What are the possible reasons why the injection manipulator is not picking up the parts in time?

In addition to the common reasons mentioned before, the untimely picking of parts by injection molding manipulator may also be related to the following factors, which are often easily overlooked, but have a significant impact on efficiency:

I. Influence of environment and material characteristics

1. Abnormal surface characteristics of the workpiece

Reason:

The surface of the workpiece is too smooth (such as high-gloss products), which leads to insufficient vacuum adsorption force of the sucker and requires multiple attempts to grab it;

There is oil stain or moisture on the surface of the workpiece, which reduces the friction of the fixture, and it is easy to slide down after grasping and needs to be repositioned.

Solve:

Replace the textured sucker (such as corrugated sucker) or add a vacuum holding valve;

Add pretreatment procedures (such as blowing cleaning) to ensure that the surface of the workpiece is dry and free of impurities.

2. The material temperature is too high

Reason:

The temperature of the newly formed workpiece is too high (such as over 60℃), which leads to the deformation of the manipulator fixture, the decrease of grasping accuracy or the delay of action;

High temperature environment affects the stability of the sensor (such as photoelectric switch shifting due to thermal expansion and cold contraction).

Solve:

Extend the cooling time of the mold, or add a water cooling/air cooling device in the fixture;

Select high-temperature resistant sensors (such as metal proximity switch, which can withstand up to 120℃), and do a good job of heat insulation protection.

3. Workshop air pressure fluctuation

Reason:

The air supply system in the factory is unstable (such as the sudden drop of air pressure caused by the simultaneous use of gas by multiple devices), which affects the cylinder speed and clamping force of pneumatic manipulator.

Solve:

Install an independent gas storage tank to stabilize the air pressure (it is recommended that the volume of the gas storage tank is more than or equal to 3 times the gas consumption per minute of the manipulator);

Check the pressure of the main gas pipe (the standard value is 0.5~0.7MPa) to avoid sharing the same pipeline with other high gas-consuming equipment.

Second, the mechanical structure design defects

1. The arm inertia matching is unreasonable.

Reason:

The mass distribution of manipulator arm (such as transverse axis, upper and lower axis) is uneven, and the start-stop impact is caused by excessive inertia when moving at high speed, so it is forced to slow down;

When the load exceeds the design specification (e.g., the grab weight is more than 80% of the rated load of the manipulator), the motor overload alarm is frequent.

Solve:

Optimize the lightweight design of fixture (such as replacing steel with aluminum alloy) to reduce the inertia of moving parts;

Check the weight of the workpiece. If it is overloaded for a long time, it is necessary to replace the manipulator with larger specifications (for example, upgrade the 50kg load manipulator to 100kg).

2. Transmission chain clearance accumulation

Reason:

The backlash of rack and pinion drive is too large (> ＞0.1mm), or the position feedback deviation is caused by the relaxation of synchronous belt, so the manipulator needs to correct the path repeatedly;

The wear of the joint bearing produces a gap, which leads to the decrease of the repeated positioning accuracy of the picking point (for example, more than ±0.5mm).

Solve:

Adjust the pre-tightening force of the rack and pinion (such as installing a double-gear backlash elimination mechanism), or tension the synchronous belt (use a tensiometer to detect the tension value);

Replace worn bearings (such as harmonic reducer bearings) and re-calibrate the original position of each shaft.

3. Offset of the center of gravity of fixture

Reason:

The installation position of the fixture deviates from the center of the end of the manipulator, which leads to torque during movement. The servo motor needs to overcome the eccentric load torque to reduce the response speed.

Solve:

Adjust the center of gravity of the fixture with a torque balance tool (such as a balance crane) to ensure that it coincides with the central axis of the manipulator;

Enable the "inertia compensation" function in the program (supported by some high-end manipulators) to automatically correct the influence of unbalanced load.

