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Electrical Control of NC Machine 's Active Coordinate
The electrical control of an active coordinate of the CNC machine consists of a current (torque) control loop, a rate control loop and a position control loop.
(1) The current loop is the circuit that provides the torque for the servo motor. As in the usual environment, it has been set by the manufacturer with the corresponding room parameters, the feedback signal is also connected within the servo system to complete, so no wiring and mediation.
(2) The rate loop is the circuit that controls the motor speed, that is, the operating speed of the axis. The rate adjuster is a proportional integral (PI) modulator whose P, I mediation value is entirely dependent on the load size of the driven axis and the machine characteristics such as the drive stiffness and drive clearance of the machine drive system (rail, drive mechanism) When the characteristics are significantly changed, it is necessary to hold the machine drive system to repair things, and then re-adjust the rate loop PI controller.
The optimal regulation of the rate loop is done under the condition that the position of the ring is open, and that the active axis and the axis of rotation are easier to hold, and against the vertical axis of the axis when the position is open , Can accept the first off the motor no-load mediation, and then install the motor and the location of the ring with the mediation of the position with the ring directly with the mediation, then there must be a certain resume and careful.
(3) The position loop is the control key that controls the precise positioning of the coordinate axes according to the command position. The position loop will ultimately affect the position accuracy and accuracy of the axis. There are two things in this:
First, the accuracy of the location measurement components and CNC system pulse equivalent of the vertical room title. The number of pulses emitted by the moving element unit is matched with the resolution rate defined by the numerical control system after the multiplication of the external multiplication circuit and / or the CNC internal multiplication factor. For example, the measurement element 10 pulse / mm, CNC system identification rate that is equivalent to 0.001mm pulse equivalent, then send the components sent to the pulse must be 100 times the frequency of the room.
Second, the position loop gain coefficient Kv value of the precise set and regulation. Normally the Kv value is set as the machine data, and the setting point and the numerical unit of the Kv value are assigned to each axis in the numerical control system. The setting of the Kv value after the optimization of the rate loop is an important factor affecting the performance of the machine. Kv value is the performance of the machine's own coordinates of the performance of the direct expression of the advantages and not can be arbitrarily amplified. Kv on the value of the set to be detailed two topics, from the first satisfaction with the following formula:
Kv = v / Δ
Where v - coordinate operating rate, m / min
Δ - tracking deviation, mm
Meticulous, poor other numerical control system to accept the unit is about the difference, set the meticulous numerical control system to set the unit. For example, if the unit of the coordinate running rate is m / min, then the Kv value unit is m / (mmmin). If the unit of v is mm / s, the unit of Kv should be mm / (mms).
Second, the satisfaction of the linkage axis of the Kv value must be the same, to ensure the accuracy of synthetic activities. Normally the Kv value is the lowest axis.
There are three kinds of location feedback: one is no position measurement components, for the location of open-loop control that is no position feedback, stepper motor drive is usually open loop; one is semi-closed-loop control, landing on the measurement element is not the final axis Active parts, that is to say that another sector drive key in the location of the closed-loop control, this environment requires the ring outside the transmission sector should have a commensurate transmission stiffness and transmission accuracy, to participate in backlash compensation and pitch deviation compensation, you can Get the high position control accuracy; the third is the whole closed-loop control, landing on the measurement element placed in the final axis of the moving parts, theoretically the best position of the control environment, but it is the whole machine drive system Require a higher and not low, if otherwise, will be a serious impact on the dynamic accuracy of the two coordinates, making the machine can only be in the low rate loop and location accuracy of the environment. Another important issue that affects the accuracy of closed-loop control is the accurate placement of measurement components, and it is not despised.
(4) feedforward control and feedback the opposite, it is the instruction value taken out of the department to the back of the conditioning circuit, its important role is to reduce the tracking bias to improve the dynamic characteristics of the corresponding position control accuracy. To be meticulous, feedforward participation must be in the above three control rings are the best debugging before being held.