Dual-motor coaxial driving differential type test tube mixing system and method

Abstract

The invention discloses a dual-motor coaxial driving differential type test tube mixing system and method, and belongs to the technical field of industrial robots. According to the system, a 57 stepping motor (revolution driving) and a 42 stepping motor (rotation driving) are coaxially installed, a differential transmission mechanism is formed through a cylindrical spur gear and a bevel gear set, and a dual-motor differential rotation speed cooperative control algorithm, a mixing-cap screwing motion mode switching algorithm and a load self-adaptive rotation speed adjusting algorithm are integrated. And the integrated operation of revolution and rotation two-degree-of-freedom composite uniform mixing and precise cap screwing of the test tube is realized. The technical problems that a traditional blending device is large in number of motors, complex in structure, large in size, poor in adaptability, insufficient in movement collaboration and low in function compatibility are solved.

Description

Technical Field This invention belongs to the field of industrial control technology, and specifically discloses a dual-motor coaxial drive differential test tube mixing system and method. Background Technology In automated analytical workflows across fields such as biological detection, medical diagnostics, and food testing, automated test tube capping devices are core equipment for sample pretreatment, while test tube mixing is a crucial preliminary step to ensure accurate test results. Test tube mixing must achieve thorough mixing of the sample to avoid detection errors caused by uneven local concentrations; simultaneously, after mixing, it is necessary to quickly switch to capping to achieve sealed preservation of the sample or opening for testing. However, the test tube mixing module in existing automated test tube capping devices suffers from the following three major technical challenges, severely restricting operational efficiency and testing accuracy: Firstly, their complex and bulky structure leads to poor spatial adaptability. Traditional test tube mixing devices require 3-4 independent motors to drive the revolution mechanism, rotation mechanism, and positioning mechanism, along with multiple sets of gears, belts, guide rails, and other transmission components, resulting in more than 50 parts and an overall size generally exceeding 500mm×400mm×300mm. This bulky design makes it difficult to fit into the confined spaces of laboratory benches, mobile testing vehicles, and primary healthcare facilities, limiting the mobility and integration of the equipment. For example, the mixing module of a certain model of fully automatic test tube processor measures 550mm×420mm×310mm, which cannot be installed on the workbench of a conventional mobile testing vehicle (size ≤400mm×300mm), forcing manual mixing to be still required for on-site testing, resulting in low efficiency. Secondly, the motion coordination is poor, resulting in uneven mixing. Traditional methods employ independent control modes for multiple motors, lacking an effective coordination mechanism. This easily leads to problems such as asynchronous revolution and rotation speeds, and excessive phase fluctuations, causing disordered test tube trajectories and sample mixing uniformity of less than 85%. For example, when the revolution motor speed fluctuates by ±5 rpm and the rotation motor speed by ±4 rpm, local vortices easily form in the liquid sample within the test tube, preventing omnidirectional mixing and resulting in a relative error exceeding 15% in subsequent test results, affecting accuracy. Furthermore, existing methods struggle to adjust motion parameters according to sample type (liquid / semi-solid), limiting adaptability. Third, functional compatibility is low and the operation process is cumbersome. In traditional designs, the mixing device and the capping device are independent modules that need to be installed and debugged separately. This not only increases the cost of equipment integration but also requires a dedicated switching mechanism or movement path, resulting in a lengthy operation process. For example, in a laboratory automation system, test tubes need to be transferred from the mixing module to the capping module by a robotic arm, with a transfer time of more than 20 seconds and a risk of sample spillage during the transfer (test tube breakage rate of about 3%). Some integrated solutions attempt to combine the two, but this is achieved by adding a transmission gear set to achieve functional switching, resulting in a more complex structure (30% more parts) and a significantly higher failure rate (annual failure rate exceeding 15%).

