Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On 2 August 2010 05:49, Jon Elson el...@pico-systems.com wrote: Well, if you made tiny jogs in each direction, small enough so that they didn't cause a following error, then the servo amp would go live and all would be fine. You _could_ do it explicitly in the HAL file, before the pins are linked and before the axes are enabled (which would avoid following errors.) Something like: setp hm2_7i43.0.gpio.001-out true # amp enable pin setp hm2_7i43.0.pwmgen.00.value 0.05 setp hm2_7i43.0.pwmgen.00.value -0.05 net pwm-output pid.0.out = hm2_7i43.0.pwmgen.00.value net Xenable axis.0.amp-enable = hm2_7i43.0.gpio.001-out -- atp -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Andy Pugh wrote: On 2 August 2010 05:49, Jon Elson el...@pico-systems.com wrote: Well, if you made tiny jogs in each direction, small enough so that they didn't cause a following error, then the servo amp would go live and all would be fine. You _could_ do it explicitly in the HAL file, before the pins are linked and before the axes are enabled (which would avoid following errors.) Something like: setp hm2_7i43.0.gpio.001-out true # amp enable pin setp hm2_7i43.0.pwmgen.00.value 0.05 setp hm2_7i43.0.pwmgen.00.value -0.05 net pwm-output pid.0.out = hm2_7i43.0.pwmgen.00.value net Xenable axis.0.amp-enable = hm2_7i43.0.gpio.001-out It must be done EVERY time the servo amp comes out of Estop. Disabling the amp sets the shutdown latches, and they have to be cleared EVERY time the amp is enabled. So, it can't be done before the amps themselves are enabled. It could be done when the amps are enabled (F1) but before the positioning loop is enabled (F2). I don't know if the above code will work for other reasons. It sets the PWM output VERY rapidly to the two polarity outputs. My code waits a full servo cycle before flipping to the other direction. That much time isn't needed, but you need to make sure at least one 5% wide pulse gets to the amp before you reverse it. Anyway, the above scheme would only do this during program startup, not every time you come out of E-stop. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On Sat, 31 Jul 2010, Kirk Wallace wrote: Date: Sat, 31 Jul 2010 21:46:44 -0700 From: Kirk Wallace kwall...@wallacecompany.com Reply-To: Enhanced Machine Controller (EMC) emc-users@lists.sourceforge.net To: Enhanced Machine Controller (EMC) emc-users@lists.sourceforge.net Subject: Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller On Sat, 2010-07-31 at 23:15 -0500, Jon Elson wrote: I know a number of people are using my PWM servo amps with Mesa controller boards. A feature of the dumb control logic on the servo amp is that it needs a short pulse in each direction to clear the shutdown latches on the FET driver chips. I built a little state machine into the driver to accomplish this, it is called the bootstrap parameter. It gives 5% duty cycle pulses in each direction on consecutive servo cycles, then goes to normal operation as commanded by the PWM input. If you don't do this, the drive can act like it is disabled until you attempt to move it both directions, then it will suddenly come live. So, has anyone written up a couple lines of HAL to do this, or how else do you solve the problem? (This applies only to the brush version of the servo amp, the brushless amp has a CPLD that manages this function.) Thanks, Jon Is this the high side bootstrap that creates the high side FET gate control voltage? This has always seemed to create more trouble than it is worth. Why not have another supply with the proper voltage and not have to deal with the bootstrap? Or use N and P FET's? I know the bootstrap method may save a portion of the parts cost, but for the product quantities for the CNC market, it doesn't seem worth it. I may be showing my ignorance here. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA Yes, this is the high side gate supply voltage. We have PWM amps that use separate supplies (7I27) and bootstrap supplies (7I30,7I29, 8I20). The advantages of the bootstrap supply are that it is cheaper and has fewer components. Supplying the top MOSFET gate power is awkward because the power supply is floating on the high side MOSFETs (or IGBTs) source electrode. This source electrode is switching at ~10 to 100 KHz with full motor bus voltage so the supply must be isolated for the full motor power supply voltage switching with a high frequency square wave. Because the high side gate power supplies are referenced to each MOSFET source, each high side MOSFET gate driver needs a separate supply (so a HBridge needs 2 separate high side gate supplies and a 3 phase bridge needs 3). If separate high side gate supplies are used, this adds considerable cost and complexity (and lowers reliability). Its certainly possible to have a high voltage transformer coupled isolated DC supply for each high side gate driver (like our 7I27) but whether its a good design decision is open to arguement. The disadvantage of boostrap PWM is than you cannot have 100% output duty cycle. Normally you will be limited to about 95-98% (depending on switching speeds, PWM rates, etc) This is because each HBridge legs lower MOSFET must turn on for some portion of time to charge the boostrap capacitors. For 3 phase drives it is possible to get 100% output from a bootrap supplied