation actions as drift and corrects them through the following mechanisms: (i) When the modulation command arrives, drift detection of the string is automatically paused and automatically resumed after modulation is completed; (ii) The tension change caused by the modulation command has clear preset characteristics in terms of rate and amplitude, which are clearly distinguished from the slow unidirectional characteristics of natural drift at the control logic level; (iii) During modulation, the target tension value itself is temporarily replaced by the modulation dynamic value, and drift determination is based on "actual value vs. current dynamic target value" rather than "actual value vs. original stored target value". After modulation ends, the system restores the original stored target value and reactivates drift detection.

[0066] Platform Architecture Description: All the above modulation modes are implemented by the firmware / software of the control circuit (50), regardless of the hardware structure. New modulation modes, new controller types, new mapping curves, and interaction logic can all be implemented on the deployed hardware through firmware upgrades (OTA or local updates) without any hardware modifications. The type of control input device (pedal-type, handheld, wearable, voice control, eye tracking, etc.) only needs to implement the basic function of "sending tension modulation commands to the control circuit" to be integrated with this system—the system does not restrict the specific physical form of the controller.

[0067] Defensive disclosure: Alternative detection methods It should be clarified that although the embodiments of the present invention use a tension sensor to directly measure the string tension as the tuning reference, there are various equivalent alternatives to the detection method of the auxiliary sensing unit without departing from the core concept of "linear screw transmission" of the present invention. The following detection methods can all be used in conjunction with the screw transmission mechanism in the present invention, and this specification discloses them as part of the prior art to support the inventive step argument of the present invention and to prevent others from obtaining patent protection for the following simple substitutions: (1) Optical detection: An optical scale (such as a grating ruler or encoder) is set on the lead screw nut or related moving parts, and the displacement is read in conjunction with a photoelectric sensor. The string tension is indirectly determined through the displacement-tension calibration relationship. Alternatively, a laser displacement sensor is set on the side of the string path to directly measure the lateral displacement response of the string when the tension changes; (2) Hall effect detection: Install permanent magnets on the lead screw or motor shaft, detect the rotation angle and speed through Hall sensors, calculate the nut displacement by combining the lead screw pitch, and then indirectly determine the tension through the displacement-tension calibration relationship; (3) Piezoelectric detection: Piezoelectric elements are installed between the string end fixing device and the screw nut, or between the bridge and the body of the instrument. The amount of charge or voltage signal generated by the piezoelectric element under pressure indirectly reflects the string tension. (4) Capacitance detection: Capacitor plates are set between the end fixing device or the lead screw nut and the reference surface. The small displacement is indirectly detected by the capacitance change caused by the change in the distance between the plates, and then the tension is calculated. (5) Strain gauge testing: Strain gauges are attached to the extension arm of the lead screw nut or the module housing. The elastic deformation of the stressed structure is detected by the change in the resistance of the strain gauges, and the tension of the string is indirectly calculated. (6) Magnetostriction detection: Utilizing the inverse effect of magnetostrictive materials, a magnetostrictive element is connected in series in the tension transmission path of the string, and stress is detected by changes in magnetic field or electrical signal. All of the aforementioned alternative detection methods can be combined with the screw drive mechanism of this invention (which converts rotary motion into linear motion) to form a tension adjustment system, and all fall within the protection scope of this invention. However, the scheme of directly placing the tension sensor in the string tension transmission path is a particularly effective implementation method because it requires no calibration conversion, is unaffected by temperature drift and environmental interference, and provides direct and reliable measurement.

[0068] The tension adjustment system of the present invention can be used as: - Independent modification parts: can be directly installed on the string fixing end of existing instruments such as guitars, basses, and ukuleles, replacing or covering traditional tuning pegs (or nut, tuning pins, etc.) without requiring irreversible modification to the instrument itself; - Integrated instrument assembly: Integrated inside the string fixing end of the newly manufactured instrument, powered centrally by the instrument body, and serves as a standard functional module of the instrument; - Subsystems of modular musical instruments: Working in conjunction with other functional modules such as finger position detection neck and detachable body, they form a complete modular intelligent musical instrument system.

[0069] Those skilled in the art should understand that the technical features in the above embodiments can be arbitrarily combined without conflict to form new implementation methods, and these combined implementation methods also fall within the protection scope of this invention. The above descriptions are merely embodiments of this invention and do not limit the patent scope of this invention. Any equivalent structural or procedural transformations made based on the description and drawings of this invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this invention.

