Abstract:
A positioner and method for generating an output signal for setting a controlled object to a control condition corresponding to an input signal, including a memory unit for storing a conversion relation for converting the input signal to a command signal; a signal conversion unit for converting the input signal to the command signal based on the conversion relation; a control unit for generating the output signal for controlling the controlled object corresponding to the command signal; and a setting unit for adjusting the command signal to obtain a desired control condition for each of a plurality of selected input signals, thereby generating a modified conversion relation between the input signal and the command signal. The modified conversion relation generated by the setting unit is stored in the memory unit as the conversion relation.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention: 
     The present invention relates to a positioner which can easily set an output signal such that a controlled object is set to an arbitrary control condition corresponding to an input signal and its setting method. 
     2. Description of the Related Art: 
     Positioners have been used for controlling actuators such as diaphragm motors, cylinders and the like. The positioner controls a pressurized fluid in response to an input signal inputted as an electric signal, an air pressure signal or the like and sets a rotational angle of a rotary shaft of the diaphragm motor, a displacement position or the like of a piston of the cylinder to a given angle and position. 
     For example, in case the diaphragm motor which is controlled by this positioner is used for opening or closing a valve, a flow rate of a fluid which flows through the valve can be controlled in response to an input signal such as an electric signal, an air pressure signal or the like inputted to the positioner. 
     In the above flow rate control, the rotational angle of the rotary shaft of the diaphragm motor is not necessarily proportional to the flow rate of the fluid which passes through the valve. Conventionally, in setting the input signal inputted to the positioner and the flow rate of the fluid which passes through the valve to have a proportional relation, flow rate characteristics respectively corresponding to a large number of input signals are required to be measured and a conversion relation which makes the flow rate characteristics linear must be obtained. Accordingly, an operation for setting the conversion relation is complexed and such a setting operation takes a considerably long time and pushes up the cost. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide a positioner which can set a conversion relation in a short time and can reduce the cost needed in setting such a conversion relation and a method for performing such a setting. 
     It is a main object of the present invention to provide a positioner which can easily set an arbitrary conversion relation and a method for performing such a setting. 
     The above and other object, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative examples. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial cross-sectional view of a positioner according to an embodiment of the present invention; 
     FIG. 2 is a longitudinal cross-sectional view of the positioner shown in FIG. 1; 
     FIG. 3 is a circuit block diagram of the positioner shown in FIG. 1; 
     FIG. 4 is a circuit block diagram showing the relation among the positioner shown in FIG. 1, a valve connected with the positioner and a pipeline connected with the valve; 
     FIG. 5 is a flow chart showing the manner of using the positioner according to the embodiment of the present invention; 
     FIG. 6 is a flow chart of the manner of setting the positioner according to the embodiment of the present invention, which shows steps for setting a minimum command and a maximum command; 
     FIG. 7 is a flow chart of the manner of setting the positioner according to the embodiment of the present invention, which shows steps for setting given commands; and 
     FIG. 8 is a graph showing the relation among the input signals inputted in accordance with the method for setting the positioner according to the embodiment of the present invention, the commands and the flow rate. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A positioner and its setting method according to the present invention are explained in detail hereinafter with reference to a preferred embodiment in conjunction with attached drawings. 
     In FIG.  1  and FIG. 2, numeral  10  indicates a positioner according to this embodiment. The positioner  10  includes a casing  12  in which a printed board  14  is disposed. A display unit  16  and a key entry unit  18  which constitutes a setting unit are mounted on the printed board  14 . The key entry unit  18  is provided with an up key  20   a , a down key  20   b  and a set key  20   c . A feedback shaft  22  is pivotally mounted on the casing  12 . One end of the feed back shaft  22  is connected to an angle sensor  24 . The other end of the feed back shaft  22  is connected to a rotary shaft  30  of a diaphragm motor  28  which constitutes a controlled object of this positioner  10 . As shown in FIG. 3, the rotary shaft  30  of a diaphragm motor  28  is connected to a drive shaft  33  of a valve  32  and a degree of opening of the valve  32  is regulated by an amount of rotation of the rotary shaft  30 . 
     The casing  12  is provided with a supply passage  34  for introducing compressed air, inlet and outlet passages  36 ,  38  which are connected with the diaphragm motor  28 . Pressure gages  40   a - 40   c  are respectively mounted on the supply passage  34  and the inlet and outlet passages  36 ,  38 . A cable connector  42  connected to the printed board  14  is disposed for the casing  12 . 
     Next, the positioner  10  is explained with reference to the circuit block diagram of FIG.  3 . 
     Input signals a which are indicated as voltage values or the like are inputted to an input unit  52  of the printed board  14  of the positioner  10  from an input terminal  50  by way of the cable connector  42 . The input unit  52  includes an A/D converter, for example, and converts input signals to digital values and inputs them to a command operation unit (a signal conversion unit)  54 . The display unit  16 , the key entry unit  18  and a memory unit  56  made up of rewritable RAM and the like are connected to the command operation unit  54 . 