bridge at medium-high motor speeds (where you may need the 100%) because the normal phase rotation will charge the bootstrap capacitors. Peter Wallace Mesa Electronics -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Kirk Wallace wrote: Is this the high side bootstrap that creates the high side FET gate control voltage? No, not really. That may be where John Kasunich got the name to call it the bootstrap parameter of the driver (I didn't supply that name to him). These servo amps do have such a bootstrap scheme to supply the high side bias. But, what this one pulse each direction thing does is to reset the shutdown latches in the IR2113S FET driver chips. I would have been fine without such a latch, but it is a feature of the chip, I can't change it. When the positioning loop starts up, EMC may decide the motor needs to move in one direction to null the error, and if the amp hasn't seen at least one tiny pulse in the opposite direction, it won't produce any output. This has always seemed to create more trouble than it is worth. Why not have another supply with the proper voltage and not have to deal with the bootstrap? Or use N and P FET's? I know the bootstrap method may save a portion of the parts cost, but for the product quantities for the CNC market, it doesn't seem worth it. I may be showing my ignorance here. I really don't see it as a problem. It does mean you can't go to 100.0% duty cycle, somewhere around 95% is a good limit. I did put a high-side supply on my first generation servo amp. It required winding a custom transformer, and having a power driver circuit for it. The reason is this is not just a fixed voltage a little above the motor supply voltage, it is a FLOATING supply that tracks the source terminal of the high-side FET. So, this whole power supply swings the entire range of the motor supply in 200 ns or so, every time the transistors switch. And, you need TWO of them, one for each high side transistor. The capacitive coupling between the drive winding and the output windings causes problems with blowing out the driver chip, so isolation of the windings is needed. A TOTAL pain! So, that's why these bootstrap circuits are so popular, they work and are elegantly simple. Using P-channel FETS would work, and avoid the loating supplies, but. I use 40 milli-Ohm transistors in my drives. Try to find a 200 V 40 mOhm P-channel FET. They don't exist. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Gene Heskett wrote: By normal fab techniques, there is not a P type FET, they all need a + signal on the gate to turn them on. That said, a separate + and - 5 volt supply winding whose center tap rail is common to the FET's source rail is the much preferred method of deriving the high sides on pulse drive voltage. I generally detest the bootstrap methods because the voltage so developed isn't as dependable (IMO). The capacitors that are the isolation/storage elements of a bootstrapped circuit are usually common electrolytics, with their failure rates being 100x that of the semiconductors involved. When a semiconductor in one of these circuits fails, there is about a 100/1 chance a failing capacitor was the first circuit fault. 5 V isn't enough bias, I use 12 V. I use a 0.1 uF SMT ceramic cap for the bootstrap capacitor. That is plenty of charge as it is recharged every 20 us. I have never had one of these caps fail. The FET driver chips have an undervoltage lockout, so it will not even turn on if the supply is too low. If you go to 100% PWM duty cycle, this will eventually happen, and the drive handles it gracefully and just goes limp. Hitting E-stop and resetting it clears the trouble. Driving a power FET is almost a separate chapter in the design tomes, as the gates in high powered versions of these can represent quite a large capacitance just from the sheer size of all the actual gates in the devices, with figures well above .05 microfarads, some of which gets amplified by miller feedback effects as its turned on and off. In order to minimize the junction heat during the on-off or off-on transitions, the driving waveform must be very fast, and capable of charging or discharging that large capacitance in nanoseconds. That implies a driver capable of several amps with rise fall times of 10 or so nanoseconds. Many a power FET aka HEXFET has been destroyed by drivers that take a microsecond to make that nominally 9 volt swing. 5 volt + to fully turn them on, and about -4 to turn them absolutely off in the shortest time. I'm with Kirk on this one, we are a relatively small market, one that will never find a profit in 'simplicating' the right way out of a circuit, so it should be done right, not to consumer grade standards but better. I figure that I'd have to raise the price on my servo amps by $100 each to cover the cost of winding the transformer by hand, and providing the extra components for it. That's completely out of the question to solve a problem that doesn't even exist. Despite the name of this PPMC driver feature, it actually has NOTHING to do with bootstrap power supplies. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
