Patent Application
20130238101
The present invention relates to a load inertia estimation method and a control parameter adjustment method applicable to industrial machines such as machine tools.
Feedback control which is a classical control theory is generally used for load position control of a feed system in an industrial machine such as a machine tool.
The table 2 is disposed on the bed 1 and the column 33 is disposed in such a manner as to straddle the table 2. A workpiece W is mounted on the table 2 at the time of machining, and the table 2 moves linearly in an X-axis direction along guiderails 1a on the bed 1 with the assistance of a feed system (not shown in
Accordingly, when the workpiece W is machined with the tool 9, the tool 9 is driven to rotate by the main spindle 7. The main spindle 7 and the tool 9 move linearly in the Z-axis direction together with the crossrail 4 or the ram 6 and move linearly in the Y-axis direction together with the saddle 5, and the table 2 and the workpiece W move linearly in the X-axis direction. In order to achieve high-precision machining of the workpiece W at this time, positions to which the main spindle 7 (the tool 9) and the table 2 (the workpiece W) are moved are required to be precisely controlled by the feedback control.
However, it is difficult to achieve a sufficient following performance with the feedback control system 16 as in the illustrated example, and a delay of the load position θL in following the position command θ (namely, a delay in the load position) occurs as a consequence. In order to deal with the follow delay (the delay in the load position), it is a common practice to add, to the feedback control system 16, a feed-forward control function, which is not illustrated, to differentiate the position command θ and compensate for a position delay.
However, addition of the feed-forward control function to the feedback control system cannot compensate for a position delay or vibration caused by dynamic deformation such as deflection or torsion that occurs in a mechanical element in a controlled object. For example, in the case of the feed system 11 in
In this context, Patent Document 1 listed below discloses a technique for compensating for a delay in a load position or a delay in a velocity caused by torsion or deflection of a ball screw in a feed system by finding a characteristic model (a transfer function) that approximates a characteristic of the feed system, then finding an inverse characteristic model (an inverse transfer function) of the characteristic model, and adding the inverse characteristic model to a feedback control system (see
However, in
As a consequence, if the load inertia included in the inverse characteristic model (the inverse transfer function) of the feed system is always set to a constant value, then the load inertia included in the inverse characteristic model of the feed system differs from actual load inertia of the feed system when the workpiece W having a different weight from the constant value is mounted on the table 2 for machining. Accordingly, even when the inverse characteristic model of the feed system is added to the feedback control system, the inverse characteristic model cannot sufficiently compensate for the follow delay of the load position θL caused by torsion, deflection or the like of the ball screw 15 when the workpiece W having a different weight from the constant value is machined. Hence, a position deviation between the position command P and the load position θL is increased. As a consequence, the workpiece W cannot be machined at high precision.
For this reason, in order to enable the feedback control system, to which the inverse characteristic model of the feed system is added, to perform high-precision machining on the workpiece W having any weight, it is necessary to estimate the load inertia corresponding to the weight of the workpiece W and to adjust the load inertia included in the inverse characteristic model of the feed system based on the estimated load inertia.
In view of the aforementioned circumstances, it is an object of the present invention to provide a load inertia estimation method of estimating load inertia corresponding to the weight of a workpiece, and a control parameter adjustment method of adjusting load inertia included in an inverse characteristic model of a feed system based on the estimated load inertia.
Incidentally, the above-mentioned Patent Document 4 discloses a method of calculating the weight of a load by using a difference between a motor torque when no load is applied and a motor torque when a load is applied. In contrast, the method of the present invention estimates the load inertia based on a position deviation and so forth.
A load inertia estimation method according to a first aspect of the invention for solving the above problems is a load inertia estimation method of estimating load inertia of a feed system for a load position control system configured to cause a feedback control system, to which an inverse characteristic model of the feed system is added, to control a load position of the feed system on the basis of an amount of compensation outputted from the inverse characteristic model and used for compensating for a dynamic error factor of the feed system. The method is characterized in that the method comprises: in the load position control system, conducting a load position control test using the feedback control system by issuing a position command to the feedback control system, and measuring a position deviation between the position command and the load position arising at a prescribed load position at this time; and in a load inertia estimation model being a model of the load position control system, conducting load position control simulation on a model of the feed system using a model of the feedback control system by issuing the position command to the model of the feedback control system, repeating the load position control simulation while the load inertia included in the model of the feed system is adjusted until a position deviation between the position command and the load position arising at the prescribed load position in the load position control simulation becomes equal to the position deviation measured in the load position control test, and as a consequence, if the position deviation arising at the prescribed load position in the load position control simulation becomes equal to the position deviation measured in the load position control test, estimating the load inertia included in the model of the feed system at this time as the load inertia of the feed system.