[0001] In summary, existing technologies have not yet resolved the core contradiction of "miniaturization of structure, coordination of motion, and integration of functions." There is an urgent need to develop a test tube mixing system based on innovative transmission structure and intelligent control algorithm, which can reduce the number of motors and the size of the equipment while achieving integrated operation of efficient mixing and precise capping, thus meeting the needs of integrated operation in confined spaces. Summary of the Invention This invention provides a differential test tube mixing industrial robot system with dual motor coaxial drive for automated test tube capping device, including a dual motor differential drive unit, a collaborative control and processing unit, a job execution and monitoring unit, and an auxiliary adaptation unit; The dual-motor differential drive unit includes a 57-stepper motor (revolution drive) and a 42-stepper motor (rotation drive) mounted coaxially, a differential transmission mechanism, and an electromagnetic clutch module. The 57-stepper motor has a torque of 1.2 N·m and a step angle of 1.8°, while the 42-stepper motor has a torque of 0.5 N·m and a step angle of 1.8°. The axial distance between the two motors is ≤50 mm. The differential transmission mechanism consists of a spur gear (transmission ratio 2:1) and a bevel gear set (transmission ratio 1:1) to achieve speed and direction adjustment. The electromagnetic clutch module is a single-coil electromagnetic clutch with a response time ≤20 ms, used to control the locking and unlocking of the revolution mechanism. The collaborative control and processing unit includes a main controller, a motor drive module, and an encoder interface module. The main controller is an industrial-grade MCU (STM32H743) with a main frequency of 480MHz and a control cycle of ≤0.5ms. It runs a dual-motor differential speed collaborative control algorithm, a mixing-capping motion mode switching algorithm, and a load-adaptive speed adjustment algorithm. The motor drive module is a dual-channel stepper motor driver that supports 16-256 microstepping adjustable values, a current adjustment range of 0.1-3A, and overcurrent and overheat protection. The encoder interface module is a two-channel incremental encoder interface (1000-line resolution) used for real-time acquisition of motor speed and phase data. The operation execution and monitoring unit includes a test tube clamping mechanism, a status monitoring module, and a human-machine interface; the test tube clamping mechanism is a three-finger flexible gripper with a clamping range of 8-25mm and the fingertips are covered with a silicone layer; the status monitoring module collects motor current, speed, and clutch status data at a sampling frequency of 100Hz; the human-machine interface is a 5-inch touch screen that supports operation mode selection, parameter setting, and manual control. The auxiliary adapter unit includes a tabletop mounting base, a dustproof cover, and an emergency stop module; the tabletop mounting base is made of lightweight aluminum alloy, with dimensions of 300mm×200mm, and supports horizontal adjustment; the dustproof cover is made of transparent acrylic material with a dustproof rating of IP54; the emergency stop module is a mechanical emergency stop button with a response time of ≤50ms. Further, a control method for the system is provided, comprising the following steps: S1: System initialization and motor calibration, start the industrial robot system, complete the zero-point calibration of the 57 stepper motor and the 42 stepper motor and the reset of the differential transmission mechanism; S2: Load the operation parameters. Select the operation mode (automatic / manual) and sample type (liquid / semi-solid) through the human-machine interface. The system will automatically load the corresponding mixing parameters (revolution speed, rotation speed, speed ratio, mixing time) and capping parameters (torque threshold, initial speed). S3: Dual-motor differential cooperative start-up, running the dual-motor differential speed cooperative control algorithm, establishing the cooperative control relationship between the two motors based on the loaded speed ratio parameters, and completing the motor start-up preprocessing; S4: Test tube gripping and fixing. The robotic arm drives the test tube clamping mechanism to move to the test tube storage position, clamps and fixes the test tube, and ensures that the test tube axis is coaxial with the output shaft of the differential transmission mechanism. S5: "Revolution + Rotation" composite mixing, controlled by dual motor differential drive, drives the test tube to achieve composite mixing motion through differential transmission mechanism, and the status monitoring module collects motor speed, phase difference and clamping force data in real time; S6: Closed-loop adjustment of motion state. Based on the state monitoring data, the dual-motor differential speed collaborative control algorithm dynamically compensates for phase difference deviation and speed fluctuation to ensure smooth mixing motion. S7: Mixing completion judgment. When the mixing time reaches the preset value and the motion stability meets the requirements (speed fluctuation ≤ ±2 rpm), the mixing is judged to be complete; otherwise, return to step S5 to continue mixing. S8: Mixing-capping mode switching, running the mixing-capping motion mode switching algorithm, locking the revolution mechanism through the electromagnetic clutch module, and the motor speed is switched to the capping parameter through a smooth transition stage, with a switching time ≤10 seconds; S9: Load adaptive cap tightening operation. It runs a load adaptive speed adjustment algorithm, calculates the real-time torque based on the motor current, dynamically adjusts the rotation speed, and completes the tightening or loosening of the test tube cap. S10: Cap tightening completed. When the torque reaches the preset threshold and the angle change is ≤0.5° / s, the cap tightening is completed; otherwise, return to step S9 to continue tightening the cap. S11: Test tube release and mechanism reset. The test tube clamping mechanism releases the test tube, the robotic arm transfers the test tube to the target station, and the dual motors and differential transmission mechanism reset to the initial state. S12: The job is completed. The system waits for the next job instruction or starts a continuous job process according to the preset program. Furthermore, the dual-motor differential speed collaborative control algorithm adopts a "speed ratio preset - phase difference compensation - closed-loop synchronization correction" mechanism, specifically including: A1: Preset rotation speed ratio. The rotation speed ratio between the revolution and rotation speed is set according to the sample type. The rotation speed ratio is adjustable in the range of 3:1-1:3. The default rotation speed ratio for liquid samples is 1:2, and the default rotation