Claims

1. A tension adjustment device for stringed instruments based on screw drive, used to replace traditional wound-wound tuning pegs, characterized in that, include: The lead screw drive mechanism (10) includes a lead screw (11) and a lead screw nut (12) that is threadedly engaged with the lead screw, wherein the lead screw nut (12) can move linearly along the axial direction of the lead screw (11); A string end fixing device (20) is provided on or connected to the lead screw nut (12) and is used to fix one end of the string (90); The rotation of the lead screw (11) drives the lead screw nut (12) to move axially, thereby directly and linearly changing the tension of the fixed string (90); the lead screw (11) can be operated manually or driven by a motor.

2. A tension adjustment system for stringed instruments based on screw drive and tension memory, characterized in that, include: At least one tension adjustment module (100), the tension adjustment module (100) comprising: (1) A lead screw drive mechanism (10) includes a lead screw (11) and a lead screw nut (12) that is threadedly engaged with the lead screw, wherein the lead screw nut (12) can move linearly along the axial direction of the lead screw (11); (2) String end fixing device (20), which is set on the lead screw nut (12) or connected to the lead screw nut (12) and is used to fix one end of the string (90); (3) Tension sensor (30), which is set on the force transmission path between the string end fixing device (20) and the string (90), is used to detect the current tension value of the string (90); (4) A drive motor (40) is connected to the lead screw (11) through a transmission mechanism to drive the lead screw (11) to rotate; The control circuit (50) is electrically connected to the drive motor (40) and the tension sensor (30). The control circuit (50) includes a microcontroller and a memory. The memory is used to store at least one set of target tension values, and each set of target tension values ​​corresponds to the target tension of each string under a tuning configuration. The control circuit (50) is configured to: read the target tension value from the memory, compare the current tension value detected by the tension sensor (30) with the target tension value, and control the drive motor (40) to drive the lead screw (11) to rotate based on the comparison result, so that the lead screw nut (12) moves axially to change the string tension until the current tension value matches the target tension value.

3. A tension modulation system for stringed instruments based on screw drive, characterized in that, include: At least one tension adjustment module (100), the tension adjustment module (100) comprising: (1) A lead screw drive mechanism (10) includes a lead screw (11) and a lead screw nut (12) that is threadedly engaged with the lead screw, wherein the lead screw nut (12) can move linearly along the axial direction of the lead screw (11); (2) String end fixing device (20), which is set on the lead screw nut (12) or connected to the lead screw nut (12) and is used to fix one end of the string (90); (3) Tension sensor (30), which is set on the force transmission path between the string end fixing device (20) and the string (90), is used to detect the current tension value of the string (90); (4) A drive motor (40) is connected to the lead screw (11) through a transmission mechanism to drive the lead screw (11) to rotate; The control circuit (50) is electrically connected to the drive motor (40) and the tension sensor (30); The control circuit (50) is configured to: respond to the modulation trigger signal, control the drive motor (40) to actively change the tension of a specified string to produce a pitch modulation effect; the generation method of the modulation trigger signal is not limited.

4. A method for adjusting the tension of a stringed instrument, characterized in that, Includes the following steps: Calibration steps: Perform initial calibration on each string, including adjusting the string tension to achieve the target pitch, and storing the tension value measured by the tension sensor (30) at this time as the target tension value of the string in the memory; wherein, the tension adjustment method includes, but is not limited to, manually rotating the lead screw, driving the lead screw by a motor, or remotely driving the lead screw by a motor through an external terminal device; the method of confirming the target pitch is not limited; Recovery steps: In response to the recovery trigger signal, the target tension value corresponding to each string is read from the memory, and the drive motor (40) drives the lead screw nut (12) to move to adjust the string tension until the current tension value matches the target tension value; Continuous maintenance procedure: When the system is powered on, continuously monitor the current tension value of each string. When the deviation between the current tension value of a string and the target tension value exceeds a preset threshold and continues for more than a preset time window, automatically perform fine-tuning correction without user triggering. Modulation response steps: In response to the modulation trigger signal, control the drive motor (40) to actively change the tension of the specified string to produce a pitch modulation effect; the generation method of the modulation trigger signal is not limited.

5. The tension adjusting device according to claim 1, the tension adjusting system according to claim 2, or the tension modulation system according to claim 3, characterized in that, A multi-layered pure mechanical anti-loosening system is adopted to maintain the string tension in a completely de-energized state. The system includes: the first line of defense - the self-locking of the trapezoidal screw thread friction, which uses the thread friction angle greater than the lead angle to achieve irreversible transmission and prevent the string tension from driving the screw thread (11) to loosen in the reverse direction; the second line of defense - the backlash elimination nut, which uses two half nuts that are elastically offset along the axial direction to abut against both sides of the screw thread to eliminate the thread backlash and prevent micro-movement loosening under vibration environment; the third line of defense - the friction retaining ring, which is pressed on the screw shaft or bearing seat by an elastic element to provide an additional constant friction torque independent of the thread friction force; all three lines of defense are pure mechanical structures and do not rely on electricity or electromagnetic force to maintain tension.