In addition, a load inertia estimation method according to a second aspect of the invention is a load inertia estimation method of estimating load inertia of a feed system for a load position control system configured to cause a feedback control system, to which an inverse characteristic model of the feed system is added, to control a load position of the feed system on the basis of an amount of compensation outputted from the inverse characteristic model and used for compensating for a dynamic error factor of the feed system. The method is characterized in that the method comprises: in the load position control system, conducting a load position control test using the feedback control system by issuing a position command to the feedback control system and measuring a position deviation between the position command and the load position arising at a prescribed load position at this time, or in a model of the load position control system, conducting load position control simulation on a model of the feed system using a model of the feedback control system by issuing the position command to the model of the feedback control system and measuring the position deviation between the position command and the load position arising at the prescribed load position at this time; and finding load inertia corresponding to the position deviation measured in the load position control test or the load position control simulation on the basis of position deviation characteristic data which is preset based on the position deviation between the position command and the load position being measured in advance and arising at the prescribed load position when no load is applied and on the position deviation between the position command and the load position being measured in advance and arising at the prescribed load position when a certain load is applied and which increases linearly in proportion to an increase in the load inertia, and estimating the load inertia thus found as the load inertia of the feed system.
Further, a control parameter adjustment method according to a third aspect of the invention is a control parameter adjustment method of adjusting load inertia included in an inverse characteristic model for a load position control system configured to cause a feedback control system, to which the inverse characteristic model of a feed system is added, to control a load position of the feed system on the basis of an amount of compensation outputted from the inverse characteristic model and used for compensating for a dynamic error factor of the feed system. The method is characterized in that the method comprises adjusting the load inertia included in the inverse characteristic model on the basis of the load inertia estimated by the load inertia estimation method according to the first or second aspect.
The load inertia estimation method of the first aspect of the invention provides the method of estimating the load inertia of the feed system for the load position control system configured to cause the feedback control system, to which the inverse characteristic model of the feed system is added, to control the load position of the feed system on the basis of the amount of compensation outputted from the inverse characteristic model and used for compensating for the dynamic error factor of the feed system. Here, the method is characterized in that the method includes, in the load position control system, conducting a load position control test using the feedback control system by issuing a position command to the feedback control system, and measuring a position deviation between the position command and the load position arising at a prescribed load position at this time; and in a load inertia estimation model being a model of the load position control system, conducting load position control simulation on a model of the feed system using a model of the feedback control system by issuing the position command to the model of the feedback control system, repeating the load position control simulation while the load inertia included in the model of the feed system is adjusted until a position deviation between the position command and the load position arising at the prescribed load position in the load position control simulation becomes equal to the position deviation measured in the load position control test, and as a consequence, if the position deviation arising at the prescribed load position in the load position control simulation becomes equal to the position deviation measured in the load position control test, estimating the load inertia included in the model of the feed system at this time as the load inertia of the feed system. For this reason, even when the weight of a load on the feed system (such as the weight of a workpiece mounted on a table of a machine tool) varies, the load inertia corresponding to the load weight can easily be estimated.
The load inertia estimation method of the second aspect of the invention provides the method of estimating the load inertia of the feed system for the load position control system configured to cause the feedback control system, to which the inverse characteristic model of the feed system is added, to control the load position of the feed system on the basis of the amount of compensation outputted from the inverse characteristic model and used for compensating for the dynamic error factor of the feed system. Here, the method is characterized in that the method includes, in the load position control system, conducting a load position control test using the feedback control system by issuing a position command to the feedback control system and measuring a position deviation between the position command and the load position arising at a prescribed load position at this time, or in a model of the load position control system, conducting load position control simulation on a model of the feed system using a model of the feedback control system by issuing the position command to the model of the feedback control system and measuring the position deviation between the position command and the load position arising at the prescribed load position at this time; and finding load inertia corresponding to the position deviation measured in the load position control test or the load position control simulation on the basis of position deviation characteristic data which is preset based on the position deviation between the position command and the load position being measured in advance and arising at the prescribed load position when no load is applied and on the position deviation between the position command and the load position being measured in advance and arising at the prescribed load position when a certain load is applied and which increases linearly in proportion to an increase in the load inertia, and estimating the load inertia thus found as the load inertia of the feed system. For this reason, even when the load weight on the feed system (such as the weight of the workpiece mounted on the table of the machine tool) varies, the load inertia corresponding to the load weight can easily be estimated.
