servoj_rt

This function performs real-time joint position control from an external controller. It commands the robot joints to move toward the target position at each RT cycle based on the target position, velocity, acceleration, and interpolation time.

Definition
DRFLEx.h within class CDRFLEx, public section

bool servoj_rt(float fTargetPos[NUM_JOINT],
               float fTargetVel[NUM_JOINT],
               float fTargetAcc[NUM_JOINT],
               float fTargetTime) {
    return _servoj_rt(_rbtCtrlUDP, fTargetPos, fTargetVel, fTargetAcc, fTargetTime);
};

Caution

• The current servoj_rt command is still in early implementation.
  Jerky motion may occur depending on communication latency or jitter.

• It is recommended to tune fTargetTime carefully and use a slow response speed
  or use speedj_rt instead for smoother motion control.

• fTargetTime is not the send interval. See the second Caution section below for how to choose it.

Parameter

Parameter Name	Data Type	Default Value	Description
fTargetPos	float[6]		Target joint position [deg].
fTargetVel	float[6]		Target joint velocity [deg/s]. If set to None (-10000), velocity is automatically computed from fTargetPos.
fTargetAcc	float[6]		Target joint acceleration [deg/s²]. If set to None (-10000), acceleration is automatically computed.
fTargetTime	float		Target motion duration [s].

Note

• This command is asynchronous.

• The inner motion profile interpolates the path from current state to fTargetPos at fTargetTime using fTargetVel and fTargetAcc.

• If fTargetTime ≤ controller cycle period (~1 ms),
  the robot moves directly to the target without interpolation.

• If the next command is not received before reaching fTargetPos, the system decelerates according to the global acceleration value.

Caution

• The current version is not synchronized with the system’s operation speed [%].

• Jerky motion may occur if the interval between commands exceeds 1 ms.

• fTargetTime is the time the controller is given to reach fTargetPos, and it is not the interval at which commands are sent. Set it comfortably larger than the send interval so consecutive commands overlap; a value at or below the send interval produces the jerky motion described above.

• The controller enforces a minimum fTargetTime and raises smaller values to it: 0.001 s on DRCF v2, and 0.025 s on DRCF v3, to which v3 adds a further 0.005 s. A value below the minimum is silently replaced, so a value tuned on one controller generation must be re-checked on the other.

• The send interval must match the period declared to set_rt_control_input. Sending more slowly than the declared period trips the input watchdog and the controller ends the session, while servoj_rt keeps returning 1 because it is asynchronous.

• For continuous position control, consider speedj_rt.

Return

Value	Description
1	The command datagram was sent.
0	The command datagram could not be sent.

Note

This function is asynchronous. It returns as soon as the datagram is sent and does not wait for the controller to accept or reject the command, so a return value of 1 does not confirm that the robot acted on it. Rejected commands and motion faults are reported through set_on_rt_log_alarm.

Example

#include <chrono>
#include <cmath>
#include <thread>

drfl.connect_rt_control("192.168.137.100", 12347);

std::string version = "v1.0";
float period = 0.001f; // 1 ms
int lossCount = 4;

// Configure RT streaming
drfl.set_rt_control_input(version, period, lossCount);
drfl.set_rt_control_output(version, period, lossCount);
drfl.start_rt_control();

float fTargetPos[6] = {0.f, 0.f, 0.f, 0.f, 0.f, 0.f};
float fTargetVel[6] = {0.f, 0.f, 0.f, 0.f, 0.f, 0.f};
float fTargetAcc[6] = {0.f, 0.f, 0.f, 0.f, 0.f, 0.f};
float fTargetTime = 0.03f;   // above the controller minimum; see the notes above

for (int i = 0; i < 5000; ++i) {
    // Example: oscillate Joint 1
    fTargetPos[0] = 10.f * sin(i * 0.01f);
    drfl.servoj_rt(fTargetPos, fTargetVel, fTargetAcc, fTargetTime);
    std::this_thread::sleep_for(std::chrono::milliseconds(1));
}

drfl.stop_rt_control();
drfl.disconnect_rt_control();

This example demonstrates how to perform continuous joint streaming control by repeatedly sending servoj_rt commands at 1 ms intervals.

Tips

• Always run servoj_rt in a deterministic loop (1 kHz or lower).

• Use smoothed joint trajectories or low-pass filtered signals to prevent jerk.

• For Cartesian streaming, use servol_rt instead.