Generic Linear Actuator

Universal linear actuator operating from a DC voltage source or PWM driver.

generic linear actuator

Description

The Generic Linear Actuator unit implements a universal linear actuator model designed to be controlled from a DC voltage source or PWM driver. Define force-velocity characteristics as tabulated values to supply the motor at rated voltage. This functionality allows the motor to be modelled without referring to an equivalent circuit.

The architecture of the motor or drive determines how the electrical losses are force-dependent. For example, in a DC motor, the losses are proportional to the square of the current. Since the force is proportional to the current, the losses are also proportional to the mechanical force. In most motors, the electrical losses are proportional to the square of the mechanical force. The Generic Linear Actuator block calculates this loss value using the provided parameters Motor efficiency (percent) and Speed at which efficiency is measured.

Some motors also have a loss factor that is independent of force. An example would be a shunt motor where the field winding draws a constant current regardless of the load. The Force-independent electrical losses parameter takes this effect into account.

The Motor efficiency is the mechanical power divided by the sum of the mechanical power and both electrical losses. The block assumes that the speed at which the motor efficiency is determined is in the motor quadrant and is therefore positive.

It is possible to use the block in the opposite direction by changing the sign of the applied voltage. For example, the H-Bridge block reverses the direction of motor rotation if the voltage at the REV port is greater than the Reverse threshold voltage parameter. However, if the block is used in the reverse direction, the power-speed data for forward operation is specified:

Positive forces and positive velocities in the motor quadrant;
Positive force and negative velocities in the counterclockwise generation quadrant;
Negative forces and positive velocities in the clockwise generating quadrant.

Thermal effects of the model

You can open the thermal port to model the effects of losses when converting energy to heat. To open the thermal port, select the Enable thermal port checkbox.

Assumptions and limitations

The force-velocity curve data corresponds to nominal voltage only, so the block only produces accurate results at plus or minus nominal voltage.
The block requires that it be provided with force-velocity data for the entire range over which the drive is used. To use the drive in the generation and braking region, provide additional data beyond the normal range of motion.
The behaviour of the model is sensitive to force-velocity data. For example, the idle speed is correctly defined and is finite only when the data crosses the velocity axis.
To control a block from the H-Bridge block:
- Do not place any other blocks between the H-Bridge block and the Generic Linear Actuator block.
- In the H-Bridge block dialogue box, set the Freewheeling mode parameter to Via one semiconductor switch and one freewheeling diode. Selecting Via two freewheeling diodes does not set the bridge output voltage to zero when the input PWM signal is low.
- In the H-Bridge, Generic Linear Actuator and Controlled PWM Voltage block dialogues, make sure that the Simulation mode value is the same for all three blocks.

Ports

Conserving

# + — positive terminal
electricity

Details

A non-directional port associated with the positive terminal of the drive.

Program usage name

p

# - — negative terminal
electricity

Details

Non-directional port associated with the negative terminal of the drive.

Program usage name

n

# R — piston
`rotational mechanics

Details

A mechanical non-directional port associated with a piston.

Program usage name

rod_flange

# C — hull
`rotational mechanics

Details

A mechanical non-directional port associated with the actuator housing.

Program usage name

case_flange

# H — heat port
heat

Details

Heat port.

Dependencies

To use this port, select the Enable thermal port checkbox.

Program usage name

thermal_port

Parameters

Electrical Force

# Speed values — velocity vector
fpm | fps | kph | mph | m/s | cm/s | ft/s | in/s | km/s | mi/s | mm/s

Details

A vector of velocity values to build an interpolation table of matching force and velocity values.

Units	`fpm` \| `fps` \| `kph` \| `mph` \| `m/s` \| `cm/s` \| `ft/s` \| `in/s` \| `km/s` \| `mi/s` \| `mm/s`
Default value	`[-15.0, -10.0, -5.0, 0.0, 5.0, 10.0, 15.0, 20.0, 25.0, 30.0] m/s`
Program usage name	`velocity_vector`
Evaluatable	Yes

# Force values — vector of force values
N | kN | lb | mN | dyn | lbf

Details

A vector of force values to construct an interpolation table of force and velocity values.

Units	`N` \| `kN` \| `lb` \| `mN` \| `dyn` \| `lbf`
Default value	`[4.0, 3.5, 3.0, 2.5, 2.0, 1.5, 1.0, 0.5, 0.0, -0.5] N`
Program usage name	`force_vector`
Evaluatable	Yes

# Rated voltage — rated voltage
V | MV | kV | mV

Details

Specify the voltage for which the device to be modelled is designed.

