'Lathes' have the following machinics:
1. Rotating tables
2. Motors for table rotation
3. Materials (Round stick or Square stick)
4. Cutters
A Material is put on the rotating table of lathes, and they are rotated by the motor. The cutter whittles the material into slim shape or round shape.
This rotating table is heavy to keep constant speed at any load
Merits of inverter drives
Lathes with inverters have the following merits:
- Stable speed
Inverters can control rotation tables to be stable speed at any load by sensor-less control methods.
- Heavier rotation tables
Lathes with inverters can be used heavier rotation tables. Because inverters control motors with low speed and low frequency when motors start to move. In this case, it is necessary to set an acceleration time to a long setting value.
- Cost reducing of mechanical brakes
Inverters can decrease motor speed instead of mechanical brakes. Therefore maintenance costs of mechanical brakes are reduced. In this case, it is necessary to install a braking resistor to an inverter.
Notices
Notices regarding the use of inverter drives
- Acceleration and deceleration time
'Inline duct fans' have variable torque characteristics, and some of them have a large load inertia. When you set a short acceleration/deceleration time. you sometimes have the following problems:
While accelerating: Trip caused by overcurrent
While decelerating: Trip caused by overvoltage
If you have a fixed acceleration/deceleration time. please be careful with the inverter capacity selection.
- High speed operation
Output torque of motors are decreasing at high speed.
Ex.
Base frequency of a motor: 60Hz
Frequency reference: 80Hz
Output torque of motors will be about 75% ( = 60Hz / 80Hz).
When Lathes have a rushed load at a high speed operation, inverters control to decrease motor speed by the 'stall preventing function'
- Electromagnetic noise
The inverter is generating 'electromagnetic noise'.
If there are some high accuracy sensors or other sensitive equipment near the inverter drive, the inverter's noise may cause some trouble or a malfunction.
Electromagnetic noise can be avoided by installing an external noise filter or using a different wiring method.
- Harmonics
The inverter is generating 'harmonics'.
These harmonics sometimes cause a malfunction in other control equipment that is connected to the same power source.
Harmonics can be avoided by installing an external 'reactor'.
To decrease 'harmonics', we recommend to install DC reactors in all our inverter models.
(NOTE: 100V input models require AC reactors.)
Selection
In almost all cases, the capacity of the inverter is the same as the motor capacity.
However the folloing cases, the inverter capacity should be larger than the motor capacity:
- Lathes require a fixed acceleration/deceleration time.
- The inertia of rotation tables is larger than the allowance inertia of its motor.
Conditions that require an inverter capacity increase:
- Large starting torque over 200%.
- Short acceleration/deceleration time settings.
Application samples
In case of Lathes, motors can be controlled by the inverter using the following methods:
- Speed adjustment by an analog input
- 3 wire type operations with momentary switches
- Emergency stop signal input
- Braking resistor installation
Connection of inverters (VFS11)
Setting table for inverters (VFS11)
Title
Function
Setting range
Recommended setting
Command mode selection
0: Remote, 1: Local
0
Frequency setting mode selection
0: Built-in potentiometer, 1: VIA, 2: VIB
2
Acceleration time 1
0.0 ~ 3200
Depends on the system
Deceleration time 1
0.0 ~ 3200
Depends on the system
Input terminal selection 4 (S1)
0 ~ 65
11
(Emergency stop)
Input terminal selection 6 (S3)
0 ~ 65
49
(HOLD)
Dynamic braking selection
0: Disabled, 1: Enabled
1
Overvoltage limit operation
0: Enabled, 1: Disabled
1
Explanation of three-wire operations (one-touch operations)
You can carry out operation by simply pressing the ON/OFF button.
Selecting HD (operation holding) with the input terminal selection parameter.
Select HD (operation holding) using the input terminal selection parameter and turn HD on to get the inverter ready or operation or turn HD off to stop operation.
