Machine tool and parameter adjustment method therefor

Abstract

A machine tool comprises: a servomotor feeding a workpiece or a tool; a motor control section controlling the servomotor; and a processor connected to the motor control section, in a parameter adjustment mode while rotating a load by the servomotor with a given speed command issued to the motor control section under a condition where torque is limited, the processor calculating load inertia based on the torque and an angular acceleration of the servomotor that is obtained based on an output from the servomotor, calculating a parameter based on the load inertia, and adjusting a control parameter set to the motor control section based on the parameter.

Claims

1. A machine tool comprising: a servomotor feeding a workpiece or a tool; a motor control section controlling the servomotor; and a processor connected to the motor control section, in a parameter adjustment mode while rotating a load by the servomotor with a given speed command issued to the motor control section under a condition where torque is limited, the processor calculating load inertia based on the torque and an angular acceleration of the servomotor that is obtained based on an output from the servomotor, calculating a parameter based on the load inertia, and adjusting a control parameter set to the motor control section based on the parameter.

2. The machine tool as defined in claim 1, the processor adjusting the control parameter of the motor control section based on a value as a result of comparison between a basic parameter in a state with a reference load different from the load and the calculated parameter.

3. The machine tool as defined in claim 2, the processor calculating a parameter P.sub.1 based on P.sub.1=P.sub.0(1+CI.sub.1/I.sub.0), where I.sub.0 denotes reference inertia in the state with the reference load, P.sub.0 denotes the basic parameter corresponding to the reference inertia I.sub.0, I.sub.1 denotes the load inertia, P.sub.1 denotes the parameter corresponding to the load inertia I.sub.1, and C denotes a correction coefficient.

4. The machine tool as defined in claim 3, the motor control section including a proportional control section in a speed loop, the processor setting a proportional gain basic parameter K.sub.P0 corresponding to the reference inertia to the proportional control section in the parameter adjustment mode and calculating a proportional gain K.sub.P based on K.sub.P=K.sub.P0(1+CI.sub.1/I.sub.0).

5. The machine tool as defined in claim 3, the motor control section including an integral control section in a speed loop, the processor setting an integral gain basic parameter K.sub.I0 corresponding to the reference inertia to the integral control section in the parameter adjustment mode and calculating an integral gain K.sub.1 based on K.sub.1=K.sub.I0(1+CI.sub.1/I.sub.0).

6. A parameter adjustment method for adjusting a control parameter of a motor control section controlling a servomotor used in a drive system for a machine tool, the method comprising: in a parameter adjustment mode while rotating a load by the servomotor with a given speed command to the motor control section under a condition where torque is limited, calculating load inertia based on the torque and an angular acceleration of the servomotor that is obtained based on an output from the servomotor, calculating a parameter based on the load inertia; and adjusting the control parameter of the motor control section based on the parameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a machine tool.

(2) FIG. 2 is a schematic block diagram illustrating a control system for a servomotor.

(3) FIG. 3 is a functional block diagram illustrating a drive control system for the servomotor.

(4) FIG. 4 is a flowchart illustrating an example of a parameter adjustment system according to the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(5) FIG. 1 illustrates a lathe that is a machine tool according to one embodiment of the present invention. The lathe 1 includes a numerical control (NC) device 2. A spindle chuck 5 is detachably attached to a spindle 4 supported by a headstock 3. The chuck 5 holds a workpiece (not illustrated). A spindle motor 10 feeds the workpiece in a rotating manner. The spindle 4, the chuck 5, and the workpiece are loads drivingly rotated by the spindle motor 10. A tool turret 6 is attached to a tool rest 7. Motors 20 and 30 drivingly feed the tool rest 7 in directions of two orthogonal axes. The motor 20 drivingly feeds the tool in a direction orthogonal to the spindle. The motor 30 drivingly feed the tool in a direction along the spindle. The spindle motor 10 and the tool feeding motors 20 and 30 are each a servomotor connected to the NC device 2.

(6) As illustrated in FIG. 2, the NC device 2 include a processor (main control device) 40 and a motor control section 50. The NC device 2 is described based on an example of adjusting a parameter for driving the spindle motor 10. The parameter may be similarly adjusted for the tool feeding motors 20 and 30. For example, the processor 40 uses hardware, such as a central processing unit (CPU) and a memory, and software (such as a program, data, and a parameter) stored in the memory to control the motor control section 50. Specifically, the processor 40 may include: a storage section 40A that stores system software; a storage section 40B that stores data, a parameter, an NC program, and the like; a storage section 40C that stores an application program that performs operations such as operation command, data reference, parameter read/write, and the like; and the CPU (not illustrated). The motor control section 50 may include: a storage section 50A that stores motor control software; a storage section 50B that stores a control parameter for limiting torque or for other like operations; and a current control means (amplifier) (not illustrated) that controls current flowing in the spindle motor 10. The spindle motor 10 includes an internal or external sensor 11 such as an encoder, and feeds back position information or speed information.

(7) The spindle motor 10 is driven with the processor 40 transferring a parameter to the motor control section 50, and the motor control software in the motor control section 50 controlling the current flowing in the spindle motor 10 based on the parameter.

(8) FIG. 3 is a functional block diagram illustrating various functions implemented by software or the like of the motor control section 50. FIG. 3 illustrates an example of Proportional Integral (PI) control. However, the present invention is not limited to this, and may be applied to any one of Integral (I) control, Proportional (P) control, and Derivative (D) control, or a combination of more than one of these.