     A control operation unit (a control unit)  60  is connected to the command operation unit  54  and outputs of the control operation unit  60  are inputted to an electricity-air conversion unit (conversion means)  62 . The electricity-air conversion unit  62  converts the pressure of the compressed air supplied from a fluid pressure supply source  64  to a pressure corresponding to outputs of the control operation unit  60  and outputs it to the diaphragm motor  28  as an output signal e. The angle sensor  24  which is connected to the rotary shaft  30  of the diaphragm motor  28  detects the rotational angle of the rotary shaft  30  and inputs it to the control operation unit  60  as an angle signal c. 
     As shown in FIG. 4, a pipeline  66  for fluid is connected to the valve  32  which is connected to the positioner  10  and a flowmeter  68  is mounted on the pipeline  66 . 
     The positioner  10  according to this embodiment basically has the above-mentioned construction. The operation of the positioner  10  will be explained hereinafter in connection with the setting method according to this embodiment. 
     First of all, in case there is a key entry or key input for regulating the conversion relation from the input signals to the command signals from the key entry unit  18  of the positioner  10  (step S 1  in FIG.  5 ), the operation proceeds to a subroutine for regulating the conversion relation (step S 2 ). In case there is no key entry or key input for regulating the conversion relation at the step S 1 , the operation proceeds to a subroutine for controlling the valve  32  as originally expected (step S 3 ). 
     Here, the subroutine for regulating the conversion relation is explained with reference to FIG.  6 . 
     The conversion relation of commands (command signals) b which are angles of the rotary shaft  30  relative to the input signals a is preliminarily stored in the memory unit  56 . In this conversion relation, as shown by a broken line  70  in FIG. 8, the input signals a and the commands b are set to be in a proportional relation. Here, controlled variable, namely, the flow rate d of a fluid which flows through the valve  32  varies corresponding to the commands b so that it follows a curve  72  shown in FIG.  8 . 
     In the above condition, first of all, a minimum input signal a min  which is the smallest value among the input signals a is inputted to the input terminal  50  (step S 21 ). The minimum input signal a min  is converted to a digital value by the input unit  52  and is inputted to the command operation unit  54 . In this command operation unit  54 , a command (the minimum command signal) b which corresponds to the minimum input signal a min  is read out from the memory unit  56  (see the broken line  70 ) and the angle of the rotary shaft  30  of the diaphragm motor  28  is controlled to the command b (step S 22 ). 
     To explain this control in detail, the command b is outputted from the command operation unit  54  to the control operation unit  60 . On the other hand, the angle of the rotary shaft  30  of the diaphragm motor  28  is converted to an electric signal by the angle sensor  24  and the electric signal is inputted to the control operation unit  60  as an angle signal c. 
     In this control operation unit  60 , the difference between the command b and the angle signal c is calculated and a control operation such as a PID control or the like is implemented on this difference and its result is inputted to the electricity-air conversion unit  62 . 
     Subsequently, the electricity-air conversion unit  62  controls the pressure of the compressed air supplied from the fluid pressure supply source  64  based on the above computed result. This compressed air is outputted to the diaphragm motor  28  from the input and output passages  36 ,  38  as an output signal e and the rotary shaft  30  is rotated. The control of pressure can be performed in such a manner that a solenoid valve or the like mounted on the positioner  10  (not shown) is controlled so as to change the supply passage for compressed air to the diaphragm motor  28 . In this manner, the output of the diaphragm motor  28 , namely, the angle of the rotary shaft  30  gradually approaches the command b and finally agrees with the command b and hence, the degree of opening of the valve  32  is regulated. 
     Here, the flow rate d is measured by the flowmeter  68  (step S 23 ). Then, the setting of the minimum command b min  which can obtain a desired minimum flow rate d min  is performed at the key entry unit  18  (step S 24 ). In this case, when the up key  20   a  is manipulated, the value of the command b is increased (step S 25 ), while when the down key  20   b  is manipulated, the value of the command b is decreased (step S 26 ). Accordingly, the rotary shaft  30  is rotated corresponding to the change of the value of the command b (step S 22 ). Then, when the flow rate d measured by the flowmeter  68  reaches the desired controlled variable, namely, the minimum flow rate d min , by manipulating the set key  20   c  the changed command b is stored as the minimum command b min  in the memory unit  56  (step S 27 ). Here, it is sufficient for an operator to recognize the relation between the minimum input signal a min  and the minimum flow rate d min  and it is unnecessary for the operator to know the minimum command b min . 
     Subsequently, a maximum input signal a max  which is the largest value among the input signals a is inputted to the input terminal  50  (step S 28 ). The maximum input signal a max  is converted to a digital value by the input unit  52  and is inputted to the command operation unit  54 . In this command operation unit  54 , a command (the maximum command signal) b which corresponds to the maximum input signal a max  is read out from the memory unit  56  (see the broken line  70 ) and is outputted to the control operation unit  60 . Accordingly, the rotary shaft  30  of the diaphragm motor  28  is controlled to the angle corresponding to this command b and the flow rate d of the fluid which flows through the valve  32  is changed (step S 29 ). Then, the flow rate d is measured by the flowmeter  68  (step S 30 ). 