I used these in the past along with some IRFZ44N http://www.irf.com/product-info/datasheets/data/irf4905.pdf Regards, Alex On 8/1/2010 8:27 PM, Jon Elson wrote: Kirk Wallace wrote: Is this the high side bootstrap that creates the high side FET gate control voltage? No, not really. That may be where John Kasunich got the name to call it the bootstrap parameter of the driver (I didn't supply that name to him). These servo amps do have such a bootstrap scheme to supply the high side bias. But, what this one pulse each direction thing does is to reset the shutdown latches in the IR2113S FET driver chips. I would have been fine without such a latch, but it is a feature of the chip, I can't change it. When the positioning loop starts up, EMC may decide the motor needs to move in one direction to null the error, and if the amp hasn't seen at least one tiny pulse in the opposite direction, it won't produce any output. This has always seemed to create more trouble than it is worth. Why not have another supply with the proper voltage and not have to deal with the bootstrap? Or use N and P FET's? I know the bootstrap method may save a portion of the parts cost, but for the product quantities for the CNC market, it doesn't seem worth it. I may be showing my ignorance here. I really don't see it as a problem. It does mean you can't go to 100.0% duty cycle, somewhere around 95% is a good limit. I did put a high-side supply on my first generation servo amp. It required winding a custom transformer, and having a power driver circuit for it. The reason is this is not just a fixed voltage a little above the motor supply voltage, it is a FLOATING supply that tracks the source terminal of the high-side FET. So, this whole power supply swings the entire range of the motor supply in 200 ns or so, every time the transistors switch. And, you need TWO of them, one for each high side transistor. The capacitive coupling between the drive winding and the output windings causes problems with blowing out the driver chip, so isolation of the windings is needed. A TOTAL pain! So, that's why these bootstrap circuits are so popular, they work and are elegantly simple. Using P-channel FETS would work, and avoid the loating supplies, but. I use 40 milli-Ohm transistors in my drives. Try to find a 200 V 40 mOhm P-channel FET. They don't exist. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Peter C. Wallace wrote: Yes, this is the high side gate supply voltage. Well, no, despite the name, it actually has nothing to do with the bootstrap supply. Our amps DO, indeed, have such a supply. But, this one pulse each way thing is needed to clear the shutdown latch in the IR FET driver chip. The bootstrap supplies are kept charged any time the PWM signal is at off, so that's every PWM cycle. I know Anders Wallin in Finland is using my servo amps with the Mesa controller, but I can't find a copy of his hal files to see if he did anything special to solve this problem. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Alex Joni wrote: I used these in the past along with some IRFZ44N http://www.irf.com/product-info/datasheets/data/irf4905.pdf This is a 55 V transistor. At 200 V they are at least unobtainable at reasonable cost. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On Sunday, August 01, 2010 05:19:09 pm Jon Elson did opine: Gene Heskett wrote: By normal fab techniques, there is not a P type FET, they all need a + signal on the gate to turn them on. That said, a separate + and - 5 volt supply winding whose center tap rail is common to the FET's source rail is the much preferred method of deriving the high sides on pulse drive voltage. I generally detest the bootstrap methods because the voltage so developed isn't as dependable (IMO). The capacitors that are the isolation/storage elements of a bootstrapped circuit are usually common electrolytics, with their failure rates being 100x that of the semiconductors involved. When a semiconductor in one of these circuits fails, there is about a 100/1 chance a failing capacitor was the first circuit fault. 5 V isn't enough bias, I use 12 V. Does that not add to the stored charge, lengthening the turnoff times? I use a 0.1 uF SMT ceramic cap for the bootstrap capacitor. I TBT was thinking along the lines of a small electrolytic in order to cover the frequency range of the VFD at slow speeds. Those should never be discussed in the same book as dependable. That is plenty of charge as it is recharged every 20 us. I have never had one of these caps fail. The FET driver chips have an undervoltage lockout, so it will not even turn on if the supply is too low. If you go to 100% PWM duty cycle, this will eventually happen, and the drive handles it gracefully and just goes limp. Hitting E-stop and resetting it clears the trouble. Driving a power FET is almost a separate chapter in the design tomes, as the gates in high powered versions of these can represent quite a large capacitance just from the sheer size of all the actual gates in the devices, with figures well above .05 microfarads, some of which gets amplified by miller feedback effects as its turned on and off. In order to minimize the junction heat during the on-off or off-on transitions, the driving waveform must be very fast, and capable of charging or discharging that large capacitance in nanoseconds. That implies a driver capable of several amps with rise fall times of 10 or so nanoseconds. Many a power FET aka HEXFET has been destroyed by drivers that take a microsecond to make that nominally 9 volt swing. 