Third, software and algorithm problems

1. Trajectory planning algorithm is backward.

Reason:

The manipulator uses linear interpolation trajectory instead of better curve interpolation (such as S-type acceleration and deceleration, NURBS curve), which leads to obvious speed loss in the start-stop stage.

Solve:

Upgrade the control system software and enable the advanced trajectory planning algorithm (which can shorten the movement time by 20%~30%);

For complex paths (such as avoiding mold interference), manually teach multi-segment intermediate points to optimize the trajectory.

2. Multitask scheduling conflict

Reason:

When the manipulator performs multiple tasks, such as picking, detecting and putting, the task queue is blocked due to insufficient allocation of system resources.

Solve:

Priority ranking: ensure that the picking action takes precedence over non-critical tasks (for example, the appearance inspection can be postponed until after the placing);

Increase hardware resources: for example, configure industrial computer independently for the visual inspection module to avoid competing with the manipulator control system for computing power.

3. Anti-collision logic is too conservative

Reason:

The threshold of anti-collision detection is set too low (for example, the safety distance is more than twice the actual demand), which leads to the manipulator slowing down in advance when approaching the mold and prolonging the picking time.

Solve:

Re-calculate the safety distance according to the mold structure (it is recommended to leave a margin of 50~100mm), and turn off the anti-collision detection in unnecessary directions (such as keeping only the vertical direction);

Enable the "dynamic anti-collision" function (if supported by the system), and automatically adjust the detection threshold according to the moving speed.

Four, human operation and maintenance omissions

1. The parameter reset was not saved.

Reason:

The operator accidentally touched the control panel, resulting in the optimized speed and acceleration parameters returning to the factory settings, which were not found in time.

Solve:

Enable parameter locking function (set operation password), and check key parameters (such as speed limit values of each axis) regularly.

2. The lubrication cycle is too long

Reason:

Insufficient lubrication of guide rail and screw rod (such as not oiling for more than 3 months), increased friction resistance leads to slow movement and even "crawling" phenomenon.

Solve:

Fill the grease according to the equipment manual cycle (usually every 100 working hours), and use an automatic lubrication system (such as electric yellow oil pump) to replenish oil regularly.

3. The mould has not been recalibrated after replacement.

Reason:

After replacing the mold, the picking point is not taught again, or the installation position of the mold is deviated (for example, the matching gap between the positioning ring and the hole position of the injection molding machine is > ＞0.2mm), which leads to the manipulator running according to the old coordinates and the path becoming longer.

Solve:

Establish the process of "calibration after mold change" and use the reference block to quickly align the mold (for example, the mold reference plane is aligned with the manipulator coordinate system);

Install die positioning auxiliary devices (such as hydraulic quick die changing system) to ensure that the repeated positioning accuracy is ≤ 0.1 mm..

V. Hidden Problems in Special Scenes

1. The multi-station mold has poor synchronization.

Reason:

In multi-cavity mold, the ejector pins of each cavity are not synchronized (for example, the ejector pin of one cavity is delayed by 0.3 seconds), which causes the manipulator to wait for all the workpieces to be in place before taking them.

Solve:

Reform the oil/gas path of the ejector pin of the mold, and increase the synchronous valve or servo motor to drive the ejector pin;

Set the logic of "single-cavity priority grabbing" in the program, take the in-place workpiece first, and reduce the overall waiting time.

2. Electrostatic adsorption interference

Reason:

The plastic workpiece is electrostatically adsorbed on the surface of the mold, so the manipulator sucker can't effectively separate the workpiece, so it needs many attempts or additional blowing assistance.

Solve:

Spray anti-static coating on the surface of mold cavity, or install ion air gun to eliminate static electricity;

Adjust the position of the suction cup so that its center is aligned with the center of gravity of the workpiece to enhance the peeling force.

3. The soft start/stop time is too long

Reason:

The soft start ramp time of servo motor is set too long (such as > 0.5 seconds), which leads to slow acceleration in the initial stage of shaft movement and wastes time.