A ball bearing constraint and three-rope driving pen holding mechanism and automatic writing device

Abstract

The application discloses a pen-holding mechanism and an automatic writing device, which are constrained by a spherical bearing and driven by three ropes, and the pen-holding mechanism executes a micro track and comprises a frame, a lifting mechanism, a spherical bearing, a pen holder, three ropes, a feedback detection mechanism, three driving motors and a controller; when executed, the controller calculates the length of the ropes according to the micro track or the pen shaft posture, controls the driving motors to adjust the length of the corresponding ropes, so that the three ropes exert a traction force on the pen holder; meanwhile, the pen holder swings at a small angle around the spherical center under the constraint of the spherical bearing, drives the pen tip to produce a small two-dimensional offset on the writing surface, and forms the final handwriting after superposition with the main track. The pen-holding end of the automatic writing device is combined with the spherical bearing constraint, three-parallel-connection traction, centralized driving, feedback detection and the cooperative control of the main track and the micro track, so that the walking mechanism and the pen-holding mechanism bear different scale writing movements respectively, the track stability is improved, and the handwriting performance is more abundant.

Description

Technical Field

[0001] This invention belongs to the technical field of automatic writing devices, specifically relating to a pen-holding mechanism and an automatic writing device with spherical bearing constraint and three-rope parallel drive, which can improve writing quality, writing speed and handwriting performance. Background Technology

[0002] Existing automatic writing devices typically employ structures similar to XY plotters, small engraving machines, or gantry-type motion platforms. These devices generally consist of an X-axis motion module and a Y-axis motion module that jointly move the pen holder within the writing plane, and a pen-lifting mechanism mounted on the pen holder controls the lifting and lowering of the pen relative to the paper. Patent CN106166741A discloses a high-precision intelligent writing robot that achieves writing through the cooperation of an X-axis and Y-axis motion system and a writing module. The writing module is equipped with a pen-lifting and lowering device and grips the pen. Patent US4567565A discloses an adaptive servo pen-lifting system for XY plotters, and patent US3686681A discloses a pen drive mechanism for a drawing display plotter. These solutions typically use an X / Y platform to handle the planar trajectory, while the pen module is responsible for pen gripping, lifting, lowering, or contact control. Their structure is simple, control is intuitive, and they are suitable for general drawing or text copying tasks. However, writing is not simply two-dimensional coordinate movement. Human writing typically involves a combination of large-scale arm movements, wrist posture adjustments, and fine-grained finger movements. The arm moves the pen to its approximate position, while the wrist and fingers handle details such as the beginning and end of strokes, turns, pauses, connections, speed variations, and pen tip posture. If an automated writing device interprets writing merely as an XY-plane trajectory, it will struggle to fully capture the dynamic characteristics of real writing.

[0003] Therefore, some researchers have focused on pen-gripping devices and drawing pen accessories. For example, patent CN206426748U discloses a pen-gripping device for a drawing robot, which focuses on the gripping, installation, and fixation of the drawing pen. This type of technology can improve the installation reliability of different pens, but its technical focus is on fixing the writing tool and does not enable the pen holder to have the ability to adjust its posture and form a trajectory based on the pen tip. Other researchers have improved the writing effect from the perspectives of vision, learning, force feedback, or whole-machine robotic arms. For example, patent CN104875208A discloses a calligraphy robot, which includes a robotic arm, a soft brush, a pressure sensor, and an ink supply structure; patent CN108237544B discloses an artificial intelligence calligraphy robot, involving a robotic arm, a pen clip, an automatic ink-dispensing brush, a self-learning camera, and a learning algorithm; patent CN110271016B discloses a robotic arm calligraphy writing system and method based on boundary and force feedback, which uses vision and force feedback to improve writing control; patent CN108460369A discloses a drawing practice method and system based on machine vision, focusing on image acquisition, stroke data extraction, and trajectory planning. However, the local details of the writing motion in the above solutions are usually still handled by the robotic arm or the main motion mechanism, and the end pen clip itself is not a low-inertia independent micro-motion execution module.