speed ratio for semi-solid samples is 2:1. A2: Real-time phase difference monitoring: The speed pulse signal and phase signal of the two motors are collected through the encoder interface module, and the phase difference Δθ(i) = θ1(i) - θ2(i) at time i is calculated, where θ1(i) is the phase of the 57 stepper motor and θ2(i) is the phase of the 42 stepper motor. A3: Phase difference compensation. When |Δθ(i)|>3°, adjust the speed regulation amount Δn=k1·Δθ(i) of the 42 stepper motor, where k1 is the compensation coefficient (0.1-0.3rpm / °), until |Δθ(i)|≤3°; A4: Closed-loop synchronous correction, calculate the actual speeds n1(i) and n2(i) of the two motors and the preset speed n 10 n 20 The deviation Δn1=n 10 -n1(i), Δn2=n 20 -n2(i) is the adjustment signal output by the PID controller, which controls the motor drive module to adjust the motor speed to ensure that the speed fluctuation is ≤ ±2 rpm. The PID control formula is: u(t)=Kp·e(t)+Ki·∫e(t)dt+Kd·de(t) / dt Where u(t) is the controller output, e(t) is the speed deviation, Kp is the proportional coefficient (0.5-2.0), Ki is the integral coefficient (0.01-0.1), and Kd is the derivative coefficient (0.1-0.5). Furthermore, the mixing-capping motion mode switching algorithm adopts a "parameter preloading-clutch state switching-smooth trajectory transition" mechanism, specifically including: B1: Parameter preloading. When the system is initialized, the mixing mode parameter set (n 1h , n 2h , clutch state "unlocked") and the capping mode parameter set (n 1n = 0 rpm, n 2n , clutch state "locked") are preloaded into the main controller cache, where n 1h is the revolution speed in the mixing mode, n 2h is the rotation speed in the mixing mode, and n 2n is the rotation speed in the capping mode; B2: Clutch state switching. After receiving the mode switching instruction, the main controller sends a "lock" signal to the electromagnetic clutch module, and the electromagnetic clutch is energized to engage and lock the revolution mechanism, with a response time ≤ 20 ms; B3: Trajectory smooth transition. A 500 - ms rotation speed transition stage is set, and the motor speed transitions from the mixing parameters to the capping parameters in a linear interpolation manner. The rotation speed transition formula for the rotation speed is: n2(t) = n 2h - (n 2h - n 2n )·t / 500 where t is the transition time (0 ≤ t ≤ 500 ms), and n2(t) is the rotation speed at time t during the transition stage; B4: Completion judgment of switching. When the clutch state is confirmed to be locked and the rotation speed reaches the capping parameters (n2(t) = n 2n , with a rotation speed fluctuation ≤ ±1 rpm), it is determined that the switching is completed, and the capping operation mode is entered. Furthermore, the load - adaptive rotation speed adjustment algorithm adopts a "torque threshold monitoring - rotation speed step adjustment - in - place judgment feedback" mechanism, specifically including: C1: Torque threshold presetting. According to the test tube cap specifications (material, thread tightness), a torque threshold T0 (adjustable from 0.5 - 1.5 N·m) is set, and two warning thresholds T1 = 0.6T0 and T2 = 0.9T0 are set; C2: Real - time torque calculation. The working current I(t) of the 42 - step motor is collected through the motor drive module, and the real - time torque is calculated according to the linear relationship between the motor torque and the current T(t) = k2·I(t), where k2 is the torque coefficient (0.2 - 0.5 N·m / A), which is determined by the motor calibration experiment; C3: Rotation speed step adjustment. When T(t) < T1, the initial capping rotation speed n 2n (50 rpm) is maintained; when T1 ≤ T(t) < T2, the rotation speed is reduced to n 21 = 30 rpm; when T(t) ≥ T2, the rotation speed is reduced to n 22 = 10 rpm; C4: Cap tightening in place judgment, continuously monitor torque T(t) and motor angle change rate dα / dt. When T(t)≥T0 and dα / dt≤0.5° / s, it is determined that the cap tightening in place and a motor stop command is sent immediately; C5: Torque self-learning optimization, recording the actual torque T at the end of each operation. ai (i = 1, 2, ..., n), the torque threshold T0' = (T0 + (T...) is updated using a moving average algorithm. a1 +T a2 +...+T an ) / n) / 2, to improve the compatibility of test tube caps with different batches. Beneficial effects: The dual-motor coaxial mounting design reduces the traditional 3-4 motors to 2. The differential transmission mechanism achieves two degrees of freedom of motion through a combination of spur gears and bevel gears, reducing the number of parts from over 50 to less than 20, a reduction of 60%. The overall size is reduced from 500mm×400mm×300mm to 300mm×200mm×150mm, a 60% reduction in space occupancy, making it perfectly suited for confined spaces. The integration of the electromagnetic clutch module enables functional switching without additional mechanisms, avoiding the structural complexity caused by the addition of gear sets in traditional solutions. The dual-motor differential speed collaborative control algorithm solves the problem of poor synchronization among multiple motors through phase difference compensation and PID closed-loop correction, reducing speed fluctuation from ±5 rpm to ±2 rpm, improving sample mixing uniformity from 85% to over 98%, and reducing detection result error by 40%. The mixing-capping mode switching algorithm shortens the switching time from over 20 seconds to ≤10 seconds through parameter preloading and smooth transition, improving workflow efficiency by 50%. The load adaptive speed adjustment algorithm, through torque monitoring and stepped speed regulation, increases capping accuracy from 90% to 99%, reduces cap damage rate from 3% to below 1%, and test tube breakage rate from 3% to 0.8%. The integrated design of mixing and capping functions eliminates the installation space and transfer steps of traditional independent devices, reducing equipment integration costs by 50% (traditional solutions require 2 devices, this solution only requires 1), while avoiding the risk of splashing during sample transfer, reducing sample loss rate from 2% to below 0.5%. Attached Figure Description Figure 1 Control workflow diagram. Detailed Implementation Example 1: This invention aims to solve the following three core technical problems existing in the prior art: (1) Traditional mixing devices have a large number of motors and complex parts, resulting in a large overall size that cannot be adapted to small spaces such as laboratory benches and on-site testing vehicles; (2) The lack of coordination mechanism in the independent control of multiple motors results in poor speed and phase synchronization, leading to insufficient uniformity of sample mixing and large error in detection results; (3) The mixing and capping functions are designed independently, resulting in low compatibility, complicated operation process, high equipment integration cost, and risk of sample spillage or test tube breakage. 2. Technical Solution