Units	`V` \| `MV` \| `kV` \| `mV`
Default value	`12.0 V`
Program usage name	`V_rated`
Evaluatable	Yes

# Motor efficiency (percent) — motor efficiency

Details

The efficiency that the unit uses to calculate the force-dependent electrical losses.

Default value	`70.0`
Program usage name	`efficiency`
Evaluatable	Yes

# Force-independent electrical losses — electrical losses independent of the force
W | GW | MW | kW | mW | uW | HP_DIN

Details

Fixed electrical losses associated with the drive when the force is zero.

Units	`W` \| `GW` \| `MW` \| `kW` \| `mW` \| `uW` \| `HP_DIN`
Default value	`2.0 W`
Program usage name	`P_loss_base`
Evaluatable	Yes

# Simulation mode — simulation mode
PWM | Averaged

Details

If you set Simulation mode to PWM, apply a PWM signal switching between zero and nominal voltage to the electrical terminals of the unit. The current drawn from the mains supply is equal to the amount required to transfer mechanical energy and compensate for electrical losses. If the applied voltage exceeds the nominal voltage, the resulting force increases proportionally. However, applying a voltage other than the nominal voltage may give unrepresentative results.

If you set the Simulation mode parameter to `Averaged', the resulting force in response to the applied voltage will be:

where is the force value at the speed of . The current drawn from the power supply is such that the product of the current and is equal to the average power consumption.

Values	`PWM` \| `Averaged`
Default value	`PWM`
Program usage name	`simulation_mode`
Evaluatable	No

# Speed at which efficiency is measured — the speed at which the efficiency is measured
fpm | fps | kph | mph | m/s | cm/s | ft/s | in/s | km/s | mi/s | mm/s

Details

The speed that the unit uses to calculate the force-dependent electrical losses.

Units	`fpm` \| `fps` \| `kph` \| `mph` \| `m/s` \| `cm/s` \| `ft/s` \| `in/s` \| `km/s` \| `mi/s` \| `mm/s`
Default value	`20.0 m/s`
Program usage name	`velocity_reference_for_efficiency`
Evaluatable	Yes

Mechanical

# Plunger mass — piston weight
g | t | kg | mg | oz | lbm | slug

Details

The mass of the moving part of the motor. The value can be zero.

Units	`g` \| `t` \| `kg` \| `mg` \| `oz` \| `lbm` \| `slug`
Default value	`0.1 kg`
Program usage name	`mass`
Evaluatable	Yes

# Linear damping — linear damping
kg/s | N*s/m | N/(m/s) | lbf/(ft/s) | lbf/(in/s)

Details

Linear damping. The value can be zero.

Units	`kg/s` \| `N*s/m` \| `N/(m/s)` \| `lbf/(ft/s)` \| `lbf/(in/s)`
Default value	`1e-5 N/(m/s)`
Program usage name	`damping`
Evaluatable	Yes

Temperature Dependence

Details

Temperature coefficient of resistance.

Dependencies

To enable this parameter, select the Enable thermal port check box.

Units	`1/K` \| `1/degR` \| `1/deltaK` \| `1/deltadegC` \| `1/deltadegF` \| `1/deltadegR`
Default value	`0.00393 1/K`
Program usage name	`alpha`
Evaluatable	Yes

Details

The temperature for which the drive parameters are defined.

Dependencies

To enable this parameter, select the Enable thermal port check box.

Units	`K` \| `degC` \| `degF` \| `degR` \| `deltaK` \| `deltadegC` \| `deltadegF` \| `deltadegR`
Default value	`25.0 degC`
Program usage name	`T_measurement`
Evaluatable	Yes

Thermal Port

# Enable thermal port — switching on the heat port

Details

Modelling of thermal effects.

To enable thermal effects modelling, set the parameter checkbox to `enabled'.

Default value	`false (switched off)`
Program usage name	`has_thermal_port`
Evaluatable	No

# Thermal mass — thermal mass
J/K | kJ/K

Details

Thermal mass is the energy required to raise the temperature by one degree.

Dependencies

To enable this parameter, select the Enable thermal port checkbox.

Units	`J/K` \| `kJ/K`
Default value	`100.0 J/K`
Program usage name	`thermal_mass`
Evaluatable	Yes