How to set the trajectory accuracy of injection molding manipulator?

The core of setting the picking trajectory accuracy of injection molding manipulator is to take "benchmark calibration+trajectory planning+servo parameters+error compensation+dynamic verification" as a closed loop, and control the repeated positioning accuracy within ±0.05~±0.1mm, and the trajectory deviation is ≤±0.2mm, so as to meet the demand of picking and placing precision injection parts. The following are the step-by-step setting methods and key parameters:

First, do benchmark calibration: the basic guarantee of trajectory accuracy

Mechanical benchmark and zero calibration

Tighten the bolts of each axis of the manipulator and the slide block of the guide rail to ensure no looseness; Check the parallelism/verticality between the flange and the fixture with a dial indicator, and the error is ≤ 0.1 mm..

Enter the "zero calibration" mode of the controller, set the mechanical zero of each axis through the absolute encoder (or the incremental encoder returns to zero), and record the coordinates of the origin to avoid position loss after power failure.

If it is a multi-axis manipulator (such as X/Y/Z/A/B), it is necessary to calibrate the kinematic parameters of each axis linkage to compensate the joint clearance and connecting rod error.

Calibration of Tool Coordinate System and Workpiece Coordinate System

Tool Coordinate System (TCP): Take the clamping center of the fixture or the suction center of the sucker as the center point of the end tool, manually teach the same point in three different postures, and automatically calculate the TCP coordinate with an error of ≤ 0.05 mm..

Workpiece coordinate system: according to the mold cavity/product placement position, set the absolute coordinates of the picking position, placing position and standby position to ensure linkage with the mold opening stroke and ejector pin action of the injection molding machine.

Second, trajectory planning and motion parameter setting: control trajectory smoothness and positioning accuracy.

Key Point Teaching and Path Interpolation

Teaching points: teach in the order of "standby position → safety position → picking position → demoulding position → placing position → origin", and record the coordinates after each point stays stable; One or two intermediate transition points should be set at the picking position of precision parts to avoid path mutation.

Path interpolation: the acceleration/deceleration of S-curve is preferred (better than trapezoid), and the acceleration/deceleration (initially set to 30%~50% of the rated value) and smoothing coefficient are set by the controller to reduce the motion impact and terminal vibration and improve the accuracy of trajectory reproduction.

Optimization of servo core parameters

Function of parameter category recommendation setting

The position loop gain of 800 ~ 1500 (adjusted according to the load) improves the positioning response speed and inhibits the positioning overshoot.

The speed loop gain of 30 ~ 50 reduces the speed fluctuation and improves the trajectory stability.

Acceleration feedforward 50% ~ 80% compensates inertia error in acceleration and deceleration stage.

Load inertia ratio is set according to fixture+total weight of workpiece (such as 1: 3 ~ 1: 5) to match servo output to avoid jitter.

The vacuum/pneumatic fixture needs to be linked with the magnetic switch and negative pressure sensor, and the interlock signal of "Clamping in place → Allow to move" is set to prevent the deviation of taking parts.

Third, error compensation: the key means to improve trajectory accuracy

Geometric error compensation

Load compensation: input the weight and center of gravity coordinates of the workpiece, activate the compensation of gravity and inertia, and solve the trajectory deviation caused by load change (if the center of gravity deviation is more than 10mm, it needs to be calibrated separately).

Clearance/backlash compensation: for ball screw and gear transmission, input the measured backlash value (such as 0.02~0.05mm) into the controller to automatically compensate the reverse motion error.

Dynamic error correction

Thermal compensation: after long-term operation, the temperature rise of each shaft is monitored by temperature sensor, and the coordinate deviation caused by thermal expansion is automatically corrected.

Real-time feedback: the high-resolution encoder (≥23 bits) is used to send back the position data in real time, and PID control is used to correct the trajectory deviation in a closed loop to ensure the dynamic accuracy.

4. Verification and optimization of trajectory accuracy

Static accuracy test

With a dial indicator/laser displacement sensor, repeat positioning for 10 times at the pick-up position and the put-down position, and record the coordinate deviation. The accuracy of repeated positioning should be ≤±0.05mm (precision level) or ≤±0.1mm (ordinary level).

Check the parallelism and verticality of the key points of the trajectory, and the error is ≤0.1mm to avoid the product from being skewed and scratching the mold.

Dynamic Trajectory and Cycle Verification

Run for 50~100 modules continuously, and observe whether the picking track is smooth and jitter-free; Use a high-speed camera or trajectory recorder to analyze the trajectory deviation in the acceleration and deceleration stage. If it exceeds ±0.2mm, it is necessary to reduce the acceleration or adjust the S curve parameters.

Linked with the injection molding machine, the signal interaction of "mold opening in place → manipulator taking parts → mold closing permission" was verified to ensure that there was no interference between the trajectory and the mold action, and the success rate of taking parts was 100%.

V. Frequently asked questions and quick corrections

Correction method of possible causes of problem phenomena

Trajectory deviation, mechanical looseness, TCP calibration error, re-fastening → TCP re-calibration → compensation of load parameters.

Excessive terminal jitter acceleration and mismatched inertia reduce acceleration → adjust load inertia ratio → enable S curve.

The gain of positioning overshoot position loop is too high, reducing the gain → increasing feedforward compensation.

Large repetitive deviation, abnormal encoder feedback, and uncompensated backlash. Check the encoder wiring → enter backlash compensation value.

Six, parameter curing and maintenance

After debugging, save the teaching program, servo parameters and compensation values, and establish a parameter file to avoid misoperation and loss.

Regularly (weekly) check mechanical looseness and gas leakage, and check TCP accuracy and trajectory deviation every month to ensure long-term stability.