[0002] To achieve the above objectives, this invention provides a dual-motor coaxial drive differential test tube mixing system and method. With "dual-motor coaxial differential drive + three core intelligent algorithms" as its core technology, it achieves technological breakthroughs in structural simplification, motion coordination, and functional integration. The specific technical solution is as follows: 2.1 System Overall Design

[0003] This system comprises a dual-motor differential drive unit, a collaborative control and processing unit, a job execution and monitoring unit, and an auxiliary adapter unit. These units work together to achieve integrated mixing and capping of test tubes. The overall system dimensions are 300mm × 200mm × 150mm, and it weighs ≤8kg. It can be directly installed on a laboratory benchtop or in the work area of ​​a testing cart, requiring no additional space. 2.2 Detailed Design of Core Unit

[0004] (1) Dual-motor differential drive unit: This unit is the power core of the system. It adopts a coaxial installation method of 57 stepper motors (revolution drive) and 42 stepper motors (rotation drive), with an axial distance of only 45mm, which greatly shortens the transmission path. The differential transmission mechanism consists of cylindrical spur gears (module 1.0, number of teeth 20 / 40, transmission ratio 2:1) and bevel gear sets (module 0.8, number of teeth 15, transmission ratio 1:1), realizing speed amplification and vertical conversion of direction, ensuring that the test tube simultaneously obtains revolution (horizontal circular motion) and rotation (self-rotation motion). The electromagnetic clutch module adopts a single-coil electromagnetic clutch (model DLM0-2.5), with a response time ≤20ms. When energized, it locks the revolution mechanism, switching the system to the pure rotation capping mode. When de-energized, it unlocks and restores the compound mixing mode.

[0005] (2) Collaborative Control and Processing Unit: The main controller uses an STM32H743 industrial-grade MCU with a main frequency of 480MHz and a control cycle of ≤0.5ms. It has powerful computing capabilities to run three core algorithms. The motor drive module uses a DM542 dual-channel stepper motor driver, which supports 16-256 microstepping adjustable values ​​and a current adjustment range of 0.1-3A. It has dual overcurrent and overheat protection functions. When the motor operating current exceeds 3A or the driver temperature exceeds 75℃, it automatically cuts off the output and alarms. The encoder interface module uses a TI TS5667N100 incremental encoder with a resolution of 1000 lines and a sampling frequency of 1kHz. It collects the speed pulse signals and phase signals of the two motors in real time. The data is transmitted to the main controller via the SPI interface with a delay of ≤1ms.

[0006] (3) Operation Execution and Monitoring Unit: The test tube clamping mechanism adopts a three-finger flexible gripper made of food-grade silicone, with a clamping range of 8-25mm, suitable for common test tube sizes (such as 10mm, 16mm, and 20mm glass / plastic test tubes). The clamping force can be adjusted by air pressure (0.2-0.5MPa) to prevent test tube breakage. The status monitoring module includes a current sensor (model ACS712), a speed sensor (integrated with the encoder), and a clutch status sensor (Hall effect type). It collects motor operating current, real-time speed, and clutch engagement status data at a sampling frequency of 100Hz. The data is converted by an ADC and transmitted to the main controller. The human-machine interface uses a 5-inch TFT touch screen (resolution 800×480), supports Chinese / English switching, and displays parameters such as operation mode (automatic / manual), real-time speed, mixing time, and torque value. It also provides parameter settings (such as speed ratio and torque threshold), manual control (motor start / stop, gripper opening / closing), and fault alarm (overload, overheating) functions.

[0007] (4) Auxiliary Adapter Unit: The tabletop mounting base is made of 6061 aluminum alloy, CNC machined, with dimensions of 300mm×200mm×20mm and a weight of 1.2kg. The base has four leveling knobs at the bottom (adjustment range ±2mm) to ensure the system is installed flat. The dustproof cover is made of transparent acrylic, 3mm thick, with dimensions of 300mm×200mm×150mm and a dustproof rating of IP54. It effectively prevents samples from splashing out and contaminating the equipment, while also facilitating observation of the operation process. The emergency stop module uses a mechanical emergency stop button (model LA38-11ZS) with a response time ≤50ms. Pressing it immediately cuts off the motor power and control signal, ensuring operational safety. 2.3 Core Algorithm Technical Details

[0008] (1) Dual-motor differential speed coordination control algorithm: This algorithm achieves high-precision coordination between the two motors through three-level control: "speed ratio preset - phase difference compensation - closed-loop synchronous correction". In the speed ratio preset stage, the system has two default parameters built-in: liquid sample (speed ratio 1:2) and semi-solid sample (speed ratio 2:1). Users can customize the adjustment in the range of 3:1-1:3 via the touch screen, with an adjustment step of 0.1. In the phase difference compensation stage, the main controller calculates the phase difference Δθ(i) every 10ms. When Δθ(i) exceeds ±3°, the speed of the 42 stepper motor is adjusted according to the formula Δn = 0.2rpm / ° × Δθ(i). For example, when Δθ(i) = 5°, Δn = 1rpm, which increases the speed of the 42 stepper motor by 1rpm until the phase difference returns to within ±3°. During the closed-loop synchronous correction stage, incremental PID control is adopted with proportional coefficient Kp = 1.2, integral coefficient Ki = 0.05, and derivative coefficient Kd = 0.3. The speed deviation e(t) is calculated every 5ms, and the output adjustment signal controls the motor drive module to stabilize the speed fluctuation within ±2rpm.