[0004] It is evident that existing technical solutions still suffer from several limitations: First, the motion function is severely coupled: traditional writing machines delegate the overall character displacement, stroke details, turns, and pauses entirely to the walking mechanism, failing to distinguish between large-scale movements and fine-tuned local adjustments. This results in the walking mechanism frequently performing small-amplitude, high-frequency, variable-curvature movements, placing a heavy control burden on it. Second, the motion inertia is large: gantry or Cartesian platforms typically require the movement of the crossbeam, slider, pen holder, and pen lifting assembly. When writing small characters, complex strokes, or high-speed continuous strokes, the large inertia of the moving parts can cause response lag, vibration, overshoot, or handwriting distortion. Third, the handwriting representation is monotonous: the penholder posture in existing devices is usually fixed, and the pen-holding mechanism lacks the ability to independently modulate the micro-displacement near the pen tip and the penholder posture, making it difficult to simulate the variations in pen tip, stroke thickness, turning force, and personalized writing characteristics in human handwriting. Fourth, high speed and precision are difficult to balance: if the speed of the walking mechanism is increased, the trajectory stability is easily lost at stroke turns, starting points, and ending points; if the speed is reduced to pursue detail, the overall writing efficiency of the machine will decrease. Therefore, a precision pen-holding mechanism that can be installed at the end of the walking mechanism is needed, so that the walking mechanism mainly undertakes the large-scale path movement of characters or graphics, while the pen-holding mechanism independently undertakes the small-amplitude, high-frequency, and precise modulation near the pen tip. Summary of the Invention

[0005] The main objective of this invention is to overcome the shortcomings and deficiencies of the prior art and provide a pen-holding mechanism and automatic writing device with spherical bearing constraint and three-rope parallel drive, which can reduce the motion inertia of the pen tip, improve the local response speed of the pen tip, enable the automatic writing device to have richer handwriting expression capabilities, and improve the trajectory stability during high-speed writing.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] On one hand, a pen-holding mechanism with spherical bearing constraint and three-rope parallel drive is provided, which is installed at the end of the walking mechanism of an automatic writing device. The automatic writing device decomposes the writing trajectory into a main trajectory and a micro trajectory. The main trajectory is executed by the walking mechanism, and the pen-holding mechanism executes the micro trajectory superimposed on the main trajectory. The pen-holding mechanism includes a frame, a lifting mechanism, a spherical bearing, a pen holder, three ropes, a feedback detection mechanism, three drive motors, and a controller.

[0008] The frame is connected to the walking mechanism of the automatic writing device and is provided with a mounting part for mounting the lifting mechanism, drive motor and controller;

[0009] The spherical bearing includes an outer ring and an inner ring; the outer ring of the spherical bearing is provided with three sets of guide wheels and guide holes; the guide wheels are used to change the direction of the rope; the guide holes are used to ensure that the rope is perpendicular to the central axis of the pen holder;

[0010] The lifting mechanism is installed on the corresponding mounting part of the frame, located under the spherical bearing, and rigidly connected to the outer ring of the spherical bearing;

[0011] The pen holder is used to hold the writing pen of the walking mechanism and is fixedly connected to the inner ring of the spherical bearing.

[0012] One end of each of the three ropes is connected to the pen holder via a corresponding guide wheel and guide hole, and the other end is connected to the corresponding drive motor.

[0013] The feedback detection mechanism is used to acquire feedback signals of rope length, rope tension, pen pressure, motor position, and current or torque.

[0014] The controller is connected to three drive motors respectively. Based on the feedback signal provided by the feedback detection mechanism, the controller adjusts the control amount of the three drive motors and controls the pen holder to swing around the center of the ball under the constraint of the spherical bearing, so that the pen tip can perform a micro-trajectory.

[0015] As a preferred technical solution, the lifting mechanism is a lead screw linear module, a voice coil motor, a servo linkage mechanism, a cam mechanism, an electromagnet, a pneumatic linear actuator, or other mechanisms capable of lifting and lowering.

[0016] As a preferred technical solution, the pen holder is provided with a pen clamping hole, a clamping element, a locking screw, an elastic clamping structure, or other structures for fixing the writing pen.

[0017] As a preferred technical solution, the pen holder is provided with three equally spaced traction holes, traction ears, traction seats, hooks, crimping seats, or connecting parts integrally formed with the pen holder on its outer periphery.

[0018] One end of each of the three ropes is connected to the pen holder via a corresponding guide wheel and guide hole, through a traction hole, traction ear, traction seat, hook, crimping seat, or a connecting part integrally formed with the pen holder.

[0019] As a preferred technical solution, the drive motor is connected to the other end of the rope via a drum, winch, or other rope winding and unwinding mechanism.

