Nov 1 2013
Motion control is the key technological foundation of industrial automation. The control of motion is a key concern whether it is the path of a cutting tool, the motion of a product, the motion of an industrial robotic arm conducting seam welding, the movement of a parcel from a storage bin to a loading dock or any other application.
In manufacturing operations, it is essential to place an object accurately with the optimal amount of force and torque as well as knowing exactly where the object is positioned.
In order to control a machine process, it is important that the accurate object position is measured. Feedback comparison of the actual position and the target is a natural step for implementing a motion control system. This comparison causes an error signal that can be used for correcting the system hence providing accurate and repeatable results.
Design of Robotic Motion Control Systems
The basic structure of a motion control system includes the following:
- A motion controller for generating set points and closing a velocity or position feedback loop.
- An amplifier or a drive for transformation of the control signal from the motion controller to a high-power electric current or voltage presented to the actuator. The position and velocity loops can be closed internally resulting in highly precise control.
- An actuator such as an air cylinder, hydraulic pump, electric motor or linear actuator for output motion.
- One or more feedback sensors such as resolvers, optical encoders or Hall effect devices to inform the velocity or position of the actuator to the motion controller for closing the velocity control or position loops.
- Mechanical components for transforming the actuator motion to the desired motion including shafting, gears, belts, ball screw, linkages, rotational and linear bearings.
- The interface between the drives and the motion controller is highly critical when coordinated motion is needed since it must provide very tight synchronization.
Working of Robotic Motion Control Systems
Robust motion control algorithms are very important for the successful operation of mobile robots. Brenna D Argall (2009) explained the same in her paper titled ‘Learning mobile robot motion control from demonstration and corrective feedback’. Motion control algorithms determine the right action to take based on the present state of the environment.
The eyes of a robot are either vision systems or sensors and perform physical actions through actuation mechanisms. Sensors may be misleading at times. Developing motion control algorithms for mobile robots is a challenge even for simple motion behaviors.
The researcher has explained an approach termed the Learning from Demonstration (LfD) paradigm. In this approach, a behavior is represented as pairs of states and actions; more particularly, actions executed by a teacher and states encountered while demonstrating the motion behavior. The approaches for the motion control algorithm presented pairs demonstration learning with human feedback on execution. The kinds of feedback introduced in this paper range from binary indications of performance quality to execution corrections.
Products – Latest Advancements
Some of the most effective developments in motion control systems have been summarised below.
IRIS from Bot & Dolly
IRIS from Bot & Dolly combines the accuracy of modern robotics with the flexibility and reach required to capture not just one technical shot but every one of them. This is probably the easiest way to keep the camera where you want it to be, at the time where you want it to be, again and again.
IRIS is not just a platform for camera control it automates the entire set. Lights, actors and set pieces are moved in perfect synchronization, then you watch them matching your CG elements in real time. It just needs an intuitive touch interface to trigger hardware, automate cues and coordinate across departments. IRIS is developed for the professional filmmaker and combines with industry-standard software and hardware and includes features required for any professional film production such as real-time composite, playback, data management and rock-solid stability.
The features of IRIS are:
- Flexible configuration in which multiple robot models, linear axes, ceiling and floor mounts are used.
- It is designed to lift 110 kg, works three shifts a day and 365 days a year.
- Has a precision and repeatability of ± 0.06 mm at maximum speed, maximum reach and maximum payload.
- Real-time timeline scrubbing and speed attenuation helps the system react to actors and performances in real-time.
- Iris can coordinating multiple robots and external hardware measured to the millisecond.
- Has built-in support for real-time composing of CG and live video.
This giant sophisticated robot, IRIS made a spectacular public appearance at Cinegear 2012 at Hollywood’s Paramount Studios.
Video Courtesy of ElectricTV
SCOUT from Bot & Dolly
Scout from Bot & Dolly is as charming and as intelligent as IRIS but scrappier and faster. Scout enhances creative possibilities for tabletop and high-speed shots. It is quick, articulate and obedient hence suitable for live action and stop-motion cinematography.
The features of the Scout are:
- Multiple robots and external hardware cues can be coordinated at a millisecond scale
- ± 0.05 mm repeatability at maximum reach, speed and payload
- Is compatible with DragonFrame 3.0
- Follows nodal point and focus control calibration routines.
- Has built-in support for real-time composing of CG and live video.
Sources and Further Reading