The control parameter adjustment method according to the third aspect of the invention provides the control parameter adjustment method of adjusting the load inertia included in the inverse characteristic model for the load position control system configured to cause the feedback control system, to which the inverse characteristic model of the feed system is added, to control the load position of the feed system on the basis of the amount of compensation outputted from the inverse characteristic model and used for compensating for the dynamic error factor of the feed system. Here, the method is characterized in that the method includes adjusting the load inertia included in the inverse characteristic model on the basis of the load inertia estimated by the load inertia estimation method according to the first or second aspect of the invention. Therefore, even when the load weight on the feed system (such as the weight of the workpiece mounted on the table of the machine tool) varies, it is possible to cause parameters of the feed system to match parameters of the inverse characteristic model (such as coefficients (to be described later in detail) in differential terms of third and higher orders including the term of the load inertia). For this reason, it is possible to perform precise control over the load position such that the load position follows the position command, and thereby to cause, for example, a machine tool to perform high-precision machining.
Embodiments of the present invention will be described below in detail based on the drawings.
(Description of Feedback Control System and Feed System)
A configuration of a load position control system (a feedback control system 21 and a feed system 22) of a machine tool (see
As shown in
The brackets 26 on two sides are fixed to a bed 1 and rotatably support the screw portion 27a of the ball screw 27 via the bearings 25. The nut portion 27b of the ball screw 27 is attached to the table 2 and screwed to the screw portion 27a. The servo motor 23 is connected to the screw portion 27a of the ball screw 27 via the reduction gear unit 24. A workpiece W is placed on the table 2. In addition, the position detector (which is an Inductosyn linear scale in the illustrated example) 28 is attached to the table 2, and the pulse encoder 29 is attached to the servo motor 23.
Accordingly, when torque of the servo motor 23 is transferred to the screw portion 27a of the ball screw 27 via the reduction gear unit 24 and the screw portion 27a is rotated as indicated with an arrow A, the table 2 moves linearly in an X-axis direction together with the nut portion 27b of the ball screw 27. At this time, the position detector 28 detects a load position θL, which is a position to which the table 2 (the workpiece W) is moved, and sends a detection signal of the load position θL to the feedback control system 21 (position feedback). The pulse encoder 29 detects a motor position θM which is a rotational position of the servo motor 23. A detection signal of the motor position θM is sent to the feedback control system 21, then subjected to temporal differentiation by a differential operation unit 36, and thereby converted into a motor velocity VM which is a rotational velocity of the servo motor 23 (velocity feedback).
The feedback control system 21 is constructed by software to be executed by a personal computer, for example, and includes a position deviation operating unit 31, a multiplication unit 32, a velocity deviation operating unit 33, a proportional integral operating unit 34, a current control unit 35, and a differential operating unit 36.
Moreover, an inverse characteristic model 50 of the feed system 22 of the table 2 is added to the feedback control system 21. Although the details will be described later, the inverse characteristic model 50 is an inverse characteristic model (an inverse transfer function) of a characteristic model (a transfer function) that approximates a characteristic of the feed system 22, and is designed to compensate for a delay in the load position θL or a delay in a velocity caused, for instance, by torsion or deflection of the ball screw 27 (the screw portion 27a) of the feed system 22 (see
The position deviation operating unit 31 of the feedback control 21 finds a position deviation θΔ by calculating a deviation (θ−θL) between a position command θ, which is issued from a numerical control (NC) device 41 in order to control the load position θL, and the load position θL. The multiplication unit 32 finds a motor velocity command V for controlling the rotational velocity of the servo motor 23 by multiplying the position deviation Δθ by a position loop gain Kp. Meanwhile, the velocity deviation operating unit 33 finds a velocity deviation ΔV by calculating a deviation (V+VH−VM) between a value (V+VH), which is obtained by adding the amount VH of velocity compensation outputted from the inverse characteristic model 5 to the motor velocity command V, and the motor velocity VM.
