Contact position sensor with optical feedback

摘要

A method and apparatus is provided for determining the touch down position of a tool or probe used in bonding and placement machines. The tool holder is coupled to a Z-drive motor and comprises a fixed end coupled to a resilient member. The tool holder has a compliant end connected to the other end of the resilient member. An optical encoder is coupled to the compliant end of the tool holder. Processor means are provided for incrementally driving the Z-drive motor and observing the increments of movement of the compliant end of the tool holder with an optical sensor. When the compliant end of the tool holder no longer moves in step with the encoder of the Z-drive, the tip of the tool or probe has encountered resistance and started compression of the resilient member which connects the fixed end and the compliant end of the tool holder. The Z-axis position of the encoder and the Z-drive motor at the time of resistance is indicative of the touch down position. After touch down, the resilient member may be compressed by further movement of the Z-drive motor to apply a known and predetermined bonding or placement force.