DESCRIPTION

MOTOR CONTROLLER

TECHNICAL FIELD

[0001] The present invention relates to a motor controller, and more particularly to
acceleration/deceleration control of a servomotor at the time of performing its positional control.

BACKGROUND ART

[0002] When performing acceleration/deceleration control of a servomotor, a shortage of a driving torque sometimes occurs along with a decrease in an input voltage to an inverter, and this can lead an occurrence of overshoot or undershoot at an acceleration/deceleration time of the servomotor. Therefore, there has been proposed a method for solving the problem of overshoot or undershoot at the acceleration/deceleration time by extending the acceleration/deceleration time according to a shortage of a driving torque generated by a decrease in an input voltage (Patent Document 1).

[0003] There has also been proposed a method for shortening a positioning time while causing a feed rate amount and an acceleration/deceleration rate amount of a positioning controller to follow a position instruction value by correcting the feed rate amount and the acceleration/deceleration rate amount according to a direct-current bus voltage or an alternating-current input voltage of an inverter (Patent Document 2).

[0004] Patent Document 1: Japanese Patent Application Laid-open No. S58-54894
Patent Document 2: Japanese Patent Application Laid-open No. HlO-337088

DISCLOSURE OF INVENTION

PROBLEM TO BE SOLVED BY THE INVENTION

[0005] However, according to the conventional technique of Patent Document 1 mentioned above, overshoot or undershoot at the acceleration/deceleration time due to a torque shortage is reduced by extending an acceleration/deceleration time constant. Consequently, a positioning time of a tool and the like by a servomotor becomes long, and thus there is a problem that a processing time using the tool positioned by the servomotor is extended.

[0006] Further, according to the conventional technique of Patent Document 2 mentioned above, because the feed rate amount or the acceleration/deceleration rate amount is reduced along with a decrease in the input voltage, the acceleration/deceleration time constant is extended as a result. Therefore, there is a problem that the processing time using the tool positioned by the servomotor is extended.

[0007] The present invention has been achieved in view of the above problems, and an object of the present invention is to provide a motor controller capable of reducing overshoot and undershoot at an acceleration/deceleration time while suppressing an increase in a time taken for acceleration/deceleration even when an input voltage decreases.

MEANS FOR SOLVING PROBLEM

[0008] In order to solve the aforementioned problems and attain the aforementioned object, a motor controller according to one aspect of the present invention is constructed in such a manner as to include: an acceleration/deceleration parameter-group setting unit that sets for each input voltage an acceleration/deceleration parameter group that designates an acceleration rate to become larger in a low revolution range of a servomotor than in a high revolution range; an acceleration/deceleration parameter-group selecting unit that selects an acceleration/deceleration parameter group set by the acceleration/deceleration parameter-group setting unit, based on an input voltage to be input to a drive unit that drives the servomotor; and an acceleration/deceleration instructing unit that generates an acceleration/deceleration pattern such that a load torque curve at an acceleration/deceleration time falls within a torque characteristic of the servomotor, based on an acceleration/deceleration parameter group selected by the acceleration/deceleration parameter-group selecting unit.

EFFECT OF THE INVENTION

[0009] According to the present invention, overshoot and undershoot at the acceleration/deceleration time can be reduced while suppressing an increase in a time taken for acceleration/deceleration even when an input voltage decreases.

BRIEF DESCRIPTION OF DRAWINGS

[0010] [FIG. 1] FIG. 1 is a block diagram of a schematic configuration of a motor controller according to a first embodiment of the present invention.

[FIG. 2] FIG. 2 is an example of acceleration/deceleration parameter groups set by an acceleration/deceleration parameter-group setting unit 110 shown in FIG. 1.

[FIG. 3-1] FIG. 3-1 is an example of an acceleration/deceleration pattern generated by an acceleration/deceleration instructing unit 113 shown in FIG. 1.

[FIG. 3-2] FIG. 3-2 is an example of a speed pattern generated by the acceleration/deceleration instructing unit 113 shown in FIG. 1.

