Brake controllers are used to control braking systems. They can simply engage and disengage the brake, or control the speed of engagement, breakaway torque, and other variables. Brake controllers receive inputs from sensors which monitor parameters such as position, speed, torque, lockup, and slip status. Specifications for brake controllers include number of inputs, number of outputs, input types, and output types. The number of inputs equals the total number of signals sent to the brake controller. The number of outputs equals the total number of outputs used to control, compensate or correct the braking process. Input types for brake controllers include: direct current (DC) voltages, current loops, analog signals from resistors or potentiometers, frequency inputs, and switch or relay inputs. Output types include analog voltages, current loops, switch or relay outputs, and pulses or frequencies. Most brake controllers can also send inputs or receive outputs in serial, parallel, Ethernet or other digital formats which indicate a process variable. Some brake controllers can send and/or receive commands and inputs from information converted to an industrial fieldbus protocol.
There are three basic types of brake control systems: timing-activated, inertia-activated, and proportionally-activated. Timing activated brake controllers activate the vehicle’s brakes at a specific amperage output. Inertia-activated brake controllers are similar in design, but use a pendulum sensor to monitor the inertia of the vehicle’s deceleration in order to stop the vehicle at the same rate. Proportionally-activated brake controllers are equipped with accelerometers that measure the G-force of the vehicle’s stopping. All three types of braking controllers may include digital displays and diagnostics.
Brake controllers differ in terms of control techniques. Limit control establishes set points or limits that, when reached send a signal to stop or start a process variable. This off-on or bang-bang control is a fairly simple type of control. Linear control matches a variable input signal from a brake controller with a correspondingly variable control signal. Signal conditioning, filtering, and amplification can be used to produce the proper output control signal. Proportional, integral, and derivative (PID) control requires real-time system feedback. Feedforward control provides direct-control compensation from the reference signal. It may be open-loop or used in conjunction with more advanced PID control. Fuzzy logic is a type of control in which variables can have imprecise values (as in partial truth) rather than a binary status (completely true or completely false). Brake controllers that include advanced or nonlinear controls use algorithms such as neural networking and adaptive gain.