The proportional integral operating unit 34 finds a motor torque command τ to the servo motor 23 by performing a proportional integral operation of τ−ΔV×(KV(1+1/(TVs))) using a velocity loop gain KV and an integration time constant TV. The current control unit 35 controls a current to be supplied to the servo motor 23 in such a way that the torque generated by the servo motor 23 follows the motor torque command τ. Although illustration is omitted, the current control unit 35 performs feedback control on the current such that the supply current to the motor 23 becomes a current that corresponds to the motor torque command τ.
As described above, the feedback control system 21 performs the feedback control using the triple loops of the position loop serving as a main loop, and the velocity loop as well as the current loop serving as minor loops, thereby performing control such that the load position θL follows the position command θ.
(Description of Load Inertia Estimation Model)
Furthermore, in the first embodiment, a model 60 for estimating load inertia JL that corresponds to the weight of the workpiece W is added to the feedback control system 21. The load inertia estimation model 60 will be described based on
In the example shown in
As shown in
When a characteristic model of the table 2 inclusive of the ball screw 27 is expressed by transfer functions, the characteristic model is expressed by a transfer function (CLs+KL) in a block 64, a transfer function (1/(JLs+DL)) in a block 65, and a transfer function (1/s) in a block 66. Here, JL is load inertia, which is the inertia determined by the weight (a constant value) of the table 2 and the weight of the workpiece W mounted on the table 2. Therefore, when the weight of the workpiece W mounted on the table 2 varies, the load inertia JL also changes accordingly. Here, DL is viscosity of the load (the table), CL is spring viscosity of the ball screw 27 unit (the screw portion 27a, the nut portion 27b, and the brackets 26) in an axial direction, and KL is spring rigidity of the ball screw 27 unit (the screw portion 27a, the nut portion 27b, and the brackets 26) in the axial direction.
A position deviation operating unit 67 finds a position deviation ΔθML by calculating a deviation (θM−θL) between the motor position θM and the load position θL. When the position deviation ΔθML is inputted, the block 64 finds reactive torque τL by performing calculation of τL=ΔθML×(CLs+KL) and outputs the reactive torque τL. When the reactive torque τL is inputted to the block 65, the load position θL is found by performing calculation of θL=τL(1/(JLs+DL))×(1/s) in the block 65 and the block 66, and the load position θL is outputted from the block 66.
A torque deviation operating unit 61 finds a torque deviation Δτ by calculating a deviation (τ−τL) between the torque command τ and the reactive torque τL. The block 62 finds the motor velocity VM by performing calculation of VM=Δτ×(1/(JMs+DM)). The motor velocity VM is outputted to the block 63 and fed back to the velocity deviation operating unit 33 of the feedback control system 21. The block 63 finds the motor position θM by performing calculation of θM=VM×(1/s). The motor position θM is outputted to the position deviation operating unit 67. The load position θL is fed back to the position deviation operating unit 31 of the feedback control system 21.
The inverse characteristic model 50 includes a first-order differential term operating unit 51, a second-order differential term operating unit 52, a third-order differential term operating unit 53, a fourth-order differential term operating unit 54, a fifth-order differential term operating unit 55, an addition unit 56, and a proportional integral inverse transfer function unit 57.
A transfer function for compensation control, which is provided for performing compensation control in such a manner as to compensate for dynamic error factors at the servo motor 23, the ball screw 27, and the table 2 of the feed system 22 and thereby to cause the load position θL to match (follow) the position command θ, is set to each of the differential term operating units 51 to 55 and the addition unit 56. The transfer functions for compensation control are inverse transfer functions of the aforementioned transfer functions of the feed system 22 (a mechanical system including the servo motor 23, the ball screw 27, and the table 2). Note that the inverse transfer functions are formed as functions where operational elements are partially curtailed.
Specifically, the differential term operating units 51 to 55 of the inverse characteristic model 50 include operands a1s, a2s2, a3s3, a4s4, and a5s5, respectively. The differential term operating units 51 to 55 multiply the position command θ by the operands a1s, a2s2, a3s3, a4s4, and a5s5, respectively, and output multiplied values to the addition unit 56. The addition unit 56 adds the multiplied values outputted from the differential term operating units 51 to 55.