[0009] (2) Algorithm for switching between mixing and capping modes: During the parameter preloading stage, the default parameters for mixing mode (100 rpm revolution, 200 rpm rotation, clutch unlock) and capping mode (0 rpm revolution, 50 rpm rotation, clutch lock) are stored in the SRAM cache during system initialization, with a read time ≤10μs. During the clutch state switching stage, the main controller outputs 24V voltage through the GPIO port to control the electromagnetic clutch, with an engagement time ≤20ms. At the same time, the clutch state is detected by the Hall sensor, and after confirming the lock, the speed transition stage begins. During the trajectory smooth transition stage, the rotation speed is linearly reduced from 200 rpm to 50 rpm within 500ms. The real-time speed is calculated using the formula n2(t)=200-(200-50)×t / 500. For example, when t=100ms, n2(t)=170 rpm; when t=300ms, n2(t)=110 rpm, to avoid test tube shaking caused by sudden speed changes. During the switching completion judgment stage, when the speed is stable at 50±1rpm and the clutch status is "locked", the switching is judged to be complete, and the time is ≤8 seconds.

[0010] (3) Load Adaptive Speed ​​Adjustment Algorithm: In the torque threshold preset stage, the system provides a default threshold based on the material of the test tube cap (0.5-0.8 N·m for plastic caps and 1.0-1.5 N·m for metal caps), which can be fine-tuned by the user via the touch screen. In the real-time torque calculation stage, the current sensor collects the operating current I(t) of the 42 stepper motor, and calculates the torque according to T(t) = 0.35 N·m / A × I(t) (k2 = 0.35 is determined by the motor calibration experiment. In the experiment, the actual torque under different currents is measured by the torque sensor, and the linear relationship is fitted to obtain the result). During the speed step adjustment phase, when T(t) < 0.6T0, maintain 50 rpm; when T(t) is between 0.6T0 and 0.9T0, reduce to 30 rpm; when T(t) ≥ 0.9T0, reduce to 10 rpm. For example, when T0 = 1.0 N·m, 0.6T0 = 0.6 N·m, 0.9T0 = 0.9 N·m, and when T(t) = 0.7 N·m, adjust the speed to 30 rpm. During the cap tightening judgment phase, the encoder calculates the motor angle change rate dα / dt. When T(t) ≥ T0 and dα / dt ≤ 0.5° / s, immediately stop the motor to avoid over-tightening. During the torque self-learning optimization phase, after every 10 cap tightening operations, adjust the speed according to T0' = (T0 + (T... a1 +T a2 +...+T a10 The threshold is updated using (1 / 10) / 2. For example, if the initial T0 = 1.0 N·m and the average actual torque after 10 measurements is 1.1 N·m, then T0' = (1.0 + 1.1) / 2 = 1.05 N·m, thus improving adaptability. 3. The innovativeness and efficiency-enhancing principles of the technical solution

[0011] (1) Structural Innovation: The coaxial mounting design of the dual motors reduces the traditional 3-4 motors to 2. The differential transmission mechanism achieves two degrees of freedom of motion through a combination of spur gears and bevel gears, reducing the number of parts from over 50 to less than 20, a reduction of 60%. The overall size of the machine is reduced from 500mm×400mm×300mm to 300mm×200mm×150mm, reducing space occupation by 60%, perfectly adapting to confined spaces. The integration of the electromagnetic clutch module enables functional conversion without additional mechanism switching, avoiding the structural complexity caused by the addition of gear sets in traditional solutions.

[0012] (2) Algorithm innovation: The dual-motor differential speed collaborative control algorithm solves the problem of poor synchronization of multiple motors through phase difference compensation and PID closed-loop correction. The speed fluctuation is reduced from ±5rpm to ±2rpm, the sample mixing uniformity is increased from 85% to over 98%, and the detection result error is reduced by 40%. The mixing-capping mode switching algorithm shortens the switching time from over 20 seconds to ≤10 seconds through parameter preloading and smooth transition, and improves the efficiency of the work process by 50%. The load adaptive speed adjustment algorithm increases the capping completion rate from 90% to 99% through torque monitoring and stepped speed regulation, reduces the cap damage rate from 3% to below 1%, and reduces the test tube breakage rate from 3% to 0.8%.

[0013] (3) Functional integration innovation: The mixing and capping functions are integrated into one design, eliminating the installation space and transfer process of traditional independent devices, reducing equipment integration costs by 50% (the traditional solution requires 2 devices, while this solution can achieve this with only 1 device), while avoiding the risk of splashing during sample transfer, reducing the sample loss rate from 2% to below 0.5%. Example 1: Laboratory Liquid Sample Processing Scenario

[0014] Scenario Description: A biological laboratory needs to process 16mm glass test tubes (liquid samples, such as blood diluent), with an average daily testing volume of 150 tubes. The laboratory workbench size is 350mm×300mm. The requirements are that the sample mixing uniformity is ≥95%, the capping rate is ≥98%, and the equipment volume is ≤350mm×250mm×200mm. Step 1: System Installation and Initialization

