Technical Principles

Linear Drive Advantages

*MTBF: Mean Time Between Failures

Linear Motor Characteristics

Linear drives enable linear motion without the need for motion converters or intermediate gears.

A linear motor consists of a primary part and a secondary part. The primary part contains the winding coils, and the secondary part consists of a set of permanent magnets arranged opposite the primary part. Motor types can be classified as slotted, slotless, and ironless, as well as stepper motors (synchronous reluctance hybrid motors).

The motor produces uniform and typical force within a specific speed range. The magnitude of the force is determined by the effective air gap area between the primary part and the secondary part.

When current is applied to the primary part, the electromagnetic field around the winding coils generates a force acting on the secondary part, producing linear motion.

A linear axis system requires an appropriate guidance system to maintain the air gap between the primary part and the secondary part, as well as a linear measurement system to detect the motor position.

Each motor series includes selections of different lengths and widths to meet various force and installation requirements, and offers multiple mounting and connection variants.

L1 Linear Motor: Primary Part and Secondary Part

Linear Motor Series Overview

Slotted Motors

Low-Iron Motors / Slotless

Ironless Motors

Reluctance Motors

Motor Parameters — Efficiency Criteria

Based on the motor size, the power losses (copper losses) generated by force and process at different operating points are fixed and independent of winding design. Since linear motors do not output mechanical power at standstill, it is not meaningful to cite an efficiency coefficient here.

The motor constant k_m can be used as a means of comparing the efficiency of different motors. A higher motor constant represents a more efficient conversion of force relative to power loss.

k_m vs. Temperature

The motor constant k_m depends on the ohmic resistance and therefore also on the winding temperature of the motor. In motor technical data, k_m is referenced at 25 °C.

The figure below shows the dependence of the reference motor constant on temperature: at a winding temperature of 100 °C, k_m decreases to approximately 88% of its value at 25 °C.

Motor constant k_m dependence on winding temperature (referenced to 100% at 25 °C)

Winding Design and Dependencies

The achievable limit speed of any linear motor depends largely on the winding design and the DC bus voltage (U_DCL). The internal voltage drop of the motor increases with speed. At the specified limit speed, the voltage demand for field-oriented control corresponds to the bus voltage of the servo converter. Beyond this point, speed drops sharply.

The higher the bus voltage, the lower the winding-related voltage constant (k_u), and the higher the achievable limit speed. Due to the relationship between voltage constant and force constant, the force constant increases at higher speeds as the current demand for the same force increases.

The force-current characteristic describes the force at different operating points. The force-speed characteristic shows the relationship between force and speed at different operating points.

L1 Linear Motor Series

Force-Speed Characteristics

The F(v) characteristic of a permanent magnet synchronous motor is nearly independent of speed in the low-speed range. This applies to F_p, F_cw, and F_c up to their corresponding corner speeds v_lp, v_lcw, and v_lc. At higher speeds, the force gradually decreases due to the effect of back EMF*, ultimately dropping to zero.

Higher bus voltages compensate for larger back EMF, allowing higher speeds to be reached.

Operating Conditions

The motor can operate at any operating point below the F(v) characteristic curve:

• In uncooled continuous operation, force can reach up to F_c
• In water-cooled continuous operation, force can reach up to F_cw
• In cyclic intermittent operation (S3**), force can reach up to F_p

For closed-loop controlled motor motion, an appropriate margin must be maintained between the potential operating point and the declining region of the F(v) characteristic. A margin of approximately 0.2 times the maximum speed is typically reserved as control reserve.

*Back EMF: Back Electromagnetic Force
**S3: Operating mode per VDE 0530 standard

Force-Speed (F-v) characteristic: Fp (peak force), Fcw (water-cooled continuous force), Fc (uncooled continuous force) and their corresponding corner speeds

Force-Current Characteristics

The characteristic curve from the origin (0,0) to (F_pl, I_pl) is approximately linear, defined by the force constant k_f:

The operating point for uncooled operation (F_c, I_c) and the operating point for water-cooled operation (F_cw, I_cw) both lie within this linear region.

Saturation Region

At high currents, the non-linearity of the force-current characteristic results from saturation of the motor's magnetic circuit. This segment of the curve is described in data sheets and diagrams by the force-current operating points (F_p, I_p) and (F_u, I_u), with a slope much flatter than k_f.

The motor can operate at the operating point (F_p, I_p) for short periods (cyclically for ≤3 seconds), provided that the average thermal losses have been taken into account. For acceleration processes, this is the maximum operating point to be used.

