Motion system delivers precise speed control for dip coating process

Heason’s motion expertise has played a significant role in a manufacturing project involved the design and supply of a single-axis servo motor driven actuator and control system for a novel thin-film dip coating process. The positioning system required ultra-precise speed control for the withdrawal cycle of a large, heavy and irregular shaped component to ensure a highly uniform and precise coating thickness.

The components’ asymmetrically distributed mass and dimensions combined with the buoyancy effect of the coating fluid caused a load variation that would result in a significant series of stepped fluctuations in the reflected inertia seen at the motor as the product was vertically retracted from the coating bath. This load variation was a challenging factor for the low-speed control required for the process.

The customer specified a stand-alone system where an operator could simply program the actuator to a load position and adjust the dipping and retraction speed with recordable values to maintain a consistent and repeatable coating thickness over the process. Heason delivered a 700 mm stroke length actuator driven by a servo motor fitted with an absolute encoder for precise closed loop speed and position control from a servo drive.

The speed control parameters were programmed between the servo drive and an HMI to complete the autonomous system. The servo drive chain included a planetary reduction gearbox to achieve the low speed required and a holding brake ensured safety for the vertically mounted system.

The specific choice of components for the stand-alone system fell to a PC32 series actuator from Thomson, a leading linear motion component manufacturer and a valued partner for Heason. Its PC32 series features a smooth IP65 rated aluminium housing protecting a precision ball screw whilst a stainless-steel extension tube and rod adapter perfectly suit the environment and load mounting arrangement for the dip-coating process.

A 7:1 ratio precision grade planetary gearbox, also from Thomson, is included to reduce the linear speed within the set range as well as help smooth speed fluctuations by reducing the effect of reflected motor inertia due to the irregular load distribution of the component during the process.

The actuator assembly is driven by a Kollmorgen AKM21E servo motor complete with integral holding brake and absolute multi-turn encoder. Heason enjoys a long-term distribution partnership and several years’ experience with Kollmorgen, as a UK certified partner and silver-status supplier for its industrial automation systems, servo motors and drives. With precise servo control from Kollmorgen’s AKD BASIC series servo drive through its built-in BASIC programmable motion and machine software, the digital drives’ 62.5 microsecond servo update rate constantly maintains the exact desired motor speed despite the torque variation due to the irregular load.

A Kollmorgen AK12G series 7” HMI touchscreen, programmed with Kollmorgen Visualization Builder software allows full stand-alone operator control of the coating process. As an absolute encoder is used for servo feedback, homing the actuator to a loading position is a simple command. The operator then enters a retraction speed value into the graphic panel and a sequence is called from the intelligent servo drive delivering and retracting the component at the desired speed.

Heason provided the complete system pre-programmed and fully operational based on the speed range and speed tolerance specifications supplied for the dip coated component following extensive in-house testing before delivery to the customer. The motion system was supplied with operation manuals and servicing information.