The coefficients a1, a2, a3, a4, and a5 in the operands a1s to a5s5 are set as follows. Of the terms included in the formulae of the respective coefficients a1 to a5, KV is the velocity loop gain, KL is the spring rigidity of the ball screw 27 in the axial direction, τV is the integration time constant, DM is the viscosity of the servomotor 23, DL is the load viscosity, JM is the inertia of the servomotor 23, and JL is the load inertia as discussed previously.
A calculation method of setting (calculating) the coefficients a1 to a5 as below will be described later.
A term (TV/KV(TVs+1)) in an inverse transfer function (TV/KV(TVs+1))×s of the transfer function KV(1+1/(TVs)) of the proportional integral operating unit 34 is set to the proportional integral inverse transfer function unit 57. The differential operators in (TV/KV(TVs+1))×s is assigned to each of the operands a1s to a5s5 in the differential term operating units 51 to 55.
Then, load position control of the feed system 22 is conducted while the amount VH of velocity compensation outputted from the inverse characteristic model 50 including the set coefficients a1 to a5 is applied to the feedback control system 21. Thus, it is possible to compensate for error factors such as distortion, deflection, and viscosity which may occur in the servo motor 23, the ball screw 27, the table 2, and so forth of the feed system 22, and thereby to perform precise control over the load position θL such that the load position θL follows the position command θ. As a consequence, high-precision machining is enabled.
(Description of Load Inertia Estimation Method and Control Parameter Adjustment Method)
However, if the weight of the workpiece W mounted on the table 2 varies (when a workpiece W having a different weight is mounted on the table 2), the load inertia JL also changes in response to the variation in the weight of the workpiece W. Hence, parameters of the feed system 22 no longer match parameters of the inverse characteristic model 50. Specifically, the coefficients a3 to a5 of the differential terms of the third and higher orders (i.e., the terms a1s3 to a5s5) including the term of the load inertia JL do not match the corresponding parameters of the feed system 22. At this rate, the position deviation Δθ is increased whereby the load position θL causes a delay in following the position command θ.
Therefore, the load inertia JL corresponding to the weight of the workpiece W is estimated in accordance with the following method prior to the machining of the workpiece W.
First, in the actual load position control system (the feedback control system 21 and the feed system 22) shown in
Next, in the load inertia estimation model 60 shown in
Here, the load position control simulation is repeated while the load inertia JL of the table 2 as well as the workpiece W included in the model of the feed system 22 are adjusted until position deviation Δθ arising in the load position control simulation becomes equal to the position deviation Δθ measured in the load position control test conducted by the actual system.
However, as described previously, the spring rigidity KL varies depending on the load position θL. Accordingly, the position deviation Δθ arising at the point of time when the table 2 reaches the prescribed load position θL (i.e., the point of time when the table 2 reaches the load position θL where the spring rigidity becomes the prescribed spring rigidity KL) is compared with the position deviation Δθmeasured in the load position control test conducted by the actual system to estimate whether or not both of the position deviations Δθ are mutually equal. Meanwhile, the load inertia JL in the inverse characteristic model 50 at the time when the load position control test is conducted by the actual system is set to the same value as the load inertia JL in the inverse characteristic model 50 at the time when the load position control simulation is conducted. For example, these values are set equal to load inertia JL0 when no load is applied, i.e., no workpiece W is mounted on the table 2.
If the position deviation Δθ arising in the load position control simulation becomes equal to the position deviation Δθ measured in the load position control test conducted by the actual system as a consequence of repeating the load position control simulation while adjusting the load inertia JL included in the model of the feed system 22, then the load inertia JL included in the model of the feed system 22 at this time is estimated as the actual load inertia JL corresponding to the weight of the workpiece W mounted on the table 2.