All parameters are explained in the glossary.

Force-Current (F-I) characteristic: linear region (defined by kf) and saturation region (Fp/Fu operating points)

Thermal Protection

Linear drives are often operated near their thermal performance limits. In addition, unforeseen overloads may occur during operation, causing the current to exceed the allowable rated current. Therefore, the servo controller for the motor should generally be equipped with overload protection to control the motor current. It must be ensured that the RMS value of the motor current is only allowed to exceed the permissible rated current for a short period. This indirect temperature monitoring is both fast and reliable.

IDAM motors are equipped with temperature sensors (PTC and KTY) that can be used for thermal protection.

Monitoring Circuit I — PTC Sensor

Each of the three phase windings is equipped with a series-connected PTC (Positive Temperature Coefficient thermistor) to ensure motor protection. The PTC is a positive temperature coefficient thermistor, and once installed its thermal time constant is less than 5 seconds.

A commercially available motor protection trip device is connected downstream, typically triggering between 1.5 kΩ and 3.5 kΩ. In this way, overtemperature can be detected within a few degrees of each winding.

The trip device also responds when the PTC circuit resistance is too low, which usually indicates a defect in the monitoring circuit. This also ensures electrical isolation between the controller and the motor sensors. The motor protection trip device is not included in the scope of supply.

PTC sensor resistance-temperature characteristic: resistance rises sharply above nominal response temperature Tn

Monitoring Circuit II — KTY84-130 Sensor

One of the motor phases is additionally equipped with a KTY84-130 sensor. This is a semiconductor resistor with a positive temperature coefficient that produces a temperature-equivalent signal (with a delay that depends on the motor type).

To protect the motor from overtemperature, a shutdown threshold is set in the controller. When the motor is at standstill, a constant current flows through the windings, the magnitude of which depends on the respective pole position. Therefore, the motor does not heat uniformly, which may lead to overheating of unmonitored windings.

KTY84-130 sensor resistance-temperature characteristic: linear positive temperature coefficient for precise winding temperature measurement

Standard Connection of PTC and KTY

Standard connection of PTC and KTY: PTC sensors connected in series within all three-phase windings; KTY sensor connected to one winding

The PTC and KTY sensors have basic insulation and are not suitable for direct connection to PELV/SELV circuits (per DIN EN 50178 standard).

Additional monitoring sensors can be integrated at customer request.

Electrical Connections

The standard connection for IDAM motors exits from the end face. The standard cable length from the cable exit point on the motor is 1000 mm. Different lengths can be provided on request. The cross-section of the power cable depends on the continuous motor current and is documented in the catalog drawings. As standard, L1A and L1B are dimensioned for the natural-cooling continuous current I_c at power loss P_l, while L1C is dimensioned for the water-cooled continuous current I_cw at power loss P_lcw.

The motor cable cross-section starts from 4G0.75 mm². The sensor cable 4 × 0.14 mm² (d = 5.1 mm) allows temperature monitoring via PTC and KTY. The cable ends are open with end sleeves. The cables used are UL certified and suitable for cable carriers.

A motor version with terminals (WAGO Series 236 terminal block, suitable for up to 1.5 mm² wire cross-section) is available as an alternative to end sleeves. The position of the cable outlet or terminal is indicated in the data sheets. For variants without water cooling and with continuous current not exceeding 16 A, terminal use is unrestricted.

Terminal Assignment

Positive Direction of Motion

In all three-phase motors, the electrically positive direction of motion corresponds to a clockwise rotating field, i.e., the phase voltages are induced in the sequence U, V, W. For IDAM motors, the positive direction of motion is:

• Towards the side without cable (cable version)
• Towards the side without terminal (terminal version)

Cable version: positive direction is towards the side without cable

Terminal version: positive direction is towards the side without terminal

Motor Cable Selection

Commutation

Commutation operation is preferred for synchronous motors. IDAM linear motors are not equipped with Hall sensors as standard. IDAM recommends using a measurement system for commutation.

Insulation Resistance

Insulation Resistance for Bus Voltage Not Exceeding 600 V_DC

IDAM motors comply with EC Directive 73/23/EEC and European Standards EN 50178 and EN 60204. They undergo staged high-voltage testing before delivery and are vacuum-impregnated.

Please ensure the rated operating voltage of the motor is observed.

