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Tips for checking wear of rack and pinion of injection robot?

2025/06/07 By Topstar

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Injection robot that are calibrated before injection molding production can ensure fast and repeatable part pick and placement. The core of one of them is the rack-and-pinion transmission mechanism. However, over time, the continuous meshing between the rack teeth and the pinion will cause metal fatigue, pitting and dimensional wear. Therefore, rack and pinion wear inspection is required before production or during maintenance to ensure positioning accuracy, extend equipment life and reduce unplanned downtime.

Visual observation of the rack wear of the injection robot

Visual inspection is the first line of defense against excessive wear on the rack of the injection robot. After cleaning, use a high-intensity flashlight and a 10x magnifying glass or an endoscope to inspect each tooth on the rack. Look for pitting (and rounded teeth, which indicate material loss. Also, check for discoloration or burnt lubricant, which are signs of excessive friction. For these linear robots, wear is often concentrated at the travel limits where the carriage decelerates, so pay special attention to these end areas. Also, check the rack mounts for loose fasteners or misalignment, as even the slightest misalignment can cause uneven wear patterns to accelerate.

In observation, if you find that pitting or rounding exceeds 1/4 of the tooth face width (10%) or discover deep gouges, you may need to refurbish or replace the rack. Addressing these signs promptly helps prevent shock loads from damaging the internal gearbox and bearings, thereby maintaining the servo motor’s efficiency.

Dimensional Measurements for Backlash Monitoring

In addition to visual cues, quantifying backlash can indicate wear. Mount a magnetic base dial indicator to the robot carriage and place its stylus against a flat machined surface adjacent to the rack. With the injection robot in manual jog mode and holding torque disabled, gently reverse the drive direction while watching the indicator. The travel measured before the carriage begins to move is the backlash of the system. For injection robots, the acceptable backlash range is 0.05 mm to 0.15 mm. You can detect uneven wear by recording the backlash value at multiple points along the rack’s travel. If the measured value continuously exceeds the maximum tolerance, you can adjust the preload of the pinion bearing or schedule the replacement of the rack or pinion.

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Inspect and lubricate the pinion of the injection robot

The pinion of the injection robot is also susceptible to wear. After removing the protective cover, rotate the pinion of the injection robot by hand and inspect each tooth under a magnifying glass. Check for wear, micro-cracks at the root fillet, or uneven wear. Additionally, inspect the pinion mounting hole for signs of fretting wear or keyway deformation, which may cause the gear to slip. Worn-bearing seals can allow contaminants to penetrate; therefore, inspect adjacent seals and replace them if you find them hardened or cracked.

Proper lubrication can prevent the cornerstone of wear. Use a precision grease gun equipped with a flexible hose to apply a thin, even layer of grease to the gear meshing area for targeted delivery. However, we must avoid over-lubrication, which can accumulate debris and increase operating temperatures. For 3-axis robots operating in highly contaminated injection molding production environments, consider every 200-300 hours To clean the gear mesh and relubricate to minimize friction, keep out moisture, and extend the life of the rack and pinion.

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Alignment Verification and Correction

Misalignment between the rack and pinion accelerates wear and degrades performance. To verify the alignment of the injection molding robot, use a precision ruler or laser alignment tool. Place the ruler along the linear path of the rack and slowly move the pinion. Any visible play or sticking points indicate a parallelism error. For angular misalignment, mount a dial indicator on the pinion shaft and rotate the gear to check if the runout exceeds 0.02 mm. On injection molding robots, guide misalignment is often accompanied by rack misalignment, requiring confirmation of parallelism between the rack shaft and linear guide-bearing surfaces.

If misalignment is detected, realign by adjusting the rack mounting slot. Loosen, reposition, and retighten the anchor bolts while monitoring the indicator readings. For pinion runout, replace worn bearings or adjust the shaft seats as needed. After making the necessary alignment adjustments, relubricate the gear mesh and recheck the backlash.

Perform overall maintenance regularly

As important as a stand-alone rack and pinion inspection procedure is, incorporating it into a comprehensive injection robot maintenance program will multiply its benefits. Combining rack and pinion inspections with servo drive diagnostics, linear guide lubrication, and mold temperature controller maintenance can optimize downtime windows. Additionally, monitor environmental conditions and perform routine maintenance after completing mold remediation. Schedule a gear inspection immediately after the robot shows signs of wear.

Leverage data from the robot control software as an indicator that gear wear may be increasing. By correlating mechanical wear data with operational analytics, operators can adopt a predictive maintenance approach to improve the reliability of injection molding robots by replacing components based on usage patterns rather than fixed schedules.

Perform regular inspections and maintenance for smooth operation

Performing regular inspections and maintenance on the rack and pinion drive system of an injection robot can help maintain high precision, prevent unexpected downtime, and ensure part quality. Consistent performance of the injection robot can be ensured by combining comprehensive visual inspections, precise backlash measurements, and targeted lubrication measures. Integrating these techniques into a broader preventive and predictive maintenance framework can lead to operational excellence, ensuring the smooth operation of high-speed production lines.

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