[0015] Install the system on the laboratory benchtop and adjust the equipment level using the base leveling knob to ensure an error ≤0.1mm / m. Connect a 220V AC power supply and compressed air (0.4MPa), start the system, and the main controller will automatically complete the zero-point calibration of the 57 / 42 stepper motor (calibration time ≤3 seconds) and the reset of the differential transmission mechanism (reset accuracy ±0.05mm). Select the "Liquid Sample" mode via the touchscreen, and the system will automatically load the mixing parameters (revolution 100rpm, rotation 200rpm, speed ratio 1:2, mixing time 30 seconds) and capping parameters (torque threshold 0.8N·m, initial speed 50rpm). Step 2: Mixing in the test tubes

[0016] The robotic arm (external, ABB IRB120 model) transfers a 16mm glass test tube to the test tube clamping mechanism. The grippers are ventilated and closed, and the clamping force is adjusted to 0.3MPa to ensure that the coaxiality of the test tube is ≤0.1mm. The main controller starts the dual-motor differential speed collaborative control algorithm. The 57-stepper motor (revolution) starts at 100rpm, and the 42-stepper motor (rotation) starts at 200rpm. The encoder collects speed data in real time, and the phase difference is controlled within ±2°. The speed fluctuation is 100±1rpm (revolution) and 200±2rpm (rotation). The status monitoring module updates the data every 100ms and displays it in real time on the touch screen. The mixing operation lasts for 30 seconds. Step 3: Mixing effect test

[0017] After mixing, the uniformity of the sample was tested using a UV spectrophotometer: 10 μL of sample was taken from different positions (top, middle, and bottom) in the test tube, the absorbance value was measured, and the relative deviation was calculated to be ≤2%. If the mixing uniformity was 98.5%, it was determined to meet the requirement of ≥95%. Step 4: Mode switching and cap tightening

[0018] The main controller sends a mode switching command, the electromagnetic clutch module is energized and engaged (response time 18ms), locking the revolution mechanism; the rotation speed transitions linearly from 200rpm to 50rpm in 500ms, with no obvious shaking of the test tube during the switching process; entering the capping mode, the current sensor collects the current of the 42-stepper motor in real time and calculates the torque T(t): when T(t) = 0.48N·m (0.6×0.8N·m), the speed drops to 30rpm; when T(t) = 0.72N·m (0.9×0.8N·m), the speed drops to 10rpm; when T(t) = 0.8N·m and the rate of change of rotation dα / dt = 0.3° / s, the motor stops, the capping is completed, and the time is 6 seconds. Step 5: Work completed and reset

[0019] The gripper releases air and opens the test tube, and the robotic arm transfers the test tube to the testing station; the dual motors and differential transmission mechanism reset to their initial state (reset time ≤ 2 seconds); the system records the data for this operation (mixing time 30 seconds, capping torque 0.8 N·m, operation time 40 seconds), and waits for the next test tube to be processed. Implementation effect

[0020] 150 test tubes were processed continuously. Statistical results showed that the sample mixing uniformity was ≥98% (average 98.3%), the capping rate was 99.3% (only 1 tube failed to be capped due to abnormal screw thread), the test tube breakage rate was 0.7% (1 tube), the equipment operated stably, and there were no overload or overheating failures. The processing time for a single test tube was ≤45 seconds, which is 35.7% shorter than the traditional method (30 seconds for mixing + 20 seconds for transfer + 20 seconds for capping, totaling 70 seconds), meeting the high-efficiency processing needs of the laboratory. Example 2: On-site testing vehicle semi-solid sample processing scenario

[0021] Scenario Description: A disease control center's field testing vehicle needs to process 20mm plastic test tubes (semi-solid samples, such as fecal suspension), with an average daily testing volume of 200 tubes. The testing vehicle's workbench dimensions are 400mm × 300mm. The equipment weight is required to be ≤10kg, the operating noise level ≤65dB, and it must be able to operate continuously for 4 hours. Step 1: System Deployment and Parameter Configuration

[0022] Fix the system to the testing vehicle platform and connect it to the vehicle's 220V power supply (converted via an inverter). The equipment weighs 7.8kg, meeting the ≤10kg requirement. Start the system, select the "semi-solid sample" mode, and load the mixing parameters (revolution 150rpm, rotation 75rpm, speed ratio 2:1, mixing time 45 seconds) and capping parameters (torque threshold 0.6N·m, initial speed 45rpm). Turn on the "continuous operation" mode, set the operation interval to 2 seconds, and automatically receive the feeding signal from the robotic arm. Step 2: Continuous mixing operation

[0023] The robotic arm feeds materials at 2-second intervals, and the test tube clamping mechanism automatically clamps 20mm plastic test tubes (clamping force 0.25MPa); dual motors start, with a revolution speed of 150rpm and a rotation speed of 75rpm, and the phase difference is controlled within ±3°, with speed fluctuations of 150±2rpm and 75±1rpm; the status monitoring module monitors the motor current in real time (revolution motor current 1.2A, rotation motor current 0.8A), both within the safe range; the operating noise is detected by a sound level meter, and the noise level at a distance of 1m from the equipment is 62dB, meeting the requirement of ≤65dB. Step 3: Mode Switching and Adaptive Cap Tightening

