Although motion control is not often discussed in the context of I4.0, it is most vital in realizing some of its main objectives. In this article, case analyses of two Surface Mount Technology (SMT) P&P machines are compared.
Both machines are employed to perform highly challenging manufacturing tasks with excellent quality and high throughput. Both have a double gantry structure including Z-axis mounting heads that control the linear and angular component orientation, and both manage PCBs of the same size, where analogous small and high-density parts are positioned.
However, they vary significantly in their design, component per hour (cph) throughput, and motion approach. Machine “A” has a weight of 2,000 kg and a volume of 5.2 m3. By contrast, Machine “B” has a weight of just 1,200 kg with a volume of 3.9 m3 (33% less) and a higher overall cph throughput. How can the lighter, smaller, and apparently less “equipped” machine perform better than the “heavy-duty” machine?
What is “Pure Power”?
Smart servo drives that operate in systems where most of the consumed power is spent entirely to move the loads (“Pure Power”) offer a major benefit in the I4.0 ecosystem. Servo drives that have high-resolution servo and are highly responsive have the potential to correctly sense, monitor, and analyze machine movements, parts, and devices that are motion-controlled.
High-level, real-time sensing of torque, force, speed, and position provides an exclusive high-resolution magnitude and time-stamp data for each of the parameters. Using this data, it could be possible to use multi-dimensional plant analysis to offer useful information about the current condition of the machine and the analysis could provide indications for predictive maintenance, eventually minimizing failures and downtime
Figure 1. The role of Smart Control in I4.0
How is “Pure Power” Achieved?
1. Unique Gantry Control
In a conventional technique, complex centralized Gantry control architecture with a master controller and multiple drives for each axis would be used. Apart from physical complexity, such architecture is also susceptible to excessive field bus network loads.
However, Machine “B” was developed with a lean control philosophy where just two servo drives make a distributed Gantry control to function. There is a considerable overhead reduction without controller and load-mounted drives. Connectors, cables, cable guides, and heat-sinks which otherwise would use too much power are minimized or eliminated. This allows a real “Pure Power” operation.
Figure 2. Gantry operation with just two servo drives.
2. Pick-and-Place—It’s All in the Head
The lighter Machine “B” was also realized by decreasing the mounting head design. Light, ultra-small, and robust servo drives were directly attached to the moving XY axes. Therefore, the mounting heads use less power, as parasitic power needed by connectors, cable-carriers, and flexible cables is considerably minimized.
This enables the drives to be more sensitive and accustomed to the load itself. Precise “sensor-less” force control in the range of 0.3–10 N is one of the several problems faced by Machine “B” due to “Pure Power.” This was also realized with a current loop resolution ratio better than 2000:1 and with a broad bandwidth (as high as 4 kHz) and an extremely fast response time.
Figure 3. Ultra-compact 16 high-power servo drives.
3. Smart Motion and Servo Control
In order to achieve high performance with high throughputs, P&P machines should be highly dynamic. Intelligent servo drives fitted deep within a machine enable high-precision telemetry and analysis with high sensitivity and resolution, as well as rapid response time.
As illustrated in the following graph, consider motion effects within Machine “B” where oscillations of vertical head units (Z-axis) were correctly measured in response to high-speed coordinated motions along the XY plane. At high operational XY speed, system nonlinearity and intensive parasitic mechanical oscillations are apparent.
Figure 4. Advanced detection of parasitic behaviors. These can be overcome with smart control.
Machine builders mostly turn to conventional techniques to overcome such “undesirable” behaviors. They are usually addressed with the incorporation of heavy and bulky mechanics, eventually needing larger motors, gears, and higher power drives. This gives rise to a much heavier and less agile machine, as observed in Machine “A,” rendering it more difficult to reach high dynamics and throughputs.
An improved technique covers light and agile mechanics, supervises the important behaviors, and deals with the inevitable parasitic resonances with smart motion and servo control functionality like position-based gain scheduling, multidimensional plant identification, oscillation predictive signal-conditioning, high order filters, etc.
In addition to being more economical when compared to the mechanical fix, this approach also helps with focusing “Pure Power” within the system, as not much power is spent on bulky mechanics.
Utilizing “Pure Power”
High-Precision (Sensor-Less) Force Control
The potential of “Pure Power” to quickly and precisely monitor the mounting force of the placement process enables the detection of short- and long-term deviations in the mounting force that might be caused by mechanical component failure, mechanical wear-out, or bad batch of components with some mechanical inaccuracy.
There are two ways to manage force values and response:
- Real time: It is the immediate reaction to the monitored results in the drive level. The drive can gather, analyze, and respond to a considerable amount of data.
- Long term: The data is moved to a higher level controller, an upper-level host, or motion controller, where “Big Data” is examined by a devoted algorithm to find out any abnormalities or deviations.
Predictive Performance and Operation
Furthermore, Smart servo drives can track the short- and long-term load stability, control performance, and repeatability of the XY table. It is possible to track and record all “On the fly” variations of the Torque-Speed relation, response, the load, or appearance of “new” oscillations.
The gathered data can be examined in real time to identify future risks of mechanical wear-out, malfunctioning, and other mechanical issues. Thus, the drives can correct and/or avoid failures before any damage to the process or components, or before a machine stops working.
Figure 5. Ultra-small, high power servo drive: 80A, 80V.
“Pure Power” is realized as a “bonus” owing to intelligent motion and servo control, intended to optimize machine performance via control instead of (expensive) mechanical design. Since 80%–90% of the power used is “Pure Power,” high-resolution and high-sensitivity monitoring may be realized.
This article has demonstrated an innovative motion control technology to offer intelligent I4.0 capabilities to a P&P machine.
This information has been sourced, reviewed and adapted from materials provided by Elmo Motion Control Ltd.
For more information on this source, please visit Elmo Motion Control Ltd.