Next, the load inertia JL thus estimated is outputted from the load inertia estimation model 60 to the inverse characteristic model 50 of the actual system as shown in
As described above, the load inertia estimation method of the first embodiment provides the method of estimating the load inertia JL of the feed system 22 for the load position control system configured to cause the feedback control system 21, to which the inverse characteristic model 50 of the feed system 22 is added, to control the load position θL of the feed system 22 on the basis of the amount VH of compensation outputted from the inverse characteristic model 50 and used for compensating for the dynamic error factor of the feed system 22. Here, the method is characterized in that the method includes: in the load position control system, conducting the load position control test using the feedback control system 21 by issuing the position command θ to the feedback control system 21, and measuring the position deviation Δθ arising at the prescribed load position θL at this time; and in the load inertia estimation model 60 being the model of the load position control system, conducting the load position control simulation on the model of the feed system 22 using the model of the feedback control system 21 by issuing the position command θ to the model of the feedback control system 21, repeating the load position control simulation while the load inertia JL included in the model of the feed system 22 is adjusted until the position deviation Δθ arising at the prescribed load position θL in the load position control simulation becomes equal to the position deviation Δθ measured in the load position control test, and as a consequence, if the position deviation Δθ arising at the prescribed load position θL in the load position control simulation becomes equal to the position deviation Δθ measured in the load position control test, estimating the load inertia JL included in the model of the feed system 22 at this time as the load inertia JL of the feed system 22 of the actual system. For this reason, even when the weight of a load on the feed system 22 (the weight of the workpiece W mounted on the table 2) varies, the load inertia JL corresponding to the load weight can easily be estimated.
In addition, the control parameter adjustment method of the first embodiment is characterized in that the method includes adjusting the load inertia JL included in the inverse characteristic model 50 of the actual system on the basis of the load inertia JL estimated by using the load inertia estimation method. Accordingly, even when the load weight on the feed system 22 (the weight of the workpiece W mounted on the table 2) varies, it is possible to cause the parameters of the feed system 22 to match the parameters of the inverse characteristic model 50 (the coefficients a3 to a5 of the differential terms of the third and higher orders including the term of the load inertia JL). For this reason, it is possible to perform precise control over the load position θL such that the load position θL follows the position command θ, and thereby to achieve high-precision machining.
(Description of Load Inertia Estimation Method and Control Parameter Adjustment Method)
A load inertia estimation method and a control parameter adjustment method according to a second embodiment of the present invention will be described based on
As shown in
A relational expression F=ma=KLΔθ (F: force, m: weight of workpiece, KL: spring rigidity of ball screw, Δθ: position deviation) holds between the position deviation Δθ (i.e., deflection of the ball screw 27 and the like) and the weight of the workpiece W. When the force F and the spring rigidity KL are made constant, the position deviation Δθ is thought to increase linearly in proportion to the increase in the weight of the workpiece W.
In the meantime, the amount of compensation in proportion to the load inertia JL is determined for the differential terms of the third and higher orders (a3s3 to a5s5) in the inverse characteristic model 50. Hence, the position deviation Δθ can be thought to increase linearly in proportion to the increase in the weight of the workpiece W mounted on the table 2.
Therefore, if data on the position deviation Δθ under the load inertia JL0 when no load is applied, i.e., no workpiece W is mounted on the table 2 and on the position deviation Δθ under the load inertia JL when a maximum load is applied, i.e., a workpiece W having a maximum probable weight is mounted on the table 2 are available, then it is possible to estimate load inertia JL1 at the time of mounting a workpiece W having an unknown weight on the table 2 by use of the data.
Accordingly, in the actual load position control system (the feedback control system 21 and the feed system 22) shown in
Alternatively, using the models of the load position control system as shown in
Here, as described previously, the spring rigidity KL varies depending on the load position θL. Accordingly, the position deviations ΔθL0 and ΔθLM each arising at the point of time when the table 2 reaches the prescribed (predetermined) load position θL (i.e., the point of time when the table 2 reaches the load position θL where the spring rigidity becomes the prescribed spring rigidity KL) are measured.
Moreover, in order to define the position deviation ΔθL0 when no load is applied as a reference, the load inertia JL in the inverse characteristic model 50 is set at the load inertia JL0 when no load is applied. As a consequence, the position deviation ΔθL0 when no load is applied is substantially equal to 0.
Position deviation characteristic data ΔVD which increases linearly in proportion to an increase in the load inertia JL is set in the position deviation characteristic data unit 70 on the basis of the position deviation ΔθL0 when no load is applied and the position deviation ΔθLM when the maximum load is applied, which are measured in advance.
Then, the load inertia JL corresponding to the weight of the workpiece W is estimated prior to the machining of the workpiece W in accordance with the following method.
First, in the actual load position control system (the feedback control system 21 and the feed system 22) shown in
Then, the position deviation characteristic data unit 70 measures (inputs) the position deviation Δθ (which is Δθ1 in the illustrated example) arising at this time. However, as described previously, the spring rigidity KL varies depending on the load position θL. Therefore, the position deviation characteristic data unit 70 measures (inputs) the position deviation Δθ (which is Δθ1 in the illustrated example) arising at the point of time when the table 2 reaches the prescribed (predetermined) load position θL (i.e., the point of time when the table 2 reaches the load position θL where the spring rigidity becomes the prescribed spring rigidity KL).
