Abstract:
A built-in module for an inverter and having tension control with integrated tension and velocity closed loops, where required tension feedbacks can be obtained by internal calculations of the inverter or feedback signals of a tension sensor. The tension control module is applied to provide a tension control for a winding mechanism which is operated by driving at least one motor. The tension control module firstly builds a tension control to provide a balanced tension to the winding mechanism. Afterward, the tension control module builds a velocity control to provide an accelerated or decelerated adjustment for the winding mechanism. Accordingly, the winding mechanism can stably maintain a tension-balanced operation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a tension module, and more particularly to a built-in module for an inverter and having tension control with integrated tension and velocity closed loops. 
         [0003]    2. Description of Prior Art 
         [0004]    For machine equipment of papermaking, metal-manufacturing, textile, plastic-manufacturing, or cable industries, a tension-balance control is an essential and important requirement to ensure consistent qualities of manufactured products. 
         [0005]    PID (Proportional-Integral-Derivative) controllers are focused much attention and are most commonly used in industrial control because the PID controllers are simple and easy to implement. More particularly, the PID controllers can be employed to eliminate steady-state errors and to obtain relative stability and damping characteristics of controlled systems. 
         [0006]    Nowadays, a line speed control is the major control scheme for a tension control system which is built in an inverter. In this scheme, however, the line speed (not the tension force) is the major controlled variable. Thus, an unbalanced tension control tends to happen due to inconsistent line speeds when machine equipment is instantaneously started or stopped and even is operated under a tremendous speed-varying condition. 
         [0007]    Reference is made to  FIG. 1  which is a schematic view of providing a tension control for a winding mechanism by driving a motor through a prior art inverter. The scheme of the tension control for the winding mechanism mainly includes two inverters (namely, a first inverter  14   a  and a second inverter  24   a ) and two motors (namely, a first motor  12   a  and a second motor  22   a ). The winding mechanism is referred to as a controlled mechanical system  100   a . The controlled mechanical system  100   a  mainly includes a first rotating shaft  10   a , a second rotating shaft  20   a , a winding object  30   a , and a sensing unit  40   a . The first rotating shaft  10   a  and the second rotating shaft  20   a  are used to rotate the winding object  30   a  in the winding process. The first inverter  14   a  is electrically connected to the first motor  12   a , and the first motor  12   a  is mechanically connected to the first rotating shaft  10   a . The first inverter  14   a  is provided to drive the first motor  12   a  to rotate the first rotating shaft  10   a . Similarly, the second inverter  24   a  is electrically connected to the second motor  22   a , and the second motor  22   a  is mechanically connected to the second rotating shaft  20   a . The second inverter  24   a  is provided to drive the second motor  22   a  to rotate the second rotating shaft  20   a . In addition, the first motor  12   a  and the second motor  22   a  further install a first encoder  16   a  and a second encoder  26   a  onto a shaft to measure the angular velocity thereof, respectively, in a closed-loop velocity control. 
         [0008]    The sensing unit  40   a  is installed between the first rotating shaft  10   a  and the second rotating shaft  20   a . The sensing unit  40   a  can be a tension sensor or a line speed sensor to sense the magnitude of the tension force and the velocity of the winding object  30   a  between the first rotating shaft  10   a  and the second rotating shaft  20   a , respectively. Furthermore, the sensed magnitude of the tension force and the sensed velocity are used for a closed-loop tension control and a velocity control. 
         [0009]    However, the use of either the tension sensor or the line speed sensor results in higher equipment costs and different feedback sources. Thus, it is not convenient for users to adjust and control the conventional inverters with tension control functions because different control modes and parameters have to be properly set. 
         [0010]    Accordingly, it is desirable to provide a built-in module for an inverter and having tension control with integrated tension and velocity closed loops for an easy-use, high-acceptable, and wide-applicable tension-balanced control without any sensor. 
       SUMMARY OF THE INVENTION 
       [0011]    In order to solve the above-mentioned problems, a built-in module for an inverter and having a tension control with integrated tension and velocity closed loops is disclosed. The tension control module is applied to provide a tension control for a winding mechanism which is operated by driving at least one motor. The tension control module includes a first arithmetic unit, a second arithmetic unit, a tension controller, a tension feedback calculation unit, a third arithmetic unit, a velocity controller, and a fourth arithmetic unit. 
