Servo valves are electro hydraulic valves or EHSV (Electro hydraulic servo valves) which can transform analog or digital signal into a step less hydraulic output.
accurate control of position, velocity, pressure and force
valve includes valve design with brushing spool assembly the movement of the spool in the valve is controlled by the servo which is attached to the valve
valve controls the direction of fluid flow to the cylinder.
electric pulses are sent to the coils by the servo the valve changes its position so that the cylinder will be actuated.
shows the function of AC motor in various stages during unloading of cups
Fig 3. 13 Torque Vs Speed curve
driving a load and again taking power. In second quadrants and fourth quadrant opposed directions that are the torque of the motor is opposing its g a braking effect. As per the conservation of the energy mechanical and kinetic energy of the load is being converted into electrical energy. The motor is behaving as a generator delivering power. Thus a VFD is required to control the AC motor in order to better processes control and regulation of the cycle time.
control and servo motor operated control:
o valves are electro hydraulic valves or EHSV (Electro hydraulic servo valves) which can transform analog or digital signal into a step less hydraulic output. Servo valves provide the accurate control of position, velocity, pressure and force in the hydraulic system. The term servo valve includes valve design with brushing spool assembly the movement of the spool in the valve is controlled by the servo which is attached to the valve and based on the movement of the spool the fluid flow to the cylinder. The servo valves have coils when the electric pulses are sent to the coils by the servo the valve changes its position so that the cylinder ges during unloading of cups
second quadrants and fourth quadrant the the torque of the motor is opposing its mechanical and kinetic energy of the load is being converted into electrical energy. The motor is behaving as a generator Thus a VFD is required to control the AC motor in
control:
o valves are electro hydraulic valves or EHSV (Electro hydraulic servo valves) which can Servo valves provide the lic system. The term servo valve includes valve design with brushing spool assembly the movement of the spool in the valve is and based on the movement of the spool the The servo valves have coils when the electric pulses are sent to the coils by the servo the valve changes its position so that the cylinder
The components of the servo valves are:
• Torque motor
• Two stages of hydraulic regulation.
were, the torque motor consist of coils, upper and lower pieces, armature and two magnets. The torque motor converts input signal from a valve driver or valve controller into a physical movement for the armature which inturn moves the spool.
Fig 3. 14 Servo valve
Principle of operation of servo valve:
The electromagnetic first stage produces a torque which may be assumed proportional to current and the flapper generates pressure that are applied to each end of the spool. The feedback wire which is coupled to the spool and the flapper creates the feedback. With a current applied the flapper rapidly returns to its central position within the spool displaced such that the wire feedback torque balances the electromagnetic torque as shown in the Fig 3.15. As the flapper in the valve tilts to an angle due the supply of current in the armature the spool displaces in the valve and allows the fluid to flow through the valve and when by the supply of current makes the armature to be vertical without any tilt of angle the flapper becomes vertical and does not allow the fluid to flow.
Fig 3. 15 Cut section of servo valve
The block diagram of the servo valve control system shown in the Fig 3.16.
When the current is supplied to the torque motor it sends to the torque summation unit which tilts the armature or flapper to the angle as per the supplied voltage of current which inturn moves the spool. From the spool the feedback wire is connected to the to the torque summation unit which in turn as per the flow requirement increases or decreases the angle of tilt of the flopper so as the spool will be displaced for the required flow. This is the closed loop system as it functions based on the feedback.
3.4.2 Servo motor:
The servomotor is the motor which is controlled by the servo mechanism usually the servomechanism controlled motor is called servo motor. But all servo mechanism needs not to have the motors and therefore the servo can be identified as a separate unit. The servo motor can provide precise motor output generally with the used of the microcontroller the servo motors are controlled. The servo mechanism present in the servo motor provider precise position control of the motor. The servo motors operate on the principle of negative feedback were the input given to the motor is verified by the feedback devices such as transducers at the output shaft of the motor. The difference between the input and the actual output is called error and this is amplified and corrected as the input value will be equal to the actual output based on the feed back in the servo motor.
Fig 3. 17 Servo motor
Working principle of servo motor:
Servo motors are controlled by sending them a pulse of variable width. The control wire is used to send this pulse the various types of pulse send to the motor is minimum pulse, a maximum pulse, and a repetition rate. Given the rotation constraints of the servo, neutral is defined to be the position where the servo has exactly the same amount of potential rotation in the clockwise direction as it
does in the counter clockwise direction. The pulse supplied to the servo motor is shown in the Fig3.18.
Fig 3. 18 Pulse input to servo motor
The rotation of the motor shaft is determined by the duration of the pulse supplied to the motor. Three basic types of servo motors are used in modern servo systems: ac servo motors, based on induction motor designs; dc servo motors, based on dc motor designs; and ac brushless servo motors, based on synchronous motor designs. The block diagram of servo motor is shown in Fig3.19.
Fig 3. 19 Block diagram of servo motor
In servo motor from digital controller the input goes to the amplifier which generate the pulses and run the servo motor the encoder or resolver connected to the motor gives back the feedback of the position to the digital controller and velocity feedback to servo amplifier based on the feedback the amplifier generates the pulses and runs the motor to correct the error.