5 volt + to fully turn them on, and about -4 to turn them absolutely off in the shortest time. I'm with Kirk on this one, we are a relatively small market, one that will never find a profit in 'simplicating' the right way out of a circuit, so it should be done right, not to consumer grade standards but better. I figure that I'd have to raise the price on my servo amps by $100 each to cover the cost of winding the transformer by hand, and providing the extra components for it. That's completely out of the question to solve a problem that doesn't even exist. Despite the name of this PPMC driver feature, it actually has NOTHING to do with bootstrap power supplies. That puts a different complexion on it entirely, thanks Jon. What I had in mind, and which does a bootstrap thing for both capacitor charge and transformer core reset, is a circuit similar to that which drives the H scan circuitry on older crt monitors. It is 'bootstrapped' in the sense that the bottom winding end of the driver transformers secondary, a teeny little ferrite thing, is tied to the hexfets src terminal, and IIRC a small, say 4.7 ohm resistor is used to limit gate current during the on period, the current then flowing in reverse through another diode when the driver transistor is turned off. Turn on time is about 15ns, turnoff time about 50ns. And its a none too reliable circuit that I'd not ever use in a fresh design. I think it could be made reliable, but I've not found that 'magic twanger' yet. It has 4 or 5 electrolytic caps in it, and any one of them developing an ESR above 2 ohms and the whole circuit goes up in smoke. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- Cheers, Gene There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) A diplomat is a person who can tell you to go to hell in such a way that you actually look forward to the trip. -- Caskie Stinnett, Out of the Red -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On Sunday, August 01, 2010 05:40:41 pm Alex Joni did opine: I used these in the past along with some IRFZ44N http://www.irf.com/product-info/datasheets/data/irf4905.pdf Wow Alex, I obviously need to update my library, that looks like a quite decent P channel device. [...] -- Cheers, Gene There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) Pollyanna's Educational Constant: The hyperactive child is never absent. -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On 1 August 2010 18:44, Jon Elson el...@pico-systems.com wrote: Our amps DO, indeed, have such a supply. But, this one pulse each way thing is needed to clear the shutdown latch in the IR FET driver chip. Would setting the direction to be opposite to the home direction in the HAL suffice? ie, at startup the direction is set one way, then homing sets it the other way, at which the drive comes up and homing starts. -- atp -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On 8/2/2010 2:06 AM, Andy Pugh wrote: On 1 August 2010 18:44, Jon Elsonel...@pico-systems.com wrote: Our amps DO, indeed, have such a supply. But, this one pulse each way thing is needed to clear the shutdown latch in the IR FET driver chip. Would setting the direction to be opposite to the home direction in the HAL suffice? ie, at startup the direction is set one way, then homing sets it the other way, at which the drive comes up and homing starts. That means you can't jog before homing... -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Andy Pugh wrote: On 1 August 2010 18:44, Jon Elson el...@pico-systems.com wrote: Our amps DO, indeed, have such a supply. But, this one pulse each way thing is needed to clear the shutdown latch in the IR FET driver chip. Would setting the direction to be opposite to the home direction in the HAL suffice? ie, at startup the direction is set one way, then homing sets it the other way, at which the drive comes up and homing starts. Hmmm, as long as the PID routine is outputting a non-zero PWM value, then just flipping the direction would sure do it. The PWM pulse needs to be wide enough to make it through the opto-isolator, so somewhere around 5% duty cycle would be ideal, but anything over 2.5% should work (that will give a 500 ns pulse at 50 KHz frequency). This is essentially what I do in my driver. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
Alex Joni wrote: That means you can't jog before homing... Well, if you made tiny jogs in each direction, small enough so that they didn't cause a following error, then the servo amp would go live and all would be fine. That's why I put this in the driver so it just got done immediately after coming out of E-stop, and took care of the problem. I emailed Anders Wallin to see how he dealt with this, but haven't heard back yet. Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
