Further parameters

Load angle

The load angle provides information about the current mechanical load at the motor axis. It is shown as a 3-bit value (SB.1-SB.3) and updated after each full step. Since the load angle is determined via the motor current, it directly depends on the following factors:

• Velocity - A medium velocity is an advantage for an analyzable load angle; high or low velocities result in a high load angle.
• Resonances - Motor resonances generate high mechanical load at the motor and distort the measuring result.
• Acceleration - Acceleration phases also generate high load at the motor.
• Mixed Decay - If this option is enabled, the motor current is actively impressed. Deactivation via CW.9 therefore has a positive effect on load angle resolution.
• Motor current - The set coil current has a direct influence on the load angle resolution, i.e. the smaller the current, the smaller the resolution.

For each application, the user should therefore determine the optimum velocity for achieving a satisfactory load angle resolution.

Current table

It is conceivable that in some applications it may be necessary to adapt the current (which usually is sinusoidal) to the stepper motor. To this end feature bit R32.7 has to be enabled. The user should save the adjusted current table in Register page 1.

Mixed Decay

The Mixed Decay parameter can be used to refine and reduce the coil current. This is achieved by the auxiliary transistor actively impressing a coil current onto a half bridge during the second half of the microstep phase through pulsing. In microstep mode, this has a positive influence on the motor movement. The motor operates more smoothly and can by positioned more accurately. Mixed Decay should be switched off for low velocities and at standstill.

Mixed Decay can be disabled via control bit CW.9.

CAUTION

Position shift on deactivation of Mixed Decay possible

When Mixed Decay is deactivated, in the worst case the position may shift by a few microsteps due to the change in coil currents!

Automatic / manual current reduction

The stepper motor terminal offers the user the option of reducing the current in order to prevent unnecessary heating of the motor:

• automatic, specified via register R44
• manual, specified via register R45

While the motor is at standstill (v=0), the holding current from R44 is set automatically. This value refers to the set terminal coil current, not to the rated terminal current!

In order to achieve maximum control for the user, this value can be set to 100 % while R45 is set to 50 %, for example. A holding current can be applied manually onto the motor windings by setting control bits CB.3 or CW.11. This can be done at standstill or while the motor is in operation.

Setting the target position (via register)

The user can set or delete the target position value. Registers R2 and R3 are used as reference:

• a rising edge at CW.13 deletes the set target position (higher priority than CW.10 if CW.10 and CW.13 have the same setting)
• a rising edge at CW.10 sets the target position to the value from register R2 and R3

Acknowledgement occurs via status bit SW.2.

Path control

For positioning taken over from a PLC, path control is the optimum solution. In this operation mode, a 32 bit position value and various parameter such as velocity and acceleration are specified for the terminal. Once enabled, the terminal automatically travels to the target position.

Detecting position errors

The terminal determines the relative position error of the motor via an external sensor (e.g. inductive proximity limit switch) connected to digital input 2 (only for internal positioning). Register RP0.R51 is used to specify the number of pulses per revolution specified (if a pinion is used, for example). By setting bit CW.7 of the control word, the user can show the error in the process data and subsequently analyses it with the PLC.

The terminal uses these parameters to calculate a position offset:

Legend:

The user must analyse the relative position error individually. No direct conclusions can be drawn for the actual number of lost microsteps. This is due to the fact that the terminal does not take the initial error (number of microsteps between the start of the motor and the first sensor pulse) into account. In addition, it is not possible to include the tolerance (delay), with which the sensor switches the 24 V.

These preliminary considerations results in a velocity dependence, which must be taken into account in the evaluation. At constant velocity the error fluctuates around a few microsteps, but remains the same on average. In practice, the small deviation is irrelevant, since in the event of an error the motor:

• either loses many steps at once (this is clearly indicated by a suddenly increasing error), or
• stops altogether, which is indicated by a steadily increasing position error.

Encoder interface

The encoder operates with fourfold evaluation.

Latch functions

The internal encoder offers the option of registering one or several latch events. A latch event can be generated through the input signals C, latch/gate, input 1 or input 2. By default, the terminal only stores one latch value. The latch array can be enabled and the number of latch values increased by setting the feature bit R32.9 and paramétrisation of register R37, so that several latch values can be stored.

The terminal response to the latch events is enabled as follows:

• Setting control bit CW.0 activates a rising edge at the C input (maximum priority if several control bits are set at the same time)
• Setting the control bits CW.3 activates the rising edge at the latch/gate input (second-highest priority)
• Setting the control bits CW.4 activates the falling edge at the latch/gate input (third-highest priority)
• Setting the control bits CW.1 activates the rising edge at digital input E1 (fourth-highest priority)
• Setting the control bits CW.2 activates the rising edge at digital input E2 (lowest priority)

By activating R32.8 a latch event may also be used for deleting the current position. To this end, one of the above-mentioned events must be enabled first, followed by control bit CW.13. The current position is deleted during the next latch event.

Once the user has enabled the function, the terminal saves the current position value at the next latch event and indicates this by setting status bit SW.4. If the latch array is activated, this only happens once the number of latch events specified in R37 has occurred. Reading of latch values must be initiated by setting CW.5, which causes the low-order word to be shown in the DataIN process data (the terminal indicates this via status bit SW.5). The high-order word can only be read from register R5 via register communication. The following latch values can be retrieved by changing control bit CW.6. The terminal acknowledges this by changing status bit SW.6. The next latch value now applies and is shown in DataIN. The last latch value has been reached once terminal SW.6 no longer changes according to CW.6.

Enable must be maintained! The enable that was set previously must be retained while reading out the latch value. The latch values are lost if the enable is removed!

Digital inputs

The digital inputs can be configured individually for N/C contacts. To this end, for input 1 bit RP0.R52.14 and for input 2 bit RP0.R52.15 of feature register 2 is set to 1_bin. In delivery state both inputs are configured for N/O contacts.