Automatic Electrostatic Powder Coating Line With Reciprocators and Multi-Axis Machines

Reciprocators

Reciprocators use a variety of electronics to control both stroke and speed. In these machines, the mechanical linkage between the motor and guns is fixed; therefore, speed and stroke control must be adjusted electrically. The adjustments sometimes be made at the control panel or at the unit itself. For instance, stroke adjustment can be made by moving electrical limit switches in the unit or by adjusting an electronic feedback loop variable in the control panel. Speed control is finished by a variety of methods based on the type of motor used. For instance, those designs that use a DC motor will provide speed control by varying voltage to the motor. Reciprocators which use AC motors have the variable speed-control circuits to adjust speed. Both of the types allow adjustment during the operation. This oprovides some flexibility on the oscillator design when different stroke lengths and speeds are required to coat different parts during the production cycle.

 

Multi-Axis Machines

Oscillators and reciprocators only can provide movement in one plane . Multi-axis machines were developed to provide increased coating flexibility and meet a demand for total automation. Multi-axis machines are successful in eliminating few or all of the manual touch-up necessary on some products. Though costly, this increased automation often will pay for itself by providing consistent part coating with minimal, if any, touch-up. The multi-axis machine is be made up of two or three reciprocators that will move the gun(s) in two or three planes. The convention used to label the three axes of motion is as below:

 

X = parallel to the conveyor travel

Y = up and down

Z =in and out

 

The design of these parts is the same as reciprocators with respectiion to the control of speed and stroke adjustment; however, because the units must track parts moving along the conveyor, the addition of a programmable logic controller (PLC) is required. The PLC will accept inputs from encoders (that determine conveyor speed) and photo cells or limit switches (that determine part position). This information is used to determine at what speed the multi- axis machine must run to track the part and when the multi-axis motion program is to be executed. The purpose of this complex tracking and motion system is to provide gun dwell time and powder pattern direction.