1. Power PMAC Electronic Cam Tables April 2014
(From Wikimedia Commons, CCA 3.0)

2. Power PMAC Cam Table Functionality
Table-based commanded motion as function of another position
Up to 256 total cam tables stored simultaneously
Table size limited only by total memory
Three separate table outputs as a function of master position
Commanded position/position-offset for target motor
Torque offset for slaved motor
General-purpose output word (multiple discrete outputs or analog command)
Outputs computed every servo cycle
3rd-order interpolation between table points for position and torque
Automatic indefinite rollover of table in both directions
Position and torque values are floating-point, scalable units
Easy to offset both source and target position references
Easy to switch from one table to another

3. Cam Table Data Structure Overview
Data structure elements about source motor
CamTable[m].Source // Source motor number
CamTable[m].Nx // Number of data zones in table
CamTable[m].X0 // Starting (minimum) position of source
CamTable[m].Dx // Span of source position
Data structure elements about target motor
CamTable[m].Target // Target motor number
CamTable[m].PosSf // Position output scale factor
CamTable[m].DacSf // Torque-offset output scale factor
Data structure elements for table entries
CamTable[m].PosData[i] // Individual position output value
CamTable[m].DacData[i] // Individual torque-offset output value
CamTable[m].OutData[i] // Individual general-purpose output value

4. Cam Table Source Motor
“Source” position for cam table must be from Power PMAC “motor”
Table uses desired position from motor specified by CamTable[m].Source
Source motor (real or virtual) should be in separate coordinate system from target motors (often C.S. 0)
Can be from actual physical motor controlled by Power PMAC
Can be from position sensor for motion not controlled by Power PMAC
Sensor must be used as position feedback for Power PMAC virtual motor
Motor must be activated (to process feedback) but should not be enabled
Sensor position automatically copied into motor desired position register
Can be from desired trajectory of virtual motor
Commonly used for “virtual line shaft”
Jogging this motor can be enough to cause all action of cam table(s)

5. Returning vs. Non-Returning Cam Tables
“Returning” cam tables have same position at beginning and end
PosData[Nx] must be exactly the same value as PosData[0]
Typically used for (reciprocating) linear action from table
Every cycle of table covers same range
“Non-returning” cam tables have different beginning and end position values
PosData[Nx] has different value from PosData[0]
Typically used for rotary action from table (one revolution per cycle)
Each cycle of table covers different position range
Torque offset and general-purpose output values always “returning”

6. Returning Cam Table Position Action

7. Non-Returning Cam Table Position Action

8. Establishing Position Lock on Enabling
In general, target motor will not be at table-commanded position when table is enabled
Power PMAC sets CamTable[m].PosOffset to (signed) difference between present and desired values on enabling
Then, each servo cycle, offset is reduced by CamTable[m].SlewPosOffset until difference is eliminated
For non-returning table, choice of which “instance” of table curve to lock onto, controlled by value of CamTable[m].Enable
Enable = 1: Always slew in positive direction
Enable = 2: Always slew in negative direction
Enable = 3: Slew to closest curve

9. Position Action of Cam Table
Each servo cycle, Power PMAC computes position of source motor within table
Using two PosData points on each side of this position, uses cubic interpolation to compute cam position value
Automatically handles rollover of table, returning or non-returning
This value multiplied by CamTable[m].PosSf (usually 1.0)
Result is written to Motor[x].CompDesPos register for target motor
This desired position compensation value is added to trajectory desired position and master position for target motor (possible to superimpose)
If want compensation value to be reported when querying motor position, set Motor[x].PosReportMode to 1.

10. Torque Offset Action of Cam Table
Each servo cycle, Power PMAC computes position of source motor within table
If CamTable[m].DacEnable = 1, will compute torque offset based on this position
Using two DacData points on each side of this position, uses cubic interpolation to compute cam torque-offset value
This value multiplied by CamTable[m].DacSf (usually 1.0)
Result is written to Motor[x].CompDac register for target motor
This servo-output compensation value is added to value computed by selected servo algorithm of target motor this servo cycle
Can be used to compensate for known repeatable load torques in cycle
Table values can be adjusted automatically with “iterative learning control” algorithms
Many applications will not use at all – just leave all DacData points at 0.0, and/or DacEnable at 0

11. General-Purpose Output Action of Cam Table
Each zone of table has user-specified output “word” OutData[i]
1 to 32 bits can be written to single specified register
Can represent group of discrete digital outputs
Can represent single analog output value
Can represent value for further software action
CamTable[m].pOut specifies address of destination register
e.g. = Acc68E[2].DataReg[4].a
CamTable[m].pOutBuf specifies address of holding register
Used if cannot read back from output destination register
Holding register is modified, then copied to actual output register
CamTable[m].OutBits specifies number of bits to control
Must be consecutive bits in output word
CamTable[m].OutLeftShift specifies shift of table value before writing
Typically set to number of LSB used in output register

12. Adjusting Cam Table Reference Positions
Adjusting source motor table reference position
CamTable[m].X0 specifies reference position (where PosData[0], DacData[0] are used)
X0 can be changed at any time
Actual reference position used (ActiveX0) changes at rate set by SlewX0.
Can set X0 based on trigger position using Motor[x].CapturePos function
Adjusting target motor table reference position
CamTable[m].PosOffset specifies value to be added to table result
Power PMAC automatically sets PosOffset on enabling table to control lock-in
After lock-in, user can change PosOffset at any time
Actual reference position used (ActivePosOffset) changes as rate set by PosOffsetSlew
Can also adjust effective reference position through trajectory moves (e.g. jogging) or position following (e.g. handwheel adjustment) of target motor

13. Cam SculptorTM Table Design Tool
Interactive design tool for specifying Power PMAC electronic cam tables
Not required to generate cam tables, but very useful tool in many cases
Supports traditional (e.g. harmonic, cycloidal) and modern (e.g. minimum power) cam sections
Permits viewing of cam position, velocity, acceleration, and/or jerk
Flags discontinuities and user-set magnitude limits in derivatives
Automatically generates cam table points from user-specified sections
Can download generated table directly to Power PMAC

14. Comparing Cam Tables to External Time Base
Cam table features
Fully reversible: master can go in either direction indefinitely
Motion defined by table, not motion program
Motion of multiple motors must be defined by multiple tables
No point computation or logic during execution of table
Table points must be evenly spaced
Cam tables have torque offsets and direct outputs as standard features
External time base features
Limited reversibility: master must generally move in positive direction
Motion defined by program, not table
Motion of multiple motors can be defined by a single program
Possibility for point computation and logic during program execution
Programmed moves do not need to be evenly spaced
No torque offsets; synchronous assignments for direct outputs