By knowing the application requirements, design engineers will be best served when selecting the appropriate type of actuator.

“Pay special attention to environmental conditions in which the actuator will be operating,” says Gary Rosengren, director of engineering, Tolomatic. “Conditions that will subject the actuator to high vibration, particulates, water or chemicals will need to be factored into the selection process.”

In addition, Rosengren adds, the system resolution and thrust requirements will determine whether a stepper or servo motor and drive technology should be used.

An actuator, like any other component in a motion control system, must work efficiently with all components to achieve the best performance. Understanding all the application variables will achieve the best actuator solution for the job and avoid over- and under-sizing. It will keep costs under control and it will reduce downtime caused by under-performing components.

Unintentional Stalling Prevention

Unintentional stalling is often the result of an incomplete understanding of the application parameters, according to Rosengren.

To make a successful component selection, users need to be aware of all of the operational possibilities which may occur.

“Some stalls can be prevented by incorporating intelligence such as vision or advanced sensors that detect obstructions before equipment collides,” Rosengren reports.

Al Wroblaski, product manager of industrial linear actuators at Thomson, a mechanical motion technology company considered to be the inventor of anti-friction linear technology, recommends doing an upfront mapping of the actual load in the machine application with a load cell and acquisition software.

Wroblaski also notes that unintentional stalling can be prevented by ensuring that the adequate amperage is supplied to the actuators in extreme cold applications. In DC actuators, to prevent a voltage drop that could cause stalling, ensure that the proper wire gauge is specified.

“In guided load applications, unintentional stalls can occur when something changes or fails in the guided load system,” adds Rosengren. “It is important to design a well thought out guided load system that will not be subjected to component fluctuations throughout operation.” 

RS-485 vs. CANopen

RS-485 is a simple, low-cost protocol that allows a master controller to communicate with several devices. However, the protocol doesn’t have the high bandwidth for tightly coordinated automation decisions such as updating a motion profile trajectory. CANopen is a more capable communication bus that requires additional cost to implement into a controller.

Consider the number of devices, or nodes, that will be needed on the network. Normally RS-485 is limited to 32 nodes, but it can be expanded past 32 with the addition of a repeater, which forces additional cost. CANopen allows up to 127 nodes, depending on the bus traffic, and operates at a higher speed than RS-485, allowing for deterministic update rates that enable motion control over the bus.

“Another application consideration is data collision.” says Rosengren. “The CANopen protocol specifies a means for data collision avoidance and detection, but this isn’t always the case with RS-485.”

Data collision occurs when two or more nodes send data at the same time. This typically happens in a high activity environment.

For RS-485 to have data collision avoidance and detection, it must be implemented with a communication protocol. RS-485 specifies a physical (electrical) layer and not a communication protocol, such as Modbus and Profibus. When designing a RS-485 network, it is important for all devices on the network to have the same communication protocol.