         [0012]    The first arithmetic unit receives an external tension command. The second arithmetic unit receives an external velocity command. The tension controller is electrically connected to the first arithmetic unit to receive a tension force difference and perform a PID operation to the tension force difference to output a torque. The tension feedback calculation unit is electrically connected to the first arithmetic unit to receive an angular velocity outputted from the motor and the torque calculated by the tension controller to output a feedback tension force; wherein the tension force difference is obtained by subtracting the feedback tension force from the external tension command through the first arithmetic unit. The third arithmetic unit is electrically connected to the tension feedback calculation unit to multiply the feedback tension force outputted from the tension feedback calculation unit by a winding radius of a rotating shaft of the winding mechanism to obtain a resisting torque. The velocity controller is electrically connected to the second arithmetic unit to receive a velocity difference and perform a PID operation to the velocity difference to output a compensation torque; wherein the velocity difference is obtained by subtracting the angular velocity from the external velocity command through the second arithmetic unit. The fourth arithmetic unit is electrically connected to the tension controller, the tension feedback calculation unit, the velocity controller, and the third arithmetic unit to obtain a net torque by subtracting the resisting torque from the torque to build a tension control; further the net torque is added by the compensation torque to obtain another net torque to build a velocity control. 
         [0013]    Therefore, the tension control module firstly builds the tension control to provide a balanced tension to the winding mechanism; afterward, the tension control module builds the velocity control to provide an accelerated or decelerated adjustment for the winding mechanism so that the winding mechanism can stably maintain a tension-balanced operation. 
         [0014]    It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. Other advantages and features of the invention will be apparent from the following description, drawings and claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWING 
         [0015]    The features of the invention believed to be novel are set forth with particularity in the appended claims. The invention itself, however, may be best understood by reference to the following detailed description of the invention, which describes an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which: 
           [0016]      FIG. 1  is a schematic view of providing a tension control for a winding mechanism by driving a motor through a prior art inverter; 
           [0017]      FIG. 2  is a schematic view of providing a tension control for a winding mechanism by driving a motor through an inverter according to the present invention; 
           [0018]      FIG. 3  is a block diagram of a tension control with tension closed loops; 
           [0019]      FIG. 4  is a block diagram of the tension control with integrated tension and velocity closed loops. 
           [0020]      FIG. 5  is a schematic view of building the tension control; and 
           [0021]      FIG. 6  is a schematic view of building the velocity control. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    Reference will now be made to the drawing figures to describe the present invention in detail. Reference is made to  FIG. 2  which is a schematic view of providing a tension control for a winding mechanism by driving a motor through an inverter according to the present invention. In the winding mechanism, a tension sensor or a line speed sensor is absent (namely, not necessary). The scheme of the tension control for the winding mechanism mainly includes two inverters (namely, a first inverter  14  and a second inverter  24 ) and two motors (namely, a first motor  12  and a second motor  12 ). The winding mechanism is referred to as a controlled mechanical system  100 . The controlled mechanical system  100  mainly includes a first rotating shaft  10 , a second rotating shaft  20 , and a winding object  30 . The first rotating shaft  10  and the second rotating shaft  20  are used to rotate the winding object  30  in the winding process. The first inverter  14  is electrically connected to the first motor  12 , and the first motor  12  is mechanically connected to the first rotating shaft  10 . The first inverter  14  is provided to drive the first motor  12  to rotate the first rotating shaft  10 . Similarly, the second inverter  24  is electrically connected to the second motor  22 , and the second motor  22  is mechanically connected to the second rotating shaft  20 . The second inverter  24  is provided to drive the second motor  22  to rotate the second rotating shaft  20 . In addition, the first motor  12  and the second motor  22  further install a first encoder  16  and a second encoder  26  onto a shaft to measure the angular velocity thereof, respectively, in a closed-loop velocity control. 
         [0023]    More particularly, a line tension force of the winding object  30  is calculated by a first inverter  14  and a second inverter  24  for a PID controller. Besides, a tension command is a desired value for the tension control. The detailed description of the above-mentioned PID control will be made hereinafter with reference to  FIG. 3  and  FIG. 4 . 