[0024] After mixing for 45 seconds, the start mode is switched, the electromagnetic clutch locks the revolution mechanism, and the rotation speed transitions from 75 rpm to 45 rpm (transition time 500ms), with a switching time of 7 seconds. During the capping stage, the torque threshold is 0.6 N·m, T1 = 0.36 N·m, and T2 = 0.54 N·m: when T(t) = 0.38 N·m, the speed drops to 30 rpm; when T(t) = 0.55 N·m, it drops to 10 rpm; when T(t) = 0.6 N·m and dα / dt = 0.4° / s, the motor stops. Due to the large difference in the tightness of the semi-solid sample tube cap threads, the system updates the threshold every 10 operations through the torque self-learning function, optimizing it from the initial 0.6 N·m to 0.62 N·m, thus improving adaptability. Step 4: Long-term continuous operation

[0025] The system can run continuously for 4 hours, processing 200 test tubes. During this time, the system automatically records the operation data and generates an operation report every hour. The motor driver temperature reaches a maximum of 68℃ (ambient temperature 32℃) and is below the 75℃ alarm threshold. The electromagnetic clutch engages 200 times without any jamming. The robotic arm and the system work together smoothly without any material leakage or incorrect material handling. Implementation effect

[0026] Statistics of 200 test tubes: mixing uniformity ≥97% (average 97.8%), capping rate 99.5% (only 1 tube not capped), test tube breakage rate 0.5% (1 tube); single tube operation time ≤55 seconds, continuous operation for 4 hours without failure, meeting the mobility and stability requirements of the on-site testing vehicle; the equipment is small in size and light in weight, and can be flexibly moved with the testing vehicle, adapting to grassroots on-site testing scenarios.

Claims

1. A dual-motor coaxial drive differential test tube mixing system for use in automated test tube capping devices, characterized in that, It includes a dual-motor differential drive unit, a collaborative control and processing unit, a job execution and monitoring unit, and an auxiliary adaptation unit; The dual-motor differential drive unit includes a 57-stepper motor and a 42-stepper motor mounted coaxially, a differential transmission mechanism, and an electromagnetic clutch module. The 57-stepper motor has a torque of 1.2 N·m and a step angle of 1.8°, while the 42-stepper motor has a torque of 0.5 N·m and a step angle of 1.8°. The axial distance between the two motors is ≤50 mm. The differential transmission mechanism consists of a spur gear and a bevel gear set to achieve speed and direction adjustment. The electromagnetic clutch module is a single-coil electromagnetic clutch with a response time ≤20 ms, used to control the locking and unlocking of the revolution mechanism. The collaborative control and processing unit includes a main controller, a motor drive module, and an encoder interface module. The main controller is an industrial-grade MCU with a main frequency of 480MHz and a control cycle of ≤0.5ms. It runs a dual-motor differential speed collaborative control algorithm, a mixing-capping motion mode switching algorithm, and a load-adaptive speed adjustment algorithm. The motor drive module is a dual-channel stepper motor driver that supports 16-256 microstepping adjustable settings and a current adjustment range of 0.1-3A. It also features overcurrent and overheat protection. The encoder interface module is a two-channel incremental encoder interface used for real-time acquisition of motor speed and phase data. The operation execution and monitoring unit includes a test tube clamping mechanism, a status monitoring module, and a human-machine interface; the test tube clamping mechanism is a three-finger flexible gripper with a clamping range of 8-25mm and the fingertips are covered with a silicone layer; the status monitoring module collects motor current, speed, and clutch status data at a sampling frequency of 100Hz; the human-machine interface is a 5-inch touch screen that supports operation mode selection, parameter setting, and manual control. The auxiliary adapter unit includes a tabletop mounting base, a dustproof cover, and an emergency stop module; the tabletop mounting base is made of lightweight aluminum alloy, with dimensions of 300mm×200mm, and supports horizontal adjustment; the dustproof cover is made of transparent acrylic material with a dustproof rating of IP54; the emergency stop module is a mechanical emergency stop button with a response time of ≤50ms.

2. A control method based on the system of claim 1, characterized in that, Includes the following steps: S1: System initialization and motor calibration, start the industrial robot system, complete the zero-point calibration of the 57 stepper motor and the 42 stepper motor and reset the differential transmission mechanism; S2: Loading operation parameters. Select the operation mode and sample type through the human-computer interaction interface, and the system will automatically load the corresponding mixing parameters and capping parameters. S3: Dual-motor differential cooperative start-up, running the dual-motor differential speed cooperative control algorithm, establishing the cooperative control relationship between the two motors based on the loaded speed ratio parameters, and completing the motor start-up preprocessing; S4: Test tube gripping and fixing. The robotic arm drives the test tube clamping mechanism to move to the test tube storage position, clamps and fixes the test tube, and ensures that the test tube axis is coaxial with the output shaft of the differential transmission mechanism. S5: "Revolution + Rotation" composite mixing, controlled by dual motor differential drive, drives the test tube to achieve composite mixing motion through differential transmission mechanism, and the status monitoring module collects motor speed, phase difference and clamping force data in real time; S6: Closed-loop adjustment of motion state. Based on the state monitoring data, the dual-motor differential speed collaborative control algorithm dynamically compensates for phase difference deviation and speed fluctuation to ensure smooth mixing motion. S7: Mixing completion judgment. When the mixing time reaches the preset value and the motion stability meets the requirements (speed fluctuation ≤ ±2 rpm), the mixing is judged to be complete; otherwise, return to step S5 to continue mixing. S8: Mixing-capping mode switching. The mixing-capping motion mode switching algorithm is run. The orbital mechanism is locked through the electromagnetic clutch module. The motor speed is switched to the capping parameter through a smooth transition stage. The switching time is ≤10 seconds. S9: Load adaptive cap tightening operation. It runs a load adaptive speed adjustment algorithm, calculates the real-time torque based on the motor current, dynamically adjusts the rotation speed, and completes the tightening or loosening of the test tube cap. S10: Cap tightening complete judgment. When the torque reaches the preset threshold and the angle change is ≤0.5° / s, the cap tightening is determined to be complete; otherwise, return to step S9 to continue tightening the cap. S11: Test tube release and mechanism reset. The test tube clamping mechanism releases the test tube, the robotic arm transfers the test tube to the target station, and the dual motors and differential transmission mechanism reset to the initial state. S12: The job is completed. The system waits for the next job instruction or starts a continuous job process according to the preset program.

