Controller for machining gears

Details Controller for machining gears Controller for machining gears

2002-12-20

2004-11-23

Paladini, Albert W. (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C318S632000

Reexamination Certificate

active

06823235

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a controller for controlling rotational axes of a machine tool for machining gears, and in particular to a controller for machining gears by a gear generating motion between a workpiece, i.e. a gear blank and a tool having the shape of a gear and being in engagement with the workpiece.
2. Description of Related Art
A gear-generating method has been generally adopted for machining a gear by a gear-generating motion between a workpiece and a tool having the shape of a gear and meshing with a workpiece for machining a gear for gear-cutting and gear-grinding. There are known form cutting and the gear-generating using a hobbing cutter in the gear cutting and there are known polishing, shaving, lapping and honing in gear finishing.
In these gear machining, a driving method is known in which an axis for driving a gear blank (workpiece) and an axis for driving the tool are rotated in accordance with respective motion commands at respective velocities with a predetermined ratio in accordance with specifications of a gear to be generated and the tool, such as modules and the numbers of teeth of the gear and the tool. Another driving method is known in which a motion command for one of servo systems for driving the motors for driving the workpiece and the tool is determined to be a value obtained by multiplying a feedback signal from the other of the motors by a ratio predetermined in accordance with the specifications of the gear to be generated and the tool, so that the two axes are rotated in synchronism.
FIG. 6
is a block diagram of a control system constituted by a conventional controller in which the axes for the workpiece and the tool are driven in synchronism in accordance with respective motion commands. In this example, a tool axis to which a tool
1
is attached is driven by a first motor
15
, and a workpiece axis to which a workpiece
2
is attached is driven by a second motor
25
.
A servo system for the first motor
15
comprises a position control section
11
, a velocity control section
12
, a current control section
13
and a current amplifier
14
. The first motor
15
is equipped with a position/velocity detector
17
for detecting position and velocity of the first motor
15
and outputs a position feed back amount PFB
1
and a velocity feedback amount VFB
1
. A servo system for the second motor
25
comprises a position control section
21
, a velocity control section
22
and a current control section
23
and a current amplifier
24
. The second motor
25
is equipped with a position/velocity detector
27
for detecting position and velocity of the second motor
25
and outputs a position feed back amount PFB
2
and a velocity feedback amount VFB
2
.
A position command issued from a host controller such as a numerical controller is directly inputted to the servo system for the first motor
15
for driving the tool
1
. On the other hand, the position command issued from the host controller is multiplied by a ratio K in a multiplier term
3
and the obtained product is inputted to the servo system for the second motor
25
for driving the workpiece
2
. The ratio K is predetermined in accordance with specifications of a tool and a gear to be formed, such as modules and the numbers of teeth of the tool and the gear.
The position control sections
11
and
21
perform position loop controls by multiplying position deviations between the position commands and the position feedback values PFB
1
and PFB
2
by position gains, respectively, to obtain velocity commands.
The velocity control sections
12
and
22
perform velocity loop controls such as proportional control and integral control based on velocity deviations between the velocity commands outputted from the position control sections
11
and
21
and the velocity feedback values VFB
1
and VFB
2
, respectively, to obtain current commands.
The current control sections
13
and
23
perform current loop controls based on current deviations between the current commands outputted from the velocity control sections
12
and
22
and the current feedback values CFB
1
and CFB
2
form current sensors (not shown), respectively, to obtain voltage commands.
The current amplifiers
14
and
24
provide driving currents for the first and second motors
15
and
25
in accordance with the voltage commands outputted from the current control sections
13
and
23
, respectively, to drive the first and second motors
15
and
25
.
Since the position command for the second motor
25
has a value of the product of the position command for the first motor
15
and the ratio “K”, the second motor
25
is driven at a speed having the ratio K with respect to the speed of the first motor
15
, to be synchronized with the rotation of the first motor
15
, so that the workpiece
2
is driven at a speed having the ratio K with respect to the tool
1
synchronously with the tool
1
.
In the example shown in
FIG. 6
, the position command from the host controller is directly into the servo system for the first motor
15
and the value obtained by multiplying the position command from the host controller by the ratio K is inputted to the servo system for the second motor
25
for driving the workpiece
2
. Alternatively, the position command from the host controller is directly into the servo system for the second motor
25
and a value obtained by multiplying the position command by a predetermined ratio may be inputted into the servo system for the first motor
15
.
The position control sections
11
and
21
, the velocity control sections
12
and
22
, and the current control sections
13
and
23
are constituted by digital servo processing by a processor of the controller.
FIG. 7
is a block diagram of a control system constituted by another conventional controller in which a feedback signal of one of the servo systems is multiplied by a predetermined ratio to obtain the position command for the other of the servo systems.
In the arrangement shown in
FIG. 7
, a position command from the host controller is inputted to the servo system for the first motor
15
for driving the tool
1
, and the position feedback amount PFB
1
from the position/velocity detector
17
of the fist motor
15
is multiplied by a ratio K and the obtained product is inputted as a position command for the servo system for the second motor
25
for driving the workpiece
2
. The ratio K is predetermined in accordance with specifications of the tool and a gear to be generated such as module or the number of teeth of the tool and the gear. The arrangements and functions of the position control sections
11
and
21
, the velocity control sections
12
and
22
, the current control sections
13
and
23
, the current amplifiers
14
and
24
, and the position/velocity detectors
17
and
27
as shown in
FIG. 7
are the same as those in the control system as shown FIG.
6
.
In this example, the first motor for driving the tool
1
is driven based on the position command from the host controller and the second motor
25
is driven based on the position command obtained by multiplying the feedback amount of the first motor
15
by the ratio K, so that the second motor
25
is rotated to follow the rotation of the first motor
15
, so that the tool
1
and the workpiece
2
are synchronously driven.
In the above described control systems by the conventional gear machining controllers, precision of machining of gears depends on characteristics of suppressing disturbance of the servo systems for controlling the axes of the tool
1
and the workpiece
2
. Therefore, in the case of machining a gear of a large diameter, a disturbance torque (load torque) in machining increases to lower the precision of machining of the gear.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gear machining controller capable of performing a high-precision machining of a gear.
A gear machining controller of the present invention has servo systems for controlling a first moto

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