An underwater winch tension control system

Abstract

The underwater winch tension control system comprises a cable storage winch, a towing winch and a tension controller; the cable storage winch is a cable storage mechanism and is provided with a servo motor, is used for cable arrangement, cable storage and cable winding and unwinding and cooperates with the towing winch to complete towing work; the tension sensor is used for measuring the cable tension and providing a feedback signal for the system; the towing winch is used for force bearing and active winding and unwinding in the winding and unwinding and towing process; the tension controller acquires the servo motor speed feedback signal, the cable tension feedback signal and the towing winch speed signal, and outputs the winch control signal to the servo motor; in the system, the tension controller adopts a double-loop control mode for the servo motor, including the servo motor speed feedback signal control and the cable tension feedback signal control of the tension controller.

Description

Technical Field

[0001] This invention belongs to the field of underwater winch control technology, and specifically relates to an underwater winch tension control system. Background Technology

[0002] Underwater winches are specialized pieces of equipment used for the deployment and retrieval of underwater equipment. They require high standards in terms of size, weight, watertightness, and reliability. Currently, single winches use a single drum to tow the cable storage unit, which is prone to cable tangling and requires numerous sensors, compromising watertightness. Dual winch deployment and retrieval systems separate the towing winch and the cable storage winch, but these winches are large and unsuitable for underwater operations. Integrated towing and cable storage winches utilize a towing winch to retrieve the towed cable and equipment from underwater to the work vessel.

[0003] On the deck, the cable storage winch is responsible for winding the tow cable retrieved by the traction winch onto the winch reel. The key technology of this system lies in the tension control between the towing and cable storage winches. Existing technologies have the drawback that improper tension control can damage the tow cable, and even the towing and cable storage motors. Designing an underwater winch tension control system that ensures proper cable tension between the towing and cable storage winches, enabling them to work in tandem, and preventing sudden changes in cable tension during start-up and shutdown, as well as preventing tension slack after shutdown, are urgent problems to be solved. Summary of the Invention

[0004] In view of this, the present invention provides an underwater winch tension control system. This system enables the cable tension between the towing winch and the cable storage winch, and allows the cable storage winch and the towing winch to work collaboratively. During cable retrieval and release, the system can control the cable tension to prevent sudden changes during start-up and stop, and to prevent tension slack after shutdown. The system includes a cable storage winch, a towing winch, and a tension controller. The cable storage winch is a cable storage mechanism equipped with a servo motor, used for cable laying, storage, and retrieval, and works in conjunction with the towing winch to complete the towing operation. The tension sensor measures the cable tension and provides feedback signals to the system. The towing winch is used for load bearing and active retrieval during retrieval, release, and towing operations. The tension controller acquires servo motor speed feedback signals, cable tension feedback signals, and towing winch speed signals, and outputs winch control signals to the servo motor. In this system, the tension controller uses a dual-loop control method for the servo motor, including control of the servo motor speed feedback signal and control of the cable tension feedback signal from the tension controller.

[0005] Specifically, the cable storage winch is driven by a servo motor via a reducer, and the cable laying mechanism and bidirectional lead screw ensure the back-and-forth cable laying of the cable storage winch; the tension controller uses a linear PID controller to control the servo motor, the speed feedback signal comes from the rotary encoder built into the motor, and the tension feedback signal comes from the tension sensor on the cable.

[0006] Specifically, the rotational speed of the towing winch is considered as an external disturbance to the system. To further improve the tension control accuracy of the winch, a feedforward controller is introduced to eliminate the rotational speed of the towing winch. Interference, which must satisfy In the formula, G o R1 is the closed-loop transfer function of the motor speed loop, R2 is the radius of the towing winch wheel, R1 is the working radius of the drum, and i is the mechanical calibration coefficient.

[0007] Specifically, in order to obtain a smooth rotational speed signal, the feedforward controller performs the following processing: filtering out noise signals in the rotational speed signal using a K-filter; constructing an AR prediction model; obtaining historical rotational speed data and using the AR prediction model to predict the rotational speed of the tractor winch; and obtaining the higher-order differential value of the rotational speed signal through B-spline interpolation.

