Improving Performance And Lowering Maintenance Cost With An Electronic Motion Control System

Application Challenge

Sliding doors that must detect impediments and jams require frequent adjustment and are therefore expensive to maintain. Intelligent door controllers must respond to many different real-world conditions and inputs. They read badges, and alter their operation on a time schedule or in response to security alerts. How do we build an intelligent door controller that tracks long term changes in the environment, triggers reliably, and has a minimum of false positives?

Figure 1: Automatic Door Controller Overview

Application Considerations:

Motion Control Solution

In this application, we will use a PMD ION 500 Digital Drive to provide the door control. The ION will control a single rotary brushless DC motor with a position encoder that drives the door mechanism by a pulley system. The ION is software configurable, and monitors numerous variables including the current output to the motor, and the position error - the difference between the desired position of the motor and the actual position of the motor as measured by the encoder.

The host entry controller communicates with the ION 500 and directs the ION 500 to open or close the gate. All the critical motion control logic resides in the ION 500, leaving the host free to perform other entry control duties.

At the heart of the system, the ION is programmed to control the motor’s movement while tracking the position error and trigger a door retraction if the error is exceeded. The servo control algorithm used by the ION is a PID (proportional, integral, derivative) loop, which has the advantage that the motor’s position error is proportional to the motor torque command when set in this mode. By tracking the servo position error versus the motor torque command, fewer false positives are generated because the instantaneous torque output to the motor contains a lot of noise, while the door’s motion is stabilized by inertia.

To track long term environmental changes, the ION can be programmed to capture an entire trace of the door’s open and close move. The host controller uploads this trace data and adjusts the trigger conditions for increases in friction from dirt in the door’s tracks, while flagging motor output profiles that indicate friction is becoming excessive. All of this means that maintenance can be proactive rather than reactive, and can be provided only when needed.

Figure 2

Figure 2 shows where the position error went out of bounds due to an impediment. By using the ION’s built-in encoder tracking function, the designer can provide a very rapid response. In this application, the distance to cause a reactive trigger is equivalent to just 1/16” in travel distance. Traditional mechanical trigger distances are, at best, about 1" before halting.

To simplify setting everything up, we use Pro-Motion, a PC-based software tool that communicates with the ION. Pro-Motion has the ability to act as a 4 channel motion oscilloscope, providing over 50 different variables to choose from for analyzing and monitoring the operation of the door system. These variables can be used to show quality, repeatability, safety, PM status, remote troubleshooting and power consumption, amongst others.

Going Further

Many door motion profiles are a constant speed, or at best a trapezoidal profile. S-curve profiles, available as a standard feature in the ION, can be used to provide smoother and safer motion for intelligent doors and gates.

By using an electronic motion-control system, it is possible to standardize on a basic controller design, and then make simple variations in software to accommodate different door and motor sizes. This significantly reduces the complexity of designing solutions for different customers, and allows OEMs to lower the cost of documentation while improving quality.

ION Digital Drives provide high performance motion control supporting multiple motor types including DC brush, brushless DC, step, and microstepping motors, and are based on PMD’s Magellan® Motion Processor , which provides user-selectable profile modes including S-curve, trapezoidal, velocity contouring, and electronic gearing.

Click to learn more about the PMD ION Digital Drive.

Contact our customer support team at +1 781 674 9860 for more information including details on Developer’s Kits and application support. We would like to assist you in improving your motion system.