CNC milling machine spindle quasi stop and positioning

In addition to the basic speed control, the CNC milling machine spindle also has position control, such as spindle quasi stop, spindle positioning, thread turning, rigid tapping and other control methods.

1. Spindle quasi stop

Spindle quasi stop is also called spindle orientation. The instruction code is M190 and the general spindle stop (M05) is different. When the spindle is stopped, the spindle must be stopped at the specified position, while the milling machine spindle motor has a torque to keep the spindle in a quasi-stop position and against the external load of the spindle. Spindle quasi-stop for the following occasions: the center of the machining center when the spindle orientation, so that the handle keyway into the spindle end key, as shown; fine boring retract the spindle when the first directional quasi-stop, the radial offset a short distance, and then axially retract the knife to avoid scratching the machined surface, as shown.

To achieve the milling machine spindle directional control, there must be a turn signal support. A turn signal is obtained according to the different spindle configuration has three ways: one is the spindle motor is installed with a rotary encoder signal; two is a rotating spindle encoder signal; three is the main external a turn signal (proximity switch).

2. Spindle positioning

In the full-function CNC milling machine, the spindle can be fixed angle positioning, such as 45°, 90°and 135°. Spindle positioning function with the power tool holder can be parts of the drilling and milling and other processing. When the workpiece cylindrical cylindrical cutting is completed, the tool holder from the drive head to the processing position. At the same time spindle positioning, drilling from the drive head.

Milling machine spindle rigid tapping

Rigid tapping is also one of the important control modes of the milling machine spindle. In the tapping process, the spindle speed and the Z-axis feedrate f_Z must be satisfied:

                    f_Z = tap pitch x spindle speed

In the normal way to tapping processing, due to the spindle and Z axis feed acceleration and deceleration characteristics are inconsistent, tapping screw on the tap must be equipped with spring chuck, in order to compensate for the Z axis feed and spindle does not synchronize the pitch error. 

The handle with a spring chuck is shown in the figure. When the thread is tapped in this way, when the tap is rotated and the Z axis is stopped, the spindle does not stop immediately, the tapping spring chuck is compressed for a distance; when the tap is rotated in the reverse direction of the Z axis, the milling machine spindle accelerates, the spring chuck is stretched again. Common way to attack the thread cycle can only meet the general accuracy of the processing of screw holes. In addition, if the spindle speed is high when the thread is tapped, the telescopic range of the spring chuck must be large enough so that the spindle speed can only be limited to 600r/min or less when tapping the thread in this way.

Rigid tapping, also known as synchronous feed tapping. Rigid tapping does not require a spring chuck and a rigid taper shank as shown. Rigid tapping, the milling machine spindle speed and Z-axis feed speed to establish a synchronous relationship, so that the spindle speed and Z-axis feed speed to ensure a linear proportional relationship, as shown.

When the tapped thread is machined with a rigid tapping thread, the spindle rotates synchronously with the Z axis feed and decelerates simultaneously when the Z axis is tapped to the command position. The spindle reverse start acceleration is also synchronized with the Z axis reverse feed start acceleration. In addition, the rigid tapping in the tap strength allows the case, the milling machine spindle speed can be high, up to 4000r/min, processing efficiency significantly improved, and the thread accuracy is guaranteed.

Siemens milling machine spindle motor and driver

Siemens milling machine spindle motor and driver are commonly used on machines. Let's get to know it today.

1. Siemens AC spindle motor

As shown in the figure for the Siemens 1PH7 AC spindle motor appearance and composition.

1PH7 AC milling machine spindle motor is a forced air-cooled asynchronous motor that is dissipated through a separately installed fan. The stator winding is embedded with a thermistor for detecting the temperature of the motor. The rotor shaft ends are connected to an encoder for detecting rotor speed and angular displacement. The encoder is connected to an external device via a cable plug or DRIVE- CLiQ interface, and the encoder can select an incremental encoder or an absolute encoder.

2. Siemens 611Ue driver

Siemens 611Ue driver is a DC common bus inverter, composed of power modules and power modules. 611Ue driver and Siemens SI-NUMERIK 802D CNC system supporting the use of milling machine spindle and servo drive. The appearance and composition of the 611Ue drive are shown in the figure.