[0008] Specifically, an AR prediction model is constructed; historical rotational speed data is obtained, and the AR prediction model is used to predict the rotational speed of the traction winch, including: treating the rotational speed ω of the cable caused by the motion of the traction winch as a stationary random process, thus obeying the following AR model:

[0009]

[0010] Where: p is the order of the AR model, {a j {j = 1, 2, ..., p} represents the autoregressive coefficient system of the AR model, and {ξ(n), n = 1, 2, ..., N} represents the white noise sequence; the least squares method is used to determine the vector a of its autoregressive coefficients. j Estimate the parameters; use the maximum likelihood method to estimate the parameters and solve for the order p to determine the order of the AR prediction model; after obtaining the autoregressive coefficients and order of the AR model through historical data, predict the rotational speed data for the next step.

[0011] Specifically, obtaining the higher-order differential value of the rotational speed signal through B-spline interpolation includes: representing it using a linear combination of available basis functions and control vertices.

[0012]

[0013] Where: t∈[t k ,t n+1 The node vector is defined as: T = (t0, t1, ..., t2)n+k+1 ),t0≤t1≤...≤t n+k+1

[0014] Define the basis functions as:

[0015]

[0016]

[0017] At this point, the spline curve is of order k+1, and its degree is k, meaning it consists of k+1 sampling points; it is set at the node vector T = (t0, t1, ..., t n+k+1 Above, with As the control vertex, the continuity order of the entire curve is C ≥ k-max(m j ), where m j Indicates t j The multiplicity of , j = k, k+1, ..., n+1.

[0018] In particular, to ensure the feasibility of the tension controller, a bilinear transformation method based on the trapezoidal integral rule is used to make the number of poles and zeros of the resulting discrete controller the same, and the order of the discrete control, i.e. the number of poles of the discrete controller, is the same as the order of the original continuous controller.

[0019] Specifically, a Simulink model was established for simulation to verify the effectiveness of the feedforward controller, the impact of cable stiffness on the system, and the rotational speed signal of the towing winch obtained by the AR prediction and B-spline interpolation preprocessing.

[0020] Beneficial effects:

[0021] 1) The system achievable by the present invention can control the cable tension between the towing winch and the cable storage winch, and enable the cable storage winch and the towing winch to work together. When the cable is being pulled up and released, the cable tension can be controlled to prevent sudden changes during start-up and stop, and the tension will not slacken after the machine stops.

[0022] 2) By introducing a feedforward controller through this invention, the interference of the towing winch speed is eliminated, making the tension control more accurate;

[0023] 3) By using the K-filter in this invention to filter out noise signals in the speed signal, it is easier to obtain an accurate and reliable speed signal;

[0024] 4) By using the AR forecasting model and B-spline interpolation in this invention to predict the rotational speed of the towing winch, a high-order differential value can be obtained. Compared with other forecasting methods, the AR forecasting model and B-spline interpolation have the advantages of simple algorithm, high forecast accuracy, simple calculation, and good real-time performance.

[0025] 5) By establishing a Simulink model in this invention for simulation, the effectiveness of the feedforward controller, the influence of cable stiffness on the system, and the rotational speed signal of the towing winch obtained by the preprocessing of AR prediction and B-spline interpolation can be verified. Attached Figure Description

[0026] Figure 1 This is a block diagram of the underwater winch tension control system proposed in this invention;

[0027] Figure 2 This is a block diagram of the dual-loop control system proposed in this invention;

[0028] Figure 3 This is a block diagram of the feedforward control system proposed in this invention;

[0029] Figure 4 This is a block diagram of the control system for incorporating AR forecasting proposed in this invention;

[0030] Figure 5 The flowchart shows the program for writing the forecasting algorithm in MATLAB as proposed in this invention.

[0031] Figure 6 This is a schematic diagram of the Simulink simulation model proposed in this invention;

[0032] Figure 7 This is a schematic diagram of the tension control results achieved by the continuous feedforward controller proposed in this invention.