I know a number of people are using my PWM servo amps with Mesa controller boards. A feature of the dumb control logic on the servo amp is that it needs a short pulse in each direction to clear the shutdown latches on the FET driver chips. I built a little state machine into the driver to accomplish this, it is called the bootstrap parameter. It gives 5% duty cycle pulses in each direction on consecutive servo cycles, then goes to normal operation as commanded by the PWM input. If you don't do this, the drive can act like it is disabled until you attempt to move it both directions, then it will suddenly come live. So, has anyone written up a couple lines of HAL to do this, or how else do you solve the problem? (This applies only to the brush version of the servo amp, the brushless amp has a CPLD that manages this function.) Thanks, Jon -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On Sat, 2010-07-31 at 23:15 -0500, Jon Elson wrote: I know a number of people are using my PWM servo amps with Mesa controller boards. A feature of the dumb control logic on the servo amp is that it needs a short pulse in each direction to clear the shutdown latches on the FET driver chips. I built a little state machine into the driver to accomplish this, it is called the bootstrap parameter. It gives 5% duty cycle pulses in each direction on consecutive servo cycles, then goes to normal operation as commanded by the PWM input. If you don't do this, the drive can act like it is disabled until you attempt to move it both directions, then it will suddenly come live. So, has anyone written up a couple lines of HAL to do this, or how else do you solve the problem? (This applies only to the brush version of the servo amp, the brushless amp has a CPLD that manages this function.) Thanks, Jon Is this the high side bootstrap that creates the high side FET gate control voltage? This has always seemed to create more trouble than it is worth. Why not have another supply with the proper voltage and not have to deal with the bootstrap? Or use N and P FET's? I know the bootstrap method may save a portion of the parts cost, but for the product quantities for the CNC market, it doesn't seem worth it. I may be showing my ignorance here. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Use of Pico Systems PWM servo amp with Mesa 5i20 controller
On Sunday, August 01, 2010 12:56:35 am Kirk Wallace did opine: On Sat, 2010-07-31 at 23:15 -0500, Jon Elson wrote: I know a number of people are using my PWM servo amps with Mesa controller boards. A feature of the dumb control logic on the servo amp is that it needs a short pulse in each direction to clear the shutdown latches on the FET driver chips. I built a little state machine into the driver to accomplish this, it is called the bootstrap parameter. It gives 5% duty cycle pulses in each direction on consecutive servo cycles, then goes to normal operation as commanded by the PWM input. If you don't do this, the drive can act like it is disabled until you attempt to move it both directions, then it will suddenly come live. So, has anyone written up a couple lines of HAL to do this, or how else do you solve the problem? (This applies only to the brush version of the servo amp, the brushless amp has a CPLD that manages this function.) Thanks, Jon Is this the high side bootstrap that creates the high side FET gate control voltage? This has always seemed to create more trouble than it is worth. Why not have another supply with the proper voltage and not have to deal with the bootstrap? Or use N and P FET's? I know the bootstrap method may save a portion of the parts cost, but for the product quantities for the CNC market, it doesn't seem worth it. I may be showing my ignorance here. By normal fab techniques, there is not a P type FET, they all need a + signal on the gate to turn them on. That said, a separate + and - 5 volt supply winding whose center tap rail is common to the FET's source rail is the much preferred method of deriving the high sides on pulse drive voltage. I generally detest the bootstrap methods because the voltage so developed isn't as dependable (IMO). The capacitors that are the isolation/storage elements of a bootstrapped circuit are usually common electrolytics, with their failure rates being 100x that of the semiconductors involved. When a semiconductor in one of these circuits fails, there is about a 100/1 chance a failing capacitor was the first circuit fault. Driving a power FET is almost a separate chapter in the design tomes, as the gates in high powered versions of these can represent quite a large capacitance just from the sheer size of all the actual gates in the devices, with figures well above .05 microfarads, some of which gets amplified by miller feedback effects as its turned on and off. In order to minimize the junction heat during the on-off or off-on transitions, the driving waveform must be very fast, and capable of charging or discharging that large capacitance in nanoseconds. That implies a driver capable of several amps with rise fall times of 10 or so nanoseconds. Many a power FET aka HEXFET has been destroyed by drivers that take a microsecond to make that nominally 9 volt swing. 5 volt + to fully turn them on, and about -4 to turn them absolutely off in the shortest time. I'm with Kirk on this one, we are a relatively small market, one that will never find a profit in 'simplicating' the right way out of a circuit, so it should be done right, not to consumer grade standards but better. -- Cheers, Gene There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order. -Ed Howdershelt (Author) marriage, n.: Convertible bonds. -- The Palm PDK Hot Apps Program offers developers who use the Plug-In Development Kit to bring their C/C++ apps to Palm for a share of $1 Million in cash or HP Products. Visit us here for more details: http://p.sf.net/sfu/dev2dev-palm ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
