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How to solve the problem of inaccurate positioning of linear robots?

2025/05/02 By Topstar

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Linear robots, also known as injection molding robots, are used in injection molding to insert inserts into the mold and to pick up and place finished parts after molding. However, positioning inaccuracies can seriously disrupt production, leading to misaligned inserts, damaged parts, and increased scrap rates. To remain competitive, manufacturers need linear robots that can provide reliable repeatability and precise positioning accuracy, especially when handling delicate operations such as inserting plastic inserts into mold cavities and accurately placing molded parts on conveyors or packaging.

By integrating servo motor drive technology on each axis of the linear robot, Topstar ensures high-speed motion and precision gearbox speed change. This approach can achieve positioning accuracy of up to ±0.1 mm. The following sections will explore specific technologies such as precision gearboxes, 5-in-1 servo drive architecture, and advanced motion control algorithms to overcome positioning inaccuracies.

Linear robots achieve sub-millimeter positioning with servo motor drives

An essential element in addressing positioning errors is using servo motor drive systems on each axis of the linear robot. Unlike pneumatic or general-purpose stepper motors, servo motors integrate high-resolution encoders to monitor their rotational position continuously. In Topstar’s linear robots, these encoders provide real-time feedback to the drive controller, enabling instant course corrections.

Fast response times (typically less than 1 millisecond) combined with closed-loop control enable linear robots to maintain accuracy of ±0.1 mm even under dynamic loads or high speeds. The servo-driven axes can precisely decelerate for insertion as the fixture approaches the mold cavity, allowing the insert to be placed gently and without jerk. Similarly, during the pick-and-place process, the linear robot decelerates smoothly with the help of precision guides to eliminate overshoot, ensuring the molded part is accurately clamped at the intended pickup point.

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Precision-grade reducers for enhanced motion control

In addition to the servo motor drive, Topstar transmits power through precision reducers to accurately position the linear robot. Standard planetary or gear reducers typically introduce backlash and compliance, reducing repeatability. Topstar solves this problem by specifying precision harmonic or zero-backlash reducers for each axis. These reducers provide consistent gear meshing with minimal play, maintaining the servo motor’s rotational accuracy.

When used with servo motor drives, these precision-grade reducers ensure that the actuator’s linear motion directly converts motor commands into guide motion without lag or lost motion. During insertion, the reducers enable the robot to always reach the same depth and orientation in each mold cavity. The pick-and-place sequence ensures that the system executes the path from the ejector slot to the conveyor with precisely the same trajectory in every cycle. This allows the linear robot to combine fast dynamic response and mechanical precision.

5-in-1 Servo Drive Architecture for Linear Robots

The 5-in-1 servo drive architecture combines the control of up to five servo motors into a single modular drive unit. This design reduces communication delays between axes, simplifies system integration, and ensures that coordinated motion remains perfectly phased. The 5-in-1 servo drive enables the linear robot to perform complex five-axis motion within a single motion command, such as descending to the mold, adjusting the gripper direction, and moving forward simultaneously. This unified drive approach eliminates the slight delays that occur when independent drives communicate over a Fieldbus network. For functions such as insertion, the drive automatically coordinates the vertical insertion speed with the lateral motion to prevent misalignment. In pick-and-place tasks, the end effector smoothly passes through multi-axis waypoints and precisely aligns with the bracket or pallet.

Automatic optimization of the removal process

Topstar linear robots can support host call signals to achieve integrated operation. The control system automatically optimizes the removal process, aiming to achieve optimal trajectory control, especially in complex injection molding environments. Through automatic optimization of the control system, overshooting at high speeds can be prevented, and vibration can be reduced, ensuring smooth movement and high precision. In dynamic molding environments, it also includes automatic compensation functions to account for mold wear and adjust robot motion in response to changes in mold geometry over time. This ensures consistent insert accuracy and extends the mold’s life. This real-time adjustment is critical when dealing with warped or asymmetric parts, as it can effectively reduce positioning errors caused by subtle inconsistencies in product geometry.

Vibration reduction technology

The high-speed operation of linear robots often presents vibration-related challenges, especially when handling heavy payloads accurately. To jointly improve the stability and accuracy of the robot. One of the core improvements is using a high-rigidity precision slide structure and a lightweight aluminum alloy injection molding robot arm. This reduces inertial loads and improves response time and motion smoothness. Complementing this is an active vibration reduction system that uses real-time servo torque control to counteract oscillations during high-speed transitions. This torque modulation method can fine-tune the motor’s output to suppress undesirable movements. These technologies enable Topstar robots to operate at speeds of up to 2 meters per second while always maintaining positioning accuracy within ±0.15 mm.

Precision Slides

Achieving precision and reliability in molding automation

Topstar’s integrated solution – each axis has a servo motor drive system, precision-grade reducers, and advanced five-in-one servo drives to ensure high-speed operation and achieve sub-millimeter accuracy of up to ±0.1 mm. By adopting servo motor-driven linear robots, molders can eliminate familiar sources of position errors, reduce scrap rates, and achieve consistent product quality in high-volume production.

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