[0033] Figure 8 This is a schematic diagram of the motor input voltage change obtained from simulation in this invention;

[0034] Figure 9 A schematic diagram of the linear velocity variation under continuous feedforward control obtained by simulation in this invention. Detailed Implementation

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] This invention provides an underwater winch tension control system, such as... Figure 1As shown, the system includes a cable storage winch, a towing winch, and a tension controller. The cable storage winch is a cable storage mechanism equipped with a servo motor, used for cable laying, storage, and winding, and works in conjunction with the towing winch to complete the towing operation. The tension sensor measures the cable tension and provides feedback signals to the system. The towing winch is used for load bearing and active winding during winding and towing operations. The tension controller acquires the servo motor speed feedback signal, the cable tension feedback signal, and the towing winch speed signal, and outputs the winch control signal to the servo motor. In this system, the tension controller adopts a dual-loop control method for the servo motor, including controlling the servo motor speed feedback signal and controlling the cable tension feedback signal of the tension controller.

[0037] In this embodiment, the tension controller is a dual-loop composite controller. To simplify the controller design process, the servo motor model needs to be simplified to a certain extent. Since the response bandwidth of the servo motor is much larger than the overall bandwidth of the system, its mathematical model can be represented by a first-order inertial element.

[0038]

[0039] Among them, K t t is the proportionality coefficient. a is the time constant.

[0040] The system employs a traditional dual-loop motor control method, with both controllers using linear PID control strategies. Compared to single-loop control, dual-loop control increases loop damping, which enhances the stability of the closed-loop system. The block diagram of the control system is shown below. Figure 2 As shown.

[0041] It can be seen that the outermost loop of the system is the tension loop. However, in actual engineering, the tension value measured by the force sensor usually fluctuates significantly. Therefore, a second-order low-pass filter is typically added to the tension feedback channel to filter out high-frequency noise. The continuous form of this second-order low-pass filter is as follows, where ξ = 0.707, ω n =20Hz

[0042]

[0043] The dual-loop motor control includes a servo motor speed controller G. v (s) and tension controller G f (s). The speed feedback signal comes from the motor's built-in rotary encoder, while the tension feedback signal comes from the tension sensor on the cable. Controller G v (s) and G f The transfer function of (s) is a PI controller, and its specific form is as follows:

[0044]

[0045]

[0046] Among them, the servo motor speed loop adopts PI control, K vP and K vI The speed loop's proportional and integral gain servo motor speed controller is primarily used to improve the dynamic response performance and eliminate steady-state error in drive systems comprising servo motors, reducers, and drums. The tension loop's proportional and integral gain are used to track the set tension value. Dual-loop controller parameter K. vP K vI K fP K fI All were derived using the trial-and-error method.

[0047] To stabilize the system tension near the set tension value, the drum speed should be consistent with the linear velocity of the towing winch. Considering the towing winch's speed as an external disturbance, a feedforward controller G is introduced to further improve the winch's tension control accuracy. u Eliminate the speed of the towing winch The interference, the feedforward control system block diagram is as follows Figure 3 As shown. To eliminate the speed of the towing winch. Interference, which must satisfy In the formula, G o Let R2 be the closed-loop transfer function of the motor speed loop, R1 be the radius of the traction winch sheave, and i be the working radius of the drum. The feedforward controller G... u Simplified to:

[0048]

[0049] In the formula, [a0,a1,b0,b1] are the continuous controller coefficients.

[0050] As shown in equation (2.7), the feedforward controller requires the first-order derivative of the towing winch speed interference signal. This necessitates that the obtained speed signal be sufficiently smooth. However, the speed signal obtained from the motor rotary encoder contains a certain amount of noise, making it difficult to directly obtain smooth higher-order derivative terms. Therefore, the K-filter method needs to be introduced:

[0051] First, rewrite equation (2.7) in the following form.

[0052]

[0053] Furthermore, we can obtain:

[0054]

[0055] Performing a z-transform on the above equation yields:

[0056]

[0057] The output Y(n) of the discrete controller at time n can be expressed as:

[0058]

[0059] Where U(n) represents the controller input at time n.

