Linear actuators are mechanical devices that transform electrical energy into mechanical energy to perform repetitive actions that require linear motion. For example, linear actuators can be used in an assembly plant to place caps on bottles, automatically stamp or label mail, cut glass, place chips on circuits, test various buttons or touch areas on electronic devices, and perform a wide variety of other tasks known in the art.
Some tasks may require one or more linear actuators as illustrated in U.S. Patent Publication No. 2010/0133924 and U.S. Patent Publication No. 2012/0043832, the entireties of which are incorporated by reference herein. Typically, a low cost linear actuator has a single pole and a single 24 or 48 volt DC coil linear motor. Less movement occurs in typical low cost linear actuator designs because there is typically only one coil. Consequently, these designs typically provide a limited stroke distance or value (e.g., maximum stroke of 150 mm).
Long-stoke linear actuators have a magnet housing with multiple magnets and a coil assembly attachable to it. The coil assembly may have any number of coils and the magnet housing may have any number of magnets. The magnet housing can be configured to be coupled to a wide variety of configurations of magnets and coil assemblies to deliver a pre-determined magnetic field. For example, a magnet housing can be manufactured for a 3 coil assembly and a magnet housing can be manufactured for a 6 coil assembly.
Linear actuators may include a number of features (e.g., programmable positioning, speed, or force, and/or the ability to verify that one or more tasks have been successfully completed) which have great utility in automation as well as a wide range of other applications. A controller can be used to receive feedback from sensors and provide signals to the linear actuator to control these features. For example, a linear encoder sensor can send information regarding the current position of a linear actuator piston to the controller and, the controller can send a signal to the linear actuator coil to reposition the linear actuator piston.
A controller can be a single and multi-axis controller for single or multi-axis linear actuators. Controllers can receive feedback from sensors and programming instructions from a user. Controllers can include or be used together with standalone amplifiers and stepper driven drivers. Controllers include a memory and a processor and can be programmed by mnemonic type command instructions via an RS-232 interface into the memory, e.g. NVRAM, that allows code to be stored in non-volatile RAM, which is then used to enable movements to be made by the linear actuator in different modes. Controllers may require no supplementary software.
Controllers are typically mounted in junction boxes or within motor control centers. Cables typically connect the controller to the sensors within the linear actuator. Cables also connect the controller to the coils within the linear actuator housing. For example, a long-stroke linear actuator with having an encoder reader (sensor) typically has 8 wires (A+, A−, B+, B−, I+, I−, 5 volts DC, and a ground) traveling from the linear actuator piston. A three coil design multi-pole, long-stroke linear actuator also has six separate power lines that provide separate voltage/current to each coil set. This makes for a large amount of cabling between the linear actuator and the controller. The setup becomes even more complicated because encoder signal lines are low power and must be isolated and shielded from coil power lines. This means that at least two separate bundles of cables must be used. This setup can be expensive, and is also prone to failure given the number of cables and cable connections. This setup can also result an increased latency between the sensor feedback and actuation of the coil due to the distance between the remotely mounted controller and the linear actuator.
Accordingly, a need exists for methods and apparatus for reducing the cost and the complexity of the cabling between the controller and the linear actuator. A need also exists to reduce the risk of failures and improve the response time between the controller and the linear actuator.