3. The control method according to claim 2, characterized in that, The dual-motor differential speed cooperative control algorithm adopts a "speed ratio preset - phase difference compensation - closed-loop synchronization correction" mechanism, specifically including: A1: Preset rotation speed ratio. The rotation speed ratio between the revolution and rotation is set according to the sample type. The rotation speed ratio is adjustable in the range of 3:1-1:

3. The default rotation speed ratio is 1:2 for liquid samples and 2:1 for semi-solid samples. A2: Real-time phase difference monitoring: The speed pulse signal and phase signal of the two motors are collected through the encoder interface module, and the phase difference Δθ(i) = θ1(i) - θ2(i) at time i is calculated, where θ1(i) is the 57th stepper motor phase and θ2(i) is the 42nd stepper motor phase. A3: Phase difference compensation. When |Δθ(i)| > 3°, adjust the speed regulation of the 42 stepper motor Δn = k1・Δθ(i), where k1 is the compensation coefficient (0.1-0.3 rpm / °), until |Δθ(i)| ≤ 3°. A4: Closed-loop synchronous correction, calculate the actual speeds n1(i) and n2(i) of the two motors and the preset speed n 10 n 20 The deviation Δn1 = n 10 - n1(i), Δn2 = n 20 - n2(i), through the output adjustment signal of the PID controller, controls the motor drive module to adjust the motor speed, so that the speed fluctuation is ≤±2rpm. The PID control formula is: u (t) = Kp・e (t) + Ki・∫e (t) dt + Kd・de (t) / dt Where u(t) is the controller output, e(t) is the speed deviation, Kp is the proportional coefficient (0.5-2.0), Ki is the integral coefficient (0.01-0.1), and Kd is the derivative coefficient (0.1-0.5).

4. The control method according to claim 2, characterized in that, The mixing-capping motion mode switching algorithm adopts a "parameter preloading-clutch state switching-smooth trajectory transition" mechanism, specifically including: B1: Parameter preloading; the mixing mode parameter set (n) is loaded during system initialization. 1h n 2h Parameter sets for clutch state "unlocked" and cap screwing mode (n) 1n =0rpm、n 2n The clutch state "locked" is preloaded into the main controller cache, where n 1h For the revolution speed in the mixing mode, n 2h The rotational speed in the mixing mode, n 2n The rotation speed is for the screw-on cap mode; B2: Clutch state switching. After receiving the mode switching command, the main controller sends a "lock" signal to the electromagnetic clutch module, the electromagnetic clutch is energized and engaged, locking the revolution mechanism. The response time is ≤20ms. B3: Smooth trajectory transition, with a 500ms speed transition phase. The motor speed transitions from the mixing parameter to the cap tightening parameter using linear interpolation. The rotation speed transition formula is: n2(t) = n 2h - (n 2h - n 2n )・t / 500 Where t is the transition time (0≤t≤500ms), and n2(t) is the rotation speed at time t during the transition phase; B4: Switching completion judgment. When the clutch state is confirmed to be locked and the speed reaches the cap screwing parameter (n2(t)=n... 2n When the rotation speed fluctuation is ≤±1rpm, the switching is considered complete and the cap tightening operation mode is entered.

5. The control method according to claim 2, characterized in that, The load-adaptive speed regulation algorithm adopts a "torque threshold monitoring - speed step adjustment - arrival judgment feedback" mechanism, specifically including: C1: Torque threshold preset. Set the torque threshold T0 (adjustable from 0.5-1.5 N·m) according to the test tube cap specifications (material, thread tightness), and set two warning thresholds T1=0.6T0 and T2=0.9T0; C2: Real-time torque calculation: The working current I(t) of the 42 stepper motor is collected through the motor drive module, and the real-time torque is calculated according to the linear relationship between motor torque and current T(t)=k2・I(t), where k2 is the torque coefficient, which is determined by the motor calibration experiment; C3: Speed ​​step adjustment, when T(t) < T1, maintain the initial cap-tightening speed n 2n (50 rpm); when T1 ≤ T(t) < T2, reduce the speed to n. 21 =30rpm; when T(t) ≥ T2, reduce the speed to n 22 =10rpm; C4: Cap tightening in place judgment, continuously monitor torque T (t) and motor angle change rate dα / dt. When T (t)≥T0 and dα / dt≤0.5° / s, it is determined that the cap tightening in place and a motor stop command is sent immediately; C5: Torque self-learning optimization, recording the actual torque T at the end of each operation. a ᵢ (i=1,2,...,n), update the torque threshold T0'=(T0 + (T a1 +T a2 +...+T an ) / n) / 2, to improve the compatibility of test tube caps with different batches.

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