[0060] Besides K-filtering to obtain the higher-order derivative of the signal, the AR forecasting model combined with B-spline interpolation can also yield good higher-order derivative values. Compared to other forecasting methods, the AR forecasting model features simple algorithms, high forecast accuracy, simple computation, and good real-time performance. After forecasting the rotational speed after a certain period, B-spline interpolation is performed, and the higher-order derivative value is obtained using interpolation. The block diagram of the control system incorporating AR forecasting is shown below. Figure 4 As shown.

[0061] Let {x(i), i = 1, 2, 3, ..., N} be a known sequence of towing winch rotation speeds over a period of time. Within this relatively short timeframe, the cable rotation speed ω caused by the towing winch's motion can be considered a stationary random process, thus following the AR prediction model:

[0062]

[0063] Where: p—order of the AR forecast model

[0064] {a j ,j=1,2,...,p}——Autoregressive system of AR forecast model

[0065] {ξ(n), n = 1, 2, ..., N} — White noise sequence

[0066] The modeling of AR forecasting models is quite similar to the least squares identification method introduced earlier. The key to obtaining a highly accurate AR forecasting model lies in estimating the model's autoregressive coefficients {a}. j ,j=1,2,...,p}.

[0067] Let n = p+1, p+2, ..., N, (N ≥ 2p) in equation (2.13), then we can obtain Np {a} j The system of equations for}:

[0068]

[0069] At this point, define the matrix:

[0070] X N= [x(p+1)x(p+1)...x(N)] T (2.15)

[0071]

[0072] a = [a1 a2 ... a] p ] T (2.17)

[0073] ξ=[ξ(p+1) ξ(p+2) ... ξ(N)] T (2.18)

[0074] Substituting equations (2.15) to (2.18) into equation (2.14) yields:

[0075] X N =Ψ N a+ξ(2.19)

[0076] Because equation (2.19) contains a white noise sequence ξ, it cannot be solved. Therefore, the least squares method is used here to estimate the vector a of its autoregressive coefficients. Let the estimated vector be... The estimated objective function is:

[0077]

[0078] set up Let be the estimated value of the autoregressive coefficient vector 'a' obtained using the least squares method. Then, when When J is at its minimum, then:

[0079]

[0080] get:

[0081]

[0082] From equation (2.13), it can be seen that the autoregressive coefficient {a} is completed. j After estimating the AR model for the sequence {j = 1, 2, ..., p}, the order p of the AR model needs to be determined to obtain the complete AR prediction model. Solving for the order p is also known as determining the order of the AR model.

[0083] Methods for determining the order of AR models include white noise test, criterion function, and corner angle determination. Here, we choose the AIC criterion method, which has the advantage of ensuring the real-time performance and adaptability of the forecast model.

[0084] The AIC criterion order determination method belongs to the optimal criterion function method. Its principle is to estimate the parameters using the maximum likelihood method on a given model to find the model order. The method is as follows:

[0085]

[0086] in:

[0087] —Parameter values ​​estimated by the maximum likelihood method

[0088] ——Maximum likelihood function

[0089] k — the number of independent parameters in the model.

[0090] Equation (2.23) shows that the AIC criterion number consists of two parts. First, the number of independent parameters in the model, which increases with the order; second, the model's goodness of fit, which decreases with the order. Based on Equation (2.13), the maximum likelihood function of the AIC model can be expressed as follows:

[0091]

[0092]

[0093] The number of independent parameters in the model can be expressed as follows:

[0094]

[0095] Based on the above derivation, the AIC criterion order determination method is divided into three steps. First, the maximum order M of the model is determined through offline estimation. Then, the order is sequentially taken from 1 to M, and each order p is substituted into equation (2.13) to estimate the autoregressive coefficients in the model using the least squares method, and the AIC criterion number AIC(p) for each model is calculated. Finally, the magnitudes of all AIC(p) are compared, and when one... Make hour, This refers to the order of the AR forecast model.

