Industrial Machine Vision Based on National Instruments Technology Goes Further in Complex Human Task Automation

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"The choice of LabVIEW as a development platform gives the software integration capabilities and optimizes multitasking to keep the processing time very short. "

- Charles Magnan, Averna Vision & Robotics

The Challenge:
Reproducing thorough human inspections with an automated system that offers a high level of precision (+/- 0.001 in.) and a high level of complexity (defect detection on reflective metallic surfaces with complex shapes and validation of pin stamped codes) for various part models and production in small batches.

The Solution:
Using a robot to handle and move the parts, multiple images are acquired on three acquisition stations. The system uses the NI LabVIEW software and NI Vision Acquisition software for processing speed optimization. The robot gives the flexibility needed for various part models and the adaptability for frequent production changeovers.

Author(s):
Sebastien Parent - Averna/Vision & Robotic
Pascal Cormier - Avera/Vision & Robotic
Charles Magnan - Averna Vision & Robotics

In some manufacturing processes parts are made with high surface quality and precision. These inspections are usually left to humans because of their complexity: highly reflective metallic surfaces that should be studied from different angles and under varying lighting conditions and part shapes not entirely visible to a static camera. NI Platinum Alliance Partner Averna Vision & Robotics developed a system that mimics the human inspection strategy for these applications using a robot, a combination of lighting setups, and multiple cameras.

Automation is usually involved when a specific product is to be produced in large volumes, but there is also a need to reduce human subjectivity in complex visual inspection tasks for small production quantities. For this situation, a complex, flexible automated system is needed, because difficulties arise when using a static camera set up, because they cannot check all aspect of the part. The difficulty comes from the efficiency limit of using static setup of cameras and lighting to see all the characteristics of the part to inspect. 

To move the part for light effect variation, we use a robot with a gripper, a combination of cameras, and special lighting. We designed a camera set up that accommodates a variety of part dimensions and shapes. The system also processes small batches of products and accommodate new products in the future. We selected the National Instruments hardware and software platform, because it met our requirement.

System Design

The system architecture is PC-based with two NI PCIe-1430 Camera Link image acquisition boards with dual port. The inspection sequence and the user interfaces were developed using NI LabVIEW. For every image processing task, the system uses NI Vision Acquisition library algorithms. The system communicates with the robot controller FANUC RJ using an NI PCI-6514 I/O board.

LabVIEW was selected for its multitasking capabilities that simplify the management of parallel tasks and also for its capability to easily integrate control and machine vision in one development platform.

The major steps of the inspection system are:

  • Learn or select a product
  • Localize the part with the robot
  • Move the part to perform the various inspection tasks

One of the critical steps is the precise localization of the part in the FANUC LR Mate 200iB robot world. First, the part is roughly inserted in a part holder. Once in place, the robot picks up the part using the gripper. Then, the robot goes through three different image acquisition stages: the optical character validation station, the random surface defect detection, and the dimensional measurements.

Optical Character Validation (OCV)

The purpose of this inspection is to verify that the part model and the batch number are good. The actual system is designed to evaluate characters made by pin stamping directly on the part surface. This kind of marking is difficult for an Optical Character Recognition (OCR)/OCV algorithm, because each character is made of dots instead of a continuous line, but the IMAQ OCR VIs work well for these types of characters.

The components of the acquisition system include an LED ring light from Boreal Vision and a high-resolution camera, JAI CV-M4CL, from JAI PULNIX. The camera is connected in the first Camera Link port of an NI PCIe-1430 board. Based on the actual camera field of view, the resolution for this inspection is 0.001 inches per pixel.

Random Surface Defect Detection

A large advantage of using a robot for this solution is the flexibility of moving the parts so that all aspects are inspected, even if the part has a complex shape. The robot is programmed to position the part in front of the camera. Multiple images are acquired as the part is tilted and rotated. During inspection, any abnormality is evaluated more closely to determine if it is a defect. For the classification of the defect, the criteria are based on the morphological analysis from the NI Particule Analysis VI. The kinds of defects detected include dents, scratches, die marks, grinding marks, pits, and discoloration.

To inspect possible defects, a second JAI CV-M4CL camera is used with an LED diffuse surface for lighting. The camera is connected in the second Camera Link port of the same NI PCIe-1430 board used for the OCV inspection. Based on the actual camera field of view, the resolution of this acquisition station is 0.001 inches per pixel.

Dimensional Measurement

The last inspection station gives a measurement precision of +/- 0.001 inches. This is evaluated with statistical tools such as Gage R&R and linearity analysis that compares values from a coordinate measuring machine (CMM). To reach such precision, the part is scanned through two high-resolution line scans at 90 degrees apart. Using these two orthogonal points of view, it is possible to compensate for the robot’s imprecision.

This acquisition device uses two DALSA P2-22-04K30 line scan cameras with LED backlights. The cameras are connected in the ports of the second NI PCIe-1430 board. The line acquisitions are triggered to obtain the same resolution as the field of view, which is 0.0005 inches per pixel.

This inspection system pushes the capability of automated inspection systems further into the domain of complex human inspection tasks. Using a robot gives enough flexibility to the system to process a number of part models. Because the change between products is mainly software, it is easy to perform small product batches.

The choice of LabVIEW as a development platform gives the software integration capabilities and optimizes multitasking to keep the processing time very short. At this moment, the targeted cycle time is always less than 12 seconds, but it is directly related to the amount of robot manipulation to perform on each part.

Author Information:
Charles Magnan
Averna Vision & Robotics
269 Prince Street
Montreal
Canada
Tel: 514-788-1420
Fax: 514-866-5830
info@averna-vr.com

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