[0020] As a preferred technical solution, the equivalent traction point of the three ropes to the pen holder is recorded as the end point, and the target length of the three ropes is determined according to the following formula:

[0021] ,

[0022] ,

[0023] ,

[0024] Where x and y are the target coordinates of the end point in the local plane, L0 is the length of each rope in the initial state, and L1, L2, and L3 are the target lengths of the three ropes, respectively.

[0025] As a preferred technical solution, the controller performs consistency checks, error compensation, and closed-loop correction on the target lengths of the three ropes based on the over-constraint relationship between their lengths.

[0026] The over-constraint relationship is as follows:

[0027] ,

[0028] Where L0 is the length of each rope in the initial state, and L1, L2, and L3 are the target lengths of the three ropes, respectively;

[0029] The consistency check, error compensation, and closed-loop correction are performed as follows:

[0030] The controller calculates the target length of the three ropes based on the target end point coordinates and target pen holder posture obtained from the feedback detection mechanism, and controls the drive motor to change the effective length of the corresponding rope according to the target length.

[0031] After modification, the actual lengths of the three ropes are obtained, and the coordinates of the actual end points are estimated based on the target length determinant.

[0032] Perform a consistency check: determine whether the positional error between the actual end point coordinates and the target end point coordinates is within the preset allowable range, and determine whether the lengths of the three actual ropes satisfy the over-constraint relationship corresponding to the same end attitude;

[0033] Error compensation: When the position error or geometric constraint residual exceeds the preset range, the controller generates a compensation amount based on the error; the compensation amount is obtained by proportional control, proportional-integral control or proportional-integral-derivative control, and is converted into the target length correction amount of the three ropes by inverse kinematics.

[0034] Closed-loop correction is performed: the controller drives three drive motors to perform correction actions based on the target length correction amount, obtains the actual rope length again and performs a consistency check until the position error and geometric constraint residual meet the preset range, or meet the preset abnormal handling conditions.

[0035] On the other hand, an automatic writing device is provided, including a walking mechanism with the pen-holding mechanism mounted at its end.

[0036] In another aspect, an automatic writing method for use in the automatic writing device is provided, comprising the following steps:

[0037] After receiving the trajectory to be written, the automatic writing device decomposes it into a main trajectory and a micro trajectory.

[0038] The walking mechanism executes the main trajectory;

[0039] The pen-holding mechanism executes a micro-trajectory and superimposes it onto the main trajectory to form the final handwriting.

[0040] As a preferred technical solution, when the pen holding mechanism executes the micro-track, the controller in the pen holding mechanism calculates the extension and retraction of the three ropes according to the target micro-track or the target pen posture, and controls the three drive motors to adjust the length of the corresponding ropes respectively, so that the three ropes apply traction forces in different directions to the pen holder; the pen holder swings at a small angle around the center of the sphere under the constraint of the spherical bearing, causing the pen tip to produce a small two-dimensional offset on the writing surface, and the offset is superimposed with the main trajectory of the walking mechanism to form the final handwriting;

[0041] When it is necessary to stop writing, move the pen, change lines, or end writing, the lifting mechanism drives the outer ring of the spherical bearing and its inner ring, the pen holder, and the writing pen to rise as a whole, so that the pen tip leaves the writing surface. The traveling mechanism moves to the next writing position, and the lifting mechanism puts the pen down to continue writing or the automatic writing device returns to its position and stops operating.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] This invention combines spherical bearing constraint, three-rope parallel traction, centralized drive, feedback detection, and coordinated control of the main trajectory and micro trajectory at the end of the pen in an automatic writing device, enabling the walking mechanism and the pen-holding mechanism to undertake writing movements of different scales, thereby achieving the following beneficial effects:

[0044] 1. Reduce the rotational inertia of the pen holder's swing end. Three drive motors are located on or near the frame, and the mass of the drive motors does not swing with the pen holder around the center of the ball. Power is transmitted to the pen holder via a rope. The components involved in the swing mainly include the pen holder, the writing pen, the rope connection, and related lightweight connecting structures. This structure helps to reduce the rotational inertia of the pen holder when it swings around the center of the ball, enabling the pen holder's end to respond to local, small-amplitude attitude modulation commands.