         [0024]    The present invention provides a tension control strategy: a tension adjustment is as the main control and a velocity adjustment is as the auxiliary control. Namely, for controlling the controlled mechanical system  100 , a tension control is firstly built to provide a balanced tension to the winding object  30 ; afterward, a velocity control is built to provide an accelerated or decelerated adjustment for the winding object  30 . Accordingly, the winding object  30  can be stably controlled under a tension-balanced operation. The detailed description of the tension control and the velocity control will be made hereinafter with reference to  FIG. 3  and  FIG. 4 , respectively. Reference is made to  FIG. 3  which is a block diagram of a tension control with tension closed loops. In this example, a winding mechanism is exemplified for further demonstration. With reference to  FIG. 2 , the controlled mechanical system  100  has the following parameters: 
         [0025]    a first winding radius R 1  represents a radius of the first rotating shaft  10 ; 
         [0026]    a first rotational inertia J 1  represents a moment of inertia of the first rotating shaft  10 ; 
         [0027]    a first angular velocity W 1  represents a rotating velocity of the first rotating shaft  10  (namely, the first motor  12 ); 
         [0028]    a first torque T 1  represents a generated torque of the first rotating shaft  10 ; 
         [0029]    a first angular acceleration α 1  represents a rotating acceleration of the first rotating shaft  10  (namely, the first motor  12 ); 
         [0030]    a first tension force F 1  represents a tension force of the winding object  30  near the first rotating shaft  10 ; 
         [0031]    a second winding radius R 2  represents a radius of the second rotating shaft  20 ; 
         [0032]    a second rotational inertia J 2  represents a moment of inertia of the second rotating shaft  20 ; 
         [0033]    a second angular velocity W 2  represents a rotating velocity of the second rotating shaft  20  (namely, the second motor  22 ); 
         [0034]    a second torque T 2  represents a generated torque of the second rotating shaft  20 ; 
         [0035]    a second angular acceleration α 2  represents a rotating acceleration of the second rotating shaft  20  (namely, the second motor  22 ); and 
         [0036]    a second tension force F 2  represents a tension force of the winding object  30  near the second rotating shaft  20 . 
         [0037]    Dynamic equations of the controlled mechanical system  100  can be represented as follows: 
         [0000]        T 1− F 1× R 1= J 1×α1
 
         [0000]        T 2− F 2× R 2= J 2×α2
 
         [0000]    Accordingly, the line tension force of the winding object  30  can be represented as follows: 
         [0000]        F 1=( T 1 −J 1×α1)/ R 1  (equation 1)
 
         [0000]        F 2=( T 2 −J 2×α2)/ R 2  (equation 2)
 
         [0038]    In addition, the first angular velocity W 1  (or the first angular acceleration α 1 ) and the second angular velocity W 2  (or the second angular acceleration α 2 ) can be obtained from the first motor  12  and the second motor  22 , respectively. Hence, the tension feedback parameters of the winding mechanism can be calculated to perform the PID operations (including a proportional operation, an integral operation, and a derivative operation) so as to obtain a torque command to control the first motor  12  and the second motor  22  to balance the first tension force F 1  and the second tension force F 2 . 
         [0039]    The first inverter  14  and the second inverter  24  are built-in the first tension control module  140  and the second tension control module  240 , respectively. The first tension control module  140  has a first tension PID controller  142 , a first tension feedback calculation unit  144 , a first arithmetic unit  141 , a third arithmetic unit  145 , and a fourth arithmetic unit  147 . The second tension control module  240  has a second tension PID controller  242 , a second tension feedback calculation unit  244 , a first arithmetic unit  241 , a third arithmetic unit  245 , and a fourth arithmetic unit  247 . Also, an external tension command Fc is received by the first arithmetic unit  141  and the first arithmetic unit  241 , respectively. 
         [0040]    The first tension feedback calculation unit  144  is electrically connected to the first arithmetic unit  141  to receive the first torque T 1  outputted from the first tension PID controller  142  and the first angular accelerational outputted from the first motor  12 . Because the first winding radius R 1  and the first rotational inertia J 1  are given after the first rotating shaft  10  being designed, the first tension force F 1  can be calculated according the equation 1 and the equation 2. In addition, a first tension force difference ΔF 1  is calculated by subtracting the first tension force F 1  from the tension command Fc (namely, ΔF 1 =Fc−F 1 ). The first tension force difference ΔF 1  is the difference between the expected tension force and the actual tension force generated from the first tension control module  140 . The first tension PID controller  142  is electrically connected to the first arithmetic unit  141  and receives the first tension force difference ΔF 1  to perform a PID operation to the first tension force difference ΔF 1  to output the first torque T 1 . In addition, the third arithmetic unit  145  is electrically connected to the first tension feedback calculation unit  144  to multiply the first tension force F 1  (outputted from the first tension feedback calculation unit  144 ) and the first winding radius R 1  of the first rotating shaft  10  to obtain a first resisting torque (F 1 ×R 1 ) of the first rotating shaft  10 . Because a direction of the first resisting torque (F 1 ×R 1 ) is opposite to that of the first torque T 1 , the net torque of the first motor  12  is equal to the difference between the first torque T 1  and the first resisting torque (F 1 ×R 1 ). More particularly, the first motor  12  is driven by a first motor drive (not shown) according to the torque mode to rotate the first rotating shaft  10  of the controlled mechanical system  100  so as to build the tension control. 