[0096] The prediction of towing winch rotational speed using an AR (Autoregressive) model is based on the principle of linear minimum variance. Once historical rotational speed data is obtained, and the autoregressive coefficients and order of the AR model are derived from this data, the next step in predicting rotational speed data is as follows:

[0097]

[0098] Using the above method, a forecasting algorithm program was written in MATLAB, and its flow is as follows: Figure 5The advantage of B-spline interpolation is that the resulting curve has excellent characteristics of locally adjustable shape and adjustable continuous order. A B-spline curve can be represented by a linear combination of basis functions and control vertices, as shown in the following formula:

[0099]

[0100] Where: t∈[t k ,t n+1 The node vector is defined as: T = (t0, t1, ..., t2) n+k+1 ),t0≤t1≤...≤t n+k+1

[0101] Define the basis functions as:

[0102]

[0103]

[0104] The spline curve at this point is of order k+1, and its degree is k (meaning it consists of k+1 sampling points). It is set in the node vector T = (t0, t1, ..., t...). n+k+1 Above, with As the control vertex, the continuity order of the entire curve is C ≥ k-max(m j ), where m j Indicates t j The multiplicity of , j = k, k+1, ..., n+1.

[0105] Based on equations (2.28) and (2.30), it can be deduced that N i,p The higher-order derivative of the rotational speed signal is obtained by directly interpolating the derivative of (t) with respect to time.

[0106]

[0107] Furthermore, the use of the bilinear transform method for discretization ensures the realizability of the controller. The bilinear transform method is a digital integral transform method based on the trapezoidal integral rule, mapping the left half-plane of the s-plane to the unit circle in the z-plane. Its advantages include maintaining the stability of the controller while ensuring that the number of poles and zeros in the resulting discrete controller D(z) is the same, and that the order of the discrete control (i.e., the number of poles) is the same as that of the original continuous controller. The frequency response of the resulting D(z) is similar to that of the continuous controller in the low-frequency range.

[0108] The specific form of the discrete controller is obtained by the following formula, where T is the sampling time (s).

[0109]

[0110] Further, we can obtain

[0111]

[0112] In the formula, [α0…α3,β0…β3] are the discrete controller coefficients, the specific form of which is given by equation (3.12).

[0113]

[0114] Further, we can obtain

[0115]

[0116] To verify the stability and speed of the controller designed based on the simplified model, this embodiment also establishes a Simulink model for simulation. The simulation model is as follows: Figure 6 As shown in the table below, the parameters selected for the model are as follows.

[0117]

[0118]

[0119] In the simulation results of the feedforward controller, to verify whether using only the derivative term can achieve a good control effect, first-order, second-order, and third-order derivative continuous feedforward controllers were used respectively. The initial cable tension was set to 7000N, and the towing winch started working after 2s. The speed of the towing winch during operation was about 2rad / s, and the disturbance amplitude was 0.4rad / s. The speed disturbance during the winch motion was simulated using a sinusoidal signal as follows: Figure 7 As shown, the specific form of the sinusoidal signal is given by equation (3.2), and the simulation results are as follows:

[0120]

[0121] analyze Figure 7 It can be seen that the control effect of first-order feedforward compensation is already comparable to that of second-order and third-order feedforward compensation, while the effect of no feedforward compensation is slightly worse. Therefore, in practical selection of the feedforward controller order, a first-order controller can achieve satisfactory control results. Without a feedforward controller, the effect of towing winch speed fluctuations is more pronounced, with tension fluctuating with the towing winch speed. With a feedforward controller, however, fluctuations in towing winch speed can be suppressed, maintaining a constant tension value. Tension fluctuations without feedforward compensation are around 5%, while tension fluctuations with feedforward compensation are controlled to within 1%.

[0122] Depend on Figure 7 It can be seen that at the 2nd second, the towing winch starts to work. The system without a feedforward controller experiences a large sudden change in acceleration, while the system with a feedforward controller quickly suppresses the interference caused by the sudden acceleration of the towing winch.

[0123] In practical engineering applications, it is also necessary to consider whether the controller output control quantity is saturated, and the change in motor input voltage obtained from the simulation, such as... Figure 8 As shown, the controller's output voltage is within 10V.

[0124] Figure 9 This is a schematic diagram of the linear velocity variation under continuous feedforward control. Figure 9 It can be seen that under feedforward control, the cable storage winch can follow the movement of the towing winch very well, even when the speed of the towing winch changes drastically, thus maintaining constant cable tension during cable laying. Simulations verified the effectiveness of the designed feedforward controller.