Motor Terminal Overvoltage in Inverter Operation

Due to the high du/dt loads generated by rapidly switching power semiconductors, voltage spikes significantly higher than the actual inverter voltage may appear at the motor terminals, especially when using longer connection cables (over 5 m). This places very high loads on the motor insulation.

To protect the motor, it is recommended to always measure the inverter voltage (PWM) applied to the motor windings relative to PE using an oscilloscope in a specific configuration. Existing voltage spikes should not significantly exceed 1 kV. From approximately 2 kV, gradual insulation damage should be expected.

IDAM engineers will assist you in determining the application solution and reducing excessive voltages.

Cooling and Cooling Circuits

The power losses generated during operation are transferred through the motor assembly to the connected components. The entire system is carefully designed to control heat distribution through convection, conduction, and radiation.

For L1C motors, a cooling system can be optionally selected as an accessory to improve heat dissipation. The continuous force of a liquid-cooled motor is approximately twice that of an uncooled motor.

Active Cooling

Active cooling should be prioritized for machines operating at high performance and high dynamic conditions, as well as in corresponding high bearing load applications.

If complete thermal isolation between the motor and machine is required (e.g., to prevent thermal deformation in high-precision machinery), an additional thermal insulation layer and precision cooling are needed. The actual cooling constitutes the primary or power cooling system.

Cooling Plate

The motor cooling system is implemented in the form of a cooling plate installed between the motor and the machine table, which should be connected by the customer to the cooling circuit of a cooling device. The thermal insulation layer and cooling plate can be supplied as optional accessories for motor components or as part of the customer's machine design.

The cooling medium flows through internal copper tubes from the inlet to the outlet. The inlet and outlet connections can be distributed to two ports, with connection fittings of G 1/8 internal thread.

When using water as coolant, additives against corrosion and biological deposits must be added.

Cooling plate for water cooling

Cooling plate installed between motor and machine table

Dependency of Characteristic Data on the Supply Temperature of Cooling Medium

The continuous current I_cw indicated in the data sheet for water cooled operation can be achieved at a rated supply temperature θ_nV of 25 °C. Higher supply temperatures θ_V result in a reduction of the cooling performance and therefore also the nominal current.

The reduced continuous current I_{c red} can be calculated by the following quadratic equation:

I_{c red} / I_cw = √((θ_max − θ_V) / (θ_max − θ_nV))

• I_{c red}: Reduced continuous current [A]
• I_cw: Continuous current, cooled at θ_nV [A]
• θ_V: Current supply temperature [°C]
• θ_nV: Rated supply temperature [°C]
• θ_max: Maximum permissible winding temperature [°C]

(Applies to a constant motor current)

L1C motor with terminal

Relative continuous current I_{c red} / I_cw vs. supply temperature θ_V (θ_nV = 25 °C)

Selection of Direct Drives for Linear Motions

Cycled Applications

In cycled operation, sequential positioning movements are interspersed with pauses during which no motion takes place. A simple positioning sequence takes the form of a positively accelerated motion followed by a deceleration (negative acceleration of usually the same magnitude, in which case acceleration and deceleration time are equal). The maximum speed v_max is reached at the end of an acceleration phase.

A cycle is described in the v(t) diagram (v: speed, t: time). The diagram shows a forward-backward movement with pauses (t_M: motion time, t_P: dwell time with no load).

v-t diagram for cycled operation

This yields the following a(t) diagram as well as the curve for the force required for the motion:

a-t diagram for cycled operation

Three Selection Criteria

The motor is selected according to three criteria in accordance with the force curve for a desired cycle:

1. Maximum force: Maximum force in the cycle ≤ F_p according to the data sheet
2. Effective force: Effective force in the cycle ≤ F_c (motor non cooled) or F_cw (motor water-cooled) according to the data sheet
3. Maximum speed: Maximum speed in the cycle ≤ v_lp according to the data sheet

Effective Force Calculation

The effective force is equal to the root mean square of the force curve (here: six force segments in the cycle):

Using the forces F₁ = F, F₂ = −F, F₃ = 0, F₄ = −F, F₅ = F, F₆ = 0 and times t₁ = t_M/2, t₂ = t_M/2, t₃ = t_P, t₄ = t_M/2, t₅ = t_M/2, t₆ = t_P, this simplifies to:

Acceleration and Maximum Speed

The described positioning motion is performed with a (theoretically) infinite rate of jerk. If jerk limitation is programmed into the servo converter then the positioning times are extended accordingly. In this case, greater acceleration would be needed in order to maintain unchanged positioning times.

Example: Cycled Applications