Next, the position deviation characteristic data unit 70 finds the load inertia JL (which is JL1 in the illustrated example) corresponding to the position deviation Δθ (which is Δθ1 in the illustrated example) measured (inputted) either in the load position control test conducted by the actual system or in the load position control simulation, on the basis of the preset position deviation characteristic data ΔVD, and estimates that the load inertia JL (which is JL1 in the illustrated example) is the load inertia JL corresponding actually to the weight of the workpiece W mounted on the table 2. The estimated load inertia JL is outputted from the position deviation characteristic data unit 70 to the inverse characteristic model 50 of the actual system.
In the inverse characteristic model 50 of the actual system, the coefficients a3 to a5 of the differential terms of the third and higher orders including the term of the load inertia JL are adjusted (set) on the basis of the load inertia JL (which is JL1 in the illustrated example) outputted from the load inertia estimation model 60. In this way, the parameters of the feed system 22 match the parameters (the coefficients a3 to a5 of the differential terms of the third and higher orders including the term of the load inertia JL) of the inverse characteristic model 50. For this reason, when the workpiece W is machined, it is possible to perform precise control over the load position θL such that the load position θL follows the position command θ, and thereby to achieve high-precision machining.
Although the position deviation characteristic data ΔVD is set by using the position deviation ΔθLM when the maximum load is applied in the above-described embodiment, the present invention is not limited only to this configuration. The position deviation characteristic data ΔVD may be set by using a position deviation ΔθL when a certain load other than the maximum load is applied. Specifically, in the state where a workpiece W having a certain weight other than the maximum weight on the table 2 (i.e., in the state where the certain load other than the maximum load is applied), the position deviation Δθ when the certain load is applied may be measured by causing the actual system to conduct the load position control test or conducting the load position control simulation as similar to the above description, and the position deviation characteristic data ΔVD which increases linearly in proportion to the increase in the load inertia JL may be set on the basis of the measured position deviation 48 when the certain load is applied as well as the position deviation Δθ0 when no load is applied.
(Operation and Effect)
As described above, the load inertia estimation method of the second embodiment provides the method of estimating the load inertia JL of the feed system 22 for the load position control system configured to cause the feedback control system 21, to which the inverse characteristic model 50 of the feed system 22 is added, to control the load position θL of the feed system 22 on the basis of the amount VH of compensation outputted from the inverse characteristic model 50 and used for compensating for the dynamic error factor of the feed system 22. Here, the method is characterized in that the method includes: in the load position control system, conducting the load position control test using the feedback control system 21 by issuing the position command θ to the feedback control system 21, and measuring the position deviation Δθ (Δθ1) arising at the prescribed load position θL at this time, or in the model of the load position control system, conducting the load position control simulation on the model of the feed system 22 using the model of the feedback control system 21 by issuing the position command θ to the model of the feedback control system 21, and measuring the position deviation Δθ (Δθ1) arising at the prescribed load position θL at this time; and finding the load inertia JL (JL1) corresponding to the position deviation Δθ (Δθ1) measured either in the load position control test or the load position control simulation on the basis of the position deviation characteristic data ΔVD which is preset based on the position deviation Δθ (Δθ0) being measured in advance and arising at the prescribed load position θL when no load is applied and on the position deviation Δθ (ΔθM) being measured in advance and arising at the prescribed load position θL when the certain load is applied and which increases linearly in proportion to the increase in the load inertia JL, and estimating the load inertia JL (JL1) as the load inertia JL of the feed system 22 of the actual system. For this reason, even when the load weight on the feed system 22 (the weight of the workpiece W mounted on the table 2) varies, the load inertia JL corresponding to the load weight can easily be estimated.
In addition, the control parameter adjustment method of the second embodiment is characterized in that the method includes adjusting the load inertia JL included in the inverse characteristic model 50 of the actual system on the basis of the load inertia JL estimated by using the load inertia estimation method. Accordingly, even when the load weight on the feed system 22 (the weight of the workpiece W mounted on the table 2) varies, it is possible to cause the parameters of the feed system 22 to match the parameters of the inverse characteristic model 50 (the coefficients a3 to a5 of the differential terms of the third and higher orders including the term of the load inertia JL). For this reason, it is possible to perform precise control over the load position θL such that the load position θL follows the position command θr and thereby to achieve high-precision machining.