[FIG. 4] FIG. 4 depicts a relationship between a load torque curve obtained from acceleration/deceleration parameter groups P1 to Pn and a torque characteristic of a
servomotor.

[FIG. 5] FIG. 5 is an example of a method for generating an acceleration/deceleration pattern by the acceleration/deceleration instructing unit 113 shown in FIG.1.

[FIG. 6] FIG. 6 is an example of numerical values of acceleration/deceleration parameter groups set for each input voltage.

[FIG. 7-1] FIG. 7-1 depicts an acceleration/deceleration pattern generated from the acceleration/deceleration parameter groups shown in FIG. 6.

[FIG. 7-2] FIG. 7-2 depicts speed patterns generated from the acceleration/deceleration pattern shown in FIG. 7-1.

EXPLANATIONS OF LETTERS OR NUMERALS

[0011] 10 Drive unit II Servomotor 100 Motor controller PI to Pn Acceleration/deceleration parameter group 110 Acceleration/deceleration parameter-group setting unit

III Input-voltage measuring unit
112 Acceleration/deceleration parameter-group selecting unit
113 Acceleration/deceleration instructing unit
114 Nonvolatile memory
115 Volatile memory
121 Ladder program
122 Input voltage value
123 Parameter group number

BEST MODE(S) FOR CARRYING OUT THE INVENTION

[0012] Exemplary embodiments of a motor controller according to the present invention will be explained below in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments. First embodiment

[0013] FIG. 1 is a block diagram of a schematic configuration of a motor controller according to a first embodiment of the present invention. In FIG. 1, a motor controller 100 includes an acceleration/deceleration parameter-group setting unit 110, an input-voltage measuring unit 111, an acceleration/deceleration parameter-group selecting unit 112, an acceleration/deceleration instructing unit 113, a nonvolatile memory 114, and a volatile memory 115. The motor controller 100 is connected to a drive unit 10 that drives a servomotor 11.

[0014] A flash memory, an EEPROM and the like can be used for the nonvolatile memory 114, for example. A DRAM, an SRAM and the like can be used for the volatile memory 115, for example. An inverter and the like can be used for the drive unit 10, for example.

[0015] The acceleration/deceleration parameter-group setting unit 110 can store in the nonvolatile memory 114 a plurality of acceleration/deceleration parameter groups P1 to Pn that are input to the acceleration/deceleration parameter-group setting unit 110.

[0016] FIG. 2 is an example of the acceleration/deceleration parameter groups P1 to Pn that are set by the acceleration/deceleration parameter-group setting unit 110 shown in FIG. 1. In FIG. 2, the acceleration/deceleration parameter groups P1 to Pn can include a rapid feed rate vs, a rated speed vk, an acceleration time tk up to the rated speed vk, and an acceleration rate ra relative to a maximum acceleration am, respectively, for example. For the acceleration/deceleration parameter groups P1 to Pn, the rapid feed rate vs, the rated speed vk, the acceleration time tk up to the rated speed vk, and the acceleration rate ra relative to the maximum acceleration "am" can be set for each input voltage Vi. The acceleration rate ra relative to the maximum acceleration am can be given by ra=as/am where "as" represents an acceleration when the acceleration reaches the rapid feed rate vs.

[0017] The acceleration/deceleration parameter groups P1 to Pn can set the acceleration rate ra to become larger in a low revolution range of the servomotor 11 than in a high revolution range. That is, the acceleration rate ra of the servomotor 11 can be set large in the low revolution range which has some margin in the driving torque, and the acceleration rate ra can be set small in the high revolution range which has a shortage in the driving torque.

