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FREQUENTLY ASKED QUESTIONS

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GENERAL QUESTIONS

How long has Delta Tau been developing Motion Control Technology?

Dimitri S. Dimitri founded Delta Tau in 1976. By 1981, proprietary motion control hardware was being developed and by 1985, this was the primary focus of the company. In 1995, the bar was raised as the focus elevated to complete machine control.

How many people are employed by Delta Tau?

There are more than 180 people employed by Delta Tau Data Systems Inc. The employees are distributed throughout the world with offices located in the United States, the United Kingdom, Switzerland, Japan, and Korea.

What is the hardware product history?

The 2-Axis Multibus controller was the first product offered by Delta Tau in 1982. In 1985, the single axis MCC was added and in 1987, the 2-axis SMCC was introduced. The need for parabolic trajectories prompted the SMCC Parabolic in 1988 and in 1990, the first PMAC. The PMAC2 and MACRO were unveiled in 1994 and the Turbo CPU option became available in 1997.

Until 1997, the majority of product development was focused on board level products designed to meet the various card level form factors. Since that time, focus has shifted toward the enhancement of system level products. These products retain the open architecture qualities of the original hardware but are better packaged to ease integration, servicing, and expansion. The primary system product, and present Delta Tau flagship controller, is the UMAC. The UMAC has been in production since 1999 and provides more performance than any previous PMAC design. In 2001, Compact UMAC and QMAC were made available.

In 2009, the newest, most powerful controller, Power PMAC, was released and continues to be the focus of innovation at Delta Tau, along with developing software and peripherals to enhance the functionality of Delta Tau’s products.

Why use Delta Tau Products?

Delta Tau's PMAC and Turbo PMAC families of controllers justly have the reputation as being the most powerful and flexible in the world. Many people do not realize that PMAC controllers have many features that make them among the easiest to use as well. These features aid in the ease of use for both basic and more advanced applications.

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ABOUT PRODUCTS

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What kind of products does Delta Tau make?

Delta Tau’s products fall into eight general categories as follows.


Machine & Motion Controllers

These are controllers for controlling up to 256 axes with unparalleled built-in features for any motion control application, using a variety of output control signals and communication protocols.
Our controllers fall into three categories: PMAC, Turbo PMAC, and Power PMAC. PMAC is for low- to medium-end applications, Turbo is for medium- to high-end applications, and Power PMAC is for high-end to the most extreme applications.


Modular Rack Systems

Our modular rack system, the UMAC, permits the user to choose his or her own hardware composition, including controller, I/O, amplifiers, communications cards, and axis interfaces. Turbo and Power PMAC can be used as the controller for these systems. These types of control systems are the most diverse and flexible that Delta Tau offers.


Integrated Controller-Amplifiers (a.k.a. Intelligent Amplifiers)

These devices combine a controller with an amplifier in a single, enclosed package. This pairs the versatility and strength of PMAC with 1 to 8 channels of power amplification for controlling a wide variety of motor types in a convenient, enclosed, easily-wired package.


MACRO Ring Products

MACRO is a high-bandwidth, non-proprietary fiber optic or wired field bus protocol for machine control networks. Delta Tau provides controllers, amplifiers, and I/O products which can be used through this MACRO protocol.


Amplifiers

Delta Tau provides power amplification devices (a.k.a. “drives”) that have 1 to 4 channels for controlling a wide variety of motors via a wide variety of control signals and communications methods. We have amplifiers that receive Direct PWM signals and are used for driving commutated motors, and amplifiers receiving ±10 VDC used for controlling analog motors. These amplifiers come in several formats: board level PCB format, enclosed panel mount format, and 3U UMAC rack format.


Software

These are products for programming Delta Tau controllers, making human-machine interface GUIs, designing servo algorithms, analyzing your system, and more.


CNC Solutions

These are packages grouping human-machine interface console PCs and control panels for operating CNC milling and lathing applications.