6. The tension adjusting device according to claim 1, the tension adjusting system according to claim 2, or the tension modulation system according to claim 3, characterized in that, The string end fixing device (20) is selected from at least one of the following: (a) A ball head slot, comprising a groove for receiving a string ball head and a narrow slit through which the string passes, the width of the narrow slit being greater than the diameter of the string and less than the diameter of the ball head, wherein the string tension pulls the ball head toward the bottom of the slot to form a self-locking mechanism; (b) A wedge-shaped self-locking mechanism, comprising: a base having a V-shaped groove thereon, wherein the narrow opening of the V-shaped groove faces the direction of string tension and the wide opening faces the opposite direction of the narrow opening; A wedge-shaped locking block is set in the V-shaped groove, and the wedge-shaped locking block has a through hole for the string to pass through; the string (90) enters from the narrow opening of the V-shaped groove, passes through the through hole on the wedge-shaped locking block and then loops back, and then exits from the same narrow opening to form a U-shaped path; when the string is pulled towards the narrow opening by tension, the wedge-shaped locking block is dragged towards the narrow opening, and the two side walls of the V-shape squeeze the wedge-shaped locking block to press the string tight. The greater the tension, the greater the clamping force. (c) A tortuous path friction locking mechanism, including at least two staggered string holes, each hole being non-coaxial along the string passing direction, the string passing through each hole in sequence to form an S-shaped or Z-shaped bending path, the normal force between the string and the edge of the hole at the bending point constitutes a multi-level friction locking.

7. The tension adjustment system according to claim 2, characterized in that, The control circuit (50) is also configured to: continuously read the current tension value of the tension sensor (30) at a preset frequency when the system is powered on; when the deviation between the current tension value of a string and the target tension value exceeds a preset threshold and the duration exceeds a preset time window, automatically control the corresponding drive motor (40) to perform fine-tuning correction so that the current tension value is restored to the tolerance range of the target tension value, and the whole process does not require user triggering; Furthermore, the control circuit (50) distinguishes between natural tension drift of the string and tension change caused by playing actions by at least one of tension change rate determination, change direction continuity determination and / or periodic feature determination, so as to avoid misjudging the playing action as drift and thus correcting it.

8. The tension adjustment system according to claim 2 or the tension modulation system according to claim 3, characterized in that, The control circuit (50) is further configured to: control the drive motor (40) to actively change the tension of a specified string in response to a modulation trigger signal to produce a pitch modulation effect; the generation method of the modulation trigger signal is not limited; for the system of claim 2, the tension drift detection of the modulated string is paused during modulation and automatically resumed after modulation ends; The pitch modulation effect includes at least one of the following: (a) Continuous pitch bending: The continuous variable input is mapped to the target tension offset, and the motor (40) of the corresponding string is driven to adjust the tension in real time to produce continuous pitch changes; (b) One-click string bending: Automatically executes string bending-returning action according to preset string bending parameters - including target pitch offset, pitch bend rate and pitch bend curve; (c) Pre-programmed tension modulation sequence: Automatically executes the tension changes of each string according to a preset timing sequence; (d) One-click string tuning switch: Adjust each string in parallel to a set of target tension values ​​corresponding to the selected preset number; (e) Virtual capo: The tension of each string is changed proportionally to produce a uniform pitch shift effect (positive values ​​increase, negative values ​​decrease). (f) Tension vibrato: Periodically changes the tension of a specified string with a preset frequency, amplitude and waveform to produce a vibrato / string vibrato effect.

9. The tension adjustment system according to claim 2 or the tension modulation system according to claim 3, characterized in that, The control circuit (50) also includes a communication interface for outputting the real-time tension data detected by the tension sensor (30) to an external processing device in the form of a digital signal.

10. A stringed instrument, characterized in that, The instrument comprises any one of the tension adjustment device, tension adjustment system or tension modulation system as claimed in claims 1 to 9; the stringed instrument includes, but is not limited to, guitar, bass, violin, viola, cello, ukulele, banjo, mandolin, guzheng, pipa, erhu, yangqin, piano, and any other stringed instrument whose pitch is determined by string tension.

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