[0045] 2. A micro-motion execution method for the pen tip with a defined swing center is provided. The outer ring of the spherical bearing is connected to the lifting mechanism, and the inner ring is connected to the pen holder. The spherical bearing provides a defined swing center for the pen holder and limits its large-range translation. When the three ropes pull the pen holder from different directions, the pen holder undergoes a small-angle posture change around the spherical center; the writing pen swings with the pen holder, and its tip forms a corresponding local two-dimensional displacement on the writing reference surface. Thus, the micro-displacement of the pen tip is generated by a clear relationship of "rope length change—pen holder posture change—pen tip projected displacement".

[0046] 3. The three-rope circumferential traction helps maintain the effective working state of the pen-holding mechanism. The three ropes are respectively connected to the traction connection parts distributed around the axis of the writing pen, and act together on the pen holder within a preset tension range. This arrangement allows the pen holder to obtain traction in different swing directions. The controller can coordinate the effective length of the three ropes according to the target posture, and combine tension feedback to keep the ropes within the preset working range, thereby reducing the posture modulation limitation or response lag caused by unidirectional traction.

[0047] 4. The redundancy of the three rope lengths can be used for state verification and error processing. The local attitude of the pen holder mainly corresponds to a limited number of attitude degrees of freedom, while the three ropes provide three sets of length information. The controller can estimate the actual end point position based on the actual rope lengths and compare it with the target end point position; simultaneously, it performs a consistency check on the actual rope lengths according to the geometric relationship that the three rope lengths should satisfy under the same end attitude; when the position error or geometric constraint residual exceeds the preset range, the controller can generate a length compensation amount and perform closed-loop correction. This technology provides a basis for the detection and compensation of factors such as assembly errors, rope elastic deformation, guide friction, and drive errors.

[0048] 5. Layered execution of the main trajectory and micro-trajectory facilitates the allocation of writing motion tasks. The walking mechanism performs large-scale positional movements and basic directions of characters, graphics, or lines; the pen-holding mechanism performs local micro-displacements or pen posture modulation superimposed on the main trajectory. The controller superimposes the main trajectory and micro-trajectory in the same writing reference coordinate system, so that the final pen tip trajectory is formed by the combined displacement of the walking mechanism and the micro-displacement of the pen-holding mechanism. This layered approach allows local variations such as local turns, stroke beginnings, endings, pauses, or preset handwriting textures to be handled by the low-inertia pen-holding mechanism, while preserving the walking mechanism's large-scale motion capability.

[0049] 6. The feedback detection mechanism enables the pen-holding mechanism to adjust the control quantity according to the actual state. Rope length feedback or motor position feedback can be used to estimate the pen holder posture and end-point position; tension feedback can be used to determine whether the rope is within the preset traction range; current feedback or torque feedback can be used to determine the drive load state. Based on at least one of the above feedback signals, the controller corrects the target length of the three ropes, the change in target length, or the control quantity of the lifting mechanism, so that the pen tip micro-motion control corresponds to the actual writing state.

[0050] 7. The lifting mechanism, spherical bearing, pen holder, and writing pen form an integrated lifting system. When the lifting mechanism performs pen-dropping, pen-lifting, pen-breaking, and pen-moving actions, it can drive the spherical bearing and pen holder to rise and fall relative to the writing surface. In the writing state, the spherical bearing still allows the pen holder to perform small-angle swinging. Thus, pen tip contact state control and local posture modulation can be implemented in conjunction within the same pen-holding module.

[0051] 8. The frame, lifting mechanism, spherical bearing, pen holder, three-rope drive, drive motor, and feedback detection mechanism can constitute a relatively independent pen-holding module. This module can be installed on automatic writing devices with a walking mechanism and participate in writing operations through the coordinated control of the main trajectory and micro trajectory, providing a structural basis for end-grip pen applications under different writing sizes and walking mechanism forms. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a schematic diagram of a pen-holding mechanism with spherical bearing constraint and three-rope parallel drive in an embodiment of the present invention.

[0054] Figure 2 This is a top view of the pen-holding mechanism in an embodiment of the present invention.

[0055] Figure 3 This is a planar equivalent schematic diagram of the three ropes and the pen holder in an embodiment of the present invention. Detailed Implementation

[0056] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort are within the scope of protection of the present application.

