Delta RMC151 User Manual download pdf (Page 83)

3 Controller Features

with SSI devices that have more than 24 bits, but you should make sure the counts will

not exceed 16,777,216. These limitations do not apply to voltage, current, or MDT

feedback types, since their values never exceed 24 bits.

Delta recommends that the Counts value not be allowed to exceed 24 bits (16,777,216)

because this causes the Actual Position to lose resolution. This occurs because the Actual

Position is stored as a 32-bit floating point number, which is limited to 24 bits of

precision. The resolution of a floating-point number depends on how large the number is.

For example, a floating point number can precisely represent any integer that fits in 24

bits (-16,777,216 to +16,777,216) or it can represent numbers at a 0.001 resolution in

the range of -16,777.216 to +16,777.216.

To determine when an axis’ Actual Position will lose resolution, look at the Counts

+16,777,216), then the Actual Position register will approximately match the resolution of

the transducer. However, as the Counts move outside that range, the Counts register and

the Actual Position register will lose resolution.

For example, if the Counts are 16,777,220 (slightly larger than 24 bits), and the

transducer counts (the counts directly from the transducer are represented exactly in the

Raw Counts

the change in counts exactly) change by one to 16,777,221, the Counts value will still

read 16,777,220. It will not change until the counts have changed by 2, to 16,777,222.

This will cause the Actual Position to become "jerky" and will affect the control. This

problem is doubled for each power-of-two increase in the Counts value. Notice that the

Counts and Actual Position registers are still accurately keeping track of the position

change, but they are losing resolution.

Notice that in order to preserve accuracy on incremental feedback types, the RMC

internally maintains a 32-bit integer accumulator. This ensures that the position does not

drift due to loss of resolution.

Rotary axes use the Count Unwind value, which will keep the Counts within a defined

range. Therefore, as long as the Count Unwind is kept below 16,777,216, this additional

loss in resolution will not occur.

For linear axes, you can keep the Counts register from exceeding 24 bits by homing the

axis, or using the Set Actual Position (49) or Offset Position (47)

commands. With

quadrature encoder inputs, the usable range with full resolution can be doubled by setting

the zero value of the Actual Position to the middle of travel. For absolute linear SSI

feedback, you can also use the Count Offset parameter to move the usable Counts range

closer to zero.

3.3. Axes

3.3.1. Axes Types

The axis types listed in this topic are available on the RMC. The required inputs and outputs

for each axis type constitute 1 axis. For example, a Position-Force application may require 3

analog inputs and 1 output, but is considered a single axis.

The RMC70 is a 1- or 2-axis motion controller with possible additional reference axes, with a

maximum of 4 axes.

The RMC150 can have up to 8 control axes and any number of reference axes, with a

maximum of 16 axes.

Note: It is possible to add more analog inputs on the RMC70 than can be assigned to axes.

However, it is still possible to view the voltage of the extra analog inputs using the Analog

Input Registers. Inputs that are unassigned to axes can have no status bits, error bits, scaling,

filtering, etc.

deltamotion.com 63

1 2 ... 78 79 80 81 82 83 84 85 86 87 88 ... 121 122

Comments to this Manuals

No comments

Delta RMC151 User Manual Page 83

Comments to this Manuals

Related products and manuals for Sensors Delta RMC151