Accessories

Accessories are optional pieces of hardware that can be interfaced with Delta Tau’s controllers and other products in order to add additional functionality.

What is the least expensive controller you offer?

Turbo PMAC Clipper.

What is the least expensive digital I/O product you offer?

This depends on the format you want. For UMAC, ACC-11E. For MACRO, ACC-11M. Our integrated controller-amplifiers also offer very cost-effective I/O expansion options. For board-level I/O without MACRO, ACC-34AA is also very cost-effective and flexible.

What is the least expensive product you offer for a 4-axis integrated controller and high voltage amplifier?

Geo Brick Drive.

What is the least expensive product you offer for a 4-axis integrated controller and low voltage amplifier?

• Turbo Clipper Drive (PC/104-stackable form factor)
• Geo Brick LV (panel mount form factor, slightly more expensive than Turbo Clipper Drive)

What is the fastest and most powerful controller you offer?

Power PMAC.

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CONTROLLERS

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How do I know what kind of controller to choose: PMAC, Turbo PMAC, or Power PMAC?

Delta Tau offers amplifiers that receive ±10 VDC analog and digital direct PWM control signals. Some of our intelligent amplifiers (e.g. Geo Brick, Geo Brick LV, Clipper Drive) can also control stepper motors directly, using a PFM signal. These amplifiers come in a very wide variety of current ratings, so please visit the Amplifiers or the Intelligent Amplifiers section of our website for more details.

• If you need to do custom, user-written servo algorithms, you should geta Power PMAC.
• If you need extremely computationally intensive kinematics (for example, kinematics with non-closed form, numerical, iterative solutions) or real-time PLC routines, Power PMAC is recommended.
• If you need to control more than 8 motors with one controller, you need at least a Turbo PMAC.
• If you need to control more than 32 motors with one controller, you need at least a Power PMAC.
• If you need to use Direct PWM, you cannot use Non-Turbo PMAC1; you need at least a Non-Turbo PMAC2.
• If your application requires very high phase, servo, or PWM clock frequencies (such as greater than 30 kHz) you need at least a Turbo PMAC, and possibly a Power PMAC, if you plan to use several motors with such high frequencies.
• If you want the smallest possible controller form factor, go with PC/104 or Turbo PC/104.
• If you exceed 8 axes in any system, you should probably choose UMAC or a MACRO solution.

How do I know what CPU speed to choose?

The baseline PMAC everyone should consider is the Turbo PMAC CPU with 80 MHz CPU speed. This will work for the vast majority of applications. However, some considerations must be taken for certain applications that may require faster processors as follows:

For Turbo PMAC, we would recommend the 100 MHz CPU in these circumstances:
• If you need to control more than 12 noncommutated motors
• If you need to control more than 8 commutated motors
• If you need a servo frequency that exceeds 8 kHz
• If you need block (programmed move) or segment rates that exceed 500 Hz

For Turbo PMAC, we would recommend the 160 MHz CPU in these circumstances:
• If you need to control more than 24 noncommutated motors
• If you need to control more than 16 commutated motors
• If you need a servo frequency that exceeds 15 kHz
• If you need block (programmed move) or segment rates that exceed 1000 Hz
• If you have two of the above 100 MHz requirements simultaneously

For Turbo PMAC, we would recommend the 240 MHz CPU in these circumstances:
• If you need to control 32 noncommutated motors
• If you need to control 24 commutated motors
• If you need a servo frequency that exceeds 20 kHz
• If you need block (programmed move) or segment rates that exceed 1.5 kHz
• If you have two of the above 160 MHz requirements simultaneously

We recommend Power PMAC if you have two of the above 240 MHz Turbo PMAC CPU requirements, or if you want to control more than 32 motors, or if you plan to write customized, user-written servo algorithms. If there is still any doubt regarding which CPU you need, we recommend that the prototyping is done with the fastest CPU available and then try running your application at lower speeds.

How do I know what kind of control signal output I need my controller to produce?