         [0041]    Similarly, the second tension feedback calculation unit  244  is electrically connected to the second arithmetic unit  241  to receive the second torque T 2  outputted from the second tension PID controller  242  and the second angular acceleration α 2  outputted from the second motor  22 . Because the second winding radius R 2  and the second rotational inertia J 2  are given after the second rotating shaft  20  being designed, the second tension force F 2  can be calculated according the equation 1 and the equation 2. In addition, a second tension force difference ΔF 2  is calculated by subtracting the second tension force F 2  from the tension command Fc (namely, ΔF 2 =Fc−F 2 ). The second tension force difference ΔF 2  is the difference between the expected tension force and the actual tension force generated from the second tension control module  240 . The second tension PID controller  242  is electrically connected to the second arithmetic unit  241  and receives the second tension force difference ΔF 2  to perform a PID operation to the second tension force difference ΔF 2  to output the second torque T 2 . In addition, the third arithmetic unit  245  is electrically connected to the second tension feedback calculation unit  244  to multiply the second tension force F 2  (outputted from the second tension feedback calculation unit  244 ) and the second winding radius R 2  of the second rotating shaft  20  to obtain a second resisting torque (F 2 ×R 2 ) of the second rotating shaft  20 . Because a direction of the second resisting torque (F 2 ×R 2 ) is opposite to that of the second torque T 2 , the net torque of the second motor  22  is equal to the difference between the second torque T 2  and the second resisting torque (F 2 ×R 2 ). More particularly, the second motor  22  is driven by a second motor drive (not shown) according to the torque mode to rotate the second rotating shaft  20  of the controlled mechanical system  100  so as to build the tension control. 
         [0042]    In the present invention, a first encoder  16  and a second encoder  26  are installed onto a shaft of the first motor  12  and the second motor  22 , respectively, to measure the first angular velocity W 1  and the second angular velocity W 2 . Furthermore, the first angular velocity W 1  and the second angular velocity W 2  can be obtained by using a velocity estimation method, where the first encoder  16  and the second encoder  26  are absent. 
         [0043]    The above-mentioned tension control closed loops based on the torque control mode are employed to drive the first motor  12  and the second motor  22  to provide the balanced tension for the winding object  30 . Reference is made to  FIG. 5  which is a schematic view of building the tension control. When the winding object  30  is in an unbalanced condition, the first motor  12  and the second motor  22  are driven to rotate slowly in different directions. In this example, the first motor  12  rotates in counter clockwise direction and the second motor  22  rotates in clockwise direction, respectively. Accordingly, once the force difference between the first tension force F 1  and the second tension force F 2  are zero (or in a range of allow error), the tension control is done. 
         [0044]    Reference is made to  FIG. 4  which is a block diagram of the tension control with integrated tension and velocity closed loops. Once the winding object  30  is in a balanced condition, and then the velocity control is performed. As shown in  FIG. 4 , a first velocity PID controller  146  of the first tension control module  140  and a second velocity PID controller  246  of the second tension control module  240  are introduced, respectively. Also, an external velocity command Wc is received by the second arithmetic unit  143  and the second arithmetic unit  243 , respectively. 