[0018] In FIG. 1, the input-voltage measuring unit 111 can measure the input voltage Vi that is input to the drive unit 10. The input voltage Vi can be a direct-current bus voltage or an alternating-current input voltage of an inverter that is used as the drive unit 10. The acceleration/deceleration parameter-group selecting unit 112 can select any one of the acceleration/deceleration parameter groups P1 to Pn that are set by the acceleration/deceleration parameter-group setting unit 110, based on the input voltage Vi that is measured by the input-voltage measuring unit 111. The acceleration/deceleration instructing unit 113 can generate an acceleration/deceleration pattern based on the acceleration/deceleration parameter groups P1 to Pn that are selected by the acceleration/deceleration parameter-group selecting unit 112, and can cause the drive unit 10 to accelerate/decelerate the servomotor 11. The acceleration/deceleration instructing unit 113 generates the acceleration/deceleration pattern such that a load torque curve at an acceleration/deceleration time is falls within a torque characteristic of the servomotor 11. The acceleration/deceleration instructing unit 113 can set the acceleration constant up to the rated speed vk of the servomotor 11 and can decrease the acceleration steppedly to reach the acceleration rate ra designated by the acceleration/deceleration parameter groups P1 to Pn from the rated speed vk to the rapid feed rate vs, in the acceleration/deceleration pattern.

[0019] The nonvolatile memory 114 can store therein the acceleration/deceleration parameter groups P1 to Pn that are set by the acceleration/deceleration parameter-group setting unit 110, as well as a ladder program 121 that designates a method for selecting the acceleration/deceleration parameter groups P1 to Pn. The ladder program 121 can cause the acceleration/deceleration parameter-group selecting unit 112 to select the acceleration/deceleration parameter groups P1 to Pn such that an acceleration/deceleration pattern is generated with a margin relative to the input voltage Vi. The volatile memory 115 can store therein an input voltage value 122 corresponding to a value of the input voltage Vi measured by the input-voltage measuring unit 111, as well as a parameter group number 123 that specifies the acceleration/deceleration parameter groups P1 to Pn that are selected by the acceleration/deceleration parameter-group selecting unit 112.

[0020] Subsequently, when the acceleration/deceleration parameter groups P1 to Pn are input to the acceleration/deceleration parameter-group setting unit 110, the acceleration/deceleration parameter-group setting unit 110 stores the acceleration/deceleration parameter groups P1 to Pn in the nonvolatile memory 114. The input-voltage measuring unit 111 measures the input voltage Vi that is input to the drive unit 10, and averages a result of the measurement by an averaging filter, thereby calculating the input voltage value 122, storing the calculated result in the volatile memory 115, and also outputting the calculated result to the acceleration/deceleration parameter-group selecting unit 112.

[0021] Subsequently, when the input voltage value 122 is calculated, the acceleration/deceleration parameter-group selecting unit 112 compares the input voltage value 122 with the rated voltage (200 volts, for example), thereby to calculate a generated decrease level of the input voltage Vi. The acceleration/deceleration parameter-group selecting unit 112 selects the acceleration/deceleration parameter groups P1 to Pn corresponding to the proportion of the decrease in the input voltage Vi, and stores the parameter group number 123 that specifies the acceleration/deceleration parameter groups P1 to Pn in the volatile memory 115.

[0022] Subsequently, the acceleration/deceleration instructing unit 113 reads the acceleration/deceleration parameter groups P to Pn that are specified by the parameter group number 123 from the nonvolatile memory 114, and generates an acceleration/deceleration pattern based on the acceleration/deceleration parameter groups P1 to Pn. The acceleration/deceleration instructing unit 113 generates an acceleration pattern R from the acceleration/deceleration pattern, and outputs the acceleration pattern R to the drive unit 10. The drive unit 10 controls a voltage to be applied to the servomotor 11 such that the rotation speed of the servomotor 11 comes close to a speed designated by the acceleration pattern R, thereby to carry out accelerating/decelerating of the servomotor 11.

[0023] The acceleration/deceleration instructing unit 113 generates the acceleration/deceleration pattern based on the acceleration/deceleration parameter groups P1 to Pn corresponding to the input voltage Vi, and sets the acceleration/deceleration parameter groups P1 to Pn such that the acceleration rate ra becomes larger in the low revolution range of the servomotor 11 than in the high revolution range. With this arrangement, even when the input voltage Vi decreases, an output torque of the servomotor 11 can be used up to a maximum extent while making a load torque curve at the acceleration/deceleration time fall within the torque characteristic of the servomotor 11, and overshoot and undershoot at the acceleration/deceleration time can be reduced while suppressing an increase in the time taken for acceleration/deceleration.