[0125] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0126] It will be apparent to those skilled in the art that the embodiments of the present invention are not limited to the details of the exemplary embodiments described above, and that the embodiments of the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the embodiments of the present invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the embodiments of the present invention is defined by the appended claims rather than the foregoing description. Therefore, all variations falling within the meaning and scope of equivalents of the claims are intended to be encompassed within the embodiments of the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units, modules, or devices recited in the system, apparatus, or terminal claims may also be implemented by the same unit, module, or device through software or hardware. The terms "first," "second," etc., are used to indicate names and do not indicate any particular order.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and are not intended to limit them. Although the embodiments of the present invention have been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the embodiments of the present invention should not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tension control system for an underwater winch, characterized in that, The system includes a cable storage winch, a towing winch, and a tension controller. The cable storage winch is a cable storage mechanism equipped with a servo motor, used for cable laying, storage, and winding, and works in conjunction with the towing winch to complete the towing operation. A tension sensor measures the cable tension and provides feedback signals to the system. The towing winch is used for load bearing and active winding during the winding and towing process. The tension controller acquires servo motor speed feedback signals, cable tension feedback signals, and towing winch speed signals, and outputs winch control signals to the servo motor. In this system, the tension controller uses a dual-loop control method for the servo motor, including controlling the servo motor speed feedback signal and controlling the cable tension feedback signal of the tension controller. The towing winch speed is considered an external disturbance to the system. To further improve the tension control accuracy of the winch, a feedforward controller is introduced to eliminate the towing winch speed. Interference, which must satisfy In the formula, This is the closed-loop transfer function for the motor speed loop. The radius of the towing winch sheave. The working radius of the drum. For mechanical calibration coefficients; The feedforward controller performs the following processing to obtain a smooth rotational speed signal: filtering out noise signals in the rotational speed signal using a K-filter; constructing an AR prediction model; obtaining historical rotational speed data and using the AR prediction model to predict the rotational speed of the towing winch; obtaining the higher-order differential value of the rotational speed signal through B-spline interpolation; constructing an AR prediction model; obtaining historical rotational speed data and using the AR prediction model to predict the rotational speed of the towing winch, including: determining the rotational speed of the cable due to the motion of the towing winch. Treating it as a stationary stochastic process, it therefore follows the AR model: in: For the order of the AR model, Represents the autoregressive coefficient system of the AR model. Represents a white noise sequence; uses the least squares method to vectorize its autoregressive coefficients. Estimate the parameters using the maximum likelihood method and solve for the order. The order of the AR prediction model is determined; after obtaining the autoregressive coefficients and order of the AR model from historical data, the rotational speed data for the next step is predicted; the higher-order differential value of the rotational speed signal is obtained through B-spline interpolation, including representation using a linear combination of available basis functions and control vertices. in: The node vector is defined as: Define the basis functions as: The order of the spline curve at this point is Order, curve degree is That is, It consists of 1 sampling point; it is set in the node vector Above, with As the control vertex, the successive order of the entire curve ,in express multiplicity, .

2. The underwater winch tension control system as described in claim 1, characterized in that, The cable storage winch is driven by a servo motor via a reducer, and the cable laying mechanism and bidirectional lead screw ensure the back-and-forth cable laying of the cable storage winch; the tension controller uses a linear PID controller to control the servo motor, the speed feedback signal comes from the rotary encoder built into the motor, and the tension feedback signal comes from the tension sensor on the cable.

3. The underwater winch tension control system as described in claim 1, characterized in that, To ensure the feasibility of the tension controller, a bilinear transformation method based on the trapezoidal integral rule is used to make the number of poles and zeros of the resulting discrete controller the same, and the order of the discrete control, i.e. the number of poles of the discrete controller, is the same as the order of the original continuous controller.

4. The underwater winch tension control system as described in claim 1, characterized in that, A Simulink model was established for simulation to verify the effectiveness of the feedforward controller, the impact of cable stiffness on the system, and the rotational speed signal of the towing winch obtained by the AR prediction and B-spline interpolation preprocessing.

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