This depends on your motor as follows:

Digital Direct PWM signals control these kinds of motors:
• Brushless DC
• Permanent Magnet Synchronous
• Stepper (Direct Microstepping)
• AC Induction

±10VDC 18-bit True DAC Output signals control these kinds of motors:
• DC Brush
• Piezoelectric
• Galvanometer
• Voice Coil
• Hydraulic

±10VDC 12-bit Filtered PWM Output signals control these kinds of motors:
• DC Brush
• Piezoelectric
• Galvanometer
• Voice Coil
• Hydraulic

Step and Direction (PFM) signals control these kinds of motors:
• Stepper (Full Stepping)

Can you backup the controller software?

Yes. All integrated development environments used on the PC for programming PMAC provide for full backup to disk and restore from disk (including verification). Power PMAC even permits the configuration to be stored on a USB flash drive to be easily restored to PMAC if needed

AMPLIFIERS

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What kind of amplifiers does Delta Tau offer?

Examine the power requirements of your motor, often found on the motor’s datasheet or nameplate. Most likely, you want to choose an amplifier that produces the same or more power per axis.

If your motor’s datasheet or nameplate does not have the power rating, multiply the motor’s DC voltage [VDC] by its current rating [Amps] to get the power rating in kW, which can then be converted to HP if needed.

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ADVANCED HARDWARE QUESTIONS

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What servo frequencies can PMAC support?

The maximum safest servo frequency really depends on how many motors you want to control, and whether they are commutated. All PMAC CPUs can simultaneously close the servo loop on multiple axes down to 55us. Power PMAC specifically can close the loop to 20 us. The default setting is 440us. All PMACs can accept encoder feedback up to 20MHz

How does PMAC handle mechanical resonance?

The PMAC PID loop can accommodate a servo notch filter. A notch filter is an anti-resonance (band-reject) filter used to counteract a physical resonance. The user can also write his or her own custom servo algorithm in order to add additional filters if need be.

What are the limits to PMAC resolution and motor size?

The PMAC PID loop has no limitations in control resolution or motor power, while size is only a function of feedback sensor and motor amplifier choice.

What feedback types does PMAC support?

PMAC is designed to take incremental encoder feedback without any additional accessories. With the appropriate accessories, it can also take:
• SSI
• EnDat 2.2
• BiSS B/C
• HiperFace
• Tamagawa
• Panasonic
• Sinusoidal
• Resolver
• Interferometers: Sinusoidal and Parallel
• LVDTs, RVDTs, MLDts
• Potentiometers and other analog sensors
PMAC never uses a tachometer but requires only a single feedback sensor for a stable and robust PID.

What types of mechanical compensation does PMAC support?

PMAC provides position compensation for distorted mechanics, such as bent leadscrews, backlash compensation for gears or other mechanical backlash, and torque compensation to compensate for, for example, an uneven torque output from a motor with a bad bearing.

The PMAC PID loop is capable of performing what is commonly called 1D, 2D, and 3D leadscrew compensation. This technique allows for a table of corrections to be entered into PMAC as a function of motor position.

What is the purpose of the high accuracy crystal clock option? (PMAC and Turbo PMAC only)

Long-term velocity absolute accuracy (over a span where the perturbations average out) is limited chiefly by the crystal’s accuracy. For the vast majority of users, the standard 100 ppm tolerance is fine. The people who need really high accuracy, like the telescope controllers, feed in their own clock signal on an extra encoder channel and set up for external time base.

What is meant by filtered PWM outputs on the PMAC2-PC/104?

The filtered PWM technique is different from a low-resolution DAC IC. The filtered PWM uses the square-wave PWM outputs from our ASIC and runs them through a low-pass filter to turn the output into a gentle sawtooth wave. We recommend setting up the PWM for 30 kHz output; the low-pass filter has a 10 kHz breakpoint. The idea is that the output can still respond quickly to new servo commands at 1-5kHz, but have little ripple at the 30 kHz frequency.