[0024] Meanwhile, when the ladder program 121 is started, the ladder program 121 instructs the acceleration/deceleration parameter-group selecting unit 112 to select the acceleration/deceleration parameter groups P1 to Pn corresponding to a lower voltage than the input voltage Vi. When there is an instruction from the ladder program 121, the acceleration/deceleration parameter-group selecting unit 112 selects the acceleration/deceleration parameter groups P1 to Pn corresponding to a lower voltage than the current input voltage Vi, and stores in the volatile memory 115 the parameter group number 123 that specifies the acceleration/deceleration parameter groups P1 to Pn. The acceleration/deceleration instructing unit 113 reads from the nonvolatile memory 114 the acceleration/deceleration parameter groups P1 to Pn that are specified by the parameter group number 123, and generates an acceleration/deceleration pattern based on the acceleration/deceleration parameter groups P1 to Pn. With this arrangement, the acceleration/deceleration pattern can have a margin relative to the current input voltage Vi.

[0025] FIG. 3-1 is an example of an acceleration/deceleration pattern generated by the acceleration/deceleration instructing unit 113 shown in FIG. 1. In FIG. 3-1, when the rapid feed rate vs, the rated speed vk, and the acceleration rate ra relative to the maximum acceleration am are given by the acceleration/deceleration parameter groups P1 to Pn, the acceleration (hereinafter, also "minimum acceleration") "as" at the time when reaching the rapid feed rate vs can be obtained by multiplying the acceleration rate ra by the maximum acceleration am. The acceleration/deceleration instructing unit 113 can increase the acceleration/deceleration rate in the low revolution range which has some margin in the driving torque and can decrease the acceleration/deceleration rate in the high revolution range which has a shortage in the driving torque by generating the acceleration/deceleration pattern such that the acceleration is maintained at the maximum acceleration am up to the rated speed vk and that the acceleration is decreased to the minimum acceleration as steppedly from the rated speed vk to the rapid feed rate vs.

[0026] In this case, from the rated speed vk to the rapid feed rate vs, when decreasing the acceleration steppedly from the maximum acceleration am to the minimum acceleration as, a straight line is drawn from the maximum acceleration am at the rated speed vk to the minimum acceleration as at the rapid feed rate vs. The acceleration can be decreased steppedly along with this straight line.

[0027] FIG. 3-2 is an example of a speed pattern generated by the acceleration/deceleration instructing unit 113 shown in FIG. 1. In FIG. 3-2, when the acceleration/deceleration instructing unit 113 in FIG. 1 generates the acceleration/deceleration pattern in FIG. 3-1, the acceleration/deceleration instructing unit 113 can generate a speed pattern from this acceleration/deceleration pattern and output the generated speed pattern to the drive unit 10. In the speed pattern in FIG. 3-2, during a period until reaching the acceleration time tk up to the rated speed vk, the speed increases linearly. During a period from the acceleration time tk to an acceleration time ts up to the rapid feed rate vs, a linear inclination of the speed becomes gradually smaller.

[0028] FIG. 4 depicts a relationship between a load torque curve obtained from the acceleration/deceleration parameter groups P1 to Pn and a torque characteristic of a servomotor. In FIG. 4, in an acceleration/deceleration process in which the acceleration is constant up to the rapid feed rate vs, when the input voltage Vi decreases, a load torque curve RtO in the high revolution range cannot be accommodated within a torque characteristic Et of the servomotor 11. Therefore, overshoot and undershoot at an acceleration time occur.