The power module consists of rectifier module, filter capacitor and control circuit, etc., through the input of the three-phase AC rectifier, filtering, power module to provide DC bus voltage, while the power supply module also provides +5 V, +15 V and +24 V control power, through the equipment bus for the power supply module and power module internal control circuit. The control circuit, in addition to monitoring the DC bus, also performs temperature and operation monitoring, as well as enable control. There are two forms of power supply module, one is the uncontrolled power supply module (also known as feeding power module); Second, regenerative feedback power supply module (also known as feed / regenerative feedback power supply module).

The above is the basic introduction about Siemens milling machine spindle motor and driver.

FANUC milling machine spindle motor

FANUC AC spindle motors have αi series and βi series. The former is a high-performance milling machine spindle motor, and αi series of drives supporting; the latter for the ordinary spindle motor, and βiSVSP series drive matching. FANUC AC milling machine spindle motor is a variable frequency dedicated motor. As shown in the figure is FANUC αi / βi AC spindle motor appearance and composition.

FANUC αi AC spindle motor stator no chassis, stator core shape was polygonal. The core of the edge of the axial ventilation holes, the motor has a separate power supply at the end of the cooling fan, the milling machine spindle motor forced cooling, the stator core in the air directly heat; rotor and ordinary three-phase AC motor, in addition, the stator winding is also equipped with thermistor. When the motor due to overload or winding short circuit caused by winding temperature rise to a certain value, the thermistor resistance changes. The temperature detection circuit in the spindle amplifier monitors the change of the resistance value and is fed back to the CNC system via the serial bus. The CNC system can stop the control signal of the spindle immediately after the judgment and processing, and issue the alarm that the milling machine spindle motor is overheating or overload.

FANUC αi spindle motor in the magnetic sensor for rotor speed and angular displacement measurement, a 128 pulse/turn, 256 pulse/turn, 512 pulse/turn three specifications, without zero position signal (also known as a turn signal) for the Mi series, with zero position signal for the MZi series.

The above is about FANUC milling machine spindle motor basic introduction, you are welcome to continue to focus on updates.

CNC milling machine spindle motor (Part 2)

In the previous article we mainly introduced the composition of the CNC milling machine spindle motor, today we come to explore the operating principle of the spindle motor and frequency control mode.

1.Operating principle

CNC milling machine three-phase AC induction motor operating principle is shown in the figure.

Three-phase AC asynchronous motor stator winding into the three-phase AC generated after the rotating magnetic field, the speed no known as the synchronous speed. n_o = 60f/p, p for the stator winding pole pairs, f for the stator winding power supply frequency, change f to change n_o. The rotating magnetic field cuts the guide bar in the rotor core and generates an induced current in the guide bar. In this way, the rotor bar with induced current interacts with the rotating magnetic field to generate electromagnetic torque, and the rotor rotates with the rotating magnetic field at the rotational speed n_M under the action of the electromagnetic torque. Because the motor running state when the rotor speed can only be less than the synchronous speed, so called asynchronous motor; and because the rotor bar in the current from the rotating magnetic induction, it is also known as induction motor. When the power frequency f decreases, the rotating magnetic field speed no decreases, but because of the rotor mechanical inertia, the rotor speed n_M instantly remain unchanged, at this time, the rotor speed is greater than the rotating magnetic field speed, the motor is in the power brake state, the motor winding flows out.

2. Frequency control

Changing the power frequency of the milling machine spindle motor can realize the speed regulation of the motor. Three-phase AC induction motor frequency conversion speed is usually U/f and vector control. In order to meet the requirements of the three-phase AC asynchronous motor stator winding electromagnetic frequency requirements, in the rated frequency (50Hz) below the frequency control, change the frequency f at the same time also change the stator voltage U, and keep the voltage / frequency is not change. In this speed range, the maximum electromagnetic torque remains constant and constant torque is achieved. Rated frequency above the frequency control, the stator winding voltage U to maintain the rated voltage (380V) unchanged. In this speed range, the electromagnetic torque decreases with the frequency rise, and the electromagnetic power unchanged, to achieve constant power speed, as shown.

The above is a brief introduction about the CNC milling machine spindle motor operation principle and frequency control mode. 