This technique will work in many applications, but it will probably not be good for very high-bandwidth applications or very high-precision applications. It depends on the physical system not being fast enough to react to the 30 kHz ripple, and the resolution is not as good as our 16-bit and 18-bit DACs, and it is a technique our competitors have used for many years. Real DACs are essentially programmable voltage dividers, where the number sent to the DAC quickly selects which resistors above and below the output are to be used to control the voltage of the output. Once these have been selected, there is really no ripple in the output.

How much error in interpolation by ACC-51P and ACC-51E will be expected?

We designed the circuitry and algorithms of the ACC-51B and ACC-51E to make the errors they introduced so small that they could not practically be measured. We believe that we have succeeded in this. We have not been able to create a test that could show any errors created by the interpolator and not the input signals.

We use 14-bit A/D converters with ± 0.5 LSB non-linearity (integral and differential) specs when we really need only 11- or 12-bit resolution to get 4096 states per line. We use very high-quality gain-stabilized op-amps with precision components on the front end. Users who are concerned about accuracy should use the differential inputs we provide to eliminate possible offset concerns. The arctangent calculation used is fundamentally ratio metric and the analog parts that we use are lot-matched so that they have a strong tendency to vary in the same way; so variations tend to be canceled out in the calculation. The arc tangent calculation is accurate to 14 bits before it is truncated to 12 bits. Adding up the sources of error, we can get at most +/-2 LSBs of a 14-bit ADC, which is equal to +/-0.5 LSBs of a 12-bit ADC. Call this a potential 1 LSB error, to be conservative. At worst case, the other reading is only half of the full range: +/-1k instead of the ideal +/- 2k. In this worst case, we get a position measurement error angle (360 degrees = 1 line cycle ) whose tangent is 1/1000. In this range, tan (theta) = theta, so the measurement error is 1/1000 radian (where 2*Pi radians = 1 line cycle) or about 0.06 electrical degrees.

By contrast, the best specification we have seen for a sine/cosine encoder is 1% of a line cycle, 9 or 3.6 electrical degrees, over 50 times bigger. This is why we have been unable to isolate the errors in the interpolator from encoder errors and also why any interpolator errors are not important in practice. In operation, your accuracy is limited by encoder errors: magnitude mismatch between sine and cosine, harmonic distortion, signal offsets (particular Note that the newest Axis Interface card available (for Power Only), ACC-24E3, can perform x16384 interpolation

Under what circumstances is Dual-Ported Ram, DPR, recommended? (Turbo PMAC only)

DPR is recommended when the communication between the host and PMAC is more than 100 data items per second, as a rule of thumb. A data item is an imprecise term, but basically a line of communications, say X14 Y20 Z25 in a program, or a position or status request. With bus communications, it is the software overhead for a line of communications, not the number of bytes that limits the amount of communications you can do.

What does “electronic board identification” mean?

We install a small electronic device that provides a unique ID number that can be read by software. The main purpose was to permit third-party software vendors to use this as a dongle. The Power PMAC System Setup software and the UMAC Configurator software can use this ID number to identify and initialize your card automatically.

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PROGRAMMING AND MOVE SEQUENCING IN PMAC

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How do I program Delta Tau’s controller (PMAC)?

PMAC, Turbo PMAC, and Power PMAC all support the “PMAC Script Language,” a proprietary but very simple, English-based programming language. It uses standard program flow names, such as IF and WHILE, and even adds new commands whose meaning can be easily learned even by casual use. Additionally, the user can name his or her variables in the code editors, permitting one’s code to read like a natural language. The user need not memorize hundreds of variable numbers but can name them logically.
If the user does not want to use the Script language, he or she can program the vast majority of the application (except for motion programs)in the C programming language if using Power PMAC.

How do I create an interface between my host PC and the PMAC?

Delta Tau provides libraries in several languages (C/C++/C# and Visual Basic .NET) for writing their own PC-based applications which can interface with PMAC.

Can I run applications on PMAC in addition to the built-in control functionality?