[0057] In this application, the reference to "embodiment" means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0058] Example 1

[0059] like Figure 1 , Figure 2 As shown, this embodiment discloses a pen-holding mechanism constrained by a spherical bearing and driven by three ropes. This mechanism is installed at the end of the walking mechanism of an automatic writing device. The automatic writing device decomposes the received writing trajectory into a main trajectory and a micro trajectory. Then, the walking mechanism executes the main trajectory to determine the large-scale position and basic direction of the writing pen on the writing surface. The pen-holding mechanism executes the micro trajectory superimposed on the main trajectory to determine the local displacement or pen posture modulation amount superimposed on the main trajectory. This forms a motion division similar to that in human handwriting, where "the arm is responsible for large-scale movement, and the fingers and wrist are responsible for local details." The decomposition of the writing trajectory can be implemented using existing trajectory planning strategy algorithms. For example, for character writing, the trajectory planning strategy can generate the main trajectory and micro trajectory according to the character position, stroke unit, and local stroke features; for artistic lines or painting trajectories, the trajectory planning strategy can generate the main trajectory and micro trajectory according to the trajectory's scale features, spatial frequency features, or preset style parameters.

[0060] The pen-holding mechanism includes a frame, a lifting mechanism, a spherical bearing, a pen holder, three ropes, a feedback detection mechanism, three drive motors, and a controller. The frame is connected to the walking mechanism of the automatic writing device and has a mounting section for the lifting mechanism, drive motors, and controller. The frame serves as the mounting base for the pen-holding mechanism, allowing the entire mechanism to move a wide range of planar distances along with the XY walking mechanism.

[0061] The spherical bearing includes an outer ring and an inner ring; the outer ring is provided with three sets of guide wheels and guide holes; the guide wheels are used to change the direction of the rope; the guide holes are used to ensure that the rope is perpendicular to the central axis of the pen holder.

[0062] The lifting mechanism is installed on the corresponding mounting part of the frame, located under the spherical bearing, and rigidly connected to the outer ring of the spherical bearing. It is used to drive the spherical bearing, pen holder, and writing pen as a whole to rise and fall relative to the writing surface. The lifting action of the lifting mechanism corresponds to the pen placement, pen lifting, pen breaking, pen moving, and line changing in the automatic writing process.

[0063] The pen holder is used to hold the writing pen of the walking mechanism. It is fixedly connected to the inner ring of the spherical bearing. The writing pen swings together with the pen holder, and the spherical bearing allows the pen holder to swing around the center of the sphere at a small angle after the pen is placed.

[0064] One end of each of the three ropes is connected to the pen holder via a corresponding guide wheel and guide hole, pulling the pen holder from different directions; the other end is connected to the corresponding drive motor.

[0065] The feedback detection mechanism is used to obtain feedback signals such as rope length, rope tension, pen pressure, motor position, and current or torque. The controller is connected to three drive motors respectively. Based on the feedback signals provided by the feedback detection mechanism, the controller adjusts the control quantities of the three drive motors and controls the pen holder to swing around the center of the sphere under the constraint of the spherical bearing, so that the pen tip produces fine micro-movements and generates local writing details.

[0066] In one specific embodiment, the lifting mechanism may be a lead screw linear module, a voice coil motor, a servo linkage mechanism, a cam mechanism, an electromagnet, a pneumatic linear actuator, or other mechanisms capable of lifting and lowering.

[0067] In one specific embodiment, the pen holder may be provided with a pen clamping hole, a clamping element, a locking screw, an elastic clamping structure, or other structures for fixing the writing pen, so as to fix the writing pen.

[0068] In one specific embodiment, the outer periphery of the pen holder may be provided with three equally spaced traction holes, traction ears, traction seats, hooks, crimping seats, or connecting parts integrally formed with the pen holder; one end of the three ropes is connected to the pen holder through corresponding guide wheels and guide holes, via traction holes, traction ears, traction seats, hooks, crimping seats, or connecting parts integrally formed with the pen holder.

[0069] In one specific embodiment, the drive motor is connected to the other end of the rope via a drum, winch, or other rope winding mechanism.

[0070] In one specific embodiment, such as Figure 3As shown, to illustrate the correspondence between the lengths of the three ropes and the local micro-movements of the pen holder, this invention denotes the equivalent traction point of the three ropes on the pen holder as the end point P. In the actual mechanism, this can be understood as the traction center on the pen holder, the reference point of the holder fixed by the inner ring of the spherical bearing, or the local micro-displacement point of the pen tip after small-angle approximation. Taking the end point in the initial state as the origin O, a local plane corresponding to the writing surface is established. Let the coordinates of the end point in the local plane be: P=(x,y). The target lengths of the three ropes are determined using the following kinematic relationship:

[0071] ,

[0072] ,

[0073] ,

[0074] Where L0 is the initial length of each rope (the three ropes are of equal length initially), and L1, L2, and L3 are the target lengths of the three ropes, respectively. Since the angle between each pair of ropes connected to the pen holder is 120 degrees, the three fixed ends form an equilateral triangle arrangement centered at O. Therefore, the controller can calculate the target length or target length increment of the three ropes based on the micro-displacement of the target end or the equivalent micro-displacement of the pen tip, using the aforementioned relationship.

