Robotics Case Studies
KUKA Robot Handles Ingress/Egress Seat Testing
(Other Application: Ingress/Egress Seat Testing)
Lear Corporation is one of the leading suppliers of automotive seats in the industry. The headquarters located in Southfield, Michigan contains the most sophisticated testing equipment for simulating car seat fatigue over an extended period of time. Terry O'Bannon, Lear's Senior Engineer for Biomechanics and Robotics, selected KUKA robots with the open architecture PC-based robot controller to replace all specific seat-testing equipment with a single multipurpose robotic manipulator. "We have the capability to measure the exact load and motion time histories of an occupant's interactions with a car interior with a high degree of precision and accuracy," Mr. O'Bannon says. "In voluntary motions, this can mean motions up to 15Hz. We looked extensively for a robot that had the flexibility to replicate whatever activity we could measure and KUKA emerged as the only viable candidate." The project is a cooperative development effort including engineers at Lear Corporation, KUKA Robotics Corporation of Sterling Heights, MI, and the University of Karlsruhe of Karlsruhe, Germany.
The goal of this project is to develop technology capable of replicating the motion and loading time histories of humans on automotive interior components, particularly seats. The initial focus of the device will be automotive ingress/egress; however, other applications such as jounce and squirm, rearward seatback fatigue, and knee loading will be developed. It is envisioned that additional uses of the combined path and load feedback will be found, such as deburring and polishing.
A system to control motion and loading of the interface with the seat is to be developed. The dynamic processing hardware requirements for the system are based on a design utilizing a KR 150 six-axis robot as a base and integrates a force/torque (F/T) sensor manufactured by ATI Industrial Automation which fits into a standard ISA PC slot. A rigid form representing a 50th percentile male will be attached to the end of the robot arm and F/T sensor.
A PCReflex motion analysis system in conjunction with a Body Pressure Distribution (BPD) sensing mat will produce three dimensional time-position histories of human movements and converted by software into a data file that the robot can use. The magnitude, location, and distribution of the load will be collected by the BPD system. The data will be collected at approximately 15Hz with no extraneous higher frequency components. The goal is to cause the robot to perform the smoothest movements possible.
Hardware and software design can be divided into three parts:
- A six-axis load cell interposed between axis six faceplate and the interface controller (KRC1). ATI's ISA-card based controller will be installed and integrated in the KRC1 controller.
- A device driver is developed to run in the robot kernel system's sensor task. This device driver is automatically loaded when the system boots up. All communication to the ATI ISA card and the KUKA KRL commands will occur through the device driver.
- A setup utility that will allow the user to specify the data files, collected by the PCReflex system, to be used and converted into KRL programs.
The system does not control position and force independently. Load data from the F/T sensor data is collected at each movement position the robot realizes. A history of actual positions and load values are collected for a given cycle. This data is compared to the data obtained from the PCReflex and BPD systems. Offsets in robot position are calculated for the next cycle. Since achieving realistic loads is the most important goal, the actual test path used for high cycle testing will not be the initial test path from the PCReflex system, but rather the initial test path altered to provide proper loading. Once the actual test path is determined, any variations in load from that point on will be small and arising only from the wear of the seat.
Future implementations of the project include utilizing six additional actuators controlled by the same robot controller to provide more realistic human motions. A special tool is developed to include the actuators, motors and a new compliant, jointed dummy known as the "LifeForm." To determine the amount of forces applied, motor current monitoring or additional F/T sensors will be applied to each of the actuators. Intelligent "neural net"-type algorithms will be used to achieve the best fit to the 512+ point BPD data set (per sample) using only the twelve degrees of freedom.
The system is capable of performing ingress/egress utilizing time based movements, sinusoidal movements to perform jounce and squirm, and constant load movements which allows the robot to alter the programmed path to achieve constant load values. All types of activities require a specific machine to perform and the KUKA robot is able to accomplish all of them. "This partnership has been very productive. KUKA's technical expertise, product and customer service are exceptional," according to Robert Stewart, Director of Lear's Product Life Simulation Department, and the man who originally patented the robotic application.