PLEASED TO MEET YOU:

It was 4 a. m. in the morning, and Mr. Arscott could not sleep. He was still thinking about great idea he had for the design of a new machine. The morning after he had a meeting at the 7th floor of the Kohinor building, downtown, with the Industrial Automation Department staff of the leading motion control company. It hadn't been easy to come to the conclusion that he needed to apply 70Nm at 100rpm to the main driving shaft on his machine. The next step could be even harder: How to choose the suitable motor, along with the best drive? Would the mechanics bear the machine load with constant start/stops? The meeting was very positive, and in the end he got a technical proposal as well as the corresponding quotation:

   

Now that all the bits and pieces were coming together, Mr. Arscott passed the information to his Purchase Department. There was a new Purchase Manager in the company. He joined a few months ago already, and it was probably the right time for him to get fullcontrol on sourcing all the necessary parts. Mr. Penny took the file containing all the information, while Mr. Arscott rushed to the airport by taxi, for a one week business trip overseas.

- Let's see what we've got..," he said, while opening the file

Price: 300 MU (monetary units) "That's definitely expensive, to start with. Indeed, the last time I bought a motor at my previous company we paid the equivalent of only 42, 00 MU, and it wasn't a low price. I remember very well we used it to drive a 20-inch high water pump. Then he took an Automation Magazine, looking for a second bid:

- Here we are; "MAVILOR MOTORS, S. A. - the best servomotors in the world. They are not modest at all, these guys. Let's find out what their price level is. These are the terms of the inquiry he sent:

"Dear Sirs, Please give us your best price and delivery for one motor 4,0Nm stall torque, rated speed: 3.000rpm, . Yours Faithfully, Mr. Penny". When Mr. Penny received the second quotation he was shocked.

Price: 450 MU (monetary units)

This is much more expensive. I'll buy the ABC-84, he said. But he was wrong!

Why?

Because what Mr. Arscott's machine requires is 2,33Nm at 3.000rpm. Then it is not necessary for MAVILOR to use a 4,0Nmbecause their motor's flat curves can do the same job as a ABC-84 with a smaller size BL-73:

Conclusion:

In the first case, the total cost is:

Motor ABC-84 (300 MU) + drive 8A (550 MU) + gearbox (575 MU) = 1.425,0 MU Note: the drive has to be of 4,0 Nm stall torque / 0,56 torque constant = 7,14 A à Drive of 8,0A = 550,0 MU

In the second case, the total cost is:

Motor BL-73 (380 MU) + drive 6A (500 MU) + gearbox (500 MU) = 1.380,0 MU Note: the drive has to be of 2,72 Nm stall torque / 0,56 torque constant = 4,86 A à Drive f 6,0A = 500,0 MU.

The total MAVILOR price was then only 3,16 % So, Mr. Penny thought, both quotations are about the same price.

However, on his return, it took Mr. Arscott only a few minutes to decide to buy MAVILOR. In fact, if you look at the dynamic response of the motor:

Theoretical max. acceleration case ABC-84 = Peak torque / inertia = 54.198 rad/s2 Theoretical max. acceleration case BL-73 = 145.946 rad/s2