The ‘E’ Difference
A significant enhancement to the Curtis AC family, the ‘E’ models utilize a powerful dual-microprocessor logic architecture to cross-check critical circuits, I/O logic and software functions. The ‘E’ models ensure the highest possible functional safety performance level is achieved and provide full compliance with the relevant requirements of EN1175-1:1998+A1:2010 and EN (ISO) 13849-1:2009.
Other new features of the ‘E’ models include:
Enhanced 64MHz microprocessors improve motor control capabilities and provides 2-3 times the VCL execution speed.
Additional FLASH memory doubles the available VCL code space
Six additional VCL-configurable CAN 'mailboxes' significantly increases CAN master capabilities.
A controller-area network (CAN or CAN-bus) is a serial communications bus standard, allowing electronic control modules to communicate with each other within a vehicle. It was originally designed by Bosch specifically for automotive applications. CANopen is an international standard, and is a higher-layer CAN protocol for embedded control systems. CANopen has become the standard communication bus for most electric vehicle applications including forklift trucks and other materials handling vehicles. SAE J1939 is an alternate higher-level protocol that is commonly used for IC engine-powered vehicle applications, such as agricultural vehicles, construction vehicles, and automobiles. Most recent Curtis controllers adhere to the CANopen protocol and support the DS401 IO-device profile standard. Earlier Curtis CAN controllers adhere to the CAN2.0B standard, but run proprietary higher-level protocols called Curtis Nodes 1.0 and Curtis Nodes 2.0. Please note that SAE J1939-compliant variants of certain Curtis products are possible -please contact us for more information.
Curtis VCL -Vehicle Control Language - is an easy to use software programming language that allows vehicle developers to create customized functionality within the Curtis controller. It includes CAN communications control, I/O configuration and mapping, feedback-loop process blocks such as Proportional-Integrator -Differentiator (PID), and many other powerful functions. A comprehensive library of VCL functions allows the rapid development of unique functions and combinational or sequential logic. For multi-controller, CANbus applications, VCL enables the developer to configure the network and fully utilise all of the I/O available. VCL also allows the easy integration of Instrumentation and other 3rd party devices, and eliminates the need for expensive dedicated vehicle system controllers. Depending on the customer's preferences, Curtis offers customers VCL training, or we can provide a VCL development service, where Curtis engineers will work together with OEM engineers to create the custom VCL code required for each project.
Most Curtis AC controllers have Dual-Drive functionality built into the operating system as a standard feature. This feature is required for vehicles with dual fixed axle drive motors and a steered wheel or axle, such a 3-wheel counterbalance trucks. The traction controllers must provide an electronic 'differential' effect which prevents excess tire wear and allows the trucks to smoothly execute tight turns. The Dual-Drive function allows the traction controllers (one master, one slave) to proportionally reduce the relative speed of the inside wheel and increase the speed of the outside wheel as the truck corners. As the steering angle increases, the direction of the inside wheel is reversed, giving the truck the smallest possible turning circle. Curtis Dual-Drive provides smooth and efficient control of vehicle speed, acceleration and motor current while turning, and ensures safe operation in the event of a fault with either of the motors, controllers, or the steering angle feedback sensor.
IFO Vector Control
IFO Vector ControlIndirect Rotor Flux Orientation ( IFO) vector control is a superior technique for AC induction motor control. IFO Vector control manipulates the magnitude, frequency, and phase of the control variables. This technique provides superior dynamic response, higher operational efficiency and maximum torque generation than is possible when using simpler V/F or 'Slip' scalar control techniques . The mathematical model of an induction motor is complex. Using a series of reference frame transformations, IFO vector control simplifies the model to enable precise control of torque and flux, similar to a DC SepEx motor controller.
The figure below shows a typical diagram of indirect rotor flux orientation. The instantaneous 3-phase currents are transformed to the rotor flux reference frame, using rotor speed and slip frequency - which means that the motor currents are now observed from the viewpoint of rotating with the rotor flux. As a result of this transformation the currents, now in what is called the d/q reference frame, lose their sinusoidal nature and look like DC signals. In the d/q reference frame, q-axis current controls torque and d-axis current controls flux. If properly oriented, the torque and flux remain independent of each other, and the motor can achieve high efficiency and dynamic response.
Curtis AC controllers are unique in the industry due to their ability to 'auto-tune' - that is, to perform the motor characterization in place on the vehicle, with any brand of AC motor. If characterizing a traction system, ensure the drive wheels are off the ground and free to spin, and that the vehicle is safely blocked from accidental movement. If characterizing a hydraulic system, the motor should be unbolted from the pump and allowed to spin freely. Unlike some competing AC controllers, Curtis AC controllers will control any brand of AC motor. All that is needed is a Curtis hand-held programmer, and the completion a simple step-by-step procedure. However, Curtis has built up an extensive library of AC motors from all major manufacturers that have already been characterized. If your project is using such a motor, these settings can be applied from the library directly to the new application.
Electric Power Steering (EPS) is the method of controlling the steering of a vehicle by use of an electric actuator to turn the steered wheel. The advantage is the elimination of the steering column and/or associated hydraulics required for conventional power assisted steering. The system comprises 4 main elements:
A steering actuator, which is typically a small AC induction gear motor.
A steering controller to control the steering motor.
A steering input device which converts the operator's steering command into an electrical signal, which is received (often via CANbus) by the controller.
A steering angle feedback sensor is required so that the steering controller knows the steered angle of the wheel.
These steer-by-wire systems are essential for man-up vehicles such as stock-pickers, swing reach and turret trucks. Variants of EPS include EPAS - Electric Power Assisted Steering - where the steering column is retained, but the steering actuator acts on the column as a torque amplifier, reducing the effort needed by the operator to steer the vehicle. EPAS is the method of power steering used on many modern automobiles. Another variant of EPS is EoHPS, or Electric over Hydraulic Power Steering. In these systems, the steering input command is still received electronically (there is no steering column) but instead of an electric actuator, the steering controller drives the pump of a dedicated hydraulic power steering system