[0075] In one specific embodiment, the controller performs consistency checks, error compensation, and closed-loop correction on the target lengths of the three ropes based on the over-constraint relationship between their lengths. The derivation process of the over-constraint relationship is as follows:

[0076] make: , , Then, the lengths of the three ropes should satisfy the following under the ideal geometric model:

[0077] ,

[0078] Right now: ;

[0079] This equation represents a closed constraint between the lengths of the three ropes. If the lengths of the three ropes do not satisfy this relationship, then in the ideal model, there is no in-plane end point that can simultaneously satisfy the length constraints of all three ropes. This is because, in the locally planarized model, the end point has two planar degrees of freedom, and its coordinates can be determined by any two ropes. Taking L1 and L2 as examples... Figure 3 As shown, two length constraints are established with connection points A1 and A2 as centers and the corresponding actual rope lengths as radii, respectively; the intersection of these two constraints gives the candidate coordinates P(x,y) of the end point, where:

[0080] , ,

[0081] Since the obtained x and y must also satisfy the length relationship of the third rope:

[0082] ,

[0083] Therefore, in a three-rope over-constraint system, the third rope is not used as a freely arbitrarily designated length, but is used together with the other two ropes to form a stable traction and geometric constraint.

[0084] Furthermore, given L1 and L2, the length that the third rope should satisfy can also be obtained from this constraint relationship:

[0085] ,

[0086] Substituting L1=L2=L0 into the initial state, we get L3=L0.

[0087] The specific steps for the controller to perform consistency checks, error compensation, and closed-loop correction are as follows:

[0088] The controller calculates the target length of the three ropes based on the target end point coordinates and target pen holder posture obtained from the feedback detection mechanism, and controls the drive motor to change the effective length of the corresponding rope according to the target length.

[0089] After modification, the actual lengths of the three ropes are obtained, and the actual end point coordinates are estimated based on the preset kinematic model (i.e., the kinematic formula for determining the target length).

[0090] Perform a consistency check: determine whether the positional error between the actual end point coordinates and the target end point coordinates is within the preset allowable range, and determine whether the lengths of the three actual ropes satisfy the redundant geometric constraints (i.e., over-constraint relationships) corresponding to the same end attitude.

[0091] Error compensation: When the position error or geometric constraint residual exceeds the preset range, the controller generates a compensation amount based on the error; the compensation amount can be obtained by proportional control, proportional-integral control or proportional-integral-derivative control, and converted into the target length correction amount of the three ropes by inverse kinematics.

[0092] Closed-loop correction is performed: the controller drives three drive motors to perform correction actions based on the target length correction amount, obtains the actual rope length again and performs a consistency check until the position error and geometric constraint residual meet the preset range, or meet the preset abnormal handling conditions.

[0093] The aforementioned kinematic model (target length determination formula) is a locally planarized model used to describe the geometric traction relationship between the three ropes and the pen holder reference point. In the actual pen-holding mechanism, the outer ring of the spherical bearing is fixed to the lifting mechanism, and the inner ring of the spherical bearing is fixedly connected to the pen holder. The three ropes directly traction the pen holder. The spherical bearing restricts the large-range translation of the pen holder; therefore, the release and retraction of the three ropes mainly manifests as driving the pen holder to swing around the center of the sphere at a small angle. When the swing angle is small, the attitude change near the center of the sphere can be equivalent to a two-dimensional micro-displacement near the pen tip. If the distance from the center of the spherical bearing to the pen tip is R, the pen barrel will produce a small-angle attitude change θ around the center of the sphere. x θ y The minute displacement of the pen tip near the writing surface can be approximated as: x≈Rθ y , y≈-Rθ x This relationship can serve as the basis for the controller to convert the micro-trajectory of the target pen tip into the attitude change of the pen holder, and further into the extension and retraction of the three ropes. Note: For ease of calculation, the connection point between the three ropes and the pen holder is simplified to a single point when solving the above kinematic model.