[0029] On the other hand, when the acceleration/deceleration parameter groups P1 to Pn are set such that the acceleration rate ra becomes large in the low revolution range and that the acceleration rate ra becomes small in the high revolution range, a load torque curve Rt1 can be generated such that the load torque curve Rtl is accommodated within the torque characteristic Et of the servomotor 11 in the high revolution range, and an increasing rate of the speed in the low revolution range can be increased. As a result, an increase in the acceleration time can be suppressed.

[0030] FIG. 5 is an example of a method for generating an acceleration/deceleration pattern by the acceleration/deceleration instructing unit 113 shown in FIG. 1. In FIG. 5, it is assumed that the acceleration rate ra relative to the maximum acceleration am is set at 58% by the acceleration/deceleration parameter groups P1 to Pn, for example. When the acceleration/deceleration instructing unit 113 decreases the acceleration steppedly by each 10% of the maximum acceleration am from the rated speed vk to the rapid feed rate vs, the acceleration/deceleration instructing unit 113 obtains the number of stages by calculating (100-58)/10+1=5, and performs an acceleration/deceleration process of five stages.

[0031] Generally, when a decreasing rate of the acceleration at each stage is D(%), the number of stages S of the acceleration from the rated speed vk to the rapid feed rate vs can be obtained by the following equation.

S=(100-ra)/D+l

[0032] FIG. 6 is an example of numerical values of acceleration/deceleration parameter groups set for each input voltage. In FIG. 6, it is assumed, for example, that an acceleration/deceleration parameter group when a decreasing rate of the input voltage value 122 relative to the rated voltage is 0% is P1 and that an acceleration/deceleration parameter group when a decreasing rate of the input voltage value 122 relative to the rated voltage is 10% is P2. The rapid feed rate vs, the rated speed vk, the acceleration time tk up to the rated speed vk, and the acceleration rate ra relative to the maximum acceleration am are set for the acceleration/deceleration parameter groups P1 and P2, respectively.

[0033] Further, when a decreasing rate of the input voltage value 122 is 0%, the acceleration/deceleration parameter-group selecting unit 112 in FIG. 1 selects the acceleration/deceleration parameter group P1, and stores in the volatile memory 115 the parameter group number 123 that specifies the acceleration/deceleration parameter group P1. When a decreasing rate of the input voltage value 122 is 10%, the acceleration/deceleration parameter-group selecting unit 112 in FIG. 1 selects the acceleration/deceleration parameter group P2, and stores in the volatile memory 115 the parameter group number 123 that specifies the acceleration/deceleration parameter group P2.

[0034] FIG. 7-1 depicts an acceleration/deceleration pattern generated from the acceleration/deceleration parameter groups shown in FIG. 6. In FIG. 7-1, when the parameter group number 123 that specifies the acceleration/deceleration parameter group P1 in FIG. 6 is stored in the volatile memory 115, the acceleration/deceleration instructing unit 113 reads from the nonvolatile memory 114 the acceleration/deceleration parameter group P1 that is specified by the parameter group number 123. The acceleration/deceleration instructing unit 113 calculates the number of stages (seven, in this case) at the time of decreasing the acceleration steppedly from the acceleration/deceleration parameter group P1, and generates an acceleration/deceleration pattern Q1 based on the acceleration/deceleration parameter group P1.

[0035] When the parameter group number 123 that specifies the acceleration/deceleration parameter group P2 in FIG. 6 is stored in the volatile memory 115, the acceleration/deceleration instructing unit 113 reads from the nonvolatile memory 114 the acceleration/deceleration parameter group P2 that is specified by the parameter group number 123. The acceleration/deceleration instructing unit 113 calculates the number of stages (six, in this case) at the time of decreasing the acceleration steppedly from the acceleration/deceleration parameter group P2, and generates an acceleration/deceleration pattern Q2 based on the acceleration/deceleration parameter group P2.