(9) In FIG. 3, a proportional control section 60 performs P control on a difference (target valuecurrent value) between a command value that has been input and a speed feedback value from the motor 10, based on a transfer function K.sub.P (K.sub.P is a proportional gain). A torque command filter 61, which is a lowpass filter, cuts off the high frequency component of the torque command. A damping filter 62 constantly monitors a change in a vibration frequency in a torque command, and recalculates a parameter of the damping filter 62 to change the characteristics of the filter in accordance with a change in frequency.

(10) The difference (target valuecurrent value) is also input to an integral control section 63. The integral control section 63 performs I control on the difference based on a transfer function K.sub.1/S (K.sub.1 is an integral gain, S is a Laplacian operator).

(11) An amplifier 64, which is an example of the current control means, controls current flowing in the spindle motor 10 based on the difference (target valuecurrent value) that has been PI controlled according to the transfer function (K.sub.P+K.sub.1/S).

(12) FIG. 4 is a flowchart illustrating an example of an operation, for adjusting a parameter of the servomotor 10, performed by the processor 40 according to the present embodiment.

(13) Upon exchanging a spindle chuck or the like of a lathe, a multifunction machine, or the like, an operator presses a parameter adjustment command button on a control panel or the like (step S.sub.1).

(14) Thus, the machine transitions to a parameter adjustment mode, in which a motor torque control means (the amplifier 64 in FIG. 3 for example) limits the motor torque so that the torque is prevented from exceeding a certain value (step S.sub.2). With the torque thus limited, the processor 40 outputs a given speed command to the motor control section 50.

(15) Thus, rotation of the motor 10 is accelerated under the loads such as the chuck and the workpiece newly installed (step S.sub.3). An acceleration calculation means (software) of the processor 40 calculates angular acceleration (rad/s.sup.2) based on rotation information (position or rotation speed) from the sensor 11 of the motor 10 (step S.sub.4). Instead of the processor 40, an acceleration calculation means (software) of the motor control section 50 may calculate angular acceleration. In any case, the processor 40 is able to acquire the angular acceleration based on the output of the servo-motor 10.

(16) A rotation inertia calculation means (software) of the processor 40 calculates load-side rotation inertia (also referred to as angular moment) I.sub.1 (kg.Math.m.Math.s.sup.2) based on I.sub.1=/, where (kg.Math.m) represents the torque limited and represents angular acceleration calculated (step S.sub.5).

(17) The processor 40 further releases the torque limitation by the motor torque limitation means (amplifier 64) of the motor control section 50 (step S.sub.6).

(18) The storage means 40B of the processor 40 stores therein in advance, servomotor-side rotation inertia and load-side reference inertia I.sub.0 in a state where the chuck 5 or the workpiece is not attached to the spindle 4.

(19) The reference inertia I.sub.0 may also be a value obtained in a state where the reference chuck is attached or in other like states.

(20) Based on these pieces of information, a gain (servo gain parameter) P.sub.1 (the gain P.sub.1 according to the present embodiment is a proportional gain K.sub.P or an integral gain K.sub.1) of a speed loop is obtained with the following Formula (1):
P.sub.1=P.sub.0(1+CI.sub.1/I.sub.0)(1)

(21) where P.sub.0 denotes a servo gain basic parameter in the state with a reference load (reference inertia), I.sub.0 denotes the reference inertia, I.sub.1 denotes load inertia at the time of measurement, C denotes a correction coefficient including at least one of coefficients M, S, and X (C=(M+S+X) for example), M denotes a coefficient depending on a motor, S denotes a coefficient depending on a spindle diameter, and X denotes a coefficient related to other mechanical systems.

(22) When a servo gain basic parameter P.sub.0 is set as a gain of a control section in the speed loop, the gain P.sub.1 is obtained with Formula (1). In the parameter adjustment mode according to the embodiment illustrated in FIG. 3, a proportional gain basic parameter K.sub.P0 is set to the proportional control section 60 and an integral gain basic parameter K.sub.I0 is set to the integral control section 63.

(23) Whether or not the parameter is appropriate is determined by using a value of the ratio P.sub.1/P.sub.0 between the servo gain parameter P.sub.1 and the servo gain basic parameter P.sub.0 thus calculated by the parameter calculation means (software) of the processor 40 (step S.sub.8).

(24) When the value is within a predetermined range of values, the parameter adjustment is completed (step S.sub.9), and the processing by the device goes on.

(25) When the value of the P.sub.1/P.sub.0 is higher or lower than the upper or the lower limit input in advance, a parameter adjustment display is output (step S.sub.10).

(26) In this case, the operator may adjust the parameter based on the parameter adjustment display (step S.sub.11). Alternatively, an adjustment program may be installed in the processor 40 in advance so that auto adjustment can be performed.

(27) Based on Formula (1), the proportional gain K.sub.P and the integral gain K.sub.I are obtained from the following Formulae (2) and (3):
K.sub.P=K.sub.P0(1+CI.sub.1/I.sub.0)(2)
K.sub.I=K.sub.I0(1+CI.sub.1/I.sub.0)(3)

(28) where K.sub.P0 denotes a proportional gain basic parameter in the state with a reference load (reference inertia) and K.sub.I0 denotes an integral gain basic parameter in the state with a reference load (reference inertia).

(29) The proportional gain basic parameter K.sub.P0 and the integral gain basic parameter K.sub.I0 are gains set to the proportional control section 60 and the integral control section 63 in the speed loop when the reference inertia in the state with a reference load is calculated.

(30) Although only some embodiments of the present invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within scope of this invention.