[0094] To improve writing stability, this embodiment also includes at least one feedback detection or equivalent feedback mechanism. The drive motor can be equipped with an encoder to detect the output shaft rotation angle, drum rotation angle, or rope winding / unwinding amount; a tension sensor can be installed in the rope path to detect rope tension; and a pen pressure detection element can be installed on the pen holder, writing pen, or lifting mechanism to detect the contact pressure of the pen tip on the writing surface. For solutions using stepper motors or servo motors, driver position feedback, current feedback, or torque feedback can also be used as equivalent feedback signals.

[0095] Example 2

[0096] This embodiment discloses an automatic writing device, including a walking mechanism and a pen-holding mechanism as described above installed at its end, so that the writing task can be completed by the walking mechanism and the pen-holding mechanism working together.

[0097] Example 3

[0098] This embodiment also provides an automatic writing method applied to the above-mentioned automatic writing device, comprising the following steps:

[0099] First, the automatic writing device decomposes the received writing trajectory into a main trajectory and a micro trajectory. The main trajectory is used to describe the main outline, large-scale position, and basic direction of the strokes of the character or graphic. The micro trajectory is used to describe the starting point, ending point, return stroke, turning and pausing, connecting strokes, local speed disturbances, or handwriting textures of a specific style.

[0100] Next, the walking mechanism executes the main trajectory, while the pen-holding mechanism executes a micro-trajectory superimposed on the main trajectory to form the final handwriting.

[0101] Furthermore, when the pen holding mechanism executes the micro-track, the controller in the pen holding mechanism calculates the amount of winding and unwinding of the three ropes based on the target micro-track or the target pen posture, and controls the three drive motors to adjust the corresponding rope lengths (winding in or extending) respectively, so that the three ropes apply traction forces in different directions to the pen holder; the pen holder swings around the center of the sphere at a small angle under the constraint of the spherical bearing, causing the pen tip to produce a small two-dimensional offset on the writing surface. This offset is superimposed with the main trajectory of the walking mechanism to form the final handwriting.

[0102] When it is necessary to stop writing, move the pen, start a new line, or end writing, the lifting mechanism drives the outer ring of the spherical bearing and its inner ring, the pen holder, and the writing pen to rise as a whole, causing the pen tip to leave the writing surface. The traveling mechanism then moves to the next writing position, and the lifting mechanism lowers the pen to continue writing, or the automatic writing device returns to its original position and stops operating. Through this collaborative writing method, the traveling mechanism does not need to handle all the high-frequency handwriting details, and the pen-holding mechanism does not handle large-scale displacement; the two have a clear division of labor.

[0103] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0104] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A pen-holding mechanism constrained by a spherical bearing and driven by three ropes, installed at the end of the walking mechanism of an automatic writing device, wherein the automatic writing device decomposes the writing trajectory into a main trajectory and a micro trajectory, the main trajectory being executed by the walking mechanism, characterized in that, The pen-holding mechanism executes a micro-track superimposed on the main track; the pen-holding mechanism includes a frame, a lifting mechanism, a spherical bearing, a pen holder, three ropes, a feedback detection mechanism, three drive motors, and a controller; The frame is connected to the walking mechanism of the automatic writing device and is provided with a mounting part for mounting the lifting mechanism, drive motor and controller; The spherical bearing includes an outer ring and an inner ring; the outer ring of the spherical bearing is provided with three sets of guide wheels and guide holes; the guide wheels are used to change the direction of the rope; the guide holes are used to ensure that the rope is perpendicular to the central axis of the pen holder; The lifting mechanism is installed on the corresponding mounting part of the frame, located under the spherical bearing, and rigidly connected to the outer ring of the spherical bearing; The pen holder is used to hold the writing pen of the walking mechanism and is fixedly connected to the inner ring of the spherical bearing. One end of each of the three ropes is connected to the pen holder via a corresponding guide wheel and guide hole, and the other end is connected to the corresponding drive motor. The feedback detection mechanism is used to acquire feedback signals of rope length, rope tension, pen pressure, motor position, and current or torque. The controller is connected to three drive motors respectively. Based on the feedback signal provided by the feedback detection mechanism, the controller adjusts the control amount of the three drive motors and controls the pen holder to swing around the center of the ball under the constraint of the spherical bearing, so that the pen tip can perform a micro-trajectory.