CNC milling machine spindle motor (Part 1)

CNC milling machine spindle is driven by the spindle motor. CNC system through the control of the spindle motor to achieve the control of the spindle. At present, CNC milling machine spindle motor commonly used three-phase AC asynchronous motor and variable frequency drive.

Spindle motor drive has two configurations: First, the ordinary three-phase AC asynchronous motor and inverter; Second, the CNC system supporting the spindle motor and spindle drive. The former is often used in ordinary CNC milling machine, to achieve frequency control, positive, reverse start and stop and other basic control; the latter for multi-function CNC milling machine, in addition to the basic control of the spindle, but also to achieve orientation, positioning and spindle servo control.

Ordinary three-phase AC induction motor is consist of stator and rotor, as shown.

The stator includes a base, stator core and stator three-phase windings. The stator core is made of silicon steel sheet, and the inner circumference is covered with a coil groove. The coil groove is fitted with three symmetrical windings. The winding terminal is introduced into the junction box on the base frame and can be connected into a triangular winding or star winding. Made of silicon steel sheet stacked, the outer circumference are covered with a coil groove, coil groove cast with aluminum guide bar.

Ordinary asynchronous motor rotor is also installed on the cooling fan, when the ordinary three-phase AC asynchronous motor with the inverter speed, and the rotor speed is low, the cooling fan air volume is not enough to cool the motor, the motor easy to heat, serious will damage the stator winding insulation, resulting in short circuit. In order to meet the needs of frequency control, the development of a special frequency asynchronous motor, as shown. Frequency conversion special asynchronous motor has a special cooling fan motor, the motor body for forced cooling, fan motor power supply alone, the fan air flow and the motor speed has nothing to do. In addition, the frequency conversion asynchronous motor also improves the insulation performance of the stator winding, some frequency conversion special asynchronous motor stator winding is also embedded in the thermistor, for the motor temperature detection.

The above is the introduction about CNC milling machine spindle motor structure, welcome you continue to pay attention to the updated content.

CNC milling machine tool changer manipulator

For the use of disc magazine CNC milling machine, tool changer manipulator is essential. Cam-type tool changer manipulator and spindle with the ability to continuously achieve grasping knife, knife exchange and insert the action, the structure shown in figure.

1) Grasping the knife. The manipulator starts the motor for the first time. The motor drives the end cam and the cylindrical cam through the bevel gear. The cylindrical cam drives the cam roller to rotate the spline shaft. The spline sleeve drives the mechanical shaft by rotating it in the counterclockwise direction 65° or 75°, the manipulator grasping knife action. When the manipulator handle the knife in place switch is turned on, the robot electric brake immediately stops, completes the manipulator grasping knife control. During this time, the manipulator does not move axially.

2) Milling machine spindle loose knife mechanism action. The claws release the milling machine spindle handle, and issued the spindle release in place signal.

3) The second start of the manipulator motor, through the bevel gears simultaneously drive the end of the cam and cylindrical cam rotation, the mechanical hand shaft order to complete the knife, exchange and insertion of three movements: ①the end of the cam control rocker swing, so that the movement of the shaft , To achieve a knife action. During this time, the cam roller does not rotate, so the manipulator does not rotate. ②the end of the knife, the cylindrical cam through the cam roller to drive the spline shaft rotation, and then by the spline shaft drive the manipulator shaft rotation 180°, to achieve tool exchange action. During this period, the rocker arm does not swing, the manipulator does not move axially. ③the end of the cam again control the rocker swing, so that the movement of the robot shaft to achieve the knife action. During this time, the cam roller does not rotate, so the manipulator does not rotate. When the knife in place switch is turned on again, the manipulator brake immediately stops.

4) Milling machine spindle loose knife mechanism action, the claw clamping spindle in the handle, and issued a spindle clamping in place signal.

5) The third time the manipulator is started, the cylindrical cam drives the cam roll to rotate the spline shaft. The spline sleeve drives the mechanical hand shaft to rotate 65°or 75°clockwise to achieve the reset action. When the manipulator returns to its original position, the home switch is turned on and the manipulator's motor stops immediately.

The above is the work of CNC milling machine tool change manipulator. Tool changer through the cam and other mechanical transmission mechanism, with the manipulator motor 3 times start and stop, to achieve the original position → grasping knife → knife (spindle loose knife) → exchange → plug (spindle cutter) → reset the action process.