Bowling is a popular sport in the US with an estimated 70 million playing a game during the course of a year. As an umbrella organisation, the United States Bowling Congress (USBC) coordinates and ensures the technical perfection of the sport by extensive material and quality tests. The association set a milestone in 2010 with the high-performance bowling robot EARL (enhanced automated robot launcher), developed by ARM Automation. A PC and EtherCAT-based platform from Beckhoff ensure precise control of the robot.
Texas-based ARM Automation develops custom automation solutions for challenging industrial applications. Founded in 1993, the focus of the company is building robots for diverse areas of use: testing systems for orthopaedic implants, robots for handling nuclear materials, underwater robotics for fountain shows, packaging and assembly lines for PC production, mobile robots for warehouse automation and laser micro-machining tools in semiconductor manufacturing are some examples. The strength of the company is the development of custom solutions precisely tailored to the application. “ARM Automation was the only company that was prepared to construct the robotic solution that we needed,” said Neil Stremmel, managing director of the USBC national governing body.
Bowling robots simulate player behaviour
The development of EARL was primarily aimed to conduct research and test the products and materials used in bowling. “The assessment of the robotic data allowed conclusion of the correlation of ball movement and scoring,” explained Stremmel. “EARL has the ability to replicate virtually any bowler’s style, which will aid coaching staff by showing how conditions change as individual bowlers compete and how to adjust properly to the ever-changing bowling environment.” In order to eliminate the variation that a human bowler would introduce during the tests, the USBC had used an older bowling robot, Harry, in the past. “Harry did not offer sufficient repeatability and was cumbersome when adjusting test conditions such as differences in position,” is how Stephen Grupinski, president of ARM Automation described the initial situation.
Optimum synchronisation and precision of movement sequences
The EARL robot’s motion system consists of a linear axis to position the ball across the width of the lane, a 5-axis positioning robot, and a ball spinner and release mechanism installed on the gripper. With what may seem like a simple swing of the arm, when the robot grips the bowling ball and bowls it down the lane there are actually many parameters that need to be captured for a single test throw. A typical EARL test setting consists of the following:
* Orientation of the robot gripper relative to the bowling ball’s centre of gravity.
* Release point of the ball relative to the bowling lane (height, position relative to foul line, position across the width of the lane, loft angle and ball trajectory).
* Ball release and rotation speed.
“The biggest challenge overall for the mechanical and electrical control development was getting the timing of the bowling ball release,” said project engineer, Greg Wiese. USBC requires a speed of about 11 m/s for the ball release. If the system dithers 1 ms it equates to roughly a degree in difference for ball loft and 13 mm difference relative to the foul line. Any additional dither and the ball could be thrown into the ceiling or slammed into the bowling lane.
“Thanks to the distributed clock function of EtherCAT, we have achieved optimum synchronisation and precision,” said Joe Geisinger, CTO of ARM Automation. “This provides the precision to coordinate the external I/O with the control and position of the drives in the sub-millisecond range: the position of EARL’s end effector is communicated to the EtherCAT drives to determine the exact time at which the ball needs to be released. That position measurement is exceptionally precise, within 1 ms, and creates the correct loft of the ball each time. EARL is able to release a bowling ball under test within 250 μs of a scan of the position.”
Adjustment of the parameters within seconds
In order to tackle the tight precision requirements of this unique robot application, ARM Automation selected the EtherCAT and PC-based control system from Beckhoff. The USBC personnel configure the robot from the control panel, specifying 11 variables for different throws and adjusting speed and pick-up orientation. The robot can be configured in less than 10 seconds.
The control system includes a Beckhoff C6920 industrial PC running TwinCAT NC PTP software and Windows CE operating system. EtherCAT serves as the communication system for I/Os and drives. The operator interface is the Beckhoff CP6901 Control Panel with 300 mm touch screen.
EtherCAT integrated motion control and I/Os
ARM Automation has been an active member of the EtherCAT Technology Group for years and has developed EtherCAT slave devices. “We switched to EtherCAT as it offered us numerous advantages compared to traditional fieldbus systems,” explained Grupinski. “The well-known Ethernet physics, general performance data, our customers’ increasing interest in Ethernet-based networks as well as the ability to combine motion control and I/O in one network were important reasons for the change.”
“EtherCAT also allows us to diagnose the bus and detect broken links on the physical layer, determining easily exactly where the problem is located along the line,” said Geisinger. “Thanks to the open architecture of TwinCAT control software, it offers the flexibility of connecting existing SERCOS devices via a mini SERCOS fieldbus card which is installed on the C6920 industrial PC.”
Development of motion control based on TwinCAT
EARL needed the ability to gather inputs from a wide range of devices and communicate with the drives in a flexible environment. “TwinCAT System Manager and EtherCAT allowed us to do just that, pulling the different platforms together easily,” commented Geisinger.
The TwinCAT automation software coordinates the acquisition of I/O and position data from the drives, performs inverse kinematics, generates the next joint position commands and outputs the new position commands and data to the drives. ARM developed a kinematic transformation for EARL which is implemented in TwinCAT and is fed into the NC via the external set value generation. “We used the motion control functions of TwinCAT for this,” said Geisinger. “With NC PTP, we control the motion axes and constantly monitor the status of the EtherCAT drives.”
The safety mechanism of the bowling robot was also reworked, in that TwinCAT monitors all the safety devices. If anything goes wrong during operation, the drives are immediately disabled and the robot goes into a safe state until the system is reset. EARL is also enclosed in a protective cage with safety sensors, light curtains and safety relays installed to ensure optimum safety.
Optimised test situation, simpler handling
“We now have more options and better resolution for release height, trajectory, ball speed and loft,” said Stremmel. “Moving EARL and changing its settings is also much simpler and far more accurate than with our previous robot solution.”
“ARM is constantly combing the automation industry for new tools and innovative processes to optimise and enhance its solutions,” concluded Grupinski. “Our applications are inherently complex and often highly custom in nature, requiring flexible control platforms that can be configured on-demand to suit our customers’ needs. Beckhoff’s open and modular control architecture provides us exactly the right toolbox to develop solid customised solutions rapidly.”
For more information contact Kenneth McPherson, Beckhoff Automation, +27 (0)11 795 2898, [email protected] , www.beckhoff.co.za
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