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RGB ENGINEERING |
HARDWARE DESCRIPTION COMPUTERIZED CROWNER RETROFIT SYSTEM
Some of the standard commercial components used in the various crowner retrofits are itemized below.
Computer: Due to fast pace technology advancements in the computer industry, the FFG computer specifications are likely to change frequently to keep current with these industry standards. The first crowner system sold in 1987 was a GE Cimstar IBM compatible AT computer and had only floppy drives. A typical system today is a Pentium III 700 Mhz with 64 Mb of RAM and a 20 GB hard drive. Since the roll grinding operation does not typically demand high speed CPU's, it is not necessary to supply cutting-edge high end computers, which helps keep the costs down. However, due to the potentially harsh operating conditions in a roll shop environment, the computer, monitor, and keyboard are all industrially rated. Although a standard "office" type IBM compatible computer can be used, the industrially rated models are recommended. More information can be obtained through RGB Engineering's supplier Cutler Computer.
Computer Interface Equipment
Some printed circuit boards and related peripheral equipment are used to interface the computer with the various external devices. Examples are: Keithley multifunction board # DAS-1802HR-DA, Keithley/Omega digital I/O board # PIO-12, Keithley/Omega 8 channel E/M relay board # ERA-01, and Cyber Research quadrature encoder board # 5312B (for precision infeed BEI incremental encoder). Also, for installations requiring a satellite work station, Cybex hardware is used to connect the remote monitor and keyboard to the FFG computer.
Carriage (Table) Encoder:
Some of the earlier systems simply used a 25 turn potentiometer driven off the existing bed crown rack to measure carriage position. These were replaced with an Allen Bradley optical encoder, and later by an Astrosystems encoder which uses a resolver as the transducer element. Another option is a Sequential Electronic Systems optical encoder. It is important to point out that all of these devices provide an absolute position reference for the carriage or table location. What this means is that no homing or initialization sequence is required after a power-down situation, which is not the case with incremental encoders. The advantage of the resolver or optical encoders verses the potentiometer is increased resolution and noise immunity, plus the ability to configure the resolution as well as other parameters to each application using software techniques.
LVDT Feedback:
Since the principles of the RGB crowner control require that the servo loop is closed around the mechanical actuator (either the Servo Cam Actuator or the Servo Linear Actuator), it is necessary to utilize an accurate displacement transducer. This is accomplished using a LVDT (Linear Voltage Displacement Transducer) supplied by Macro Systems. The advantage of a LVDT is its relatively small size, fine resolution, good repeatability, and reliable performance. The LVDT signal is conditioned using a LVDT conditioner board
Servo Drive & Motor:
A Reliance MAX 430 DC servo drive and Reliance/Electrocraft ES0643-33-004 motor provide the actuation to continuously operate the SCA or SLA mechanical system. The servo command voltage is proportional to the difference between the target signal as output by the computer, and the actual position as measured by the LVDT. A crowner summing board provides the logic junction between the LVDT conditioner and the computer, and outputs the appropriate signal to the servo drive.
Servo Drive Actuator
Whether the SCA (Servo Cam Actuator), or the SLA (Servo Linear Actuator), is used, chances are that it will incorporate a harmonic drive reducer as the primary transmission element. The advantages of this device are numerous, the most important being its compact size, high torque rating, and zero-backlash characteristics. These are supplied by Harmonic Drive Technologies.
Click on the headings below for more detailed information pertaining to the three control stations supplied with the computerized crowner system.
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