In today’s world of space-conservative technology—flat-screen televisions, inch-thick laptops and oh-so-thin smart phones—the demand for printed circuit boards is on the rise. Assembling printed circuit boards requires repeatable performance and extremely subtle precision is usually too expensive for educational and small business markets. Professor Harvey Silverman’s team at Brown University has recently devised a solution to automate the process using PBC Linear’s ML series mini-actuators in a multi-axis circuit board assembly system at a suitable cost for these areas.
Miniature actuators in a multiaxis circuit board assembly system assemble printed circuit boards for today’s increasingly smaller technology.
To accomplish the task of circuit board assembly, Silverman needed a linear motion solution that could position tiny surface mount devices (SMDs), such as capacitors and resistors of 0402 size (0.040- x 0.0240-in.) and accurately place them onto solder paste to adhere to the board. The tiny parts need to be handled delicately and adjusted mid-operation to correct for misalignment. The final piece of the puzzle was finding a way to ensure all parts are in the right place.
An ML series XYZ gantry controlled with a vision system was the solution. With a 28- x 32-mm profile, the compact mini-actuator was the optimal size for small-scale circuit board assembly. Also, the ML series is equipped with components for accurate linear positioning; such as a ‘dove-tail’ style carriage comprising 14 plane bearing surfaces for high rigidity and smooth travel, single or dual external linear guide supports for enhanced stability and a full line of accessories for use in multi-axis systems.
Designed over the course of a year with product assistance from PBC Linear application engineers, Silverman came up with a working solution. Three mini-actuators assembled in a 12- x 14-in. footprint XYZ system were used to automate the surface mount assembly process. Two ML actuators accurately determine XY position while the third moves a vacuum needle part-grabber up and down. A server was also added to allow rotation of the part.
The gripper assembly is outfitted with a small camera to locate loose parts and give feedback to the user using software designed by Ken Silverman. The camera compares images of assembled circuit boards to identify where all the pieces need to go and signals the gripper to re-align if adjustment is necessary. The system can also be switched over to manual control for special assembly projects.
Overall, the team was very pleased with the low cost PBC Linear ML solution and its ability to perform the required tasks at hand. Silverman is currently working with PBC Linear engineers to update the design with a new ML series actuator for enhanced pick-and-place assembly.
Filed Under: Linear motion • slides, Motion control • motor controls
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