In the above-described first and second embodiments, the load inertia JL in the inverse characteristic model 50 is adjusted based on the estimated load inertia JL. However, the present invention is not limited only to this configuration, but control parameters other than the load inertia JL in the inverse characteristic model 50, such as control parameters concerning machining conditions, may also be adjusted based on the estimated load inertia JL. For example, the estimated load inertia JL may be outputted from the position deviation characteristic data unit 70 or the load inertia estimation model 60 to the NC device 41 as well, and control parameters to be set by the NC device 41, including acceleration and deceleration time, corner velocity and acceleration, and so forth may be adjusted based on the estimated load inertia JL.
Meanwhile, the first and second embodiments have described the case of applying the present invention to the feed system 22 for the table 2. However, the present invention is not limited only to this configuration but is also applicable to feed systems provided for components other than the table 2 (such as a feed system for a saddle or a ram). For example, if the weight of the attachment 8 or the tool 9 in
Moreover, the first and second embodiments have described the case of applying the present invention to the feed system 22 including the servo motor 23, the ball screw 27, and the like. However, the present invention is not limited only to this configuration but is also applicable to feed systems having other configurations (such as feed systems using a hydraulic pump, a hydraulic motor, a hydraulic cylinder, and the like).
Furthermore, the first and second embodiments have described the case of application to the feed system in a machine tool. However, the present invention is not necessarily limited only to this configuration but is also applicable to feed systems in industrial machines other than machine tools.
<Description on Calculation Method of Coefficients in Inverse Characteristic Model>
Now, the calculation method of setting (calculating) the coefficients a1 to a5 in the inverse characteristic model 50 will be described.
In the mechanical system model shown in
[Expression 2]
τ−(θM−θL)·(CLs+KL)=(JMs2DMs)·θM (1)
(θM−θL)·(CLs+KL)=(JLs2DLs)·θL (2)
The following Formula (3) and Formula (4) are derived from Formula (1) and Formula (2) shown above.
In order to move the load (the table 2 and the workpiece W) with no error, compensation control should be performed such that the load position θL matches the position command θ, i.e., such that θ=θL is satisfied. In order to satisfy θ=θL, the torque command τ should be subjected to feed-forward compensation control in accordance with a formula in braces { } (a first transfer function formula) on the right side of Formula (3), and the velocity command V should be subjected to feed-forward compensation control in accordance with a formula in parentheses ( ) (a second transfer function formula) on the right side of Formula (4). Note that θMs in Formula (4) is equivalent to the motor velocity V.
In Formula (3), θL is replaced with 9 and then the formula is translated into a command velocity Vi. Thus, Formula (3) is converted into Formula (5). Formula (5) is equivalent to Formula (3) multiplied by an inverse operation expression of a proportional integral operation expression set in the proportional integral operating unit 34. In other words, Formula (5) is equivalent to Formula (3) divided by the proportional integral operation expression set in the proportional integral operating unit 34. A portion on the right side of Formula (5) excluding θ constitutes a third transfer function. Meanwhile, Formula (6) shown below is obtained by replacing θL with θ in Formula (4) and then transforming Formula (4). In order to perform the compensation control such that the load position θL matches the position command θ, the compensation velocity VH for achieving no error between θ and θL should be set equal to a sum of Formula (5) and Formula (6). Such a sum is expressed by Formula (7) below. A portion on the right side of Formula (7) excluding θ constitutes a fourth transfer function.
It is not possible to organize the original Formula (7) in terms of the differential orders. However, the following Formula (8) is obtained by deleting the term CL, which has little effect on accuracy, from Formula (7). A portion on the right side of Formula (8) excluding θ constitutes a transfer function for compensation control. The following Formula (9) is obtained by replacing Formula (8) with the coefficients a1 to a5. In this way, the coefficients a1 to a5 are obtained from Formula (8) and Formula (9).
The present invention relates to a load inertia estimation method and a control parameter adjustment method, which is useful for application to the case of adjusting load inertia included in an inverse characteristic model of a feed system that is added to a feedback control system of a machine tool and the like.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2010-233249 | Oct 2010 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2011/072917 | 10/5/2011 | WO | 00 | 5/31/2013 |
