Jason Lin,
ADLINK Technology Inc.
As high-speed, multi-axis, and high-precision requirements expand for production technologies used in the semiconductor and optronic industries, motion controller cards implemented in production and inspection systems are developed with increasingly greater focus on precise timing control. Recent application trends indicate mounting reliance on sequence motion and absolute synchronization control technologies.
Motion Control
Motion control is vital for nearly all production processes. Motion control modules are invariably found in automated systems ranging from traditional machinery such as lathes, millers, and CNC-integrated finishing tools to semiconductor and optronic manufacturing equipment.
Many industry professionals have developed controller card solutions for PC-based applications to take advantage of the PC's open architecture and low cost. With the recent advancement of vision recognition technologies combined with motion controller technologies, a growing demand for motion-vision solutions has emerged. Innovation of these technologies has led to an increase in possible applications for the industrial computing industry. Most equipment developers opt for a controller platform consisting of an open architecture PC and operating system with proprietary core technologies. This gives a competitive cost-wise advantage over other solutions.
Motion controllers typically regulate the following trajectories:
Current Motion Control Solutions
An ASIC is an Application Specific (or Specialized) Integrated Circuit. Several motion controllers utilize an ASIC with motion functionality for low-level or high-level motion control. ASICs are typically thoroughly tested by the chip developer before reaching the market, offering high dependability, functionality verification, and fast execution of the command set. However, ASICs lack programmable capabilities, are not expandable, and cannot provide absolute synchronization. ASIC-based controllers are generally suitable for stepper, linear, and servo motors on non-synchronized trajectories.
With servo controllers requiring real-time functionality and accurate timing, recent DSP-based controllers use faster DSP chips with a RISC or CPU. High-speed memory is typically selected to enable programmability and to allow users to load sequence control code to the DSP. The entire control sequence can then benefit from real-time performance.
Serial control technologies for servo motors are also widely available. They generally use proprietary protocols to transfer data between the controller and the device being controlled (i.e. servo driver) for motion control or to send corresponding servo information back to the controller. Communication to exchange data and update motion is based on a fixed clock signal and will also enable real-time motion. Servo System Control Network, or SSCNET, is a serial servo control technology offered by Mitsubishi. SSCNET II, the second generation, offers real-time capability with cycle times of 0.888ms.
Sequence Motion Control Concepts
Machinery timing is vital for complex motion, especially multi-link systems such as the complex motion pick and place machine shown below.
In a pick and place process for chips, the suction pointer must accurately press against the top of the chip and pick it up with a motion synchronized with the machine arm. Machine movements rely on sequence motion control technology from the motion control card.
If the serial motion control system uses a PC to transfer movement commands to the controller card, axes will not be accurately synchronized and the system will not function in real-time due to the time it takes to send commands and operating system time delays.
As shown in the right-hand diagram above, if sequence motion control technology is not use, time delays caused by the operating system make synchronized motion control impossible. Hence, sequence motion control was developed to meet the needs of synchronized motion. Once code is compiled and sent to the DSP, the DSP will update cycle times based on the serialized motion data.
The following figure further explains this concept:
Why is Sequence Motion Control Needed?
Sequence control technologies provide the following benefits for real-time control applications:
Core Advantages
Motion control technologies are continuously evolving. Regardless of whether an ASIC or DSP is the core of the controller card, each technology has its own strengths and weaknesses. Real-time control requirements for high-end applications are a recent trend. Users can now take advantage of precise machine control by using sequence motion control technology via serial communication and a DSP. This solution offers improved controller accuracy and effectiveness and reduced back and forth motion cycle times for increased equipment production capacity.