         [0045]    The second arithmetic unit  143  is used to calculated a first velocity difference ΔW 1 , which is calculated by subtracting the first angular velocity W 1  from the velocity command Wc (namely, ΔW 1 =Wc−W 1 ). The first velocity difference ΔW 1  is the difference between the expected velocity and the actual velocity generated from the first tension control module  140 . The first velocity PID controller  146  is electrically connected to the second arithmetic unit  143  and receives the first velocity difference ΔW 1  to perform a PID operation to the first velocity difference ΔW 1  to output a first compensation torque ΔT 1 . If the first angular velocity W 1  of the first motor  12  is not sufficient, the first compensation torque ΔT 1 , which is controlled by the first velocity PID controller  146 , is positive; whereas, if the first angular velocity W 1  of the first motor  12  is exceeded, the first compensation torque ΔT 1  is negative. In addition, the fourth arithmetic unit  147  is electrically connected to the first tension PID controller  142 , the first tension feedback calculation unit  144 , the first velocity PID controller  146 , and the third arithmetic unit  145  to calculate firstly the difference between the first torque T 1  and the first resisting torque (F 1 ×R 1 ) and then calculate the sum of the first compensation torque ΔT 1  and the above-mentioned torque difference. Thus, with the integrated tension and velocity closed loops, the net torque of the first motor  12  is equal to sum of a torque difference and the first compensation torque ΔT 1 , where the torque difference is between the first torque T 1  and the first resisting torque (F 1 ×R 1 ). More particularly, the first motor  12  is driven by the first motor drive according to the torque mode to rotate the first rotating shaft  10  of the controlled mechanical system  100  so as to build the velocity control. 
         [0046]    Similarly, the second arithmetic unit  243  is used to calculated a second velocity difference ΔW 2 , which is calculated by subtracting the second angular velocity W 2  from the velocity command Wc (namely, ΔW 2 =Wc−W 2 ). The second velocity difference ΔW 2  is the difference between the expected velocity and the actual velocity generated from the second tension control module  240 . The second velocity PID controller  246  is electrically connected to the second arithmetic unit  243  and receives the second velocity difference ΔW 2  to perform a PID operation to the second velocity difference ΔW 2  to output a second compensation torque ΔT 2 . If the second angular velocity W 2  of the second motor  22  is not sufficient, the second compensation torque ΔT 2 , which is controlled by the second velocity PID controller  246 , is positive; whereas, if the second angular velocity W 2  of the second motor  22  is exceeded, the second compensation torque ΔT 2  is negative. In addition, the fourth arithmetic unit  247  is electrically connected to the second tension PID controller  242 , the second tension feedback calculation unit  244 , the second velocity PID controller  246 , and the third arithmetic unit  245  to calculate firstly the difference between the second torque T 2  and the second resisting torque (F 2 ×R 2 ) and then calculate the sum of the second compensation torque ΔT 2  and the above-mentioned torque difference. Thus, with the integrated tension and velocity closed loops, the net torque of the second motor  22  is equal to sum of a torque difference and the second compensation torque ΔT 2 , where the torque difference is between the second torque T 2  and the second resisting torque (F 2 ×R 2 ). More particularly, the second motor  22  is driven by the second motor drive according to the torque mode to rotate the second rotating shaft  20  of the controlled mechanical system  100  so as to build the velocity control. 
         [0047]    The above-mentioned integrated tension control and velocity control closed loops based on the torque control mode are employed to drive the first motor  12  and the second motor  22  to provide an accelerated or decelerated adjustment for the winding object  30 , whereby the winding mechanism can stably maintain a tension-balanced operation. Reference is made to  FIG. 6  is a schematic view of building the velocity control. When the winding object  30  is in a balanced condition, the first motor  12  and the second motor  22  are driven to rotate in the same direction. In this example, the first motor  12  and the second motor  22  both rotate in counter clockwise direction. Accordingly, the first rotating shaft  10  and the second rotating shaft  20  are rotated to perform the winding or unwinding operations. More particularly, the tension control is operated with a higher bandwidth than the velocity control to provide an accelerated or decelerated adjustment for the winding mechanism so that the winding mechanism can stably maintain a tension-balanced operation. 
         [0048]    For the above-mentioned embodiments, the tension sensor or the line speed sensor is absent. However, the tension sensor and the line speed sensor can be also used to sense the magnitude of the tension force and the speed of the winding object  30   a , respectively. 
         [0049]    In conclusion, the present invention has following advantages: 
         [0050]    1. The integrated tension and velocity closed loops can be provided for a low-cost, easy-use, high-acceptable, and wide-applicable tension-balanced control without any sensor. 
         [0051]    2. The PID controllers of adjusting the tension control loops and the velocity control loops can be employed to increase stability of the tension control, thus maintaining the tension force and the velocity near the expected tension force and expected velocity, respectively. 
         [0052]    3. During the accelerated or decelerated operations, the PID gains (including a proportional gain, an integral gain, and a derivative gain) of the first velocity PID controller  146  and the second velocity PID controller  246  can be appropriately adjusted, respectively, to significantly improve the feedback oscillation, thus increasing the yield rate of products and reduce material costs. 
         [0053]    Although the present invention has been described with reference to the preferred embodiment thereof, it will be understood that the invention is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.