     Then, the setting of the maximum command b max  which can obtain a desired maximum flow rate d max  is performed at the key entry unit  18  (step S 31 ). In this case also, in the same manner as the steps S 25  to S 27 , when the up key  20   a  is manipulated, the value of the command b is increased (step S 32 ), while when the down key  20   b  is manipulated, the value of the command b is decreased (step S 33 ). Accordingly, the rotary shaft  30  is rotated corresponding to the change of the value of the command b and the flow rate d flown to the valve  32  is changed (step S 29 ). Then, when the flow rate d reaches the desired controlled variable, namely, the maximum flow rate d max  by manipulating the set key  20   c  the changed command b is stored as the maximum command b max  in the memory unit  56  (step S 34 ). Here, it is also sufficient for the operator to recognize the relation between the maximum input signal a max  and the maximum flow rate d max  and it is unnecessary for the operator to know the maximum command b max . 
     After setting the minimum command b min  and the maximum command b max  in the above manner, the command operation unit  54  computes a conversion relation in which a given command (given command signal) b n  relative to a given input signal a n  is arranged on a straight line which connects a cross point of the minimum input signal a min  and the minimum command b min  and a cross point of the maximum input signal a max  and the maximum command b max  as shown by a broken line  74  in FIG. 8, and such a conversion relation is stored in the memory unit  56  (step S 35  in FIG.  7 ). In this case, for example, a plurality of commands b 1  to b 9  are set  13  corresponding to a plurality of input signals a 1  to a 9  which are equally divided between the minimum input signal a min  and the maximum input signal a max . Here, the value n is 1 to 9 and the maximum value n max  of the value n is set to 9. 
     Subsequently, the command b n  is altered such that the flow rate d of the fluid becomes proportional to the input signal a and the conversion relation of the command b n  relative to the input signal a stored in the memory unit  56  is regulated. In this method, first of all, the value of a register in the command operation unit  54  (not shown) is set to 1 (step S 36 ). Subsequently, the input signal a n  which corresponds to the value of the register, namely, the input signal a 1  in this case, is inputted to the input terminal  50  (step S 37 ). This input signal a 1  is converted to a digital value by the input unit  52  and is inputted to the command operation unit  54 . At the command operation unit  54 , the command b n  which corresponds to the input signal a n  is read out from the memory unit  56  and is outputted to the control operation unit  60 . Accordingly, the rotary shaft  30  of the diaphragm motor  28  is controlled to the angle which corresponds to this command b n  (step S 38 ). Then, the flow rate d of the fluid which flows through the valve  32  is  10 . measured (step S 39 ). 
     Then, the setting of the command is performed at the key entry unit  18  (step S 40 ). In this case also, in the same manner as the steps S 25  to S 27 , when the up key  20   a  is manipulated, the value of the command is increased (step S 41 ), while when the down key  20   b  is manipulated, the value of the command is decreased (step S 42 ). Accordingly, the rotary shaft  30  is rotated corresponding to the change of the value of the command and the flow rate d of the fluid which flows through the valve  32  is changed (step S 38 ). Then, the command b is changed such that the flow rate d takes the value proportional to the input signal a as shown in a straight line  76  in FIG.  8  and the set key  20   c  is manipulated so as to store this value of the command b n  into the memory unit  56  (step S 43 ). 
     Subsequently, it is determined whether the value n set to the register is the value n max  or not (step S 44 ). Since the value n is not the value n max  in this case, the value of, the register is increased by 1 so that the value n is set to 2 (step S 45 ). Subsequently, the operation returns to the step S 37  and the input signal a n  which corresponds to the value n of the register, namely, the input signal a2 in this case, is inputted to the input terminal  50 . Thereafter, the steps ranging from the step S 38  to the step S 45  are repeated and the value of the altered command b n  namely the value of the command b 2  in this case, is stored in the memory unit  56 . 
     In the same manner, the value n of the register is increased in sequence and the values of the commands b n  corresponding to respective values n of the register are stored in the memory unit  56 . 
     The command b n  is determined in the above manner and when the value n of the register becomes n max  in the step S 44 , the operation returns to the step S 1  in FIG.  5 . As mentioned previously, in case there is no key entry or key input for regulating the conversion relation, the operation proceeds to the control subroutine so as to control the diaphragm motor  28  (step S 3 ). 
     The conversion relation of the command b relative to the input signal a which is determined in the above-mentioned manner takes a curve as shown by the curve  78  in FIG. 8, while in this case, the input signal a and the flow rate d are in a proportional relation as shown by the straight line  76 . Furthermore, it is sufficient for the operator to recognize the input signal a and the desired flow rate d, while it is unnecessary for the operator to know the command b, namely, the relation between the angle of the rotary shaft  30  and the flow rate d (the curve  72 ). Still furthermore, the relation of the flow rate d of the fluid relative to the input signal a set in the above manner is not limited to the proportional relation and includes a non-linear relation if necessary. 
     As explained above, according to the embodiment, it is unnecessary to preliminarily measure the flow rate d of the fluid relative to the angle of the rotary shaft  30  of the diaphragm motor  28  so that the characteristics of the flow rate d relative to the input signal a can be readily set.