Yes, but only on Power PMAC. Power PMAC permits you to either write your own separate applications to run on PMAC through Power PMAC’s Integrated Development Environment, or the user can integrate his or her own IDE (such as the popular, free Eclipse IDE) and download programs written in C++ or other language.

Can PMAC execute multi axis paths?

Using simple point specified programming; PMAC can describe any move through n-space of up to nine axes using combinations or six simple motion modes.
Delta Tau also offers its own threading library if the user wants to schedule these separate programs just as if they were a PMAC-scheduled task.

Can PMAC execute multi-axis paths or do I need to do some tricks to make that happen?

Using simple point-specified programming, PMAC can describe any move through n-space of up to 9 axes for Turbo PMAC or 32 axes for Power PMAC using combinations of six simple motion modes.
PMAC’s Linear and Circular blended moves are the fundamental modes of point-to-point interpolated motion. Vector speed and segment acceleration/deceleration is specified in the program. Circular moves allow for other conics such as elliptical interpolation generated from any plane normal orientation. Combinations of linear and circular can generate helical interpolation. A Rapid mode is provided that will not blend into other move modes. This is part of PMAC’s G-code capability. PMAC’s Position-Velocity-Time move mode provides for any generalized contouring programmed as a specified position at a specified velocity and time. PMAC also supports Spline modes Spline1, uniform non-rational spline and Spline2, non-uniform non-rational spline.

Are your libraries object oriented or code oriented?

We provide communication libraries for PCs using windows operating systems. These are written in C++, but do not make significant use of objects (we do not feel the objects make a significant contribution at this level of sending commands and evaluating responses). However, many users use these libraries in software that is heavily object-oriented.

Can PMAC use an automatic sequencing of moves?

Yes. In most computing environments used for motion control, the user program issues a command to start a move (with actual execution of the move handled underneath the program). It is then the responsibility of the user’s program to figure out when the move has completed, with some structure like: WHILE (MoveOver==0) WAITin order to sequence the execution of the program properly. However, in PMAC controllers, the controller’s operating system handles the sequencing of the moves and the associated calculations automatically. This means easier, simpler, shorter, programs that are easier to read as well.

What about single method of Programming moves?

Most motion controllers have completely different methods for programming point-to-point moves and blended or contoured moves. Also, there are completely different methods for programming moves that are a function of time and moves that are a function of a master position. In contrast, PMAC controllers do not have these constraints

Is the multi-block lookahead feature ever used for applications other than NC, and if so, can you give an example?

Any time it is difficult to create the minimum-time trajectory that respects machine limits, lookahead is useful. This task is difficult when you either have a complex path (such as in NV or semi-NC applications), or complex machine geometries (such as with robot arms). It may not ever be needed for point-to-point moves in a Cartesian system, but in many applications, even non-NC, with blended moves, lookahead is very useful.

When would the extended servo algorithm (ESA) be recommended? (Turbo PMAC only)

The ESA is useful mainly when you have low-frequency resonances in the system near or inside the bandwidth of the system. The ESA is not intuitively tunable like the PID, so it requires either an auto turner or an advanced user of controls to use. The old ACC-25 provided an auto tuner under DOS, but we have not had an auto tuner that runs under any version of Windows until PeWin32 Pro. The ESA comes standard on Turbo PMACs.

When would the user need to write a custom algorithm? (Turbo and Power PMAC only)

When the system is so highly nonlinear that PID does not seem to control the system adequately. Or, when the user wants to add many more digital filters to the servo algorithm than what is provided built-in in PMAC. For writing custom servo algorithms, we highly recommend getting a Power PMAC, wherein the user can write the algorithm in the C programming language or use MathWorksTM’s SimulinkTM and import the algorithm into PMAC with MathWorksTM’s Embedded CoderTM.

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Delta Tau Data Systems, Inc. © 2014. All rights reserved. USA Corporate Headquarters: 818.998.2095, 21314 Lassen St. Chatsworth, CA 91311