Len Industries (Leslie, MI) has been producing high quality, precision-machined automotive components for more than 30 years. Recently, Len Industries approached FANUC Robotics America, Inc (Rochester Hills, MI) looking for a solution to unload, or depalletize, randomly placed transmission gears from a plastic bin. At the time of the request, the gears were being manually unloaded. Len Industries wanted to reduce labor costs and increase throughput by automating the process.
FANUC Robotics designed a workcell that uses a FANUC M-16iB robot coupled with a FANUC integrated vision system for robot guidance. The vision hardware includes a Pulnix (Sunnyvale, CA) TM-200 video camera; Advanced Illumination, Inc (Rochester, VT) RL36120 red LED ring light, high flex camera power cable, high flex camera coaxial cable, and power supply; and a Matrox (Quebec, Canada) 4sightII computer. The Matrox computer includes an Orion PC104+ Frame Grabber, which is used to capture the vision information. A generic flat panel monitor, keyboard, and mouse complete the user interface to the vision system. Other major components include a custom designed and built end-of-arm-tool (EOAT), pneumatics package, robot riser, two-part rack locators, divider sheet storage rack, interface panel, and safety fence.
Multitasking Robots
In addition to unloading the gears onto an exit conveyor, the robot must transfer a plastic board that divides each gear layer. Each bin, measuring 746 (L) x 686 (W) x 721 (H) mm, holds 22 layers with 88 gears to a layer.
To meet the throughput requirements of the workcell, the vision-guided robot needed to reach an average cycle time of 4.5 seconds per part, including the removal of the plastic divider sheets. To meet this requirement, FANUC Robotics'' engineers designed the system to transfer two parts at the same time, using an inner diameter grip end-effector with two gripper modules.
The application depalletizes two different transmission gears. While each gear has the same inner and outer diameter, they differ in height. The gears are manually loaded into the bin with random orientation and positions, requiring vision to locate and transfer the parts.
An Order To Everything
The vision program resides on the Matrox computer; the robot and the Matrox computer communicate over Ethernet. Both the PC and the robot come standard with an Ethernet port. The robot moves to an area above the bin and via Ethernet, initiates the vision process on the PC that reports the total number of targets found in the field of view, and the locations of the targets. The bin is divided into 20 robot zones for taking snapshots of gears.
Parts that are identified on the wall of the bin (the outer ring of parts) are moved toward the center before any upward movement. The center move prevents the parts from being stripped off the end-of-arm-tooling (EOAT) by interferences with the bin walls.
FANUC Robotics chose a robot-mounted Advanced Illumination, Inc RL36120 red LED ring light source. Red light is often used in combination with a red light filter at the camera to negate the disruptive effects of ambient light. The system is located near a large bay door, and whether it''s day or night, with doors open or closed, ambient light does not affect the operation of the system.
A 16 mm camera lens mounted to a grayscale camera was selected for the system. Pictures are taken at a standoff height (distance between camera and gear) of 712 mm and transferred via coaxial cable to the Orion PC frame grabber where it is digitized. The camera is mounted to the robot arm, allowing the 712-mm standoff height to be maintained throughout the entire bin. The 16 mm lens, and the standoff height of 712 mm were selected to keep the camera height above the walls of the part bin, from the top layer (721 mm above the bin) to the bottom layer (10 mm above the bin). The field of view is 287 x 215 mm. Pixel resolution is .374 mm, providing enough accuracy to reliably pick the gears.
Integrated Vision Interface
Calibration is critical to robot guidance applications. The vision system must be calibrated so that it can calculate feature scaling and robot position in a 2D environment. In this application, the vision system is calibrated with a grid of a series of circles with known sizes and dimensions. The system is only calibrated when hardware is changed or damaged. When required, a fixture-mounted calibration grid is placed in the bin locators (where the bin usually sits). The known dimensions of the circle provide the scale in mm/pixel. The same grid in the exact same position is used to teach a robot frame. Teaching the robot frame calibrates the robot to the vision system. The values of the taught robot calibration frame are uploaded from the robot to the vision process on the Matrox PC. The offset position provided is relative to this frame.
Parts are trained using FANUC Robotics'' Windows-based vision program. The use of a dedicated computer provides easy access to the vision system. According to Richard Meyer, project manager for FANUC Robotics, Len Industries appreciates the immediate ability to program new parts and troubleshoot vision issues using the dedicated computer hardware versus an external interface method such as a laptop. Parts are "trained" to provide a reference to compare images taken during automatic operation. The trained parts are found by vision using FANUC Robotics'' geometric pattern-matching algorithm. The part is trained at the same height that the robot searches for parts; this provides the best opportunity to find parts, since the size and contrast will be most accurate.
The information that vision calculates and provides to the robot is the x and y location of the center of the gear with respect to the trained nominal position. Both parts are symmetrical and radial orientation is not required. The vision system interfaces directly to the robot via Ethernet through FANUC Robotics'' robot server. The offset data from the vision system is placed into position and registers on the robot. No third-party communication or interface software is required. The robot interprets the x and y information as an offset applied to the nominal position.
Locator parameters are input and monitored in the vision program. These parameters are used to provide a range of findings that determine if a part has been "found" or "not found." The key parameters used in this application are size and contrast. The size and contrast are combined to create an overall "score" that is used to determine if a part has been found. Utilizing the size characteristic, the vision system can determine if the tested part is on the current layer or one layer lower (condition exists along bin walls). Contrast can be used to differentiate between an actual part and an oil ring from a part that has been removed.
During testing, the vision system identified phantom parts that were caused by oil rings on the plastic board. The vision system recognized the oil ring as an actual part. The problem was solved utilizing the contrast locator parameter. On a contrast scale of 1 to 100, the oil ring scored a contrast value of 44 versus a contrast value above 95 for "real" parts. Phantom part finds were eliminated by adjusting the overall part score to be higher than the lowest oil ring score, in this case 44.
The vision system also located gears that were one level lower than the robot was unloading. The parts were on the outer ring and the plastic board allowed enough of the part to be "seen" so that the vision system identified it as a "found" part. The problem was resolved using the "size" locator parameter to ignore parts that were not at least 95% of the trained part size.
FANUC Robotics Moves Forward
After the system was installed, Len Industries requested that FANUC Robotics add part orientation detection. Any gears that enter the machining center upside down cause damage and downtime to the tool. Using a clockwise pointing part feature, the vision program was able to identify upside down parts and load them into a reject chute. The parts are then manually loaded to the tool.
Len Industries also requested improvements in the vision display tools that would show the operator the edges the vision system was using to locate a part. FANUC Robotics responded by adding red and green indicators on the image in the vision interface. The green edges show a positive edge find, and the red edges indicate where an edge was expected, but not found.
"The system has proven to be a success," said Meyer. "The combination of robotic reliability and the latest advances in vision has met all customer requirements. According to Len Industries, after four months of operation the FANUC Robotics vision/robot cell increased production throughput by 5%, and decreased labor costs by 30%, with a system uptime above 90%."