Using inverters od bridge cranes

[darkogorgievski]

Hallo I am planning to improve the automation of electric crane so I will try to explain in few words my ideas. If anybody has expirience with this please advice and correct. The crane has three induction motors with winded rotors (not squirrel cage) : 75 kW for lifting load 55W for forward/backwards movement of the bridge 7.5kW for left/right motion of the hook. I am planning to keep the existing motors, that are started and breaked with switching resistor packs in the rotor circuit, and use frequency inverters with vector control (Hitachi SJ300 series) for driving the motors. Theese inverters have break control option and starting torque >200%. To do this I must short circuit the rotor windings - I plan to do it on the junction box of the motor. Also breaking resistors will be necessary for the application Has any of you done this, and what problems should I expect? THX

[beegee]

Hello, I have done this with omron/yaskawa (they even have anti-sway software) you will need an encoder/resolver because you need closed loop. You still need a mechanical brake I would also use a PLC in order to be able to program the brake sequence the way you want You will have to dimension your braking resistor (I would say 12kW for the 75 would probably do the job) problems you can expect: tuning problems with the inverter on old motors with shorting outside the rotor. Depending on the motor cabling use a output choke or sinus filter.

[BobB]

Fuzzy logic?

[beegee]

no just plain physics... (it is a pendulum so you can calculate everything but you need to know the length of the cable running down. The weight you know from the hoist inverter) Edited May 31, 2007 by beegee

[BobB]

Omron have a Fuzzy Logic PLC card available. It is used in conjunction with analogue I/O. I remember some years ago seeing one of these cards set up for an anti sway crane application and wondered if the Omron/Yaskawa card had utilised the technology.

[beegee]

I remember that card... it was the time everything at omron had somthing fuzzy, TC's PLC cards, ...;that trend has changed somehow. The soft is not written by Omron or Yaskawa but some Swedish or Norwegian company. We also has a belgian university spin off who made this in a plc/pc connected to the inverters

[TimWilborne]

So how does this anti-sway work? Does it take the rise and fall of the motor current and adjust the motor speed based off it to compensate for the sway?

[BobB]

Do not know about this one but the Fuzzy solution had a semicircular resistor feeding into an analogue input when the crane was swinging. The fuzzy logic did it's calculations from the analogue input and moved the traverse motor quickly one way and then the other and stopped the sway. It certainly worked on the model I saw. Nothing to do with motor current or anything else electrical - purely mechanical movement changing a resistance. Edited May 31, 2007 by BobB

[beegee]

the anti ssway takes into account the length of the heigth at which th eload hangs and the weigth. Based on those two, the speed and the deceleration, You can calculate the sway easily (physics) You stop then in two movements: one to stop the crane chariot (sway starts) and then a second move (fast) that puts the crane chariot again above the load when it is at its extreme position of the sway. since the operator only looks at the load and not at the chariot it just looks like a slightly longer deceleration time so something like: running at speed stop chariot calculate the sway amplitude move forward over half the amplitude and stop

[TimWilborne]

Interesting. My experience is limited to smaller cranes. Never seen anything like that built into a drive

[beegee]

well, it is not applied that often since price is a sensitive issue in this market.

[darkogorgievski]

Thanks for suggestions. I have learned things I didn't know they exist (anti sway). Anyway why Hitachi Sj300 inverters have break control option and you can configure the release and brake times as you like so I think PLC won't be necessary. About the output sine filter - will it be necessary to use shielded power cables if you use sine filter? The length of the cables from the control box to the motor is more than 30 meters. Or maybe better solution is to put the control box near the motor? What about the vibrations that exist while moving the crane? Can I expect some other problems except maybe loosening of the cable connections?

[P Daniil]

Put Safety first! Here is a basic checklist: 1. Ensure that the crane will not travel past the track ends by using end limit switches which kill the power circuit directly. 2. If more than one crane is on the same tracks use an anti-collision system. 3. Alarms should be audible AND visual. 4. Ensure that the hoist drive is a dc-injecting type. 5. Do not allow lifting/hoisting of heavier-than-specified loads by using an overload alarm device. 6. Ensure that the left and right motion motors are connected in parallel and driven by the same inverter. This makes the crane stay on the tracks. When one side advances more than the other (remember that the wheels are not exactly the same and the tracks are not absolutely straight) one side slows down and the other speeds up to maintain phase synchronism.

[ParaffinPower]

Not quite correct. The weight is not significant. The company who developed/licensed the antisway software have been bought by Kone, and from August it is no longer available (except to Kone, of course). Stock up now!! Edited July 1, 2007 by ParaffinPower

[hommik]

The load weight is not significant, as long as there is enough motor torque available to follow the speed reference pattern calculated by the sway control algorithm. That is the problem of most "experimental" systems, they require unrealisticly short acceleration ramps and therefore large motor sizes. That is not possible in production cranes. When selecting the sway control supplier the number of references gives a good idea of the value of the product. These systems have been on market since 90's, and 100's (or even 1000's) of references should be found. Also, who is going to maintain your system after 10, 20, 30 years... Systems with load sway angle measurement and feedback are moe expensive, and require special skills for tuning and maintenance. The systems working based on "open loop" control are generally less expensive, due to easy installation, minimun component costs and short start-up. Both do their job. When making automation it is necessary that the sway control system supplier knows how the system behavious in positioning. There are significant differences in positioning times, and some systems require days of programming. Best systems for example adapt automatically if you need to change the acceleration ramp times in the system. As mentioned, Konecranes (not Kone) has their sway control system integrated with their AC drive systems, and they deliver 100's every year. Developing a new sway control system is like making your own PLC system out of microprocessor - possible but not efficient. I recomment you to consentrate defining what the crane should do in your process, and development of spacial lifting tools for your porposes, while hiring a crane specialist for the sway control, as well as for implementing AC drives for the hoist applications. Using your existing motors with AC drives should be OK in 400 V systems. About vector control, good idea for hoist AC drive (with the right SW), not so good for the traveling & traversing. For hoisting, make sure that there is an independent speed supervision system, which closes the hoist brake if the hoist motor control is lost.