A major consumer electronics maker had a quality problem when assembling lens for their phone cameras. The failure rate was over 30 percent. Additionally a certain percentage of those that passed were on the quality edge, leading to fears of failure in the field.
The assembly system used high quality pneumatic slides as the means of assembling six parts that nestled together. Standard sensor technology verified that the six distinct parts were present and were assembled but there was no verification that the parts were pressed into the correct locations and, since pneumatics were used, there was limited precise control of the different forces used to assemble each part.
A change was made from pneumatics to smart electric linear motor based actuators that were programmable in position and velocity modes and, unusually, in force mode. The devices also featured built in sensors that could in real time verify the assembled final location of each part.
The assembly process began with the verification of the base of the assembly nest. This was done on the micron level by the actuator using a patented “soft-land” capability that reduced surface impact to the 0.1 N level. The first part was vacuum picked up the landed into the nest. Soft-Land drop was used to prevent damage to the part. Part location was verified referencing the predetermined nest datum.
The second part was again picked up by a vacuum. (A new micro gripper is now available that also can pick up parts with gripping forces as low as 5 grams.) The part softly landed onto the first part and stopped. This position was also checked to insure start of press location was correct. Then the specified force was programmably applied (force is directly proportional to current) and the part was pressed to a designated position at which time the force was cut.
The same process was used for all other parts, and at each step information was feedback verifying that a correct assembly was / or was not made. By applying this “smart assembly” method the customer was able to reduce assembly failures to under 2 percent. The failure cause for the 2 percent was attributable to out-of-spec parts.
Additionally, the allowable tolerance range for part positioning was tightened to improve quality of “good” assemblies. In electronic assembly, any failure to assemble correctly can cause the entire circuit board to fail—hence “smart assembly” is a well-practiced method. These capabilities are useful, particularly:
• Programmable control of force, velocity and position
• The ability to feed back in real time the result of the work done—and to compare the result to what was specified
• The ability to softly land on a surface preventing damage to parts and locating surfaces in space
In many industries such as packaging, automotive, food processing, glass manufacturing, and BIO/LAB the adoption of “smart” electric actuators is raising quality while increasing productivity.
Other recent applications in the above industries will be reviewed in order to present a better view of the application of “smart” electric actuators.
For more information, visit www.smac-mca.com.