TurboTrack 2

[bernd]

<img src="/images/graemlins/confused.gif" alt="" /> Hallo,

habe mir CT6800HP mit TurboTrack 2 Treiber gegönnt <img src="/images/graemlins/smile.gif" alt="" />

Nun höre ich dazu Meinungen, die sich in zwei Lager spalten:

1.) Super Kombination - toller Kauf!

2.) Der TurboTrack 2 ist zwar gut, aber uralt und reizt die CTs lange aus...

Wer kennt sich da aus und schreibt mir seine Meinung dazu?

Danke Bernd

[pangolinlaser]

Hi Bernd,

As you may know, I designed the TurboTrack series, as well as other amps used in this industry, so I hope to present an informed opinion...

I designed the TurboTrack back in 1992, so by this standard it is an older design. However, it has been updated through the years. In 1994 we made some changes and it became the TurboTrack 2, and in 1999 or 2000, we added a "50K+ mod" which would allow it to drive GS scanners to around 40K and Cambridge scanners to 50K to 60K, depending on the scanners and mirrors.

As far as an analog servo is concerned, you can't get too much better than the TurboTrack 2. It does not have a notch filter, but it does have everything else including H-bridge drive which is not found on many other amps. And for the lack of notch, it does include several other filters to combat scanner resonances (which are almost not present on smaller scanners anyway).

I am not sure what you mean by "Super Combination". Can you please explain?

Regarding the lifetime of the TurboTrack and lifetime of scanners, the TurboTrack actually does not drive the scanner with as much "peak" current as the regular CB6580 amps from Cambridge, and so in that regard, the lifetime of the scanners should actually be greater with the TurboTrack.

Please feel free to ask any more questions. I will be glad to help if I can.

Best regards,

William Benner
Pangolin Laser Systems

[Hatschi]

Halli Hallo

Super Kombination = great combination

Where to get the newest version of TurboTrack?

Hatschi

[pangolinlaser]

Hi Hatschi,

If you already have a TurboTrack2, you can send it to LSDI (the manufacturer) to have the 50K+ mod installed. I am not sure what they charge...

Bill

[bernd]

Hallo William,

vielen Dank für deine Antworten!

Ich habe dich so verstanden, daß die Kombination CT6800HP + TurboTrack 2 OK ist und meine CTs sogar länger leben als mit anderen Treibern.

Welche Lebenserwartung haben denn die CTs überhaupt?

Schöne Ostern

Bernd

[pangolinlaser]

Hi Bernd,

The answer to your question is, "it depends". The problem that will show up with 6800s or most other moving magnet scanners is due to the bearings. The life of the bearings will be degraded if you put squarewave signals in of a constant amplitude, especially if the amplitude is small. Sometimes wear can be detected after only 12 hours of use!! And sometimes after a few months.

If you rotate the scanner shaft (with the power turned off) and it does not feel smooth, but instead if it feels "gritty", this is an indication of degradation in the bearings. Nevertheless, the closed loop servo can compensate somewhat and the appeance will be some inaccuracy in the projected imagery. Some applications are very sensitive to inaccuracy and for these applications, the scanners would have to be replaced or repaired. And some applications are not critical.

When I use the word "application" I also mean the perception of the viewer. Some people are very perceptive and they will highly object to problems caused by the bearings. Others will have a higher tolerance for slight inaccuracies or may not even notice.

So it really depends. Until recently I had one of the first sets of scanners built by Cambridge. The feel while rotating the shaft was VERY gritty, but it did still work acceptably.

Bill

[bernd]

Hallo Bill,

noch eine Frage: Auf Grund der Größe meines Wohnzimmers habe ich den Scannbereich auf ca. 25° (optisch) eingestellt. Ist es sinnvoll, den Scannbereich ab und zu zu verschieben, damit die Scanner nicht immer im gleichen Bereich arbeiten und sich an den Scanngrenzen kein "Grid" bildet?

Danke und Grüße Bernd

[jojo]

Bernd,

Ich würde mir deshalb keinen Kopf machen.
Ich weiss ja nicht, wie oft Deine Anlage im Wohnzimmer läuft, aber das Problem der
Lebensdauer tritt doch eher im Dauerbetrieb auf.
In der Industrie laufen CTs im Dreischichtbetrieb rund um die Uhr.
Da macht sich die Lebensdauer der Lager bemerkbar, aber sicherlich NICHT im Hobbybetrieb.

[pishtak]

Hi Bill,

Can you shortly explain what is the purpose of using H Bridge to drive
Galvos ? In Audio amplifiers it is used to have higher voltage swing at output load.

Regards

pishtak

[pangolinlaser]

Hi Pishtak,

H bridge is used in a scanner amplifier for a similar reason as you pointed out for use in audio amplifiers. It is similar, but not the same.