2. The pen-holding mechanism according to claim 1, characterized in that, The lifting mechanism is a lead screw linear module, voice coil motor, servo linkage mechanism, cam mechanism, electromagnet, pneumatic linear actuator, or other mechanism capable of lifting and lowering.

3. The pen-holding mechanism according to claim 1, characterized in that, The pen holder is provided with a pen clamping hole, a clamping element, a locking screw, an elastic clamping structure, or other structures for fixing the writing pen.

4. The pen-holding mechanism according to claim 1, characterized in that, The pen holder is provided with three equally spaced traction holes, traction ears, traction seats, hooks, crimping seats, or connecting parts integrally formed with the pen holder on its outer periphery. One end of each of the three ropes is connected to the pen holder via a corresponding guide wheel and guide hole, through a traction hole, traction ear, traction seat, hook, crimping seat, or a connecting part integrally formed with the pen holder.

5. The pen-holding mechanism according to claim 1, characterized in that, The drive motor is connected to the other end of the rope via a drum, winch, or other rope winding and unwinding mechanism.

6. The pen-holding mechanism according to claim 1, characterized in that, The equivalent traction point of the three ropes to the pen holder is denoted as the end point, and the target length of the three ropes is determined according to the following formula: ， ， ， Where x and y are the target coordinates of the end point in the local plane, L0 is the length of each rope in the initial state, and L1, L2, and L3 are the target lengths of the three ropes, respectively.

7. The pen-holding mechanism according to claim 6, characterized in that, The controller performs consistency checks, error compensation, and closed-loop correction on the target lengths of the three ropes based on the over-constraint relationship between their lengths. The over-constraint relationship is as follows: ， Where L0 is the length of each rope in the initial state, and L1, L2, and L3 are the target lengths of the three ropes, respectively; The consistency check, error compensation, and closed-loop correction are performed as follows: The controller calculates the target length of the three ropes based on the target end point coordinates and target pen holder posture obtained from the feedback detection mechanism, and controls the drive motor to change the effective length of the corresponding rope according to the target length. After modification, the actual lengths of the three ropes are obtained, and the coordinates of the actual end points are estimated based on the target length determinant. Perform a consistency check: determine whether the positional error between the actual end point coordinates and the target end point coordinates is within the preset allowable range, and determine whether the lengths of the three actual ropes satisfy the over-constraint relationship corresponding to the same end attitude; Error compensation: When the position error or geometric constraint residual exceeds the preset range, the controller generates a compensation amount based on the error; the compensation amount is obtained by proportional control, proportional-integral control or proportional-integral-derivative control, and is converted into the target length correction amount of the three ropes by inverse kinematics. Closed-loop correction is performed: the controller drives three drive motors to perform correction actions based on the target length correction amount, obtains the actual rope length again and performs a consistency check until the position error and geometric constraint residual meet the preset range, or meet the preset abnormal handling conditions.

8. An automatic writing device, comprising a walking mechanism, characterized in that, The end of the walking mechanism is equipped with a pen-holding mechanism as described in any one of claims 1-7.

9. An automatic writing method applied to the automatic writing device of claim 8, characterized in that, Includes the following steps: After receiving the trajectory to be written, the automatic writing device decomposes it into a main trajectory and a micro trajectory. The walking mechanism executes the main trajectory; The pen-holding mechanism executes a micro-trajectory and superimposes it onto the main trajectory to form the final handwriting.

10. The automatic writing method according to claim 9, characterized in that, When the pen holding mechanism executes the micro-track, the controller in the pen holding mechanism calculates the extension and retraction of the three ropes according to the target micro-track or the target pen posture, and controls the three drive motors to adjust the length of the corresponding ropes respectively, so that the three ropes apply traction force in different directions to the pen holder; the pen holder swings at a small angle around the center of the sphere under the constraint of the spherical bearing, causing the pen tip to produce a small two-dimensional offset on the writing surface. This offset is superimposed with the main trajectory of the walking mechanism to form the final handwriting. When it is necessary to stop writing, move the pen, change lines, or end writing, the lifting mechanism drives the outer ring of the spherical bearing and its inner ring, the pen holder, and the writing pen to rise as a whole, so that the pen tip leaves the writing surface. The traveling mechanism moves to the next writing position, and the lifting mechanism puts the pen down to continue writing or the automatic writing device returns to its position and stops operating.

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