[0036] FIG. 7-2 depicts speed patterns generated from the acceleration/deceleration pattern shown in FIG. 7-1. In FIG. 7-2, in the state that a decreasing rate of the input voltage Vi is 0%, when the acceleration/deceleration instructing unit 113 generates the acceleration/ deceleration pattern Ql, then it generates an acceleration pattern Rl from the acceleration/deceleration pattern Ql, and outputs the acceleration pattern Rl to the drive unit 10 in FIG. 1. When the drive unit 10 receives the acceleration pattern Rl from the acceleration/deceleration instructing unit 113, the drive unit 10 drives the servomotor 11 so as to match the speed given by the acceleration pattern Rl.

[0037] In the state that a decreasing rate of the input voltage Vi is 10%, when the acceleration/deceleration instructing unit 113 generates the acceleration/ deceleration pattern Q2, then it generates an acceleration pattern R2 from the acceleration/deceleration pattern Q2, and outputs the acceleration pattern R2 to the drive unit 10 in FIG. 1. When the drive unit 10 receives the acceleration pattern R2 from the acceleration/deceleration instructing unit 113, the drive unit 10 drives the servomotor 11 so as to match the speed given by the acceleration pattern R2. In the example of FIG. 6, the methods for setting the acceleration/deceleration parameter groups P1 and P2 when decreasing rates of the input voltage value 122 are 0% and 10%, respectively are explained. Also in other cases such as when decreasing rates of the input voltage value 122 are 5% and 20%, acceleration/deceleration parameter groups can be set. Second embodiment

[0038] In the first embodiment described above, a method for providing the input-voltage measuring unit 111 in the motor controller 100 is explained. Alternatively, the input-voltage measuring unit 111 can be provided at outside of the motor controller 100. For example, the input-voltage measuring unit 111 can be provided in the drive unit 10.

INDUSTRIAL APPLICABILITY

[0039] As explained above, the motor controller according to the present invention generates an acceleration/deceleration instruction based on an acceleration/deceleration parameter group, and thus the motor controller is suitable for a method for controlling a drive device that processes a workpiece by relatively moving the workpiece and a tool by a servomotor.

CLAIMS

1. A motor controller comprising:

an acceleration/deceleration parameter-group setting unit that sets for each input voltage an

acceleration/deceleration parameter group that designates an acceleration rate to become larger in a low revolution range of a servomotor than in a high revolution range and that designates the acceleration rate to become large along with an increase in a decreasing rate of the input voltage;

an acceleration/deceleration parameter-group selecting unit that selects an acceleration/deceleration parameter group set by the acceleration/deceleration parameter-group setting unit, based on an input voltage to be input to a drive unit that drives the servomotor; and

an acceleration/deceleration instructing unit that generates an acceleration/deceleration pattern such that a load torque curve at an acceleration/deceleration time falls within a torque characteristic of the servomotor, based on an acceleration/deceleration parameter group selected by the acceleration/deceleration parameter-group selecting unit.

2. The motor controller according to claim 1, further comprising a nonvolatile memory that stores a plurality of acceleration/deceleration parameter groups set for each input voltage.

3. The motor controller according to claim 1 or 2, wherein the acceleration/deceleration instructing unit generates the acceleration/deceleration pattern such that a constant acceleration is set up to a rated speed of the servomotor and that the acceleration is decreased steppedly to reach an acceleration rate designated by the acceleration/deceleration parameter group from the rated speed to a rapid feed rate.

4. The motor controller according to any one of claims 1 to 3, further comprising an input-voltage measuring unit that measures an input voltage to be input to a drive unit that drives the servomotor•

5. The motor controller according to any one of claims 1 to 4, wherein the acceleration/deceleration parameter group includes a rapid feed rate, a rated speed, an acceleration time up to the rated speed, and an acceleration rate relative to a maximum acceleration.

6. The motor controller according to claim 5, wherein the acceleration/deceleration parameter group designates such that the rapid feed rate, the rated speed, and the acceleration time become small along with an increase in a decreasing rate of the input voltage.

7. The motor controller according to claim 3, wherein the acceleration/deceleration instructing unit decreases steppedly an acceleration along with a linear line from a maximum acceleration at a rated speed to a minimum acceleration at a rapid feed rate.