With an audio amplifier, the speaker has a "characteristic impedance" -- lets say 8 ohms. The RMS Power that you can drive into the speaker is highly (and almost exclusively) dependent on the voltage that is coming out of the amplifier. It is common for audio amplifiers within a stereo to have rail voltages of +/-35 volts or so. With a normal push-pull topology (no H-bridge) you can drive perhaps +32 to -32 volts into the speaker. This will give you an RMS Power of roughly 64 watts. By using an H-bridge, you can almost double the voltage that is delivered to the speaker, while keeping the rail voltage the same. In the case of an H-bridge, you can deliver perhaps +60 to -60 volts into the speaker. Since power is proportional to E squared, the result is over 200 watts RMS.

In the case of scanners, there is a different game. First, scanners work off of current, not voltage. Actually speakers do too, but that is another (longer) story as to why people don't consider a speaker to be a current device. Second, scanners generally have a "peak current" that you can not exceed for one reason or another (you blow the coil, demagnetize the magnet, or just heat it up to the point where it becomes useless).

Lets consider a Cambridge 6800 which has a coil that gets up to 6 ohms when it is hot, and an inductance of roughly 100 microhenry. The optimum peak current for a Cambridge 6800 is 4 amps. When you deliver 4 amps into the 6800, it will produce 100000 dyne centimeters of torque. To find the rail voltage needed to develop 4 amps in a 6 ohm (hot) coil, it is simple math: E=I*R. So 4 * 6 = 24 volts. This means that you need to deliver +24Volts to produce +4Amps. If you use rail voltages of +/-28V, this looks easy to do and yes, with a rail voltage of +/-28 volts, you will *eventually* develop 4 amps in the coil. The question is when will you develop that 4 amps?

BUT, remember when I said it is a different game? And remember when I said scanners are operated by current? Well, there is "inductance" involved, and that inductance will dictate the rate at which you can produce this current, and thus the torque. The inductave time constant of a 6800 is T=L/R = 100/6 = 16 microseconds. Since it takes five time constants to develop the total current in the coil, this means that with with 28 volt rails (24 volts delivered to the scanner), it will take 5*16 microseconds = 80 microseconds to develop the full 4 amps in the coil, and thus, to produce the full 100000 dyne centimeters torque. When scanning at 30K, this generally means a small angle step response of 300 microseconds. So you can see that 80 microseconds is a pretty large portion of the total 300 microsecond time for a full step.

Now lets take a look at what happens if you use an H-bridge. If you have an H-bridge, you can nearly double the voltage to the coil -- perhaps +/-45 volts to the coil. If you put the full 45V across the 6 ohm (hot) coil, you can possibly produce 7.5 amps in 80 microseconds. But you don't need 7.5 amps -- you only need 4 amps. But by using the higher rail voltage, it allows you to develop the 4 amps faster. In fact, you can develop the complete 4 amps peak in probably 10 microseconds. So 10 microseconds is a much smaller number when compared to a 300 microsecond small step. Using an H-bridge with a 6800 will allow you to do 30K scanning "better" than not using an H-bridge. But perhaps more importantly, using an H-bridge will allow you to do more -- go 60K if you want. 60K means 150 microsecond small steps. Even at 150 microseconds, 10 microseconds is a pretty small portion of that time. That is why on the latest 6215 scanners from Cambridge, which are capable of going 60K, they use an H-bridge on the driver. Note that these same 6215 scanners can only go 30K when using a normal push-pull (no H-bridge) driver.

So, bottom line -- while with speakers, an H-bridge gives you more power, with scanners an H-bridge can possibly give you more speed, because you can overcome the inductance of the coil faster. However, that doesn't mean that if you had infinitely high rail voltages you would be able to scan infinitely fast. With scanners there are several factors which ultimately limit the speed. One HUGE factor is "resonances" which exist within the system, with the primary resonance being the torsional resonance of the rotor-mirror system. In today's scanners it is these resonances which ultimately limit the maximum speed at which you can scan.

Pangolin has developed a scanner technology with literally zero torsional resonances and we currently have three pending patents on this technology. Once the patents issue, or possibly slightly before, we will introduce these scanners onto the market. Note that even our scanners are not a magic bullet which allow infinite scanning speed. We have overcome the resonance problem, but then there is another problem in our system which ultimately limits the speed, and in our case this next problem is "heat".

I would liken this to a car. Lets say you have a car and you want it to go faster. You put in a bigger engine, and then you blow the transmission. Next you put in a bigger transmission, and you blow the differential (rear-end gear-box). Next you put in a bigger differential and you start blowing tires. So you put on bigger tires, but now you need a stronger suspension in the car to hold it all together, so you do that too. But now the whole car is heavier... So whatever problem you overcome, there will be another problem waiting for you... Nevertheless, it is a fun challenge to work on this kind of problem.

Bill